This Week on Galileo - September 29 - October 5, 1997
Playback of data from Galileo's previous encounter with the moon Callisto continues this week, but is interrupted at the start of the week when Jupiter blocks the spacecraft's view of Earth (an Earth occultation), and at the end of the week while science observations are performed while Jupiter eclipses the sun (a solar occulation).
The spacecraft's view of the Earth, and as a consequence, the path of its radio signal, is blocked by Jupiter for close to 17 hours on Monday. The time is not wasted, however, as the radio science team tracks the changes to the spacecraft's radio signal as the spacecraft moves behind Jupiter and the radio signal, travelling to Earth, is forced through more and more of Jupiter's atmosphere. The monitoring of the spacecraft's signal is repeated as the spacecraft moves out from behind Jupiter. The measurements of the changes in Galileo's radio signal will allow scientists to learn more about the density of electrons in Jupiter's upper atmospheric layer, the ionosphere.
The days between the end of this week's Earth occultation and the start of preparations for the solar occultation observations are spent returning data from Galileo's most recent encounter with the Jupiter system and Callisto. This week's playback schedule is dedicated primarily to observations of Jupiter and Io with single observations of the moons Europa and Thebe. These last two are returned by the SSI (Solid State Imaging camera) team.
Observations of Jupiter returned this week are varied in nature. Photopolarimeter Radiometer (one observation) and Near Infrared Mapping Spectrometer (four observations) return observations of the north pole auroral region as part of the campaign for complete characterization of this part of Jupiter's atmosphere. In association with this, the UVS (Ultraviolet Spectrometer) team returns an observation of the south pole aurora region. Continuing with Jupiter observations, the PPR team returns a couple of regional maps at 7 degrees north latitude, just slightly north of Jupiter's equator. These maps are part of a mission campaign to build a map at this latitude over all longitudes. Finally, the NIMS team returns four observations that will also contribute to the construction of a thermal map at about 7 degrees north latitude. Scientists are interested in this region of Jupiter's atmosphere because it contains a series of hot spots that are typical of the region that was sampled by Galileo's atmospheric probe in December of 1995.
The observations of Io returned this week are mainly geared toward the orbit-to-orbit monitoring of volcanic activity on Io. The PPR team returns two observations that will be used to characterize large, low temperature, high power hot spots with the goal of obtaining temperature maps of the surface. This will provide insight into the thermal inertia of the satellite, which in turn tells us something about the satellite's inner structure. The NIMS team returns a couple of observations at high spectral resolutions that will be used to search for both known and yet unknown features on Io's surface. Other observations returned by NIMS look at specific volcanic regions (Loki, Pele, Kanehekili) in an attempt to monitor the time variability of these regions and at Io's nightside in search of hot spots, thermal anomalies and outbursts on the surface. Finally, the SSI team returns two of three observations of Io that will provide global coverage at high spatial and spectral resolution.
On the last day of the week, the spacecraft spends close to 19 hours in darkness as Jupiter blocks sunlight from reaching it. The SSI instrument takes the opportunity to perform a series of observations of Jupiter, Io and Europa. The UVS instrument also contributes by performing an observation in search of aurora on Jupiter. The observation campaign is kicked off after a spacecraft turn improves the instruments' view of their objectives. Jupiter observations performed by SSI during the campaign will look at the darkside of the planet in hopes of finding lightning, aurorae and Jupiter's rings. While looking at Europa and Io, the SSI instrument will be looking for signs for corresponding plumes and signs of emissions that may be related to aurorae on Jupiter. Once the observations are complete, the spacecraft turns again to point its antenna back to Earth.