A Story of Ice

The fate of comet ISON as seen from the SOHO spacecraft

The fate of comet ISON as seen from the SOHO spacecraft

This post has absolutely nothing to do with ice- well, not the kind on the ground across Tennessee right now, at least. It has to do with heavenly ice- comets. I had been planning to observe tonight what has been hailed for the past year as “the comet of the century, ISON.” There is just one little problem with that plan– comet ISON no longer exists. Over Thanksgiving, the comet passed behind the sun as it followed its elliptic orbit through the inner solar system. Comets are composed primarily of ice and dust, and there’s always the danger they won’t survive the trip around the sun. ISON got its turkey cooked over Thanksgiving for precisely this reason. Some comets last for many, many trips around the sun, but others get too close and don’t make it. This is one reason when the news media reports that a comet will be an amazing experience a little caution is a good thing. Sometimes comets come through, but just as often they don’t live up to expectations or break up altogether, a la ISON.

The fun part of the ISON story is that even after the cometary break-up, ISON continued to surprise even scientists. Just after it was pronounced dead and buried, there the object was again– somehow. The head of the comet’s remains began to brighten again, leading to the following comment on the unexpected return of ISON:

“At this point, we don’t have an answer to that.” -C. Alex Young, associate director for science in the heliophysics division at NASA’s Goddard Spaceflight Center in Greenbelt, Md.

At this point, a week later, the best guess as to what happened is that a small chunk of ISON’s glory survived  and will continue in its orbit, though it is but a tenth of its previous size after its encounter with the sun. The brightening might also have just been smeared out debris from the comet. Until Hubble can check it out further, we’ll just have to be content with the uncertainty.

In 1973, Comet Kohoutek dissapointed hopes of those calling it "the comet of the century"

In 1973, Comet Kohoutek dissapointed hopes of those calling it “the comet of the century”

The story of comet  ISON in space news reporting is extremely similar to another cometary mishap years ago– that of comet Kohoutek. Like ISON, Kohoutek was hailed as a marvel of the likes of the historic comet Halley, and called (you guessed it!) “the comet of the century.” Because this was likely Kohoutek’s first visit to the inner solar system, the comet was expected to be brilliant due to the out-gassing it would go through as an Oort-candidate object as it experienced the sun’s heating, up close and personal. However, the comet didn’t brighten spectacularly and disappointed a lot of eager astronomers. In fact, this 1973 “comet of the century” was the lesson in comet-predicting humility for the previous generation of sky-watchers and why veteran observers were almost certainly a bit skeptical of ISON claims this year. It’s just hard to predict the future. When it comes to comet predictions, a cautious enthusiasm is the way to go, as some actually do turn out to be marvels of the century.

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One thought on “A Story of Ice

  1. Pingback: Comet ISON- a Tale of Ice | Considus

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