ESA/NASA/SOHO/GSFC
ISON appears as a white smear heading up and away from the sun. ISON was not visible during its closest approach to the sun, so many scientists thought it had disintegrated, but images like this one from the ESA/NASA Solar and Heliospheric Observatory suggest that a small nucleus may be intact.

Comet ISON: Dead or Alive? Astronomers Still Don’t Know

ICTMN Staff
11/30/13

Comet ISON is dead! Long live comet ISON!

Comet ISON continued to befuddle astronomers and other scientists over Thanksgiving weekend as it seemed to break up during its passage around the sun, only to possibly reemerge as a dimmer version of its former self just when everyone had declared it an ex-comet.

On Saturday November 30, astronomers were still busily analyzing the images being sent back by NASA’s Solar Dynamics Observatory (SDO), the Solar and Heliospheric Observatory (SOHO) and other instruments. If all or part of the comet’s nucleus had survived, there would still be the shred of a chance that the comet could make something of a comeback. If not, it would be game over.

Thousands of people worldwide tuned into NASA’s Google Hangout session as they chowed down on their Thanksgiving turkey, waiting to see whether the comet would emerge from behind the sun after passing less than a million miles from the sun just after 1:30 p.m. Eastern Time.

As ISON appeared to dim and fizzle in several observatories and later could not be seen at all by NASA's Solar Dynamics Observatory or by ground based solar observatories, many scientists believed it had disintegrated completely,” NASA said in a statement on the evening of November 28. “However, a streak of bright material streaming away from the sun appeared in the European Space Agency and NASA's Solar and Heliospheric Observatory later in the evening. The question remains whether it is merely debris from the comet, or if some portion of the comet's nucleus survived, but late-night analysis from scientists with NASA's Comet ISON Observing Campaign suggest that there is at least a small nucleus intact.”

NASA posted this mini-video, known as a GIF, to illustrate what the agency knows so far.

Comets are compilations of ice and rock and are thought to originate in the Oort cloud, a debris field floating in the far reaches of the solar system. The clumps’ elongated, elliptical orbit takes some of them close in to the sun, earning them the moniker “sungrazer comets.” They slingshot around the sun, whose gravitational field flings them back out to space—or eats them alive.

ISON had surprised scientists numerous times over the past few months by changing color, splitting its tail and changing in brightness unpredictably. So it was not out of comet character for the space chunk to reappear after being declared fizzled.

One thing seems certain: Even if part of the comet survived, chances are overwhelming that it will not put on the stupendous light show through December that astronomers were hoping for. But all is not lost. The comet’s breakup generated reams of data on the celestial body’s composition, and thus on the origin of the solar system.

Analyzing the images, whether the comet lives on or not, “will help scientists understand the composition of ISON, which contains material assembled during the very formation of the solar system some 4.5 billion years ago,” NASA said.

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