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  Comet ISON sightings: On Earth and off-planet

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Author Topic:   Comet ISON sightings: On Earth and off-planet
Robert Pearlman
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Posts: 28219
From: Houston, TX
Registered: Nov 1999

posted 10-02-2013 11:45 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
On Sept. 29, the Mars Reconnaissance Orbiter (MRO) maneuvered to point its High Resolution Imaging Science Experiment (HiRISE) camera at ISON, a new comet passing by Mars on its way into the inner Solar System.
HiRISE saw a small spot at the position of ISON that is relatively bright, like a star, but moving relative to actual stars. The comet's coma is apparently very faint, so this data offers useful constraints on the size of the comet nucleus and its overall brightness — key measurements to understand its behavior and useful knowledge to subsequent observers.

These images show a 256x256 pixel patch of sky at the range to the comet of 8 million miles and when the solar phase angle is 47 degrees. Three more observations of ISON are planned for 1 and 2 October as the comet moves through closest approach to Mars at 7 million miles, but with less illumination as seen from Mars.

Based on preliminary analysis of the data, the comet appears to be at the low end of the range of brightness predictions for the observation. As a result, the image isn't visually pleasing but low coma activity is best for constraining the size of the nucleus. This image has a scale of approximately 8 miles (13.3 km) per pixel, larger than the comet, but the size of the nucleus can be estimated based on the typical brightness of other comet nuclei. The comet, like Mars, is currently 241 million kilometers from the Sun. As the comet gets closer to the sun, its brightness will increase to Earth-based observers and the comet may also become intrinsically brighter as the stronger sunlight volatilizes the comet's ices.

Comet ISON (officially known as C/2012 S1) is believed to be in its first pass through the inner solar system from the distant Oort Cloud, a roughly spherical collection of comets and comet-like structures that exists in a space between one-tenth light-year and 1 light-year from the sun. The comet will pass within 724,000 miles (1.16 million kilometers) of the Sun on 28 November 2013. It was discovered on 21 September 2012, roughly between Jupiter and Saturn, by Vitali Nevski and Artyom Novichonok at the International Scientific Optical Network (ISON) near Kislovodsk, Russia.

Robert Pearlman
Editor

Posts: 28219
From: Houston, TX
Registered: Nov 1999

posted 11-28-2013 09:11 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
As Bill Harwood reports for CBS, Comet ISON may — or may not — have survived its encounter with the Sun.
After a multi-million-year plunge from the frozen fringes of the solar system, Comet ISON may have broken apart and evaporated in the fierce heat and crushing gravity of the sun before or during a close flyby Thursday, presumably scotching long-held hopes for a dramatic sky show on Earth over the next few weeks.

Or maybe not.

Well after many casual observers had given up on the comet's survival, updated pictures from the Solar and Heliospheric Observatory spacecraft — SOHO — showed what appeared to be a long trail of dust extending away from the sun along ISON's trajectory, brightening sharply toward its tip.

Whether it was just a dust trail, or perhaps dust and larger fragments of ISON — or both — was not immediately clear. As several observers tweeted and re-tweeted: "It is now clear that Comet #ISON either survived or did not survive, or... maybe both. Hope that clarifies things."

Teacher in space
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posted 11-28-2013 11:14 PM     Click Here to See the Profile for Teacher in space     Edit/Delete Message   Reply w/Quote
Some parts survived.

Blackarrow
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Posts: 2115
From: Belfast, United Kingdom
Registered: Feb 2002

posted 11-29-2013 01:41 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
I would just like to thank Comet ISON for having the decency to disappoint me in the comfort of my home, rather than the pre-dawn chill of a winter morning in some benighted spot miles from home.

Robert Pearlman
Editor

Posts: 28219
From: Houston, TX
Registered: Nov 1999

posted 11-29-2013 01:50 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Teacher in space:
Some parts survived.
Indeed, as now noted by NASA:
Continuing a history of surprising behavior, material from Comet ISON appeared on the other side of the sun on the evening on Nov. 28, 2013, despite not having been seen in observations during its closest approach to the sun. 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.

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