An Australian amateur stargazer who spotted a "one in a million" impact on Jupiter Wednesday told of his astonishment as he chanced upon the Earth-sized dent in its gassy atmosphere.
Anthony Wesley, 44, who has had a life-long passion for the stars, was photographing the planet close to midnight on Sunday when he noticed a black mark that hadn't been there two nights earlier.
The computer programmer, who watches the sky with his 14.5-inch (37 centimetre) telescope in the backyard of his farm outside Canberra, said he first thought it was a shadow cast by one of the planet's 63 moons.
"But after a few minutes I realised it was in the wrong place and it was the wrong shape to be anything like that, and then it was a case of my eyes convincing my brain," Wesley told AFP.
"The eyes are saying 'There it is, it's on the screen, you can't deny it,' but the brain is saying 'Hang on, there's such an unlikely chance of this being an impact, it's a one in a million, or worse than that,' so it did take me a while to actually believe what I was seeing."
For the next two hours, Wesley said he frantically photographed the mark and then started emailing astronomers, desperate to alert as many other people as he could "to get the professional astronomers in and let them take over."
After NASA experts spent six hours examining the spot with an infra-red telescope in Hawaii, the verdict came in -- Jupiter had been hit, possibly by a stray comet or a planet-sized block of ice.
"It was completely unlike any of the weather phenomena that we observe on Jupiter," said Glenn Orton from NASA's Jet Propulsion Lab in California, on Tuesday.
"Our first image showed a really bright object right where that black scar was, and immediately we knew this was an impact," Orton said.
Wesley took up astronomy as a hobby aged 10, and said anyone with a telescope had been watching Jupiter since Monday, keen to watch the atmospheric fallout from the impact.
"A lot of material down low in Jupiter's atmosphere gets brought up by one of these impacts, so that gives some of the planetary scientists around the world invaluable opportunity to study parts of Jupiter that they can't normally see," Wesley said.
Jupiter, which is 11 times larger than Earth, was last hit by fragments of the Shoemaker Levy 9 comet in 1994, and Wesley said Sunday's collision also raised some interesting questions about how rare such events really were.
"Maybe there are more of these cometary objects up there that Jupiter sweeps up and maybe these impacts, rather than being once in a few thousand years, maybe they're happening several times every century," he said.
"Now that we've got better telescopes and now that we've got an army of amateur astronomers looking at Jupiter all the time these things will get picked up," he added.
Jupiter's massive gravitational pull had helped to shape the solar system and, thankfully for Earth's inhabitants, continued to draw such objects into its path, Wesley said.
"I think the last time, according to fossil records, any impact like that happened on Earth we had the extinction event hundreds of millions of years ago, which appears to have finished off the dinosaurs," he said.
"So if anything like that happened on Earth it would certainly finish off all of the life that's here as we know it."
(c) 2009 AFP
Explore further: New Images Indicate Object Hits Jupiter