Paper by Rob Landis
International Planetarium Society Conference
Astronaut Memorial Planetarium & Observatory
10-16 July 1994
"Comet P/Shoemaker-Levy's Collision with Jupiter:
Covering HST's Planned Observations from Your Planetarium"
Abstract: Comet Shoemaker-Levy 9 (1993e) was discovered
in March 1993. Early ground-based observations indicated
the comet had fragmented into several pieces. The comet
is in a highly inclined, elliptical orbit around Jupiter.
P/Shoemaker-Levy 9 was tidally ripped apart during peri-
Jove in July 1992. The Hubble Space Telescope has provided
the most detailed look to date and resolved 20 separate
nuclei. The nuclei are expected to slam into Jupiter over
a five-day period beginning on 16 July 1994. The total
energy of the collisions will be equivalent to 100 million
megatons of TNT (more than 10,000 times the total destruc-
tive power of the world's nuclear arsenal at the height of
the Cold War). An armada of spacecraft will observe the
event: Voyager 2, Galileo, IUE, Ulysses, and the Hubble
Space Telescope. HST will be the astronomical instrument
of choice to observe P/SL9, and the after effects of the
energy imparted into the Jovian atmosphere. NASA Select
television may provide planetarium patrons with a ringside
seat of the unfolding drama at Jupiter.
The author and Steve Fentress (Strasenburgh Plane-
tarium) had remarkable success covering the Voyager 2/
Neptune encounter during August 1989 using existing NASA
video and still images. No special effects were needed --
nor used -- to bring Voyager 2's odyssey to the Upstate New
York community. During the first week of December 1993,
several major planetaria achieved similar success in their
coverage of the first servicing mission to the Hubble Space
Telescope . Another opportunity for planetaria to cover
fast-breaking astronomical and space science news awaits
this summer as P/Shoemaker-Levy 9 collides with Jupiter.
What follows is background material on the HST, the comet,
Jupiter, and the planned observations of the upcoming
Planetaria and science centers worldwide have a
unique opportunity to be involved in the understanding
and exploration of our solar system when you participate
in the P/Shoemaker-Levy collision with Jupiter. Public
interest in your program will have been greatly stimulated
before and during the series of collisions by daily televi-
sion broadcasts, newspapers, and magazines. In certain
areas of the nation, local cable companies will be carrying
the NASA Select signal to further stimulate interest in
We at the Space Telescope Science Institute and
National Aeronautics and Space Administration anticipate that
the public interest will be extremely high and that you may
expect large attendances at your location.
Never before in modern times has a collision between
two solar system bodies been observed. The instrument of
choice to observe this unique event will be the Hubble Space
The Hubble Space Telescope: Planned Observations of
Periodic Comet Shoemaker-Levy 9 (1993e) and Jupiter
The Hubble Space Telescope is a NASA project with
international cooperation from the European Space Agency
(ESA). HST is a 2.4-meter reflecting telescope which was
deployed in low-Earth orbit (600 kilometers) by the crew of
the space shuttle Discovery (STS-31) on 25 April 1990.
Responsibility for conducting and coordinating the
science operations of the Hubble Space Telescope rests with
the Space Telescope Science Institute (STScI) on the Johns
Hopkins University Homewood Campus in Baltimore, Maryland.
STScI is operated for NASA by the Association of University
for Research in Astronomy, Incorporated (AURA).
HST's current complement of science instruments
include two cameras, two spectrographs, and fine guidance
sensors (primarily used for astrometric observations).
Because of HST's location above the Earth's atmosphere, these
science instruments can produce high resolution images of
astronomical objects. Ground-based telescopes can seldom
provide resolution better than 1.0 arc-seconds, except
momentarily under the very best observing conditions.
HST's resolution is about 10 times better, or 0.1 arc-seconds.
It is generally expected that nearly every observatory
in the world will be observing events associated with Comet
Shoemaker-Levy's impacts on Jupiter. Most observatories are
setting aside time and resources but delaying detailed planning
until the last possible minute in order to optimize their
observations based on the latest theoretical predictions and
the latest observations of the cometary properties. Having the
advantage of being above the Earth's turbulent atmosphere, HST
is the astronomical spacecraft of choice to observe the unfolding
drama of Comet P/Shoemaker-Levy 9 collision with Jupiter. Other
spacecraft to observe the event include the International Ultra-
violet Explorer (IUE), Extreme Ultraviolet Explorer, Galileo,
Voyager 2, Ulysses, and possibly others.
From 16 July through 22 July 1994, pieces of an object
designated as Comet P/Shoemaker-Levy 9 will collide with Jupiter,
and may have observable effects on Jupiter's atmosphere, rings,
satellites, and magnetosphere. Since this is the first collision
of two solar system bodies ever to be observed, there is large
uncertainty about the effects of the impact. Shoemaker-Levy 9
consists of nearly 20 discernible bodies with diameters estimated
at 2 to 4 kilometers (km), depending on method of estimation and
assumptions about the nature of the bodies, a dust coma surround-
ing these bodies, and an unknown number of smaller bodies. All
the large bodies and much of the dust will be involved in the
energetic, high-velocity impact with Jupiter.
The Hubble Space Telescope has the capability of obtaining
the highest resolution images of all observations and will continue
to image the morphology and evolution of the comet until days before
first fragments of the comet impact with Jupiter. HST's impressive
array of science instruments will study Jupiter, P/Shoemaker-Levy
9, and the Jovian environs before, during, and after the collision
events. The objective of these observations is to better constrain
astrometry, impact times, fragment sizes, study the near-fragment
region and perform deep spectroscopy on the comet. During the
collision events it is hoped that the HST will be able to image the
fireball at the limb, and after collisions the atmosphere, rings,
satellites, and magnetosphere will be monitored for changes caused
by the collision. The HST will devote approximately 18 hours of
time with the Wide Field/Planetary Camera (WF/PC -- pronounced
"wif-pik"). The disk of Jupiter will be about 150 pixels across
in the images, a resolution of about 1000 km/pixel.
The HST program that has been approved consists of 112
orbits of observations of both the comet and Jupiter. The obser-
vations will be made by six different teams.
Table 1: Science Observation Team (SOT) Principal Investigators for
the HST Jupiter Campaign.
Principal Science Target Science Objectives
Hal Weaver WFPC+FOS SL9 morphology, breakup,
(STScI) OH emission
Heidi Hammel WFPC Jupiter seismic/gravity waves
(MIT) clouds and wind fields
Keith Noll FOS+HRS Jupiter composition changes
(STScI) at impact sites
Melissa McGrath FOS+HRS magnetosphere dust contamination
(STScI) of magnetosphere
John Clarke WFPC+FOC Jupiter UV imaging of clouds
(U Mich) and aurorae
Bob West WFPC Jupiter stratospheric haze
Table 2: HST Jupiter/Shoemaker-Levy Campaign Programs
o UV Observations of the Impact of Comet SL9 with Jupiter
o A Search for SiO in Jupiter's Atmosphere
o Abdundances of Stratospheric Gas Species from Jovian Impact Events
o SL9's Impact on the Jovian Magnetosphere
o Observations of Io's and Europa's Regions of Jovian Magnetosphere
for Cometary Products
o Dynamical Parameters of Jupiter's Troposphere and Stratosphere
o HST Observations of the SL9 Impacts on Jupiter's Atmosphere
o Comparison of Meterological Models with HST Images
o FUV Imaging of Jupiter's Upper Atmosphere
o Auroral Signature of the Interaction of SL9 with the Jovian Mag-
o HST Imaging Investigation of SL9
o Cometary Particles as Tracers of Jupiter's Stratospheric Circulation
A bit more than 1/3 of the observations will be of the comet with the
remainder focused on Jupiter and environs. The comet observations
have already begun, the first being made in late January. The next
will be in late March, with three more observations spaced in time up
to mid-July, just before impact. The Jupiter observations begin the
week before impact. The impact week has many observations, and followup
observations continue sporadically until late August. Details of the
observing program are being finalized.
Some Background on Comet Shoemaker-Levy 9 and Jupiter
A comet, already split into many pieces, will strike the
planet Jupiter in the third week of July of 1994. It is an event
of tremendous scientific interest but, unfortunately, one which is
likely to be unobservable by the general public. Nevertheless, it
is a unique phenomenon and secondary effects of the impacts will
be sought after by both amateur and professional astronomers.
The impact of Comet Shoemaker-Levy 9 onto Jupiter represents
the first time in human history that people have discovered a body
in the sky and been able to predict its impact on a planet more than
seconds in advance. The impact will deliver more energy to Jupiter
than the largest nuclear warheads ever built, and up to a significant
percentage of the energy delivered by the impact which is generally
thought to have caused the extinction of the dinosaurs on Earth,
roughly 65 million years ago.
Periodic Comet Shoemaker-Levy 9 (1993e) is the ninth
short-period comet discovered by husband and wife scientific
team of Carolyn and Gene Shoemaker and amatuer astronomer David
Levy. The comet was photographically discovered on 24 March
1993 with the 0.46-meter Schmidt telescope at Mt. Palomar.
On the original image it appeared 'squashed'. Subsequent con-
firmation photographs at a larger scale taken by Jim Scotti
with the Spacewatch telescope on Kitt Peak showed that the
comet was split into many separate fragments. Scotti reported
at least five condensations in a very long, narrow train
approximately 47 arc-seconds in length and and about 11 arc-
seconds in width, with dust trails extending from either end
of the nuclear train. Its discovery was a serendipitous product
of their continuing search for near-Earth objects. Near-Earth
objects are bodies whose orbits come nearer to the Sun than that
of Earth and hence have some potential for collisions with Earth.
The International Astronomical Union's Central Bureau
for Astronomical Telegrams immediately issued a circular,
announcing the discovery of the new comet. The comet's bright-
ness was reported as about 14th magnitude, more than a thousand
times too faint to be seen with the naked eye. Bureau director
Brian G. Marsden noted that the comet was some 4 degrees from
Jupiter and that its motion suggested that it could be near
Jupiter's distance from the Sun.
Before the end of March it was realized that the
comet had made a very close approach to Jupiter in mid-1992
and at the beginning of April, after sufficient observations
had been made to determine the orbit more reliably,
Brian Marsden found that the comet is in orbit around Jupiter.
By late May it became apparent that the comet was
likely to impact Jupiter in 1994. Since then, the comet has
been the subject of intensive study. Searches of archival
photographs have identified pre-discovery images of the comet
from earlier in March 1993 but searches for even earlier
images have been unsuccessful.
