Adding Up Light from Comet's Jovian Crash
Cowen, R., Science News
When the fragments of Comet Shoemaker-Levy 9 plowed into Jupiter last July, dozens of large telescopes on Earth and several in space recorded the light show. Last week, scientists orchestrated the data from these instruments into one giant symphony.
"Now we're putting all the pieces together," says astronomer Heidi B. Hammel of the Massachusetts Institute of Technology. She and other researchers presented their findings in Baltimore at a meeting of the International Astronomical Union devoted to the comet crash.
Intriguingly, scientists have now confirmed that even though the fragments struck the back of Jupiter, just out of view of Earth, ground-based telescopes were the first to see the initial flashes of light -- even before the Jupiter-bound Galileo spacecraft, which had a direct view of the comet crashes.
An analysis of the fireworks associated with several of the larger fragments indicates that for each event, the first emissions came as a chunk entered Jupiter's upper atmosphere, streaking like a meteor. (Cometary debris just in front of some of the fragments may also have contributed to the initial light emission.)
At an altitude of 400 to 500 kilometers above the Jovian cloud tops -- well above the darkened limb of the planet -- the fragments emitted enough light for large telescopes on Earth to record the faint entry flashes.
"It's quite understandable that Galileo didn't see this, even though the emission happened right in front of [the craft], because the flux of light was too faint for it to detect," says Philip D. Nicholson of Cornell University.
For a few impacts, Galileo caught the tail end of the entry, which occurred about 10 seconds later, after the fragments had sunk below Jupiter's limb and out of sight of telescopes on Earth. …