Washington: Gemini Observatory has taken a new series of images that shows Comet C/2012 S1 (ISON) racing toward an uncomfortably close rendezvous with the Sun.
In late November the comet could present a stunning sight in the twilight sky and remain easily visible, or even brilliant, into early December of this year.
The new Gemini time-sequence images, spanning early February through May 2013, show the comet`s remarkable activity despite its current great distance from the Sun and Earth.
The information gleaned from the series provides vital clues as to the comet`s overall behavior and potential to present a spectacular show. However, it`s anyone`s guess if the comet has the "right stuff" to survive its extremely close brush with the Sun at the end of November and become an early morning spectacle from Earth in early December 2013.
When Gemini obtained this time sequence, the comet ranged between roughly 455-360 million miles (730-580 million kilometers; or 4.9-3.9 astronomical units) from the Sun, or just inside the orbital distance of Jupiter. Each image in the series, taken with the Gemini Multi-Object Spectrograph at the Gemini North telescope on Mauna Kea, Hawaii, shows the comet in the far red part of the optical spectrum, which emphasizes the comet`s dusty material already escaping from what astronomers describe as a "dirty snowball."
The images show the comet sporting a well-defined parabolic hood in the sunward direction that tapers into a short and stubby tail pointing away from the Sun. These features form when dust and gas escape from the comet`s icy nucleus and surround that main body to form a relatively extensive atmosphere called a coma. Solar wind and radiation pressure push the coma`s material away from the Sun to form the comet`s tail, which we see here at a slight angle (thus its stubby appearance).
Discovered in September 2012 by two Russian amateur astronomers, Comet ISON is likely making its first passage into the inner solar system from what is called the Oort Cloud, a region deep in the recesses of our solar system, where comets and icy bodies dwell. Historically, comets making a first go-around the Sun exhibit strong activity as they near the inner solar system, but they can often fizzle as they get closer to the Sun.
Astronomer Karen Meech, at the University of Hawaii`s Institute for Astronomy (IfA) in Honolulu, is currently working on preliminary analysis of the new Gemini data (as well as other observations from around the world) and notes that the comet`s activity has been decreasing somewhat over the past month.
"Early analysis of our models shows that ISON`s brightness through April can be reproduced by outgassing from either carbon monoxide or carbon dioxide. The current decrease may be because this comet is coming close to the Sun for the first time, and a `volatile frosting` of ice may be coming off revealing a less active layer beneath. It is just now getting close enough to the Sun where water will erupt from the nucleus revealing ISON`s inner secrets," said Meech.
Meech concludes that Comet ISON "could still become spectacularly bright as it gets very close to the Sun," but she cautions, "I`d be remiss if I didn`t add that it`s still too early to predict what`s going to happen with ISON since comets are notoriously unpredictable."