[meteorite-list] NASA Investigating the Life of Comet ISON

[Ron Baalke]

http://www.nasa.gov/content/goddard/nasa-investigating-the-life-of-comet-ison/ 

NASA Investigating the Life of Comet ISON
Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.
December 2, 2013

After several days of continued observations, scientists continue to work 
to determine and to understand the fate of Comet ISON: There's no doubt 
that the comet shrank in size considerably as it rounded the sun and there's 
no doubt that something made it out on the other side to shoot back into 
space. The question remains as to whether the bright spot seen moving 
away from the sun was simply debris, or whether a small nucleus of the 
original ball of ice was still there. Regardless, it is likely that it 
is now only dust.  

Comet ISON, which began its journey from the Oort Cloud some 3 million 
years ago, made its closest approach to the sun on Nov. 28, 2013. The 
comet was visible in instruments on NASA's Solar Terrestrial Relations 
Observatory, or STEREO, and the joint European Space Agency/NASA Solar 
and Heliospheric Observatory, or SOHO, via images called coronagraphs. 
Coronagraphs block out the sun and a considerable distance around it, 
in order to better observe the dim structures in the sun's atmosphere, 
the corona. As such, there was a period of several hours when the comet 
was obscured in these images, blocked from view along with the sun. During 
this period of time, NASA's Solar Dynamics Observatory could not see the 
comet, leading many scientists to surmise that the comet had disintegrated 
completely. However, something did reappear in SOHO and STEREO coronagraphs 
some time later - though it was significantly less bright.

[Video]
Comet ISON is shown approaching the sun and curving away from it in this 
movie containing imagery from both NASA's Solar Terrestrial Relations 
Observatory and the joint ESA/NASA Solar and Heliospheric Observatory 
from November 2013. ISON dims dramatically as it streams away from the 
sun.
Image Credit: ESA/NASA/SOHO/STEREO/GSFC

Whether that spot of light was merely a cloud of dust that once was a 
comet, or if it still had a nucleus - a small ball of its original, icy 
material - intact, is still unclear. It seems likely that as of Dec. 1, 
there was no nucleus left. By monitoring its changes in brightness over 
time, scientists can estimate whether there's a nucleus or not, but our 
best chance at knowing for sure will be if the Hubble Space Telescope 
makes observations later in December 2013.

Regardless of its fate, Comet ISON did not disappoint researchers. Over 
the last year, observatories around the world and in space gathered one 
of the largest sets of comet observations of all time, which should provide 
fodder for study for years to come. The number of space-based, ground-based, 
and amateur observations were unprecedented, with twelve NASA space-based 
assets observing over the past year.

Related Links:

For more information on Comet ISON: www.nasa.gov/ison

To download recent ISON imagery: http://svs.gsfc.nasa.gov/Gallery/CometISON.html