Hubble Provides Great View Of Comet ISON

Lee Rannals for redOrbit.com – Your Universe Online

Astronomers have been given the clearest view yet of a comet that is supposed to light up the skies later this year.

Comet ISON is expected to create a spectacular show in the night sky in November, and NASA’s Hubble Space Telescope has provided scientists with a great preview, months before its premier debut.

Comet ISON is a “dirty snowball,” meaning it is a clump of frozen gases mixed with dust. It travels in an orbit influenced by the gravitational pull of the Sun and its planets. ISON’s orbit will bring it to a maximum approach of 700,000 miles away from the sun on November 28th.

In the new image of ISON captured by the Hubble, ISON was about 386 million miles from the Sun, which is slightly closer to the Sun than Jupiter. As a comet draws closer to the Sun, it begins to become more active because the heat from our star evaporates the comet’s ices into jets of gases and dust.

Scientists will be using the Hubble next week to gather even more information about comet ISON to try and understand just how epic this comet may be.

“We want to look for the ratio of the three dominant ices, water, frozen carbon monoxide, and frozen carbon dioxide, or dry ice,” said University of Maryland astronomy professor Michael A’Hearn. “That can tell us the temperature at which the comet formed, and with that temperature, we can then say where in the solar system it formed.”

The team will use these images to measure the activity level of this comet, and determine the size of the nucleus. This data will help predict the comet’s activity when it passes its maximum approach to the Sun. Preliminary measurements suggest the nucleus is no larger than three or four miles across, which is small when considering the high level of activity observed in the comet so far.

A detailed analysis of the dust coma surrounding the nucleus shows a strong jet blasting dust particles off the sunward-facing side. This jet is said to extend at least 2,300 miles.

Astronomers have predicted that comet ISON has the potential to become one of those once-in-a-lifetime comets.

“Comet ISON has the potential to be among the brightest comets of the last 50 years, which gives us a rare opportunity to observe its changes in great detail and over an extended period,” said Lead Investigator Dennis Bodewits, an astronomer at UMCP.

However, comets are known for being a buzz kill and with all the hype, Don Yeomans of NASA’s Near-Earth Object Program says not to get too excited yet.

“Comets are notoriously unpredictable,” said Yeomans. “I’m old enough to remember the last ‘Comet of the Century’. It fizzled.”

Scientists say that the comet could become bright enough to see in the daytime if you just hold up a hand to block out the sun.

“Past comets have failed to live up to expectations once they reached the inner solar system, and only observations over the next few months will improve our knowledge of how ISON will perform,” said Matthew Knight, an astronomer at Lowell Observatory in Flagstaff, Arizona.

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