According to the most recent computations, the comet
passed less than 1/3 of a Jovian radius (120,000 km) above
the clouds of Jupiter late on 7 July 1992 (UT). The individual
fragments separated from each other 1-1/2 hours after closest
approach to Jupiter and they are all in orbit around Jupiter
with an orbital period of about two years. Calculations of the
orbit prior to 7 July1992 are very uncertain but it seems very
likely that the comet was previously in orbit around Jupiter
for two decades or more. Ed Bowell and Lawrence Wasserman of
the Lowell Observatory have integrated the best currently
available orbit for P/Shoemaker-Levy 9 in a heliocentric
reference frame, and noted that the calculations put the
"comet" in a "Jupiter-grazing" orbit before about 1966.
Wasserman and Bowell's possible Jupiter close approaches
are in 2-, 3-, and 4-year intervals.
Table 3: Possible Close Approaches of 1993e with Jupiter
1993e 0.08963 AU from Jupiter on 1971 4 26.0
1993e 0.06864 AU from Jupiter on 1975 4 26.8
1993e 0.07000 AU from Jupiter on 1977 5 7.0
1993e 0.11896 AU from Jupiter on 1980 2 1.8
1993e 0.12453 AU from Jupiter on 1982 5 26.0
1993e 0.11937 AU from Jupiter on 1984 10 4.5
1993e 0.07031 AU from Jupiter on 1987 7 12.4
1993e 0.06090 AU from Jupiter on 1989 8 2.5
1993e 0.00072 AU from Jupiter on 1992 7 8.0
1993e Impacts Jupiter on 1994 7 16.8
Because the orbit takes the comet nearly 1/3 of an astronomical
unit (30 million miles) from Jupiter, the sun causes significant
changes in the orbit. Thus, when the comet again comes close to
Jupiter in 1994 it will actually impact the planet, moving almost
due northward at 60 km/sec aimed at a point only halfway from the
center of Jupiter to the visible clouds.
All fragments will hit Jupiter in the southern hemisphere,
at latitudes near 45 degrees south, between 16 and 22 July 1994,
approaching the atmosphere at an angle roughly 45 degrees from the
vertical. The times of the impacts are now known to within roughly
20 minutes, but continuing observations leading up to the impacts
will refine the precision of the predictions. The impacts will
occur on the back side of Jupiter as seen from Earth; that is,
out of direct view from the Earth (this also means that the comet
will strike on Jupiter's nightside). This area will be close to
the limb of Jupiter and will be carried by Jupiter's rotation to
the front, illuminated side less than half an hour after the
impact. The grains ahead of and behind the comet will impact
Jupiter over a period of four months, centered on the time of
the impacts of the major fragments. The grains in the tail of
the comet will pass behind Jupiter and remain in orbit around
The Nature of the Comet
The exact number of large fragments is not certain since
the best images show hints that some of the larger fragments may
be multiple. At least 21 major fragments were originally identified.
No observations are capable of resolving the individual fragments
to show the solid nuclei. Images with the Hubble Space Telescope
suggest that there are discrete, solid nuclei in each of the largest
fragments which, although not spatially resolved, produce a single,
bright pixel that stands out above the surrounding coma of grains.
Reasonable assumptions about the spatial distribution of the grains
and about the reflectivity of the nuclei imply sizes of 2 to 4 km
(diameter) for each of the 11 brightest nuclei. Because of the
uncertainties in these assumptions, the actual sizes are very un-
certain and there is a small but not negligible possibility that
the peak in the brightness at each fragment is due not to a nucleus
but to a dense cloud of grains.
No outgassing has been detected from the comet but
calculations of the expected amount of outgassing suggest that
more sensitive observations are needed because most ices vaporize
so slowly at Jupiter's distance from the sun. The spatial distri-
bution of dust suggests that the material ahead of and behind the
major fragments in the orbit are likely large particles from the
size of sand up to boulders. The particles in the tail are very
small, not much larger than the wavelength of light. The bright-
nesses of the major fragments were observed to change by factors
up to 1.7 between March and July 1993, although some became brighter
while others became fainter. This suggests intermittent release of
gas and grains from the nuclei.
Studies of the dynamics of the breakup suggest that the
structural strength of the parent body was very low and that the
parent body had a diameter of order 5 km. This is somewhat
smaller than one would expect from putting all the observed
fragments back together but the uncertainties in both estimates
are large enough that there is no inconsistency.
Although none of the fragments will hit any of Jupiter's
large satellites, Voyager data indicate that tidally split comets
have hit the Galilean satellites in the past. Until the discovery
of Comet P/Shoemaker-Levy 9, the strikingly linear crater chains
on Callisto and Ganymede had remained unexplained. It is quite
likely that these crater chains were formed by comets similar to
The longest of the chains, is 620 km long and comprises
25 craters. The first interpretation hinted that these were
secondary impact chains, formed by material ejected from large
basins -- very much akin to the Earth's Moon. The Callisto chains
are much straighter and more uniform than most secondary chains.
For 15 years the crater chains remained unexplained. In light of
P/SL9's nature, it is logical to conclude that the crater chains
on Callisto (and Ganymede) were formed when tidally disrupted
comets impacted the Jovian satellites.
To date, thirteen crater chains have been identified on
Callisto. Upon recent re-examination of Voyager's data, three
more similar chains have now been identified on Ganymede. The
next opportunity to identify and re-examine these features will
be when the Galileo spacecraft enters Jovian orbit in December,
The Planet Jupiter
Jupiter is the largest of the nine known planets, almost
11 times the diameter of Earth and more than 300 times its mass.
In fact, the mass of Jupiter is almost 2.5 times that of all the
other planets combined. Being composed largely of the light elements
hydrogen (H) and helium (He), its mean density is only 1.3 times
that of water. The mean density of Earth is 5.2 times that of
water. The pull of gravity on Jupiter at the top of the clouds
at the equator is 2.4 times greater than Earth's surface. The
bulk of Jupiter rotates once in 9 hours and 56 minutes, although
the period determined by watching cloud features differs by up
to five minutes due to intrinsic cloud motions.
The visible "surface" of Jupiter is a deck of clouds of
ammonia crystals, the tops of which occur at a level where the
pressure is about half that at Earth's surface. The bulk of the
atmosphere is made up of 89% molecular hydrogen (H2) and 11% helium
(He). There are small amounts of gaseous ammonia (NH3), methane
(CH4), water (H2O), ethane (C2H6), acetylene (C2H2), carbon monoxide
(CO), hydrogen cyanide (HCN), and even more exotic compounds such as
phosphine (PH3) and germane (GeH4). At levels below the deck of
ammonia clouds there are believed to be ammonium hydro-sulfide
(NH4SH) clouds and water crystal (H2O) clouds, followed by clouds
of liquid water. The visible clouds of Jupiter are very colorful.
The cause of these colors is not yet known. "Contamination" by
various polymers of sulfur (S3, S4, S5, and S8), which are yellow,
red, and brown, has been suggested as a possible cause of the riot
of color, but in fact sulfur has not yet been detected spectroscop-
ically, and there are many other candidates as the source of the
The meteorology of Jupiter is very complex and not well
understood. Even in small telescopes, a series of parallel light
bands called zones and darker bands called belts is quite obvious.
The polar regions of the planet are dark. Also present are light
and dark ovals, the most famous of these being "the Great Red
Spot." The Great Red Spot is larger than Earth, and although its
color has brightened and faded, the spot has persisted for at least
162.5 years, the earliest definite drawing of it being Schwabe's of
5 September 1831. (There is less positive evidence that Hooke observed
it as early as 1664.) It is thought that the brighter zones are cloud-
covered regions of upward moving atmosphere, while the belts are the
regions of descending gases, the circulation driven by interior heat.
The spots are thought to be large-scale vortices, much larger and
far more permanent than any terrestrial weather system.
The interior of Jupiter is totally unlike that of Earth.
Earth has a solid crust "floating" on a denser mantle that is fluid
on top and solid beneath, underlain by a fluid outer core that
extends out to about half of Earth's radius and a solid inner core
of about 1,220-km radius. The core is probably 75% iron, with the
remainder nickel, perhaps silicon, and many different metals in
small amounts. Jupiter on the other hand may well be fluid throughout,
although it could have a "small" solid core (upwards of 15 Earth
masses) of heavier elements such as iron and silicon extending out
to perhaps 15% of its radius. The bulk of Jupiter is fluid hydrogen
in two forms or phases, liquid molecular hydrogen on top and liquid
metallic hydrogen below; the latter phase exists where the pressure
is high enough, say 3-4 million atmospheres. There could be a small
layer of liquid helium below the hydrogen, separated out gravita-
tionally, and there is clearly some helium mixed in with the
hydrogen. The hydrogen is convecting heat (transporting heat by
mass motion) from the interior, and that heat is easily detected
by infrared measurements, since Jupiter radiates twice as much heat
as it receives from the Sun. The heat is generated largely by
gravitational contraction and perhaps by gravitational separation
of helium and other heavier elements from hydrogen, in other words,
by the conversion of gravitational potential energy to thermal
energy. The moving metallic hydrogen in the interior is believed
to be the source of Jupiter's strong magnetic field.
Jupiter's magnetic field is much stronger than that of Earth.
It is tipped about 11 degrees to Jupiter's rotational axis, similar
to Earth's, but it is also offset from the center of Jupiter by about
10,000 km. The magnetosphere of charged particles which it affects
extends from 3.5 million to 7 million km in the direction toward the
Sun, depending upon solar wind conditions, and at least 10 times that
far in the anti-Sun direction. The plasma trapped in this rotating,
wobbling magnetosphere emits radio frequency radiation measurable
from Earth at wavelengths from 1 m or less to as much as 30 km. The
shorter waves are more or less continuously emitted, while at longer
wavelengths the radiation is quite sporadic. Scientists will carefully
monitor the Jovian magnetosphere to note the effect of the intrusion
of large amounts of cometary dust into the Jovian magnetosphere.
The two Voyager spacecraft discovered that Jupiter has faint
dust rings extending out to about 53,000 km above the atmosphere.
The brightest ring is the outermost, having only about 800-km width.
Next inside comes a fainter ring about 5,000 km wide, while very
tenuous dust extends down to the atmosphere. Again, the effects of
the intrusion of the dust from Shoemaker-Levy 9 will be interesting
to see, though not easy to study from the ground.
