Amazing Galileo Facts  2

   Jupiter's moon Io has some of the most dramatic-appearing volcanoes around. Geysers on Io spew out at speeds as high as 1 km/sec (2,300 mph). On Earth, Mt. Etna's ejecta erupt out at a "mere" 112 mph; terrestrial volcanoes rarely exceed 200 mph. Io's gravity is low (1/6 that of Earth), so the plumes are huge--reaching as much as 162 miles high. If you could move Old Faithful to Io, it would shoot up a plume of water and ice over 21 miles high (note, though, that we have no detection of water on Io and the most likely fluid/gas for the plume geysers is sulfur dioxide).
   Io is arguably the most volcanically active body yet known. We've seen at least 200 volcanic caldera bigger than 12 miles in diameter on its surface.
   Jupiter's tug on the Galilean moon Io causes tides, just like our own moon raises tides on the Earth's surface. A typical ocean tide on Earth is about one meter (3 feet). Io's surface tides (no water!), though, are truly something to behold: as great as 330 feet high!
   How many people have worked on Galileo? Nobody knows for sure, but it's been estimated that roughly 10,000 people have worked directly on Galileo since the Project's start in 1977. That's excluding people associated with the Space Shuttle and the Inertial Upper Stage booster.
   Because the asteroid Gaspra is so small (about 19 x 12 x 11 kilometers, or 12 x 7.5 x 7 miles), its surface gravitational force is two thousand times smaller than that of the Earth's, yielding an escape speed of only 10 meters per second (22 miles per hour); an Olympic-caliber sprinter could run himself into orbit! A 200 pound person would weigh 0.1 pounds!
   The Gaspra asteroid flyby was yet another example of outstanding navigation: at closest approach, Galileo was just 1.5 seconds and 1 kilometer (0.6 miles) from the aim point. Even so, taking the picture was a dramatic achievement. One of Galileo's scientists said "It was like taking a picture of a large house in San Francisco from Los Angeles."
   When the Galileo Photopolarimeter Radiometer detected the flashes of light caused by Comet Shoemaker-Levy 9 crashing into Jupiter in July 1994, it was using a 4 inch telescope, and it was as far away from Jupiter as Mars is from the Sun.
   Galileo's second Earth flyby brought the spacecraft within 303 kilometers (182 miles) of the Earth's surface. The gravity assist added 3.7 kilometers per second (8,300 miles per hour) to the spacecraft's speed in its solar orbit. As always, Galileo's navigation was impeccable: the spacecraft was within a kilometer of its intended path, and was just 0.1 second early.
   Jupiter's volume is about 1,400 times that of the Earth. In fact, its volume is half again bigger than all of the Solar System's other planets, moons, asteroids, and comets combined.
   Since Galileo is going into orbit around Jupiter (unlike the two Voyager spacecraft, which flew by the planet), it can fly by Jupiter and its moons at far closer distances than did Voyager, which means that Galileo's pictures will be a dramatic improvement over those from Voyager. Comparing Voyager images with those to be sent back from Galileo is like viewing a book at the base of the Empire State Building from the top story, as opposed to holding that book in your hands.
   Galileo's power sources, radioisotope thermo-electric generators, are putting out only about 520 watts on 7 December. That's not even enough to run a kitchen toaster!


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