Thanksgiving Comet ISON Gets Gobbled Up

Updated Nov. 28, 2013 2:32 p.m. ET

A pristine comet called ISON, which left its home at least a million years ago, will be making its closest approach to the sun on Thanksgiving day. Gautam Naik reports.

A new guest arrived just in time for Thanksgiving dinner, but apparently didn’t survive the festivities.
The visitor, a pristine comet called ISON that left its home at least a million years ago, made its closest approach to the sun Thursday afternoon.
But based on images arriving from various spacecraft, the consensus among scientists appeared to be that ISON, like the mythical Icarus, didn’t survive its close encounter with the sun.
The comet’s sweep near the sun was a moment that thousands of astronomers around the world had anxiously awaited, and before hopes dimmed about its survival, ISON was predicted to possibly loop around the star and emerge as a bright object visible to the naked eye in the skies of the Northern Hemisphere.
However, scientists now suspect it fragmented into countless pieces—never to be seen again.
Before the close approach, observations “showed that the comet had brightened and then lost brightness. So there’s a lot of conjecture that it might be fading,” said Padma Yanamandra-Fisher, a planetary scientist at the Space Science Institute in Boulder, Colo., before the comet made its close pass with the sun.

Comet ISON approaches the sun as seen by a NASA spacecraft on Nov. 25, 2013. U.S. National Aeronautics and Space Administration

Since it was spotted more than a year ago, ISON’s behavior has constantly surprised astronomers, and they had held out hope that the comet could still put on a pretty display. On Monday, for example, it looked like it wouldn’t survive. Yet it was still there on Tuesday.
In addition to being a cosmic tease, ISON was one of the most tracked comets in history.
Thousands of telescopes—amateur, professional and space-borne—were being trained on this relatively tiny clump of ancient rock and ice no more than three or four miles in diameter.
The comet was discovered in September 2012 by Russian astronomers Vitali Nevski and Artyom Novichonok using data from the International Scientific Optical Network, whose initials provided the name.
Nothing like ISON has been seen in living memory. It is a relatively rare “sungrazer,” a comet that flies especially close to our sun.
Unlike periodic comets that come and go like the famous Halley’s, ISON is pristine and was making its first journey toward the sun. Its composition—mainly rock and ice—has barely changed since it formed some 4.5 billion years ago, making it one of the oldest objects in the solar system.
That had scientists intrigued, because ISON’s proximity to the sun, and the chance to study what it is made of, could provide valuable clues about origins of the solar system.
When a new comet flies close to the sun, the tremendous heat can help reveal rarer materials, such as metals, of which it is made.
“It’s the first time in 200 years that we’ve seen a comet that’s both a sungrazer and brand new,” said Matthew Knight from the Lowell Observatory in Arizona.
Comet ISON left its home in the faraway Oort cloud—a vast area of cosmic debris a long way from the sun.
Remarkably, space telescopes have managed to film the latter part of its passage through the solar system.
At the beginning of November, ISON was traveling at 95,000 miles an hour. Since then, the sun’s gravitational pull on it had gotten stronger and stronger. If it had survived its close encounter, ISON was expected to reach a speed of 845,000 miles an hour later on Thursday, catapulting around the sun at perihelion, its closest point to the solar surface.
At that point, it would have been about 1.9 million miles from the sun, a mere hop, skip and jump in cosmic terms. But the sun’s heat and gravitational pull at that point would prove overpowering.
If ISON had survived, scientists predicted it would have been poised to put on a display in the first week of December, at least for Northern Hemisphere viewers.
“It would have a very long and bright tail as it comes up from the horizon shortly before sunrise,” said Dr. Knight, before Thursday’s fatal close encounter.
“If you go out 30 minutes before [sunrise], you should be able to see it with the naked eye.”
But that was only if ISON had survived Thursday’s flyby.
Write to Gautam Naik at gautam.naik@wsj.com

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