Comet avoids hitting Mars but makes astronomical history
A glowing comet barreled past Mars at some 126,000 mph today, its core of ice and dust barely missing the Red Planet and Mars's flotilla of costly scientific spacecraft.
Comet Siding Spring, a cosmic leftover of the planet-building process, veered 16 times closer to Mars than any comet has come to Earth in recorded history.
Scientists had once thought the comet might actually smash into Mars. Instead Siding Spring cleared the planet by roughly 84,000 miles, which is about one-third the distance from Earth to the moon.
Confirmation of the close approach, at 2:27 p.m. ET, came from the Twitter feed of the European Space Agency's operations team, which is monitoring the health of its Mars Express spacecraft at the Red Planet.
"And that, Ladies & Gentlemen, is history! The closest (non-impacting ... ) planetary approach by a comet in our recorded history!" tweeted comet expert Karl Battams of the Naval Research Laboratory.
"I'm very happy. … It was an extremely rare thing to see," said amateur astronomer Allen Versfeld of Centurion, South Africa, who captured pictures of the comet's close approach. "To be part of that was quite exciting."
Comets have certainly brushed past Mars before, but never before have human beings had the means to scrutinize such an encounter. All five spacecraft orbiting Mars — three belonging to NASA, one to Europe and one to India — recorded the comet's mad dash. So did NASA's two Mars rovers and a Who's Who of other observatories, including the Hubble Space Telescope and a network of serious hobbyists whose images were collected online as part of a collaboration between amateur and professional astronomers.
Even a single piece of comet dust could cause dramatic damage to a spacecraft, so NASA and others took the precaution of making sure their satellites were shielded by Mars when the planet passed through the comet's trail.
Europe's Mars Express survived unscathed, and NASA said late Sunday that its three Mars orbiters suffered no ill effects from the fly-by.
"Everything went extremely well," said Mars Reconnaissance Orbiter project manager Dan Johnston. "Our spacecraft executed everything perfectly."
Spacecraft managers may curse the comet for putting their precious machines at risk, but scientists hailed the close approach as a piece of incredibly good luck. Siding Spring's home base is the Oort Cloud, an comet repository in the coldest, most isolated reaches of the solar system. Sculpted some 4 billion years ago from the same stuff that makes up the planets, the Oort-Cloud comets have been in the deep freeze ever since, making them time capsules of the solar system's early days.
Never before have astronomers gotten a good look at an Oort-Cloud comet. The Oort Cloud itself is too distant, and Oort-Cloud comets don't show up in our part of the solar system on a predictable schedule. That makes it impossible to send a spacecraft to one: by the time scientists realize an Oort-Cloud comet is close by, it's too late to plan a mission.
"If you would have told me … that we'd have the opportunity to observe a comet, I wouldn't have believed you," Johnston said. "This is once-in-a-lifetime."