August 14 - 20, 2000
Galileo 477 Million Miles from Earth
Galileo finds itself about 5.1 astronomical units (768 million kilometers, 477 million miles) from Earth this week as the spacecraft continues to orbit Jupiter and its many moons. Galileo's radio signal travels at the speed of light, which amounts to just under 300 million meters per second (1079 million kilometers per hour, 671 million miles per hour). This means that it takes Galileo's radio signal just under 43 minutes to reach Earth. One astronomical unit is equal to the average distance of the Earth from the Sun.
Galileo's week is fairly quiet. The spacecraft continues to return science data acquired during its May flyby of Jupiter's largest moon, Ganymede. Five observations are on the playback schedule. Four are returned by the Solid-State Imaging camera (SSI) and one by the Fields and Particles instruments.
The Fields and Particles instruments continue to return portions of a 60-minute high-resolution recording of the plasma, dust, and electric and magnetic fields surrounding Ganymede. Ganymede is the only planetary moon that is known to have its own internally-generated magnetic field, and these data will allow scientists to obtain a better understanding of the interaction between Jupiter's magnetic field and Ganymede's magnetic field.
SSI spends the week returning portions of four mosaics centered at the same locations on Ganymede as some previously-returned high-resolution images. These latest observations, however, provide a much more panoramic view. The high-resolution observations were designed to provide scientists with information regarding how different features and terrains came to exist on Ganymede's surface. These wider views will provide the geologic context for the higher-resolution images. In addition, combining the two data sets
will allow stereo images of these regions to be produced. The views returned this week contain smooth bright and grooved terrain, a transition region between bright and dark terrain, a region of pristine dark terrain, and a region of smooth bright terrain containing a band with a smooth plank-like appearance.
Finally, Galileo's Dust Detector was recently commanded to resume real-time data collection, and will continue to do so through September 3rd. Periodic read-outs of the instrument's memory showed unexpected increases in the number of dust particles during mid and late July, with thousands of impacts occurring on some days. Real time data collection will allow for closer monitoring of dust activity and will tell scientists about the size, speed, and origin of these micron- and submicron-sized particles.