This Week on Galileo - December 22, 1997 - January 11, 1998
Galileo spends the holiday season processing and transmiting to Earth pictures and other information stored on the spacecraft's tape recorder during its close flyby of the moon Europa in mid-December 1997. During the three week period covered by this installment of "This Week on Galileo", the spacecraft performs two turns to keep its radio antenna pointed toward Earth. The bulk of the spacecraft's transmission time is dedicated to returning science data from observations of Europa.
Two non-Europa observations are processed and transmitted to Earth during this three week period. In the first, the Solid-State Imaging (SSI) team will receive science information take from Io while the fiery moon was eclipsed from the Sun by Jupiter. This data will allow scientists to continue their study of lava temperatures on Io and the interactions between volcanic plumes and Jupiter's magnetic environment. The second involves high time resolution samples gathered by the Plasma Wave Subsystem (PWS) as the spacecraft skirted past the outer edges of the Io torus, or donut-shaped cloud of neutral and ionized gases (plasma) found along Io's orbit. The Io torus is believed to be supplied with electrically charged particles by the volcanic eruptions on Io. The information will allow scientists to study that region where particles are constantly moving into or out of the Io torus' influence.
The first data from Europa that is processed and transmitted to Earth is an observation taken by the SSI team, a global observation of Europa. The information in this observation will be used to construct an image of the trailing hemisphere of Europa. The image will be constructed of 5 different colors at a resolution of 1.4 kilometers (0.9 miles) per picture element. The trailing hemisphere of a body is that side that is pointing in the opposite direction of Europa's travel around Jupiter. For example, the trailing hemisphere of a knuckleball pitch would be the side of the baseball that is pointing back toward the pitcher as the ball travels to the catcher. This hemisphere does not change because Europa, and the rest of the Galilean satellites, are in a "locked rotation" with Jupiter. This means that, as the satellites orbit around Jupiter, they rotate so that the same side is always pointing toward Jupiter. In this way, the leading hemisphere will always lead and the trailing hemisphere will always trail. The Near Infrared Mapping Spectrometer (NIMS) follows suit with the return of their own global observation of Europa's surface. The NIMS data will contain information on a region known as Asterius Linea that was lost during Galileo's primary mission.
The Photopolarimeter Radiometer (PPR) returns the first in a Galileo Europa Mission data campaign to locate and study hot spots on Europa. These hot spots, if discovered, might be evidence that Europa has an internal heat source, a key component for the possibility of life. The SSI team returns an image of a region on Europa characterized by fretted or "ridged" terrain. The resolution of the image is expected to be 180 meters (590 feet) per picture element. Information about a region characterized by dark lines and a feature known as Minos Linea, is returned by both SSI and NIMS. The camera data was gathered through four different color filters at a resolution of 170 meters (557 feet) per picture element. Both instruments then return data from observations of the region of Europa containing the Pwyll impact crater. This information will complement data gathered during the Europa-6 orbit of Galileo's primary mission and the SSI team is expected to generate stereo images of this region.
Also processed and transmitted to Earth during this three week period is high time resolution fields and particles information adding to the knowledge of the interaction of Europa with Jupiter's magnetic and electric environment. These data were gathered during the spacecraft's closest 45 minutes to Europa.
Some of the highest resolution images of Europa are scheduled to be transmitted to Earth in the first week of 1998. Taking advantage of the incredibly close flyby distance of the last encounter with Europa, 200 kilometers (124 miles), the SSI camera will return images with resolutions between 6 and 12 meters (20 to 40 feet) per picture element. One image will cover the Conamara Chaos region of Europa while another will contain a region of mottled or "blotchy" terrain. These regions were observed at regional resolutions during the Europa-6 and Europa-11 orbits, respectively, of Galileo's primary mission.
Our next update will be on Monday, 12 January 1998! Happy Holidays from the Galileo Project!