Today on Galileo - February 20, 1997
Galileo passes its closest point (for this orbit) to Io, Europa and Jupiter during today's set of activities. As you know from the name of this encounter, only one of these flybys is close enough to be called an encounter. The flyby of Europa will occur at approximately 9:06 a.m. (PST). The spacecraft will fly at an altitude of only 586 km, even closer than its last encounter! This flyby is preceded by the closest approach to Io at about 4:03 a.m. (at an altitude of about 400,000 kilometers), and is followed by the Jupiter closest approach at about 12:54 p.m. (at a distance of 9.1 Rj, Rj = Jupiter radii, 1 Rj = 71492 km).
As can be expected, the majority of the science activity is focused on Europa. However, observations of Jupiter's White Ovals, monitoring of volcanic activity on Io, observations of Io's bright side, maps of Io's topography and observations of Amalthea and Ganymede are used to make this a very busy observing day for Galileo. Of particular interest during this days activity is a high-rate recording of Fields and Particles instrument data as Galileo flies through Jupiter's magnetic equator. As Galileo whips past Jupiter, it passes through the heart of the magnetosphere, a region where fresh plasma is constantly being generated and transported away to the outer boundaries of the magnetosphere. This observation will allow scientists to study these generation and transportation processes and understand how they affect the rest of the magnetosphere.
Europa observations are performed over unique areas at small solar phase angles (meaning that the Sun is behind Galileo and most of Europa will be lit). This geometry is good for observations that will provide data on the surface composition of Europa. High resolution observations for this orbit concentrate on lineated regions and bright plains. The global, regional and high resolution observations performed during this encounter are expected to provide an exciting fresh view of new regions on Europa's surface.
During closest approach to Europa, the Earth and Sun will become blocked from Galileo's line of sight by Europa itself. The Radio Science team will take advantage of this loss of signal to track Galileo's signal as it gets blocked by Europa and as it comes out from behind Europa. These measurements will allow scientists to determine the distribution of free electrons around Europa's surface and determine if it has a detectable ionosphere. In addition, the measurements will allow a more accurate determination of Europa's diameter. Also planned for closest approach is another high-rate Fields and Particles observation. This recording will provide data regarding the interaction of Europa with Jupiter's magnetosphere.
At the end of the day, the first set of commands that was sent to the spacecraft for this encounter will end. But having sent up the second set of commands, the spacecraft will continue to perform the encounter activities as planned.
Two more days to the encounter period and a satellite closest approach on each of them. Come back tomorrow!