The Impact into Jupiter
All 20-plus major impacts will occur at approximately the
same position on Jupiter relative to the center of the planet, but
because the planet is rotating the impacts will occur at different
points in the atmosphere. The impacts will take place at approxi-
mately 45 degrees south latitude and 6.5 degrees of longitude from
the limb, just out of view from Earth (approximately 15 degrees
from the dawn terminator). Jupiter has a rotation period of 9.84
hours, or a rotation rate of about 0.01 degrees/sec, so the impacts
will occur on the farside of the planet but the point of impact in
the atmosphere will rotate across the limb within about 11 minutes
after the impact, and cross the dawn termninator within about 25
minutes from the impact. From this point on the effects on the
atmosphere should be observable from Earth, but the viewing of
the atmosphere where the impact occurred will improve as the site
rotates towards the center of the disk and we can see it face on.
The comet particles will be moving almost exactly from (Jovian)
south to north at the time of the impact, so they will strike the
planet at an angle of 45 degrees to the surface. (The surface is
defined for convenience as the Jovian cloud tops.) The impact
velocity will be Jovian escape velocity, 60 km/sec.
The times of collision of these fragments with Jupiter
can only be currently estimated within about 20 minutes. As
measurements of the orbit are made over the next few months
the accuracy of these estimates should improve, so by 1 June
the impact time will be known with an accuracy of about 16 minutes
and by 1 July about 10 minutes. Eighteen hours before the first
impact the uncertainty will be approximately 3 minutes. The
relative positions of the fragments to each other are known much
more accurately than the absolute position, so once the first
fragment impacts Jupiter, the collision times of the remaining
fragments will be better constrained. The first fragment, A,
will collide with Jupiter on 16 July at 19:13 Universal Time
(UT). Jupiter will be approximately 5.7 AU (860 million km)
from Earth, so the time for light to travel to the Earth will
be about 48 minutes, and the collision will be observed on Earth
at 20:01 UT (16:01 PM EDT)on 16 July.
For Earth-based observations, Jupiter will rise at about
noon and set around midnight, so there will be a limited window
to observe the collisions. The head of the dust train around the
fragments will reach Jupiter 1 to 2 months before the particles
The predicted outcomes of the impacts with Jupiter span
a large range. This is due in part to the uncertainty in the
size of the impacting bodies but even for a fixed size there is
a wide range of predictions, largely because planetary scientists
have never observed a collision of this magnitude. It is not
known what the effects of the impacts of the large fragments
will be on Jupiter, the large mass (~10^12 to 10^14 kg) and high
velocity (60 km/sec) guarantee highly energetic collisions.
Various models of this collision have been hypothesized, and
there is general agreement that a fragment will travel through
the atmosphere to some depth and explode, creating a fireball
which will rise back above the cloud tops. The explosion will
also produce pressure waves in the atmosphere and "surface waves"
at the cloud tops. The rising material may consist of an equal
amount of vaporized comet and Jovian atmosphere, but details about
this, the depth of the explosion, the total amount of material
ejected above the cloud tops, and almost all other effects of the
impact are highly model dependent. Each impact (and the subsequent
fall-back of ejected material over a period of ~3 hours after the
collision will probably affect an area of the atmosphere from one
to a few thousand km around the impact site. It will be difficult
to see the objects within about 8 Jovian radii (~570,000 km).
If the cometary nuclei have the sizes estimated from the
observations with the Hubble Space Telescope and if they have the
density of ice, each fragment will have a kinetic energy equivalent
to roughly 10 million megatons of TNT (10^29 to 10^30 ergs). The
total energy of the collisions [of all fragments] may be as great
as 100 million megatons of TNT; roughly 10,000 times the total
destructive power of the world's nuclear arsen at the height of
the Cold War. The impacts will be as energetic as the collision
of a large asteroid or comet with the Earth 65 million years ago.
This latter cosmic catastrophe most probably led to the extinction
of the dinosaurs and hundreds of other species at the geologic
Cretaceous-Tertiary (K-T) boundary layer.
The predictions of the effects differ in how they model
the physical processes and there are significant uncertainties
about which processes will dominate the interaction. If ablation
(melting and vaporization) and fragmentation dominate, the energy
can be dissipated high in the atmosphere with very little material
penetrating far beneath the visible clouds. If the shock wave in
front of the fragment also confines the sides and causes the frag-
ment to behave like a fluid, then nuclei could penetrate far below
the visible clouds. Even in this case, there are disagreements
about the depth to which the material will penetrate, with the
largest estimates being several hundred kilometers below the
The short-term effects at the atmospheric site of impact may
be profound. Thermal plumes may rise to 700 km. Whether permanent
disturbances, such as a new Great Red Spot or White Ovals form, is
also a subject of great debate. The HST will monitor the atmosphere
for changes in cloud morphology as each impact site rotates into view
within a couple hours of the impact.
In any case, there will be an optical flash lasting a few
seconds as each nucleus passes through the stratosphere. The bright-
ness of this flash will depend critically on the fraction of the energy
which is released at these altitudes. If a large fragment penetrates
below the cloudtops and releases much of its energy at large depths,
then the initial optical flash will be faint but a buoyant hot plume
will rise in the atmosphere like the fireball after a nuclear explosion,
producing a second, longer flash lasting a minute or more and radiating
most strongly in the infrared. Although the impacts will occur on the
far side of Jupiter, estimates show that the flashes may be bright
enough to be observed from Earth in reflection off the inner satellites
of Jupiter, particularly Io, if a satellite happens to be on the far
side of Jupiter but still visible as seen from Earth. The flashes
will also be directly visible from the Galileo spacecraft.
The shock waves produced by the impact onto Jupiter are
predicted to penetrate into the interior of Jupiter, where they
will be bent, much as the seismic waves from earthquakes are bent
in passing through the interior of Earth. These may lead to a prompt
(within an hour or so) enhancement of the thermal emission over a very
large circle centered on the impact. Waves reflected from the
density-discontinuities in the interior of Jupiter might also be
visible on the front side within an hour or two of the impact.
Finally, the shock waves may initiate natural oscillations of Jupiter,
similar to the ringing of a bell, although the predictions disagree
on whether these oscillations will be strong enough to observe with
the instrumentation currently available. Observation of any of these
phenomena can provide a unique probe of the interior structure of
Jupiter, for which we now have only theoretical models with almost
no observational data.
The plume of material that would be brought up from Jupiter's
troposphere (below the clouds) will bring up much material from the
comet as well as material from the atmosphere itself. Much of the
material will be dissociated and even ionized but the composition of
this material can give us clues to the chemical composition of the
atmosphere below the clouds. It is also widely thought that as the
material recombines, some species, notably water, will condense and
form clouds in the stratosphere. The spreading of these clouds in
latitude and longitude can tell us about the circulation in the
stratosphere and the altitude at which the clouds form can tell us
about the composition of the material brought up from below. The
grains of the comet which impact Jupiter over a period of several
months may form a thin haze which will also circulate through the
atmosphere. Enough clouds might form high in the stratosphere to
obscure the clouds at lower altitudes that are normally seen
Interactions of cometary material with Jupiter's magnetic
field have been predicted to lead to observable effects on Jupiter's
radio emission, injection of material into Jupiter's auroral zone,
and disruption of the ring of grains that now encircles Jupiter.
Somewhat less certainly the material may cause observable
changes in the torus of plasma that circles Jupiter in association
with the orbit of Io or may release gas in the outer magnetosphere
of Jupiter. It has also been predicted that the cometary material
may, after ten years, form a new ring about Jupiter although there
are some doubts whether this will happen.
Overview of the Hubble Space Telescope
The Hubble Space Telescope is a coooperative program of
the European Space Agency (ESA) and the National Aeronautics and
Space Administration (NASA) to operate a long-lived space-based
observatory for the benefit of the international astronomical
community. HST is an observatory first dreamt of in the 1940s,
designed and built in the 1970s and 80s, and operational only in
the 1990s. Since its preliminary inception, HST was designed to
be a different type of mission for NASA -- a permanent space-based
observatory. To accomplish this goal and protect the spacecraft
against instrument and equipment failures, NASA had always planned
on regular servicing missions. Hubble has special grapple
fixtures, 76 handholds, and stabilized in all three axes.
When originally planned in 1979, the Large Space Telescope
program called for return to Earth, refurbishment, and relaunch
every 5 years, with on-orbit servicing every 2.5 years. Hardware
lifetime and reliability requirements were based on that 2.5-year
interval between servicing missions. In 1985, contamination and
structural loading concerns associated with return to Earth aboard
the shuttle eliminated the concept of ground return from the program.
NASA decided that on-orbit servicing might be adequate to maintain
HST for its 15-year design life. A three year cycle of on-orbit
servicing was adopted. The first HST servicing mission in December
1993 was an enormous success. Future servicing missions are tenta-
tively planned for March 1997, mid-1999, and mid-2002. Contingency
flights could still be added to the shuttle manifest to perform
specific tasks that cannot wait for the next regularly scheduled
servicing mission (and/or required tasks that were not completed
on a given servicing mission).
The four years since the launch of HST in 1990 have been
momentous, with the discovery of spherical aberration and the search
for a practical solution. The STS-61 (Endeavour) mission of December
1993 fully obviated the effects of spherical aberration and fully
restored the functionality of HST.
The Science Instruments
Wide Field/Planetary Camera 2
The original Wide Field/Planetary Camera (WF/PC1) was
changed out and displaced by WF/PC2 on the STS-61 shuttle mission
in December 1993. WF/PC2 was a spare instrument developed in 1985
by the Jet Propulsion Laboratory in Pasadena, California.
WF/PC2 is actually four cameras. The relay mirrors in
WF/PC2 are spherically aberrated to correct for the spherically
aberrated primary mirror of the observatory. (HST's primary mirror
is 2 microns too flat at the edge, so the corrective optics within
WF/PC2 are too high by that same amount.)
The "heart" of WF/PC2 consists of an L-shaped trio of
wide-field sensors and a smaller, high resolution ("planetary")
camera tucked in the square's remaining corner.
WF/PC2 has been used to image P/SL9 and will be used
extensively to "map" Jupiter's features before, during, and after
the collision events.
Corrective Optics Space Telescope Axial Replacement
COSTAR is not a science instrument; it is a corrective
optics package that displaced the High Speed Photometer during the
first servicing mission to HST. COSTAR is designed to optically
correct the effects of the primary mirror's aberration on the three
remaining scientific instruments: Faint Object Camera (FOC), Faint
Object Spectrograph (FOS), and the Goddard High Resolution
Faint Object Camera
The Faint Object Camera is built by the European Space
Agency. It is the only instrument to utilize the full spatial
resolving power of HST.
