[meteorite-list] NASA's Wise Finds Mysterious Centaurs May Be Comets

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 25 Jul 2013 12:21:16 -0700 (PDT)
Message-ID: <201307251921.r6PJLGdc014305_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-234

NASA's Wise Finds Mysterious Centaurs May Be Comets
Jet Propulsion Laboratory
July 24, 2013

PASADENA, Calf. -- The true identity of centaurs, the small celestial
bodies orbiting the sun between Jupiter and Neptune, is one of the
enduring mysteries of astrophysics. Are they asteroids or comets? A new
study of observations from NASA's Wide-field Infrared Survey Explorer
(WISE) finds most centaurs are comets.

Until now, astronomers were not certain whether centaurs are asteroids
flung out from the inner solar system or comets traveling in toward the
sun from afar. Because of their dual nature, they take their name from
the creature in Greek mythology whose head and torso are human and legs
are those of a horse.

"Just like the mythical creatures, the centaur objects seem to have a
double life," said James Bauer of NASA's Jet Propulsion Laboratory in
Pasadena, Calif. Bauer is lead author of a paper published online July
22 in the Astrophysical Journal. "Our data point to a cometary origin
for most of the objects, suggesting they are coming from deeper out in
the solar system."

"Cometary origin" means an object likely is made from the same material
as a comet, may have been an active comet in the past, and may be active
again in the future.

The findings come from the largest infrared survey to date of centaurs
and their more distant cousins, called scattered disk objects. NEOWISE,
the asteroid-hunting portion of the WISE mission, gathered infrared
images of 52 centaurs and scattered disk objects. Fifteen of the 52 are
new discoveries. Centaurs and scattered disk objects orbit in an
unstable belt. Ultimately, gravity from the giant planets will fling
them either closer to the sun or farther away from their current locations.

Although astronomers previously observed some centaurs with dusty halos,
a common feature of outgassing comets, and NASA's Spitzer Space
Telescope also found some evidence for comets in the group, they had not
been able to estimate the numbers of comets and asteroids.

Infrared data from NEOWISE provided information on the objects' albedos,
or reflectivity, to help astronomers sort the population. NEOWISE can
tell whether a centaur has a matte and dark surface or a shiny one that
reflects more light. The puzzle pieces fell into place when astronomers
combined the albedo information with what was already known about the
colors of the objects. Visible-light observations have shown centaurs
generally to be either blue-gray or reddish in hue. A blue-gray object
could be an asteroid or comet. NEOWISE showed that most of the blue-gray
objects are dark, a telltale sign of comets. A reddish object is more
likely to be an asteroid.

"Comets have a dark, soot-like coating on their icy surfaces, making
them darker than most asteroids," said the study's co-author, Tommy Grav
of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend
to be more like charcoal, while asteroids are usually shinier like the
moon."

The results indicate that roughly two-thirds of the centaur population
are comets, which come from the frigid outer reaches of our solar
system. It is not clear whether the rest are asteroids. The centaur
bodies have not lost their mystique entirely, but future research from
NEOWISE may reveal their secrets further.

The paper is available online at:

http://iopscience.iop.org/0004-637X/773/1/22/ .

JPL, managed by the California Institute of Technology in Pasadena,
managed and operated WISE for NASA's Science Mission Directorate. The
NEOWISE portion of the project was funded by NASA's Near Earth Object
Observation Program. WISE completed its key mission objective, two scans
of the entire sky, in 2011 and has been hibernating in space since then.

For more information about the WISE mission, visit:
http://www.nasa.gov/wise .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin at jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington
j.d.harrington at nasa.gov

2013-234
Received on Thu 25 Jul 2013 03:21:16 PM PDT