On June 3rd two lucky amateurs, Anthony Wesley in Australia and Christopher Go in the Philippines, electrified the world of planetary astronomy when they simultaneously videorecorded a tiny, two-second flare of light on Jupiter apparently the strike of a small asteroid. The flare was much too bright to be one of Jupiter's lightning flashes, as some suggested early on. This was the third known impact on Jupiter and the second discovered by Wesley. See our article from that day, Jupiter Takes Another Hit!
The two previous known Jupiter impacts, in 1994 and 2009, left big black marks that persisted for weeks. But in the hours and days after the June 3rd event, amateurs and professionals imaging the site found no trace left behind.
Might the Hubble Space Telescope see something more? Four days later, on June 7th, Hubble swung toward Jupiter to take the best possible look.
Nope, no mark.
This morning NASA finally issued the news. From the NASA press release:
"[The flare] came from a giant meteor burning up high above Jupiter's cloud tops. The space visitor did not plunge deep enough into the atmosphere to explode and leave behind any telltale cloud of debris, as seen in previous Jupiter collisions. . . .
"[The lack of debris] above Jupiter's cloud tops means that the object didn't descend beneath the clouds and explode as a fireball. 'If it did, dark sooty blast debris would have been ejected and would have rained down onto the cloud tops, and the impact site would have appeared dark in the ultraviolet and visible images due to debris from an explosion,' says team member Heidi Hammel of the Space Science Institute in Boulder, Colo. 'We see no feature that has those distinguishing characteristics in the known vicinity of the impact, suggesting there was no major explosion and fireball. . . . There was just the meteor.' "
So, why would a meteor exploding above the clouds leave no visible ash, yet one exploding below the clouds would?
We asked the principal investigator on the Jupiter observation, Amy Simon-Miller of NASA's Goddard Space Flight Center. The answer, she says, is that the black stuff seen from the previous, larger impacts wasn't meteorite ash but "primarily burnt atmosphere." The huge fireball of a deeper impact pulls up stuff from below, "and the material thrown back out in the fireball would be primarily atmosphere. Although Jupiter is composed mainly of hydrogen and a small amount of helium, even traces of ammonia, hydrocarbons (including methane), etc., are enough to leave the sooty debris we see."
The press release goes on to report an interesting estimate:
"Though astronomers are largely uncertain about the rate of large meteoroid impacts on the planets, the best guess for Jupiter is that the smallest detectable events may happen as frequently as every few weeks.
" 'The meteor flashes are so brief they are easily missed, even in video recordings, or perhaps misidentified as detector noise or cosmic ray hits on imaging devices,' says team member Mike Wong of the University of California at Berkeley. 'It's difficult to even know what the current impact rates are throughout the solar system.' "
"That's partly why we are so excited by the latest impact," says Simon-Miller. "It illustrates a new capability that can be exploited with increased monitoring of Jupiter and the other planets."
The Disappearing Belt
The Hubble view also helped show why Jupiter's usually-prominent South Equatorial Belt has vanished: the belt is currently overlayed by white, high-altitude ammonia clouds. The cloud deck may begin to clear any time now, starting with holes appearing that give views again to the darker material below.
Read the NASA article.