There are two complete detector system of the FOC. Each
uses an image intensifier tube to produce an image on a phosphor
screen that is 100,000 times brighter than the light received.
This phosphor image is then scanned by a sensitive electron-bombarded
silicon (EBS) television camera. This system is so sensitive that
objects brighter than 21st magnitude must be dimmed by the camera's
filter systems to avoid saturating the detectors. Even with a broad-
band filter, the brightest object which can be accurately measured
is 20th magnitude.
The FOC offers three different focal ratios: f/48, f/96,
and f/288 on a standard television picture format. The f/48 image
measures 22 X 22 arc-seconds and yields resolution (pixel size) of
0.043 arc-seconds. The f/96 mode provides an image of 11 X 11 arc-
seconds on each side and a resolution of 0.022 arc-seconds. The f/288
field of view is 3.6 X 3.6 arc-seconds square, with resolution down to
Faint Object Spectrograph
A spectrograph spreads out the light gathered by a telescope
so that it can be analyzed to determine such properties of celestial
objects as chemical composition and abundances, temperature, radial
velocity, rotational velocity, and magnetic fields. The Faint Object
Spectrograph (FOS) exmaines fainter objects than the HRS, and can
study these objects across a much wider spectral range from the UV
(1150 A) through the visible red and the near-IR (8000 A).
The FOS uses two 512-element Digicon sensors (light
intensifiers) to light. The "blue" tube is sensitive from 1150 to
5500 A (UV to yellow). The "red" tube is sensitive from 1800 to
8000 A (longer UV through red). Light can enter the FOS through any
of 11 different apertures from 0.1 to about 1.0 arc-seconds in diameter.
There are also two occulting devices to block out light from the center
of an object while allowing the light from just outside the center to
pass on through. This could allow analysis of the shells of gas around
red giant stars of the faint galaxies around a quasar.
The FOS has two modes of operation: low resolution and high
resolution. At low resolution, it can reach 26th magnitude in one hour
with a resolving power of 250. At high resolution, the FOS can reach
only 22nd magnitude in an hour (before S/N becomes a problem), but the
resolving power is increased to 1300.
Goddard High Resolution Spectrograph
The High Resolution Spectrograph also separates incoming
light into its spectral components so that the composition, temperature,
motion, and other chemical and physical properties of the objects can be
analyzed. The HRS contrasts with the FOS in that it concentrates entirely
on UV spectroscopy and trades the extremely faint objects for the ability
to analyze very fine spectral detail. Like the FOS, the HRS uses two
521-channel Digicon electronic light detectors, but the detectors of the
HRS are deliberately blind to visible light. One tube is sensitive from
1050 to 1700 A; while the other is sensitive from 1150 to 3200 A.
The HRS also has three resolution modes: low, medium, and high.
"Low resolution" for the HRS is 2000 A higher than the best resolution
available on the FOS. Examining a feature at 1200 A, the HRS can resolve
detail of 0.6 A and can examine objects down to 19th magnitude. At medium
resolution of 20,000; that same spectral feature at 1200 A can be seen in
detail down to 0.06 A, but the object must be brighter than 16th magnitude
to be studied. High resolution for the HRS is 100,000; allowing a spectral
line at 1200 A to be resolved down to 0.012 A. However, "high resolution"
can be applied only to objects of 14th magnitude or brighter. The HRS can
also discriminate between variation in light from ojbects as rapid as
100 milliseconds apart.
Mission Operations and Observations
Although HST operates around the clock, not all of its time
is spent observing. Each orbit lasts about 95 minutes, with time
allocated for housekeepingfunctions and for observations. "Housekeeping"
functions includes turning the telescope to acquire a new target, or
avoid the Sun or Moon, switching communications antennas and data
transmission modes, receiving command loads and downlinking data,
calibrating and similar activities.
When STScI completes its master observing plan, the schedule
is forwarded to Goddard's Space Telescope Operations Control Center
(STOCC), where the science and housekeeping plans are merged into a
detailed operations schedule. Each event is translated into a series
of commands to be sent to the onboard computers. Computer loads are
uplinked several times a day to keep the telescope operating
When possible two scientific instruments are used simul-
taneously to observe adjacent target regions of the sky. For example,
while a spectrograph is focused on a chosen star or nebula, the WF/PC
can image a sky region offset slightly from the main viewing target.
During observations the Fine Guidance Sensors (FGS) track their re-
spective guide stars to keep the telescope pointed steadily at the
In an astronomer desires to be present during the observation,
there is a console at STScI and another at the STOCC, where monitors
display images or other data as the observations occurs. Some limited
real-time commanding for target acquisition or filter changing is per-
formed at these stations, if the observation program has been set up
to allow for it, but spontaneous control is not possible.
Engineering and scientific data from HST, as well as uplinked
operational commands, are transmitted through the Tracking Data Relay
Satellite (TDRS) system and its companion ground station at White Sands,
New Mexico. Up to 24 hours of commands can be stored in the onboard
computers. Data can be broadcast from HST to the ground stations
immediately or stored on tape and downlinked later.
The observer on the ground can examine the "raw" images
and other data within a few minutes for a quick-look analysis.
Within 24 hours, GSFC formats the data for delivery to the STScI.
STScI is responsible for data processing (calibration, editing,
distribution, and maintenance of the data for the scientific
Competition is keen for HST observing time. Only one of
every ten proposals is accepted. This unique space-based observatory
is operated as an international research center; as a resource for
The Hubble Space Telescope is the unique instrument of
choice for the upcoming collision of Comet Shoemaker-Levy 9 into
Jupiter. The data gleaned from this momentous event will be
invaluable for decades to come.
Galileo is enroute to Jupiter and will be about 1.5
AU (230 million km) from Jupiter at the time of the impact.
At this range, Jupiter will be ~60 pixels across in the solid
state imaging camera, a resolution of ~2400 km/pixel. Galileo
will have a direct view of the impact sites, with an elevation
of approximately 23 degrees above the horizon as seen from the
impact point. The unavailability of the main antenna, forcing
use of the low-gain antenna for data transmission, severely limits
the imaging options available to Galileo. The low-gain antenna will
be able to transmit to Earth at 10 bits/sec, so real-time trans-
mission of imaging will not be possible. The Galileo tape recorder
can store ~125 full-frame equivalents. On-board data compression
and mosaicking may allow up to 64 images per frame to be stored,
but playback of the recorded images must be completed by January,
1995 when Galileo reaches Jupiter. This will only allow transmission
of ~5 full-frame equivalents, or approximately 320 images. There will
be the capability for limited on-board editing and the images can be
chosen after the impacts have occured, so the impact timing will be
well known, but the imaging times must be scheduled weeks before the
impacts. Each image requires 2.33 seconds, so a full frame of 64
images will cover ~2.5 minutes, and consist of ~2400 kilobits. A new
mosaic can be started in ~6 seconds. The camera has a number of
filters from violet through near-IR and requires 5 to 10 seconds to
change filters. In addition to imaging data, Galileo has a high time
resolution photopolarimeter radiometer, near-infrared mapping
spectrometer, radio reciever, and ultraviolet spectrometer which can
be used to study the collisions. The limited storage capacity and low
transmission rate of Galileo make the timing of all the impact
The Ulysses spacecraft is in a high inclination orbit
relative to the ecliptic plane, which will carry it under the
south pole of the Sun in September 1994. Its payload includes
sensitive radio receivers that may be able to observe both the
immediate consequences of the collisions of Comet Shoemaker-Levy
9 fragments with Jupiter and the long-term effects on the Jovian
Ulysses will be 2.5 AU (375 million km) south of Jupiter
at the time of impact and will also have a direct line of sight
to the impact point. From this position the Ulysses unified radio
and plasma wave (URAP) experiment will monitor radio emissions
between 1 and 940 KHz, sweeping through the spectrum approximately
every 2 minutes. URAP will be able to detect radio emissions down
to 10^14 ergs. There are no imaging experiments on Ulysses.
Voyager 2 is on it's way out of the solar system, 44 AU
from Jupiter at the time of the impact. The planetary radio
astronomy (PRA) experiment will be monitoring radio emissions
in the 1 KHz to 390 KHz range with a detection limit of 10^19
to 10^20 ergs. PRA will sweep through this spectrum every 96
seconds. The Voyager 2 imaging system will not be used.
International Ultraviolet Explorer
The International Ultraviolet Explorer (IUE) satellite
will be devoting 55 eight-hour shifts (approximately 2-1/2 weeks
total) of ultraviolet (UV) spectroscopic observations to the Comet
Shoemaker-Levy 9 impact events, with 30 shifts allotted to the
American effort (Principal Investigators: Walt Harris, University of
Michigan; Tim Livengood, Goddard Space Flight Center; Melissa
McGrath, Space Telescope Science Institute) and 25 shifts allotted
to the European effort (PIs: Renee Prange, Institute d'Astrophysique
Spatiale; Michel Festou, Observatoire Midi-Pyrenees). The observing
campaign will begin with baseline observations in mid-June, and continue
through mid-August. During the week of the actual impacts, IUE will
be observing the Jovian system
The IUE campaign will be devoted to in-depth studies of
the Jovian aurorae, the Jovian Lyman-alpha bulge, the chemical
composition and structure of the upper atmosphere, and the Io torus.
The IUE observations will provide a comprehensive study of the physics
of the cometary impact into the Jovian atmosphere, which can provide
new insights into Jupiter's atmospheric structure, composition, and
chemistry, constrain global diffusion processes and timescales in
the upper atmosphere, characterize the response of the Lyman-alpha
bulge to the impacting fragments and associated dust, study the
atmospheric modification of the aurora by the impact material deposited
by the comet and by the material ejected into the magnetosphere from
the deep atmosphere, and investigate the mass loading processes in
Many large telescopes will be available on Earth with
which to observe the phenomena associated with the Shoemaker-Levy
9 impacts on Jupiter in visible, infrared, and radio wavelengths.
Small portable telescopes can fill in gaps in existing observatory
locations for some purposes. Imaging, photometry, spectroscopy, and
radiometry will certainly be carried out using a multitude of
detectors. Many of these attempts will fail, but some should
succeed. Apart from the obvious difficulty that the impacts will
occur on the back side of Jupiter as seen from Earth, the biggest
problem is that Jupiter in July can only be observed usefully for
about two hours per night from any given site. Earlier the sky
is still too bright and later the planet is too close to the
horizon. Therefore, to keep Jupiter under continuous surveillance
would require a dozen observatories equally spaced in longitude
clear around the globe. A dozen observatories is feasible, but
equal spacing is not. There will be gaps in the coverage, notably
in the Pacific Ocean, where Mauna Kea, Hawaii, is the only
The Kuiper Airborne Observatory (KAO)
The KAO is a modified C-141 aircraft with a 36-inch (0.9
meter) telescope mounted in it. The telescope looks out the left
side of the airplane through an open hole in the fuselage. No window
is used because a window would increase the infrared background level.
The telescope is stabilized by: 1) a vibration isolation system (shock
absorbers); 2) a spherical air bearing; 3) a gyroscope controlled
pointing system; and 4) an optical tracking system. The telescope
can point to a couple of arc-seconds even in moderate turbulence.
The airplane typically flies at 41,000 feet (12.5 km),
above the Earth's tropopause. The temperature is very cold there,
about -50 degrees Celsius, so water vapor is largely frozen out.
There is about 10 precipitable microns of water in the atmospheric
column above the KAO (about the same amount as in the atmosphere of
Mars). This allows the KAO to observe most of the infrared wavelengths
that are obscured by atmospheric absorption at ground-based sites.
Flights are normally 7.5 hours long, but the aircraft has flown
observing missions as long as 10 hours. The comet impact flights
are all around 9.5 hours to maximize the observing time on Jupiter
after each impact. Because these observations will be made in the
infrared and the infrared sky is about as dark in the daytime as it
is at night, we will be able to observe in the afternoon and into
The main advantage that the airborne observatory brings
to bear is its ability to observe water with minimal contamination
by terrestrial water vapor. The observing projects focus on
observing tropospheric water (within Jupiter's cloud deck) brought
up by the comet impact, or possibly on water in the comet if it breaks
up above Jupiter's tropopause. The KAO team will also look for
other compounds that would be unobservable from the ground due
to terrestrial atmospheric absorption.
The KAO will be deployed to Australia to maximize the
number of times the immediate aftermath of an impact can be observed.
The available integration time on each flight will be typically 4-5
hours, from impact time to substantially after the central meridian
crossing of the impact point. The KAO will leave NASA Ames on 12 July,
return on 6 August. The last part of the deployment will be devoted
to observations of southern hemisphere objects as part of the regular
airborne astronomy program.
HST Science Observation Teams
HST Investigation of Comet P/Shoemaker-Levy 9
Comet P/Shoemaker-Levy 9 is being studied intensively by
HST prior to the impacts. In an investigation being led by Harold
A. Weaver (STScI), 40 orbits of HST time are being used to perform
imaging and spectroscopic observations of the comet during the
period from late January 1994 until the final hours before the
fragments make their fiery plunge into Jupiter's atmosphere during
mid-July. In addition, 4 orbits of time were awarded to a team
led by Terrence Rettig (University of Notre Dame) for further
detailed imaging of the comet.
The most important scientific objectives of the cometary
investigations are: (1) determine whether or not there are large,
solid nuclei at the condensation points in the comet and estimate
their sizes, (2) examine carefully the near-nucleus morphology of
the brightest objects to search for further fragmentation and out-
gassing activity, (3) monitor the temporal variability of the
largest nuclei, and (4) take deep spectroscopic exposures to search
for atoms and molecules in the vicinity of the comet.
Since the energy deposited into the Jovian atmosphere is
proportional to the cube of the size of the impacting object,
accurate nuclear sizes must be determined before accurate predictions
of impact phenomena can be made. HST's high spatial resolution
provides higher contrast between each nucleus and its surrounding
coma than can be achieved with any other optical telescope. Even in
the HST case the observed intensity is primarily due to light scattered
from the coma, but the improved contrast in the HST images allows for
a more accurate determination of the nuclear magnitudes, from which
sizes can be estimated.
The July 1993 HST images of P/Shoemaker-Levy 9 reveal a complex
morphology around each nucleus. At least several nuclei that seem to
be single objects at ground-based resolution emerge as multiple objects
at HST's resolution. Were these neighbors produced during the breakup
of the P/SL9's parent body, or has there been continuing fragmentation
in the ensuing period? One of the most intriguing results from the
currently available HST data is the possibility that the nuclei are
continuing to fragment. By careful examination of the HST images near
the brighter nuclei, and particularly by searching for temporal varia-
bility in the image morphology, we can detect fragmentation and "con-
ventional" cometary activity. Any evidence for fragmentation will provide
important information on the strength of the nuclei. Cometary nuclei are
known to be extremely fragile and often breakup for no apparent reason
(i.e., many nuclei split without being near any massive perturber).
Thus, we might expect to see continuing fragmentation of nuclei in
this comet well outside the Roche limit of Jupiter. At large
distances from Jupiter, the splitting of nuclei could be induced
by nuclear rotation, cometary activity (e.g., amorphous-to-crystalline
ice transitions, which has been proposed as the source of coma
activity in P/Schwassmann-Wachmann 1), or a combination of both.
Our spectroscopic program consists of two relatively deep
exposures near the brightest nucleus in order to search for atomic
and molecular emissions. Using the G270H grating of the Faint Object
Spectrograph (FOS) these observations cover the wavelength range
from 2223 to 3278 Angstroms. The new observations should be at least
three times more sensitive than previous HST observations. Besides
covering the strong hydroxyl (OH) bands, our spectrum will serendipi-
tously cover a strong emission band of carbon monoxide (CO) and
resonance transitions of several metals (i.e., Mg+, Mg++, and Si+).
The Jupiter spectroscopy team headed by Keith Noll
(STScI) will search for molecular remnants of the comet and
fireball in Jupiter's upper atmosphere. The team consists of
seven investigators: Noll (STScI), Melissa McGrath (STScI),
Larry Trafton (University of Texas), Hal Weaver (STScI),
John Caldwell (York University), Roger Yelle (University of
Arizona), and S. Atreya (University of Michigan).
Even though the comet's mass is dwarfed by the mass of
Jupiter, the impact can cause local disturbances to the
composition of the atmosphere that could be detectable with HST.
The two spectrometers on HST, the Faint Object Spectrograph (FOS)
and the Goddard High Resolution Spectrograph (HRS), will be used
to search for the spectral fingerprints of unusual molecules near
the site of one of the large impacts.
Jupiter's stratosphere will be subject to two sources
of foreign material, the comet itself, and gas from deep below
Jupiter's cloudtops. There are large uncertainties in the pre-
dictions of how deep the comet fragments will penetrate into
Jupiter's atmosphere before they are disrupted. But, if they
do penetrate below Jupiter's clouds as predicted by some, a
large volume of heated gas could rise into Jupiter's stratosphere.
As on the Earth, Jupiter's stratosphere is lacking in the gases
that condense out at lower altitudes. The sudden introduction
of gas containing some of these condensible molecules can be
likened to what happens on Earth when a volcano such as Pinatubo
injects large amounts of gas and dust into the stratosphere.
Once in this stable portion of the atmosphere on either planet,
the unusual material can linger for years.
The spectroscopic investigation will consist of 12 orbits
spread over three complementary programs. Several of the observations
will be done within the first few days after the impact of fragment
G on 18 July at 07:35 UTC. The team also wants to study how the
atmosphere evolves so some observations will continue into late
The FOS will obtain broad-coverage spectra from ~1750 -
3300 A. Quite a few atmospheric molecules have absorptions in this
interval, particularly below 2000 A. One molecule that we will look
for with special interest is hydrogen sulfide (H2S), a possible
ingredient for the still-unidentified coloring agent in Jupiter's
The spectroscopy team will focus in on two spectral
intervals with the HRS. In one experiment, the team will search
for silicon oxide (SiO) which should be produced from the rocky
material in the cometary nucleus. The usefulness of this
molecule is the fact that it can come only from the comet
since any silicon in Jupiter's atmosphere resides far below
the deepest possible penetration of the fragments. Measuring
this will help sort out the relative contributions of the comet
and Jupiter's deep atmosphere to the disturbed region of the
stratosphere. Finally, the spectroscopy team will use the HRS
to search for carbon monoxide (CO) and other possible emissions
near 1500 A. CO is an indicator of the amount of oxygen intro-
duced into the normally oxygen-free stratosphere. Any results
obtained with the HRS will be combined with ground-based observa-
tions of CO at infrared wavelengths sensitive to deeper layers to
reconstruct the variation of CO with altitude.
The HST Jupiter atmospheric dynamics team, led by Heidi
Hammel (Massachusetts Institute of Technology), will be carefully
monitoring Jupiter to observe how its atmosphere reacts to incoming
cometary nuclei. The atmospheric dynamics team consists of five
investigators: Hammel (MIT), Reta Beebe (New Mexico State
University), Andrew Ingersoll (California Institute of Technology),
Bob West (JPL), and Glenn Orton (JPL/Caltech).
Researchers at the Massachusetts Institute of Technology
have conducted computer simulations of the collisions' effect on
Jupiter's weather. These simulations show waves travelling outward
from the impact sites and propagating around the planet in the days
following each impact. The predicted "inertia-gravity" waves are on
Jupiter's "surface" (atmosphere) may emanate from the impact sites
and would be analagous to the ripples from dropping a pebble in a
Some theorists believe that the waves will be "seismic"
in nature, with the atmosphere of Jupiter ringing like a bell.
Such phenomenon may occur within the first hours after an impact.
These seismic waves would travel much faster than the inertia-gravity
waves, and quite likely more difficult to detect.
Using HST, Hammel's team hopes to detect and observe the
inertia-gravity waves which may take hours to days. The temperature
deviation in such a typical wave may be as much as 0.1 to 1 deg Celsius;
quite possibly visible from Earth in the best telescopic views.
The speed at which these waves travel depends on their
depth in the atmosphere and on stability parameters that are only
poorly known. While Hammel's team will observe the impact and its
aftermath with the Hubble Space Telescope, a team of scientists
will utilize the NASA Infrared Telescope Facility (IRTF) on Mauna
Kea, Hawaii. The IRTF and HST groups hope to measure wave speeds
and thus determine the Jovian atmospheric parameters more accurately.
Better-known parameters will, in turn, improve understanding of
planetary weather systems.
Another exciting possibility is that new cloud features
may form at the impact locations. These clouds might then be
trapped by surrounding high-speed jets and spun up into vortices
that might last for days or weeks.
