Comet ISON's leftovers fade away, right before a satellite's eyes

Image: ISON from SOHO
The white circle highlights Comet ISON's remnants toward the edge of the viewing field for the Solar and Heliospheric Observatory's LASCO C3 ultraviolet detector. The sun's glare is blocked out by an occulting disk, but a solar storm can be seen emerging toward the lower edge of the frame.

Previous reports of Comet ISON's death may have been somewhat exaggerated, but this time it looks like the real thing.

Remnants of the object once touted as the "comet of the century" passed through the viewing field of the Solar and Heliospheric Observatory in the wake of Thursday's close encounter with the sun — and as it passed, the bright spot that survived grew dimmer and dimmer.

"I do think that something emerged from the sun, but probably a very small nucleus or 'rubble pile.' and I fear that may have now dissolved," Karl Battams, an astrophysicist at the Naval Research Laboratory who has been studying ISON for months, wrote Saturday in a Twitter update.

ISON's obituary had been written before, on Thanksgiving Day, when a different sun-watching satellite known as the Solar Dynamics Observatory failed to see the comet as it was due to pass within 730,000 miles (1.2 million kilometers) of the sun.

At first, ISON was written off as an "ex-comet." But hours later, the Solar and Heliospheric Observatory — also known as SOHO — recorded a bright spot with what seemed to be a fan-shaped tail following the comet's expected orbit. The spot also showed up in images from NASA's sun-watching STEREO satellites.

Those images revived hopes that millions of skywatchers might be able to see at least a glimmer of the comet of the century as early as next week. But the fading glow suggests that ISON is now little more than a dissipating cloud of cosmic dust in the solar wind. Late Friday, Battams estimated that the cloud's brightness was magnitude +5 and fading fast. If that trend holds, ISON's remnants won't be visible to the naked eye.

Battams said skilled astrophotographers might be able to capture a picture of the comet's Thanksgiving leftovers within a couple days, when ISON has moved farther away from the sun's glare. The rest of us are almost certainly out of luck, though there's always a chance the comet will pull off yet another death-defying stunt. 

ISON may turn out to be a disappointment for casual skywatchers, but the data collected during the comet's journey should represent a bonanza for astronomers. When ISON was discovered in September 2012, scientists knew they had a special opportunity to watch a pristine comet come in from the very edge of the solar system and make its first (and apparently only) swing around the sun. 

"Over the past year, we've amassed what we believe to be the largest single cometary dataset in history from one of — if not the most — successful coordinated observing campaigns in history," Battams wrote in Friday's blog posting. "That data is going to tell us a lot, but is going to take a seriously long time to sort through. We've had a crazy year, an even crazier past few months, and a truly insane couple of days. But everything we get out of this will make it more than worth it, and for me it's just a privilege to have played a part in this unprecedented and extraordinary event."

More about Comet ISON:

For updates on Comet ISON, keep tabs on, the Comet ISON Observing Campaign, Hubblesite's and the websites for Astronomy Magazine and Sky & Telescope. On Twitter, follow @ISONUpdates@CometISONnews@CometISON2013@SungrazerComets and @Cosmos4u.

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.