March 29, 2013
Swift Gets Better Picture Of Comet ISON
Lee Rannals for redOrbit.com - Your Universe Online
Comet Pan-STARRS lit up our skies during March, but another comet is on its way that is expected to outshine it.
Astronomers from the University of Maryland at College Park (UMCP) and Lowell Observatory used NASA's Swift satellite to size up Comet ISON and make initial estimates of the comet's water and dust production.
"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.
The Comet ISON Observing Campaign (CIOC) has been put together at the request of NASA to assist ground- and space-based facilities to learn more about this comet. Not only will the comet be making a close encounter with Mars, but it will also whiz right past the sun.
A comet's water reservoir remains frozen until it comes within about three times the Earth's distance to the sun. Swift was used to detect light emitted by hydroxyl and other important molecular fragments when they were exposed to ultraviolet sunlight. These observations revealed ISON is shedding about 112,000 pounds of dust every minute, and is producing about 13 pounds of water every minute.
"The mismatch we detect between the amount of dust and water produced tells us that ISON's water sublimation is not yet powering its jets because the comet is still too far from the sun," Bodewits said. "Other more volatile materials, such as carbon dioxide or carbon monoxide ice, evaporate at greater distances and are now fueling ISON's activity."
The water and dust production rates can be used to estimate the size of ISON's icy body, helping scientists estimate the size of its nucleus.
It can be hard for scientists to really pin down how bright a comet will be at a certain time. Scientists say the comet could be twice as big as Comet Lovejoy, becoming visible to the naked eye even in broad daylight. However, it could also fizzle out.
"Comets are notoriously unpredictable,” said Don Yeomans of NASA Near-Earth Object Program. “I´m old enough to remember the last ℠Comet of the Century´. It fizzled."
The first observing opportunity will occur on October 1, when the comet passes about 6.7 million miles from Mars.
[ Watch the Video: Comet ISON's Path Through the Solar System ]
"During this close encounter, comet ISON may be observable to NASA and ESA spacecraft now working at Mars," said Michael Kelley, an astronomer at UMCP and also a Swift and CIOC team member. "Personally, I'm hoping we'll see a dramatic postcard image taken by NASA's latest Mars explorer, the Curiosity rover."
By November, the comet will approach within about 730,000 miles of the Sun, and will then release torrents of dust as the surface erodes under the intense heat it will experience. At this time, the comet may become bright enough to see by just holding up a hand to block the sun's glare.
"We estimate that as much as 10 percent of the comet's diameter may erode away, but this probably won't devastate it," said Matthew Knight, an astronomer at Lowell Observatory in Flagstaff, Ariz., and a member of the Swift and CIOC teams.
He said so far, Comet ISON looks promising, but that is all they can say now for sure.
"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," Knight added.