Finally, cometary material will impact Jupiter's upper
atmosphere. This material (ices and dust) could significantly
alter the reflectivity of the atmosphere, and could linger for
weeks or months. The goal of Hammel's HST observing plan is to
observe all of these phenomena, while simultaneously and compre-
hensively mapping of Jupiter's atmosphere.
The primary "products" will be multicolor WF/PC "maps" (images)
of Jupiter. These new WF/PC2 maps will be compared against the latest
Jupiter images with older, WF/PC1 images, as well as Voyager spacecraft
images of Jupiter. At the very least, an exquisite time-lapse series
of the best images of Jupiter ever acquired by ground-based astronomy
and spacecraft will be obtained.
Cometary Particles and Aerosols in Jupiter's Stratosphere
The search for cometary particles in Jupiter's stratosphere
is led by Robert West of the Jet Propulsion Laboratory (JPL).
West's team will image Jupiter in the ultraviolet and near-IR
methane band filters to observe these particles as tracers of
Jupiter's stratospheric winds. West's co-investigators include
A. James Friedson (JPL), Erich Karkoschka (Lunar and Planetary
Laboratory, University of Arizona), and Kevin Baines (JPL).
The impact on Jupiter of fragments of P/Shoemaker-Levy 9
will provide an unprecedented opportunity to study the dynamics,
chemistry, and aerosol microphysics of Jupiter's stratosphere.
Understanding the dynamics of the stratospheres of most planets is
difficult because there are usually no markers to track winds (the
clouds we normally see on Jupiter are deeper, in the troposphere).
For the first time, we expect to see localized stratospheric tracer
particles in Jupiter's atmosphere from directly deposited cometary
grains and from condensable gases exhumed from the deeper atmosphere.
Dust and small pieces of the comet will be deposited directly
into the stratosphere on a global scale, while the largest fragments
will enter near latitude 40 degrees South. Some calculations predict
the large impactors will penetrate into the troposphere, below the
visible clouds and create a fireball which will rebound to the top
of the atmosphere. The fireball carries with it Jovian air from
below the cloudtops. This deeper gas contains a good deal more of
condensible volatiles like water (H20), ammonia (NH3), and hydrogen
sulfide (H2S) than is usual in the cold upper atmosphere. This
material is ejected over a region a few thousand kilometers in
radius. From that localized region, the Jovian stratospheric winds
will distribute this material globally.
An analogous situation occurs in Earth's atmosphere when
large volcanic eruptions like El Chichon and Pinatubo inject obser-
vable particles into the stratosphere. From observations of the number
and size of small particles as a function of altitude, latitude, and
time, we are able to study meridional (north-south, and vertical)
circulation, planetary-scale waves and other dynamical processes by
their effects on the spreading of the haze particles.
In the search for the P/SL9 particles in Jupiter's strato-
sphere, West's team will use a powerful combination of UV and near-IR
methane-band filters available with the WF/PC2 to observe the newly
created stratospheric haze on Jupiter. The signature of aerosols
is strongest at these wavelengths. Further, the UV observations
are important in understanding any changes in stratospheric solar
heating which may occur as a result of the additional aerosol burden,
and which would perturb the stratospheric circulation.
Jupiter's Upper Atmosphere
The HST Jupiter upper atmosphere imaging team, led by
John T. Clarke (University of Michigan), will image Jupiter at
far-ultraviolet wavelengths to observe the polar aurora as a
tracer of magnetospheric activity, search for lower latitude
auroral emission "arcs" associated with the passage of the comet
fragments through Jupiter's magnetic field, and look for the
signature of the comet fragment impact sites in the sunlight
reflected from Jupiter's upper atmosphere. The upper atmosphere
imaging team consists of Clarke, Renee Prange (Institute
d'Astrophysique Spataile, Orsay, France), and 17 co-investigators
from the US and Europe.
As the comet fragments approach Jupiter, they will be
depositing trails of material in Jupiter's magnetosphere as they
move at high speeds through the Jovian magnetic field. The amount
of material they contribute is expected to be small compared with
the natural supply from the satellite Io, however the new material
may alter the normal distribution or motions of the charged particles
in Jupiter's magnetosphere. The upper atmosphere imaging team will
look for such changes by observing Jupiter's aurora, or "northern
lights," which are produced by the impact of these magnetospheric
charged particles with Jupiter's upper atmosphere near the magnetic
poles. In addition, the relative motion of the comet fragments with
respect to Jupiter's magnetic field could generate electrical currents
which pass through Jupiter's upper atmosphere at lower latitudes than
the normal auroral emissions. The team will attempt to observe these
low latitude auroral "arcs".
There is a large uncertainty in our knowledge of the mass
and stability of the comet fragments, and therefore in our knowledge
of the depth into Jupiter's atmosphere that they will penetrate.
If the fragments are small or held together weakly, they will be
vaporized by atmospheric friction in Jupiter's upper atmosphere,
and the cometary material will be deposited into the upper atmosphere
several hundred kilometers above the visible cloud tops. This part
of Jupiter's upper atmosphere can be observed by far-ultraviolet
(far-UV) sunlight reflected by the atmosphere's primary constituent
H2, and also absorbed by other species. The added material in Jupiter's
upper atmosphere may appear as dark regions in the far-UV images
both from absorption by gas from the comet fragments and also lower
atmospheric gas that convectively rises into the upper atmosphere
from the heat of the impact. If these far-UV dark regions are detected,
we will also see how they drift horizontally with time, and may for the
first time be able to measure the speed and direction of the winds in
Jupiter's upper atmosphere.
Far-UV wavelengths of light (below 2000 Angstroms) are
strongly absorbed by atmospheric gases, and it is necessary to
place an instrument above the Earth's atmosphere to take images
of celestial objects at these wavelengths. The planets also appear
very different in the far-UV. For example, far-UV images of the
Earth from space show sunlight reflected from the upper atmosphere
(altitudes above 100 km) and also bright emissions from the polar
aurora and from diffuse airglow, which is emission from the upper
atmosphere produced by a combination of fluorescence of far-UV
sunlight and charged particle collisions with atmospheric gases.
The emissions provide information about the interaction of the
upper atmosphere with charged particles in the planet's magnetic
field, and the reflected far-UV sunlight gives information about
the altitude and spatial distribution of molecules in the upper
atmosphere that absorb far-UV sunlight. Far-UV images in general
give information about the highest regions of a planet's atmosphere
which interact with the space environment. The far-UV emissions
observed from Jupiter are similar to those from the Earth, although
Jupiter's aurora (or northern and southern lights) are more than
1000 times more energetic than the Earth's. Far-UV images of Jupiter
will be taken while the comet trail and dust clouds are in Jupiter's
magnetic field, both before and after the impacts of the comet
Comet Shoemaker-Levy 9's Impact on the Io Torus
The Io torus is a donut-shaped region filled with sulfur,
oxygen and electrons that surrounds Jupiter at the orbit of its moon
Io, about 400,000 km from the planet. It is maintained by Jupiter's
magnetic field, which is about 10 times stronger than the magnetic
field at the Earth's surface. This donut of material is an indirect
result of Io's active volcanoes. A program to study this region for
evidence of the comet fragments and their associated dust will be
conducted by a team of seven investigators led by Melissa A. McGrath
(Space Telescope Science Institute) using two instruments aboard the
Hubble Space Telescope, the GHRS and the FOS. The presence of the
comet fragments and their associated dust near Jupiter may release
new material, in particular silicon and carbon, into the Io torus that
is not normally present, or may disrupt the normally prodigious UV
emissions from this structure. The Hubble investigation will search
for evidence of any new elements in the torus, as well as carefully
measure the brightness of the normal ultraviolet emissions, for evidence
of the comet passage.
The timeline below contains the most up-to-date information
RE: the HST Jupiter campaign's mission timeline and predicted
impact times of each P/SL9 fragment [based on Chodas, Yeomans,
(1) HST orbit since January's SOT meeting
Using the most recent HST ephemeris supplied by Dave Taylor (SPSS),
all orbit visibility periods occur approximately 7 minutes earlier
(than based upon the information available at the SOT meeting). This
"slip" does not affect the currently planned science for the Jupiter
However, the following orbits graze SAA contour 5 (this was not known
at the time of the January SOT meeting):
orbit 87 202:06:02 -- 3 min Hammel WFPC
102 203:06:09 -- 2 min Hammel WFPC
117 203:06:17 -- 1 min Hammel WFPC
(2) Delta_t_tot Changes for Impact Times (since Jan. SOT mtg.)
EVENT DATE Time (UTC) Jan. SOT mtg.)
A=21 16 Jul 19:50 +14 minutes
B=20 17 Jul 02:46 +08 minutes
C=19 " 06:50 +21 minutes
D=18 " 11:11 -20 minutes
E=17 " 15:17 +39 minutes
F=16 18 Jul 00:16 +02 minutes
G=15 " 07:36 +38 minutes
H=14 " 19:35 +37 minutes
K=12 19 Jul 10:26 +36 minutes
L=11 " 22:24 +26 minutes
N=9 20 Jul 10:09 +19 minutes
P2=8b " 14:58 +05 minutes
Q2=7b " 19:40 +57 minutes
Q1=7a " 20:07 +1 hr 24 min
R=6 21 Jul 05:59 -42 minutes
S=5 " 15:39 +1 hr 01 min
T=4 " 18:28 +28 minutes
U=3 " 22:52 +1 hr 45 min
V=2 22 Jul 04:06 -25 minutes
W=1 " 08:21 +1 hr 09 min
HST Shoemaker-Levy/Jupiter campaign
Scheduling results of SOT meeting 1/27-28 1994
*****************P/SL9 Timeline Revision History*******************
23 Feb 94: Extended version from Y. Wang.
01 Mar 94: Revised by R. Landis to account for new impact times.
03 Mar 94: Revised by R. Landis per A. Storrs via R. Prangee.
Changing orbit 12 observation to orbit 20. 94.234 ob-
servations changed to day 94.220.
Deleted fragments J and M from timeline as these do not
appear in most recent HST images.
14 Mar 94: Renumbered timeline orbits per Y. Wang. (Numbered se-
quence has been corrected.)
Tabs replaced with spaces in order to better enable
H. Hammel's program to utilize this timeline.
07 Apr 94: Updated A. Storrs/R. Landis.
29 Apr 94: Updated A. Storrs/R. Landis.
Revised by R. Landis to account for new impact times
based on JPL data from D. Yeomans/P. Chodas.
