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Today on Galileo
Today on Galileo
22 Nov 1998
(Source: Jet Propulsion Laboratory)

The majority of today's activity surrounds the spacecraft's close flyby of Europa. The flyby will occur at 3:38 am PST [See note 1] at an altitude of 2273 kilometers (1418 miles). Observations are also taken of Jupiter, Io and Ganymede. Galileo also passes within 2.35 million kilometers (1.46 million miles) of Callisto at about 6:00 pm PST today.

The first of today's Europa observations is performed by the spacecraft camera, and consists of a series of images near the terminator of bright polar plains. Later in the morning, the camera also looks at a dark band formation known as Rhadamanthys Linea, as well as a series of elevated features, regions of pits and plateaus near Europa's north pole, and a region of transition from bright plains to dark plains.

These observations are then followed by three performed by the near-infrared mapping spectrometer together with the ultraviolet spectrometer. The observations target a region of complex intersecting dark lines, a region of sharply defined dark lines, and Europa's northern polar region.

The camera then returns to the observation schedule by taking a series of images, split between two observations, to capture a section of Europa's surface near the terminator from 30 degrees south of the equator to 60 degrees north of the equator. The camera will image Tegid, an impact crater with an unusual domed morphology. Two images will also be taken of a region in which mottled, possibly "chaos," terrain appears to be older than the ubiquitous ridges and bands that dominate the surface of Europa. Elsewhere, chaos type terrains appear to be younger than nearby heavily ridged and grooved plains.

The photopolarimeter radiometer continues the observations of Europa with its second low resolution global scale map (the first map was collected yesterday). This is followed by another global observation of Europa performed jointly by the ultraviolet spectrometer and the near-infrared mapping spectrometer. Continuing with the global-scale observations, the camera then takes two more observations of Europa.

Three observations of Jupiter are performed today. The first two are by the near-infrared mapping spectrometer and are snapshots of the composition and temperature of Jupiter's atmosphere. The third observation is performed by the ultraviolet spectrometer and provides information on long-term changes in the amount of hydrogen in Jupiter's atmosphere. These ultraviolet measurements will allow scientists to further their understanding of interactions between Jupiter's upper cloud layers, lower layers, and Jupiter's magnetosphere.

Three observations of Io are performed late in the day, one each by the camera, near-infrared mapping spectrometer, and ultraviolet spectrometer. The observations are performed to detect changes in the surface of Io, and to use in planning for the scheduled Io flybys late in 1999. The camera will examine the potential source of a new intense volcanic hotspot first observed during Galileo's May encounter. The ultraviolet spectrometer, in conjuction with the extreme ultraviolet spectrometer, also takes a remote look at Io's plasma torus.

A single observation of Ganymede is performed during this encounter. In it, the photopolarimeter radiometer gathers polarimetric measurements from a portion of Ganymede's surface that was not completely covered during Galileo's primary mission.

Late today, after all recorded observations have been completed, Galileo begins processing and transmitting science information stored on its onboard tape recorder during the encounter period. First on the playback schedule are two observations performed by the photopolarimeter radiometer. Both observations contain polarimetric measurements which provide information on the texture and composition of the target bodies (Io and Europa).

The encounter period ends tomorrow and with it comes the return of This Week on Galileo. Come back to this URL for details on this week's exciting plans!

Note 1. All times listed correspond to the Pacific Time zone (currently standard time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, this time is 38 minutes. The current correction between Pacific Standard Time and Greenwich Meridian Time (GMT) is 8 hours.

For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page:
http://www.jpl.nasa.gov/galileo

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