Today on Galileo - December 16, 1997
The second day of the first encounter of the Galileo Europa Mission sees the spacecraft fly past a celestial body at the closest distance of the entire mission. At 4:03 a.m., Galileo will fly over the surface of Europa at a distance of only 200 kilometers (124 miles)! That is about the same as the distance between Los Angeles and San Diego! The spacecraft also passes the closest approach points to the moons Callisto and Io today. The minimum distance to Callisto, 1.2 million kilometers (750,000 miles), is reached at 7:33 a.m. and the minimum distance to Io, 480,000 kilometers (300,000 miles) is reached at 11:11 a.m.
Observations of Europa comprise the bulk of activity on the spacecraft's to-do list. With this encounter providing the closest flyby of Europa, observations will be of the highest resolution of Galileo's mission at Jupiter. Today's observing schedule starts out with a high time-resolution recording of the electric and magnetic wave environments associated with Jupiter's magnetosphere. This recording is performed by the Plasma Wave Subsystem (PWS).
The first of the many Europa observations of the day is performed by the Photopolarimeter Radiometer (PPR). The observation is one of a new campaign designed for the follow-on mission in which PPR will be looking for possible sources of high temperature areas, hot spots, on Europa. The Solid State Imaging (SSI) camera takes the first close-up images of this encounter shortly after 3 a.m. These images are of a region containing unusual plateaus with a fretted or ridged look to them. Next, the Near Infrared Mapping Spectrometer (NIMS) joins SSI and in back-to-back observations they both look at a region of dark lines on Europa. The information obtained in these observations will complement information gathered on the Europa-6 orbit of the primary mission. NIMS and SSI then turn their attention to the Pwyll crater region on Europa, with each instrument performing a single observation of the region. Information from this region will also complement data gathered on the Europa-6 orbit. The SSI data, in particular, will allow scientists to construct stereo images of this region.
For about 45 minutes surrounding the close flyby of Europa, the fields and particles instruments perform a high time-resolution recording of the magnetic, electric and particle environment surrounding Europa. These data will continue to build an information database that will allow scientists to further understand the interactions between Europa and Jupiter's magnetospheric environment.
SSI continues to take images of Europa's surface as the spacecraft passes a mere 200 kilometers (124 miles) above the surface. Several regions are imaged in this period. The Conamara Chaos region is observed at very high resolution filling in the details of regional context resolution data obtained during the Europa-6 orbit. A region of mottled or spotted terrain fills in the details of context information obtained during the Europa-11 orbit. And images of wedge or ice rift regions complement data from the non-targeted flyby of Europa during the Callisto-3 orbit.. NIMS returns to the observation schedule by also looking at this wedged region. The NIMS data will provide scientists with information about the composition or materials that can be found in this region. The last Europa observation of the encounter, like the first, is performed by PPR and is again a search for hot spots.
Observations of Io and Jupiter creep back into the schedule once the Europa flyby is complete. The NIMS team takes a quick look at Io in order to keep track of changes on Io's surface due to volcanic activity. Toward the end of the day, the Ultraviolet Spectrometer (UVS) takes a real-time (data immediately processed and transmitted) look at the darkside of Jupiter. This observation is designed to keep track of long-term changes in the amount of hydrogen in Jupiter's atmosphere.
Processing and transmission of the data recorded on the spacecraft's onboard tape recorder, also known as "playback", is initiated shortly before 1 p.m. The rest of the day, with the exception of the time spent executing the UVS observation of Jupiter's darkside, is spent processing and transmitting SSI's observation of Ganymede's Gilgamesh crater region. Scientists hope to use the crater statistics of this region, believed to have been created at the end of a heavy bombardment period, to understand the rate at which impactors have been entering the Jupiter system. This impactor rate can then be compared to crater statistics on Europa to get a better idea of the age of Europa's surface. Playback of this observation continues into the night and into tommorrow.
The set of computer instructions, known as a sequence, for the encounter period finishes executing tomorrow morning. The computer instructions that will control the spacecraft's activity through the next encounter is transmitted to the spacecraft this afternoon.
Tune in tomorrow for the return of This Week on Galileo with the details on the playback schedule for the remaining portion of the week!
Note: All times of day listed correspond to the Pacific Time zone and spacecraft event time. Radio signals indicating that an event has occured on the spacecraft reach the Earth 35 to 50 minutes later, depending on the time of year.