[meteorite-list] Comet ISON to fly by Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 23 Aug 2013 13:17:11 -0700 (PDT)
Message-ID: <201308232017.r7NKHBeT016261_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2013/23aug_marsison/

Comet ISON to fly by Mars
NASA Science News
August 23, 2013

Around the world, astronomers are buzzing with anticipation over the
approach of Comet ISON. On Thanksgiving Day 2013, the icy visitor
from the outer solar system will skim the sun's outer atmosphere and,
if it survives, could emerge as one of the brightest comets in years.

First, though, it has to fly by Mars.

"Comet ISON is paying a visit to the Red Planet," says astronomer Carey
Lisse of the Johns Hopkins University Applied Physics Lab. "On Oct 1st,
the comet will pass within 0.07 AU from Mars, about six times closer
than it will ever come to Earth."

Mars rovers and satellites will get a close-up view. It's too early to
say whether Curiosity will be able to see the comet from the surface of
Mars - that depends on how much ISON brightens between now and then. Lisse
says the best bet is NASA's Mars Reconnaissance Orbiter. The MRO
satellite is equipped with a powerful half-meter telescope named HiRISE
that is more than capable of detecting the comet's atmosphere and tail.
Observations are planned on four dates: August 20th, Sept 29th, and Oct
1st and 2nd .

HiRISE wasn't sent to Mars to do astronomy, notes the telescope's
principal investigator Alfred McEwen of the University of Arizona. "The
camera is designed for rapid imaging of Mars. Our maximum exposure time
is limited compared to detectors on other space telescopes. This is a
major limitation for imaging comets. Nevertheless, I think we will
detect Comet ISON."

The Mars flyby comes at a key time in Comet ISON's journey. It will have
just crossed the "frost line," a place just outside the orbit of Mars
where solar heating is enough to start vaporizing frozen water.

"The volatiles in a comet are 80% to 90% water ice," notes Lisse. "Right
now in August almost all the water is still frozen, and the outgassing
we see in ISON is driven by carbon dioxide and other lesser
constituents. Probably only isolated patches of the comet's nucleus are
active."

But when ISON crosses the frost line, "the whole comet could erupt in
geysers of gas," says Lisse. "Mars orbiters will have a ringside seat."

Comet ISON orbit <http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012%20S1;orb=1>
Click to view an interactive orbit of Comet ISON

The amount of outgassing at Mars will give researchers clues to the size
of ISON's nucleus, which is hidden from view deep within the comet's
dusty atmosphere.

"If ISON's nucleus is much bigger than 0.5 km, it will probably survive
its Thanksgiving Day brush with the sun," says Lisse. "It could turn
into one of the most spectacular comets in many years."

McEwen sees this as a tune-up for another comet encounter next year.
"The science value of observing Comet ISON is hard to predict. We've
never tried such a thing before. However, this is good practice for
Comet Siding Spring, which will pass much closer to Mars in 2014."

For now all eyes are on Comet ISON. An unprecedented number of NASA
spacecraft - 16 - will be observing the comet. Astronauts on board the
International Space Station will be watching, too.

Meanwhile back on Earth, Lisse is working with NASA to organize a
worldwide observing campaign for Comet ISON. "Our goal is to have every
telescope on Earth pointed at the comet when it emerges from the sun,"
says Lisse. "The Mars flyby will give us a sneak preview, providing
data we need to predict what we might see."

Credits:

Author: Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Fri 23 Aug 2013 04:17:11 PM PDT