02 Jun 94: Revised by R. Landis to account for new impact times
based on JPL data from P. Chodas.
07 Jun 94: Included Weaver's last P/SL 9 observations. Updated
HST orbit times based upon SPSS' most recent HST
ephemeris. R. Landis/A. Storrs.
15 Jun 94: Added Shemansky's FOS two-orbit sequence for o/a the
Revised by R. Landis to account for new impact times
based on JPL data from P. Chodas.
16 Jun 94: Removed the day 195 ("non-specific" time) observations
from timeline. These are vestigial as R. Prange and
K. Noll have specific time slots/HST orbits for their
respective FOC and FOS/HRS observations.
Orb# Starting Time: SAA Activity:
192:19:12:00 WFPC SL9Q-- Weaver
192:20:48:33 WFPC SL9Q-- Weaver
194:14:38:36 FOC-- Prange
194:19:28:11 HRS-- Noll
194:21:04:43 FOC-- Prange
194:22:41:15 23:17--end (05)
195:00:17:47 00:51--end (05)
195:01:54:19 02:30--end (05)
195:03:30:50 04:12--end (05)
195:05:07:22 05:54--end (05)
195:06:43:54 07:37--end (05)
195:08:20:23 WFPC SL9G-- Weaver
195:09:56:55 WFPC SL9G-- Weaver
195:11:37:45 FOS SL9G-- Weaver
195:13:09:59 FOS SL9G-- Weaver
195:14:50:40 WFPC SL9S-- Weaver
195:16:23:01 WFPC SL9S-- Weaver
195:17:59:36 FOS-- Noll
195:21:12:39 21:47--22:02 (05)
* 196:03:38:45 04:20--end (05)
* 04:23--end (02)
* 196:05:15:18 06:03--end (05)
* 196:06:51:49 07:46--end (05)
1 196:11:41:24 WFPC map-- Hammel
2 196:13:17:55 WFPC map-- Hammel
3 196:14:54:27 WFPC map-- Hammel
4 196:16:30:59 WFPC map-- Hammel
5 196:18:07:30 WFPC map-- Hammel
6 196:19:44:01 WFPC map-- Hammel
7 196:21:20:32 21:51--22:11 (05)
8 196:22:57:04 23:27--end (05)
9 197:00:33:36 01:06--end (05)
10 197:02:10:07 02:46--end (05)
11 197:03:46:38 04:27--end (05)
12 197:05:23:09 06:11--end (05)
13 197:06:59:42 07:54--end (05)
21 197:19:51:06 20:35--20:46 (05) WFPC-- Hammel A impact 197:19:50
22 197:21:28:23 21:56--22:19 (05)
23 197:23:04:54 23:34--end (05)
24 198:00:41:26 01:17--end (05)
25 198:02:17:57 02:55--end (05) B impact 198:02:46
26 198:03:54:28 04:37--end (05)
27 198:05:30:59 06:20--end (05)
06:22--end (02) C impact 198:06:50
29 198:08:43:14 WFPC-- Clarke
31 198:11:57:04 D impact 198:11:11
32 198:13:33:35 WFPC-- Hammel
33 198:15:10:06 WFPC-- Hammel E impact 198:15:17
34 198:16:46:38 WFPC-- Hammel
35 198:18:23:09 WFPC-- 1/2 Hammel,
36 198:19:59:39 20:26--20:45 (05)
37 198:21:36:11 22:02--22:28 (05)
38 198:23:12:42 23:41--end (05) 3 WFPC DARKS
*** SMS BOUNDARY *** *** BEGIN 94.199 SMS *** *** SMS BOUNDARY ***
39 199:00:34:04 01:21--end (05) F impact 199:00:16
40 199:02:10:24: 03:03--end (05)
41 199:03:48:43 04:35--end (05)
42 199:05:38:47 06:28--end (05) FOC--Prange
43 199:07:15:18 WFPC-- Hammel G impact 199:07:36
44 199:08:51:49 WFPC-- Hammel
45 199:10:28:20 FOS-- Noll
47 199:13:41:22 WFPC-- Clarke
48 199:15:17:52 WFPC SL9K-- Weaver
50 199:18:30:55 HRS-- Noll (SiO) H impact 199:19:35
51 199:20:07:27 20:32--20:54 (05)
52 199:21:43:58 22:09--22:36 (05)
53 199:23:20:29 23:48--end (05)
54 200:00:57:00 01:28--end (05)
55 200:02:33:30 03:12--end (05)
56 200:04:10:02 04:55--end (05)
57 200:05:48:33 06:37--end (05) HRS-- Noll (SiO)
58 200:07:23:04 WFPC-- Hammel
59 200:08:59:35 WFPC-- Hammel K impact 200:10:26
60 200:10:36:06 WFPC-- 1/2 Hammel,
63 200:15:25:39 HRS-- Noll (G140L)
65 200:18:38:41 19:09--19:18 (05)
66 200:20:15:13 20:37--21:02 (05)
67 200:21:51:43 22:17--22:45 (05)
68 200:23:28:14 23:55--end (05) 3 WFPC DARKS L impact 200:22:24
69 201:01:04:46 01:37--end (05)
70 201:02:41:16 03:20--end (05)
71 201:04:17:48 05:03--end (05)
72 201:05:54:18 06:46--end (05)
74 201:09:07:20 WFPC SL9Q-- Weaver N impact 201:10:09
75 201:10:43:52 HRS-- Noll (G140L)
76 201:12:20:22 HRS-- Noll (G140L)
77 201:13:56:54 WFPC-- Prange (4 ex)
78 201:15:33:25 WFPC-- 1/2 Hammel, P2 impact 201:14:58
79 201:17:09:55 WFPC SL9S-- Weaver
80 201:18:46:27 19:07--19:27 (05) Q2 impact 201:19:40
81 201:20:22:58 20:45--21:11 (05) WFPC-- Hammel Q1 impact 201:20:07
82 201:21:59:30 22:23--22:53 (05)
83 201:23:38:00 00:04--end (05)
84 202:01:12:32 01:45--end (05)
85 202:02:49:02 03:27--end (05)
86 202:04:25:34 05:11--end (05)
05:13--end (02) R impact 202:05:47
87 202:06:02:05 06:54--end (05) WFPC-- Hammel
88 202:07:38:35 WFPC-- 1/2 Hammel,
89 202:09:15:07 WFPC-- Hammel
90 202:10:51:37 WFPC-- Hammel
91 202:12:28:09 WFPC-- 1/2 Hammel,
92 202:14:04:40 WFPC-- Hammel
93 202:15:41:11 FOS-- Noll S impact 202:15:39
94 202:17:17:42 HRS-- Noll (G140L) T impact 202:18:28
95 202:18:54:12 19:14--19:37 (05)
96 202:20:30:44 20:52--21:19 (05)
97 202:22:07:15 22:31--23:00 (05) U impact 202:22:52
98 202:23:43:46 00:12--end (05) 3 WFPC DARKS
99 203:01:20:17 01:54--end (05)
100 203:02:56:48 03:37--end (05)
03:39--end (02) V impact 203:03:54
101 203:04:33:19 05:20--end (05)
102 203:06:09:50 07:03--end (05) WFPC-- Hammel
103 203:07:46:22 WFPC-- Hammel W impact 203:08:21
104 203:09:22:52 WFPC-- 1/2 Hammel,
106 203:12:35:35 HRS-- Noll (SiO, 3x8)
107 203:14:12:25 HRS-- Noll (SiO,2x12)
109 203:17:25:28 17:49--18:02 (05)
110 203:19:01:59 19:20--19:45 (05)
111 203:20:38:30 20:54--21:27 (05)
112 203:22:15:01 22:37--23:08 (05)
113 203:23:51:32 00:20--end (05)
114 204:01:28:04 02:03--end (05)
115 204:03:04:34 03:46--end (05)
116 204:04:41:05 05:27--end (05)
117 204:06:17:37 07:11--end (05) WFPC map-- Hammel
118 204:07:54:08 WFPC map-- Hammel
119 204:09:30:39 WFPC map-- Hammel
120 204:11:07:09 WFPC map-- Hammel
121 204:12:43:41 WFPC map-- Hammel
122 204:14:20:12 WFPC map-- Hammel
124 204:17:33:14 17:51--18:11 (05)
125 204:19:09:46 19:27--19:54 (05)
126 204:20:46:17 21:06--21:35 (05)
127 204:22:22:48 22:46--23:15 (05)
128 204:23:59:19 00:27--end (05)
129 205:01:35:50 02:12--end (05)
130 205:03:12:22 03:54--end (05)
131 205:04:48:53 05:37--end (05)
132 205:06:25:23 HRS-- McGrath
133 205:08:01:54 HRS-- McGrath
134 205:09:38:25 HRS-- McGrath
135 205:11:14:57 HRS-- McGrath
136 205:12:51:28 HRS-- McGrath
137 205:14:27:59 HRS-- McGrath
138 205:16:04:30 16:33--16:34 (05) HRS (Side 2)--
139 205:17:41:01 17:56--18:20 (05)
140 205:19:17:32 19:35--20:02 (05)
141 205:20:54:04 21:13--21:48 (05)
142 205:22:30:36 22:55--23:23 (05)
*** SMS BOUNDARY *** *** BEGIN 94.206 SMS *** *** SMS BOUNDARY ***
208:00:52:45 00:55--01:18 (05)
208:02:29:22 02:37--02:57 (05)
208:04:05:55 04:20--04:36 (05)
208:05:42:31 06:05--06:09 (05) FOS-- McGrath
208:06:48:55 FOS-- McGrath
208:08:25:26 FOS-- McGrath
208:10:01:57 FOS-- McGrath
208:11:38:29 FOS-- McGrath
208:13:15:00 FOS-- McGrath
208:14:51:32 15:12--15:18 (05) FOS-- McGrath
208:16:28:04 16:38--17:03 (05)
208:18:04:35 18:17--18:44 (05)
208:19:41:07 20:56--20:26 (05)
208:21:17:39 21:37--22:06 (05)
208:22:54:11 23:20--23:46 (05)
209:00:30:42 01:03--01:25 (05)
210:04:22:14 04:37--04:47 (05)
210:07:35:18 WFPC-- Clarke
210:08:41:17 WFPC-- Clarke
210:15:07:23 15:15--15:37 (05)
210:16:43:55 16:52--17:19 (05)
210:18:20:27 18:31--19:00 (05)
210:19:56:59 20:12--20:41 (05)
210:21:33:31 21:54--22:21 (05)
210:23:10:03 23:37--00:00 (05)
211:00:46:35 01:20--01:40 (05)
211:02:23:07 03:02--end (05)
211:03:59:39 04:48--04:50 (05)
211:07:12:42 WFPC map-- Hammel
211:08:49:14 WFPC map-- Hammel
211:10:25:46 WFPC map-- Hammel
211:12:02:18 WFPC map-- Hammel
211:13:38:50 13:52--14:02 (05)
*** SMS BOUNDARY *** *** BEGIN 94.213 SMS *** *** SMS BOUNDARY ***
213: FOS-- Shemansky (2 orbits)
*** SMS BOUNDARY *** *** BEGIN 94.220 SMS *** *** SMS BOUNDARY ***
220:21:41:07 begin--21:54 (05)
220:23:17:35 23:21--23:29 (05)
221:00:54:04 FOC-- Prange
221:02:06:06 FOC-- Prange
221:10:08:42 begin--10:20 (05) FOS-- Noll
221:11:45:13 begin--12:03 (05)
222:20:18:50 begin--20:29 (05)
222:21:55:18 begin--22:07 (05) HRS-- Noll
222:23:08:39 HRS-- Noll
223:00:45:10 HRS-- Noll
223:08:47:45 begin--08:54 (05)
224:05:42:28 FOC-- Prange
*** SMS BOUNDARY *** *** BEGIN 94.227 SMS *** *** SMS BOUNDARY ***
*** SMS BOUNDARY *** *** BEGIN 94.234 SMS *** *** SMS BOUNDARY ***
236:18:45:10 FOS-- Noll
236:20:08:48 FOS-- Noll
236:21:45:21 WFPC-- Hammel
### NOMINAL END OF JUPITER-COMET CAMPAIGN ###
Three digit numbers are day of year (1994): day 197 is July 16.
