UC Eyes Watch the Skies for Comet 17P Getting Its 15 Minutes of 'Stardom'

Over the past week, a rather faint comet — 17P/ Holmes — brightened by a factor of over 400,000 times in less than 48 hours. Now, many telescopes around the world are following this event. Because this is related to his area of research, UC physics professor Mike Sitko has been helping to coordinate some observations of the object, using some of the largest telescopes in the world.

According to the most recent Cincinnati Observatory newsletter, Comet Holmes is normally a “small and very faint comet.” (Comet Holmes was named for Edwin Holmes of London, who first sighted it in November 1892.) This sudden brightening has surprised observers around the world by overnight becoming bright enough to see with the unaided eye. Up until October 23 and 24, 2007, Holmes was dimmer than magnitude 17, which is about 25,000 times less bright than the faintest star that can normally be seen with the naked eye.

Normally to view such a faint celestial object, you’d need a fairly large telescope. But in a matter of hours, the comet's brightness increased to 3rd magnitude (from 17 to 2.8). (On the astronomers scale, smaller numbers mean brighter objects.)

“At the present time, none of the instruments that I would use to look at comet dust were on the major telescopes, but I helped coordinate a program by the team responsible for the TEXES spectrograph [the Texas Echelon Cross Echelle Spectrograph  at the University of Texas] and experts in comet science at Goddard Space Flight Center to observe the comet using the Gemini North 8-meter telescope in Hawaii,” explains Sitko, “This is one of the largest telescopes in the world.”

Both Sitko and fellow UC astronomer Margaret Hanson will be observing the comet in early November with NASA's Infrared Telescope Facility (IRTF), a three-meter telescope, analyzing both gas molecules and dust, in tandem with a team of scientists from many organizations (such as The Aerospace Corporation in California, the University of Toledo, the University of Minnesota, University of California–San Diego and the NASA Ames Research Center).

Hanson encourages everyone to take advantage of the opportunity.

“As soon as the skies clear over Cincinnati,” she says, “people [should] get out and look at it. It’s apparently very strange-looking through a pair of binoculars — like an orange blob. It’s been ages since we've had such an easily visible comet.”

At first, the comet was difficult to spot because of the full moon. Now that it has waned, the comet is more evident — when the skies are clear.

It’s a shame that the orientation is such that it is essentially pointing at us  — “behind us looking toward the sun and thus its tail, if it has any, is pointing away from us as the sun's radiation causes the particles to stream radially out regardless of its path,” Hanson notes. “Because of this, the comet looks very circular — not the tell-tale sign of a long-tailed comet — and perhaps not so impressive. As the comet is always outside the earth's orbit (varies from just inside Jupiter's orbit to just outside Mars'), I can't imagine any orientation that would allow us to view the tail very well.”

Experts are debating what caused the sudden “stellar performance” of Comet 17P. One possibility is that the comet exploded on its own accord due to internal stress when some of the frozen volatiles deep within the comet warmed up and went from frozen form to gaseous form.

“The immense pressure difference this generates is like a bomb going off and threw bits of the comet everywhere,” says Hanson. “This is of course why comets don't live a long time!”

Hanson is watching the comet's performance from a meeting in the United Kingdom, along with Mike A'Hearn, the head scientist for the Deep Impace mission to Comet Tempel 1. Although Comet Holmes is not the reason for their meeting in the UK, it is definitely a source of discussion around the breakfast table. Hanson's next stop will be Hawaii, where she will observe the comet.

“No one knows why such a brightening took place,” Sitko points out. “This comet has done this before, but it was still a wonderful surprise. I live for this!”

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Find sky charts for locating Comet 17P Holmes here.

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