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.
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.
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.
Throughout the year that researchers have watched Comet ISON – and especially
during its final approach to the sun – the comet brightened and dimmed in
unexpected ways. Such brightness changes usually occur in response to material
boiling off the comet, and different material will do so at different
temperatures thus providing clues as to what the comet is made of. Analyzing
this pattern 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.
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