All times are UT (at Earth). Orbit times are from the extrapolation
done on Feb 4, 1994. Impact times are from the 1 Feb. JPL posting.
All times subject to change due to uncertainty in extrapolation of HST's
orbit and in prediction of impact times.
Note that FGS control cannot be used between 197:06 and 198:13, due to
the proximity of the Moon.
Each orbit (visibility period) lasts 52 min. In the SAA duration column,
ending time labeled "end" means it lasts until the visibility period of
the HST ends.
The numbers of the orbits here are rather arbitrary. Orbit # 1 here
corresponds to orbit No. 23031 from HST's numbering convention.
HST, Jupiter, and Comet Bibliography
Kerr, Richard and Elliot, James, Rings: Discoveries from Galileo
to Voyager, The MIT Press, Cambridge, Massachusetts, 1984.
Littman, Mark, Planets Beyond: Discovering the Outer Solar System,
Wiley Science Editions, New York, New York, 1988.
Peek, Bertrand M., The Planet Jupiter: The Observer's Handbook,
Faber & Faber Limited, London, England, 1958 [revised, 1981].
Smith, Robert W., The Space Telescope: A Study of NASA, Science,
Technology and Politics, Cambridge University Press, Cambridge,
England, 1989 [revised, 1993].
Shea, J.F. et al., Report of the Task Force on the Hubble Space
Telescope Servicing Mission (1993).
Articles on HST and Comet P/Shoemaker-Levy have appeared in popular
magazines such as Astronomy, Sky & Telescope, Mercury, Discover,
Science News, New Frontier, and The Planetary Report.
Asker, James R., "Spacecraft Armada to Watch Comet Collide with
Jupiter," Aviation Week & Space Technology, 24 January 1994.
Chaisson, E.J. and Villard, R., "Hubble Space Telescope: The Mission,"
Sky & Telescope, April, 1990.
Fienberg, Richard T., "HST: Astronomy's Discovery Machine," Sky &
Telescope, April, 1990.
Fienberg, Richard T. "Hubble's Road to Recovery," Sky & Telescope,
Hawley, Steven A., "Delivering HST to Orbit," Sky & Telescope, April 1990.
Hoffman, Jeffrey A., "How We'll Fix the Hubble Space Telescope," Sky
& Telescope, November 1993.
Landis, Rob, "Jupiter's Ethereal Rings," Griffith Observer, May 1991.
O'Dell, C.R., "The Large Space Telescope Program," Sky & Telescope,
Peterson, Ivars, "Jupiter's Model Spot," Science News, 19 February
Smith, Douglas L., "When a Body Hits a Body Comin' Through the Sky,"
Caltech Alumni Magazine Engineering & Science, Fall 1993.
Tucker, W., "The Space Telescope Science Institute," Sky & Telescope,
Villard, Ray, "From Idea to Observation: The Space Telescope at Work,"
Astronomy, June, 1989.
Villard, Ray, "The World's Biggest Star Catalogue," Sky & Telescope,
HST science results are published in professional journals
such as Geophysical Research Letters, Icarus, Astronomical
Journal, Astrophysical Journal, Nature, Science, Scientific
American, and Space Science Reviews, as well as in the pro-
ceedings of professional organizations. Some specific articles
of interest include:
Chevalier, Roger A. and Sarazin, Craig L., "Explosions of
Infalling Comets in Jupiter's Atmosphere," submitted to
Astrophysical Journal, 20 July 1994.
Kerr, Richard A., "Jupiter Hits May be Palpable Afterall,"
Science, 262:505, 22 October 1993.
Melosh, H.J. and Schenk, P., "Split Comets and the Origin of
Crater Chains on Ganymede and Callisto," Nature, 365:731-733,
21 October 1993.
Scotti, J.V. and Melosh, H.J., "Estimate of the Size of Comet
Shoemaker-Levy 9 from a Tidal Breakup Model," Nature, 365:733-735,
21 October 1993.
Trepte, C.R. and Hitchman, M.H., "The Stratospheric Tropical
Circulation Deduced from Aerosol Satellite Data," Nature 335:
Weaver, H.A. et al., "Hubble Space Telescope Observations
of Comet P/Shoemaker-Levy 9 (1993e)," Science, 263:787-790,
11 February 1994.
COSTAR Corrective Optics Space Telescope Axial Replacement
ESA European Space Agency
EVA Extravehicular Activity
FOC Faint Object Camera
FOS Faint Object Spectrograph
FGS Fine Guidance Sensor
GO General Observer (also Guest Observer)
GHRS Goddard High Resolution Spectrograph, also referred to as HRS.
GTO Guaranteed Time Observer
HST Hubble Space Telescope
JPL Jet Propulsion Laboratory
LEO Low-Earth Orbit
MT Moving Targets or Moving Targets Group (at STScI)
NASA National Aeronautics and Space Administration
NICMOS Near-Infrared Camera and Multi-Object Spectrometer
OSS Observation Support Branch (at STScI)
P/SL9 Shorthand for Periodic Comet Shoemaker-Levy 9 (SL9-A
refers to one of the cometary fragments, in this example
fragment "A", of the comet)
RSU Rate-sensing unit (gyroscope)
SAA South Atlantic Anomaly
SADE Solar Array Drive Electronics
SMOV Servicing Mission Observatory Verification
SPB Science Planning Branch (at STScI)
SPSS Science Planning & Scheduling Branch (at STScI)
SOT Science Observation Team
STIS Space Telescope Imaging Spectrograph
STS-61 Space Transportation System; the first servicing mission
is the 61st shuttle mission on the manifest since the
space shuttle first flew in 1981.
STScI Space Telescope Science Institute.
WF/PC (pronounced "wif-pik") Wide Field/Planetary Camera
A variety of line art supplied by JPL, Lowell Observatory,
the University of Maryland-College Park, and the STScI.
Most is self-explanatory.
Facts at a Glance
One-way light time, Jupiter to Earth: 48 minutes
Radius of Jupiter: 71,350 km (equatorial)
67,310 km (polar)
Radius of Earth: 6378 km (equatorial)
6357 km (polar)
P/Shoemaker-Levy: 4.5? km (equivalent sphere)
P/Halley: 7.65 x 3.60 x 3.61 km
Mass of Jupiter: 1.90 x 1030 g (~318 ME)
Rotation period: 9 hours 56 minutes
Number of known moons: 16
Discovery date P/Shoemaker-Levy: 24 March 1993
Time of first impact (P/SL9-A): 16 July 1994, 20:01 UTC
Time of P/SL9-Q's impact: 20 July 1994, 19:27 UTC
Time of last impact (P/SL9-W): 22 July 1994, 08:09 UTC
HST deployment date: 25 April 1990
HST first servicing mission: 2 - 13 December 1993
Diameter of HST's primary mirror: 2.4 meters
Cost of HST: $1.5 Billion (1990 dollars)
NASA Select is carried on Spacenet 2, transponder 5, channel 9,
69 degrees West, transponder frequency is 3880 MHz, audio sub-
carrier is 6.8 MHz, polarization is horizontal.
This document would not be possible if not for the support
of the Science Observation Team and the Science Planning
Branch/Moving Targets Group at the Space Telescope Science
Institute. The selection of material and any errors are
the sole responsibility of the author.
This paper represents the combined efforts of scientists and
science writers and is a selected compilation of several texts,
original manuscript, and submitted paragraphs. The genesis of
this document is due in large part to the FAQ begun by Texas
A&M University, background material provided by the University
of Maryland, and variety of Internet resources.
Gratitude and many thanks go to Mike A'Hearn (University of Maryland),
Reta Beebe (New Mexico State University), Ed Bowell (Lowell Observa-
tory), Paul Chodas (JPL), John Clarke (University of Michigan),
Ted Dunham (NASA-Ames), Heidi Hammel (MIT), Joe Harrington (MIT),
Dave Levy, Chris Lewicki (SEDS-University of Arizona), Mordecai
MacLow (University of Chicago), Lucy-Ann McFadden (University of
Maryland), Melissa McGrath (STScI), Ray Newburn (JPL), Keith Noll
(STScI), Renee Prange (University of Orsay, France), Elizabeth
Roettger (JPL), Jim Scotti (University of Arizona), Dave Seal
(JPL), Carolyn & Gene Shoemaker, Zdenek Sekanina (JPL), Ed Smith
(STScI), Lawrence Wasserman (Lowell Observatory), Hal Weaver
(STScI), Bob West (JPL), Don Yeomans (JPL) and to all others who
may have been omitted.
All comments should be addressed to the author:
Space Telescope Science Institute
Science Planning Branch/Moving Targets Group
3700 San Martin Drive,
Baltimore, MD 21218