Remnants suggest comet ISON still going

New York Times News Service
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ISONs future remains unclear, but it has already upended scientific understanding of these sungrazing comets.PHOTO:AFP
ISONs future remains unclear, but it has already upended scientific understanding of these sungrazing comets.PHOTO:AFP

Comet ISON entered the annals of astronomical history on the night of November 28, when it flew past the Sun and, latest updates suggest, emerged in tatters on the other side after many skywatchers had given it up as dead.

Still, the most recent images hint that most of ISONs nucleus disintegrated as the comet approached the Sun, leaving only a slim chance there will be anything left to see with the naked eye over the Northern Hemisphere in coming weeks.

Analysis of the light coming from ISON will determine whether it is now just a spray of dust and gas, or whether any significant portion survived, says Gerhard Schwehm, an European Space Agency comet expert based in Noordwijk, The Netherlands and a former head of ESAs Solar System Science Operations Division.

Either there is only a small piece left, or the nucleus is really totally disintegrated and we just see the debris of the comet traveling along, he says.

ISONs future remains unclear, but it has already upended scientific understanding of these sungrazing comets. ISON was making its first, and possibly only, journey from the deep freeze of the outer Solar System into the furnace of the stars outer corona.

Never before have researchers followed a comet so pristine coming so close to the Sun.

Blazing radiation and powerful gravitational forces pummelled and stretched the dirty ice ball as comets are sometimes called in reference to their composition as it approached the star.

Pictures from Sun-watching satellites initially showed ISON as it had appeared for months: a coherent nucleus followed by a broad dust tail and narrow ion tail.

But as ISON got closer to the star, things became more confusing. Analyses of light captured by NASAs twin STEREO spacecraft seemed to show the comet growing dimmer.

Next, pictures from NASAs Solar Dynamics Observatory, which should have captured ISON on its closest approach to the Sun, showed absolutely nothing.

Then the European U.S. Solar and Heliospheric Observatory spotted a faint glimmer on the other side of the Sun, on a trajectory where ISON would have been expected to appear.

It looked like a spray that brightened and smeared out sideways as it flew.

Whether any sizeable portion of ISON remains intact will be determined during the coming hours and days.

Karl Battams, an astrophysicist at the Naval Research Laboratory in Washington, who specializes in sungrazing comets, summed up the astonishment and frustration of many.

On Twitter, after a long day of conflicting updates, he wrote that he and a colleague had looked at literally a couple of thousand sungrazing comets. We've NEVER seen one behave like ISON. Astounding!

Russian astronomers discovered ISON in September 2012 using the International Scientific Optical Network. Research suggested that millions of years ago, a passing star knocked it out of a reservoir of comets, far beyond Pluto.

There is no strict definition of sungrazing comets, and most of those known are much smaller than ISON.

Perhaps the closest analogy is comet Lovejoy, which in 2011 passed through the uppermost reaches of the solar atmosphere and emerged mostly intact.

Lovejoy disintegrated several days later, providing a skywatching delight in the Southern Hemisphere. Another sungrazer, Ikeya-Seki, shattered into fragments after flying past the Sun in 1965.

Comet scientists have argued for months whether ISON would survive passing just 1.2 million kilometer away from the Sun.

Its relatively small size, no more than about a kilometer across, suggested that it might be particularly vulnerable to disruption.

Id like to know what happened to our half-mile of material, says Dean Pesnell, project scientist for the Solar Dynamics Observatory and a solar physicist at NASAs Goddard Space Flight Center in Greenbelt, Md. -New York Times News Service



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