Today on Galileo
21 Nov 1998
(Source: Jet Propulsion Laboratory)
Galileo started the seventh encounter of the Galileo Europa Mission early this morning at 4:00 am PST [See note 1]. The encounter is the second to last that will feature a close flyby of Jupiter's icy moon Europa. The flyby of Europa will occur tomorrow, at 3:38 am PST, at an altitude of 2273 kilometers (1418 miles). The encounter period will last through Monday, with most observations occurring around tomorrow's flyby of Europa. The spacecraft is approximately 683 million kilometers from Earth. At this distance, it takes 38 minutes for radio signals to reach Earth from Galileo, or vice-versa.
Galileo passes within 1.70 million kilometers (1.06 million miles) of Ganymede at 10:40 PST. Fifty minutes later, at 11:30 pm PST, the spacecraft is within 7.9 Jupiter radii (565,000 kilometers, 351,000 miles) of Jupiter's cloudtops.
Science observations begin at 4:00 am, with the resumption of the survey of the inner portion of the Jovian magnetosphere by the fields and particles instruments. This survey provides information on the spatial and temporal variations of the innermost, and most active, portion of the magnetosphere.
Today's remote sensing schedule includes observations of Europa, Jupiter and Io, with participation from the ultraviolet spectrometer, the photopolarimeter radiometer, the near-infrared mapping spectrometer, the spacecraft camera and the radio science team.
The ultraviolet spectrometer kicks off the observing campaign by looking for atmospheric emissions from Europa, including possible detection of outgassing events. The photopolarimeter radiometer will collect a low resolution, global scale polarimetry map of Europa. Polarimetric measurements provide information on the texture and composition of Europa. Later in the day, the ultraviolet spectrometer collaborates with the near-infrared spectrometer to perform a global observation of Europa. This observation is the first of two of this type for this encounter and will provide more data on the composition of Europa's surface.
The radio science experiment is tied to tomorrow's flyby of Europa, but it starts today at about 5:38 pm PST. For 20 hours surrounding the point of closest approach, the radio science team monitors Galileo's radio signal and measures changes in frequency caused by Europa's gravitational pull on the spacecraft. Using the Doppler effect, the team will be able to refine gravity field maps produced with measurements from previous orbits.
The near-infrared mapping spectrometer is today's sole observer of Jupiter. In four observations sprinkled throughout the day, it takes snapshots of Jupiter's atmosphere that will allow scientists to study variations in composition and temperature over time. The spectrometer also takes another look at the newly created white oval. This intense storm was formed this past spring from the merging of other two white ovals. The observation will provide a second view of this new feature, which was first observed by the spectrometer during Galileo's September encounter.
Two observations of Io complete today's remote sensing schedule. First, the photopolarimeter gathers data describing Io's surface texture and composition. The data will be used to fill in a gap in the existing polarimetry map of Io. The second observation is performed by the spacecraft camera and is designed to detect any changes in the surface of Io due to volcanic activity.
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: