McGregor, Texas, McGinley Memorial Public Library Books and Friends: A Synopsis of the Post-perihelion Comet ISON Workshop

Comet ISON's Workshop Videos:

A Post Mortem Analysis

Twelve NASA spacecraft assets had an opportunity to observe Comet ISON.

The CIOC Workshop displayed this slide at the start its opening session.

Evelyn Smith

Comet ISON observer’s Workshop. (2013, December 6). Comet ISON-follow up 1 of 2. Johns Hopkins Applied Physics Observatory. (1:26:24 minutes). Retrieved from http://www.livestream.com/cometison/video?clipId=pla_e40cee69-1652-4084-b566-ef9819395120&utm_source=lslibrary&utm_medium=ui-thumb

Astronomers are interested in Comet ISON because it was both a pristine comet fresh from the Oort Cloud and a sun-grazing comet. Neither of these properties taken separately is all that unusual. But when these two characteristics combined in a single comet, this made any data derived invaluable; and since Comet ISON was the first major comet of the “high-tech, digital age”, researchers collected more data on it than any other comet.

Most particularly, it was unusual to detect a comet as far out from Earth as ISON, given its comparatively small size, for ISON only had a nucleus with the radius of a kilometer. However, early on, Comet ISON possessed a cloud of ice surrounding the nucleus that made it easy to be seen.

One of the main reasons astronomers couldn’t detect Comet ISON shortly before it reached perihelion on November 28, 2013, was by this time, its nucleus wasn't actively emitting oxygen since the satellites monitoring it picked put no water production and therefore no oxygen emissions. All the “glue” that would have held the dust together had melted away.

Comet ISON was primarily a gas comet, made up primarily of carbon dioxide (CO2), although images of the comet’s bluish-green coma and tail indicated that it was expelling carbon tetroxide (CO4). Comet’s ISON’s flaring in the last few days before perihelion revealed there was nothing particularly stable on ISON’s surface, for this abrupt rise in brightness occurred when the rock started to boil off.

The STEREO spacecraft’s Extreme Ultraviolet Lithography detected no signs of the nucleus going into the sun’s corona; and by the time SOHO picked up on Comet ISON, it couldn’t detect a signature of a nucleus, but could only make out reflections of dust. Indeed, the astronomers had never seen such a heavy trail of dust.

Consequently, immediately before perihelion on November 28th, the experts saw nothing since they were looking for signature of oxygen. Since the comet no longer contained any oxygen, its evaporation of dust went awry. Thus, whether it any broken apart earlier or not was irrelevant.

The Large Angle and Spectrometric Coronagraph Experiment (LASCO) instruments begin to detect ISON emitting mostly dust right up to its perihelion, although analysis of LASCO’s observations told the astronomers more about the solar wind than the comet. Increasingly, however, they realized they were looking at smaller and smaller debris particles.

After ISON emerged from the far side of the sun, its tail was pointing down towards the sun. If it still had actively been discharging a dust trail post perihelion, the tail should have pointed away from the sun. This was a sign that the comet was no longer active.

Astronomers, however, first hypothesized that Comet ISON was no longer an active, gas-emitting comet, but an empty husk, shortly before it skirted the sun's corona because they observed that the comet had a pointy head, which meant that it no longer had a substantial nucleus.

Comet ISON observer’s workshop. (2013, December 6). Comet ISON-follow up 2 of 2: No tag-up meeting. Johns Hopkins Applied Physics Observatory. (54:20 minutes). Retrieved from http://www.livestream.com/cometison/video?clipId=pla_e40cee69-1652-4084-b566-ef9819395120&utm_source=lslibrary&utm_medium=ui-thumb

Viewers will need to listen to all the shout outs given to fellow professional astronomers as well as the accolades given to amateur star gazers and a discussion of CIOC’s future plans before they discover any grains of interest in this video, which comes during a question and answer session at the session’s end. However, it is worth the wait! In a spirited discussion, the astronomers gathered in Baltimore dropped the following tidbits:

Clearly, a small nucleus remained after Comet ISON emerged from the sun, but the experts still don’t know how much gas in the nucleus was left to fuel the comet’s tail.

Solar winds were too symmetrical for a break up event. No one saw any fragments, although the comet broke up just before perihelion when astronomers saw the tip of a spear-like comet head forming.

The comet’s sudden brightness in the days before perihelion meant that it was exploding and “smearing out”, becoming more and more diffuse. The surface-wasting just prior to perihelion showed that Comet ISON was undergoing a great deal of stress.

Although astronomers will be still monitoring the remainders of Comet ISON as it exits the inner solar system, astrophysicist Karl Battams perhaps speaks for this community when he said, “ I am willing to let the comet go”.

Comet ISON observer’s Workshop. (2013, December 6). Closure/wrapping things up. (23:42 minutes). Retrieved from http://www.livestream.com/cometison/video?clipId=pla_d89168ab-c025-41cc-be7c-91a3aedfe344&utm_source=lslibrary&utm_medium=ui-thumb

Astronomers believe they are closer to inferring what the circumstances were like when the solar system was forming because of recent observations. Thus far, however, their analysis of Comet ISON leaves them with more questions than answers:

They don’t know whether it is [or it was] volatile rich or volatile poor, meaning whether it or not its gases vaporized relatively easily.

They don’t know whether sublimation, or the turning of solids into gases, or the photons emitted by the sun, or its electro [magnetic] levitation, fueled the comet’s activity. However, they theorize that Comet ISON flared when a particularly rich pocket of CO2 within its interior emitted the gas. Apparently, comets contain different reservoirs of volatile gases within their interior. ISON’s flat sublimation rate could also indicate that no super volatiles were left. They may, nevertheless, still be able to infer its internal structural, but this calls for long-term monitoring of its volatile production as it exits the inner solar system. They also don’t know the comet’s exact radius or its rotation ratio post perihelion.

For additional analysis of Comet ISON’s breakup go to the December 11th press reports on the annual meeting of the American Geophysical Union summarized in Comet ISON’s Sky Watch Journal:

http://evelynelainesmith.blogspot.com/2013/11/follow-comet-isons-daily-progress.html

This blog will continue to monitor reports about Comet ISON and summarize them as warranted.