[meteorite-list] WISE Makes Progress on its Space Rock Catalog

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.cfm?release=2010-176  

WISE Makes Progress on its Space Rock Catalog
Jet Propulsion Laboratory
May 24, 2010

NASA's Wide-field Infrared Survey Explorer, or WISE, is busy surveying
the landscape of the infrared sky, building up a catalog of cosmic
specimens -- everything from distant galaxies to "failed" stars, called
brown dwarfs.

Closer to home, the mission is picking out an impressive collection of
asteroids and comets, some known and some never seen before. Most of
these hang out in the Main Belt between Mars and Jupiter, but a small
number are near-Earth objects -- asteroids and comets with orbits that
pass within about 48 million kilometers (30 million miles) of Earth's
orbit. By studying a small sample of near-Earth objects, WISE will learn
more about the population as a whole. How do their sizes differ, and how
many objects are dark versus light?

"We are taking a census of a small sample of near-Earth objects to get a
better idea of how they vary," said Amy Mainzer, the principal
investigator of NEOWISE, a program to catalog asteroids seen with WISE.

So far, the mission has observed more than 60,000 asteroids, both Main
Belt and near-Earth objects. Most were known before, but more than
11,000 are new.

"Our data pipeline is bursting with asteroids," said WISE Principal
Investigator Ned Wright of UCLA. "We are discovering about a hundred a
day, mostly in the Main Belt."

About 190 near-Earth asteroids have been observed to date, of which more
than 50 are new discoveries. All asteroid observations are reported to
the NASA-funded International Astronomical Union's Minor Planet Center,
a clearinghouse for data on all solar system bodies at the Smithsonian
Astrophysical Observatory in Cambridge, Mass.

"It's a really exciting time for asteroid science," said Tim Spahr, who
directs the Minor Planet Center. "WISE is another tool to add to our
tool belt of instruments to discover and study the asteroid population."

A network of ground-based telescopes follows up and confirms the WISE
finds, including the NASA-funded University of Arizona Spacewatch and
Catalina Sky Survey projects, both near Tucson, Ariz., and the
NASA-funded Magdalena Ridge Observatory near Socorro, N.M.

Some of the near-Earth asteroids detected so far are visibly dark, but
it's too early to say what percentage. The team needs time to properly
analyze and calibrate the data. When results are ready, they will be
published in a peer-reviewed journal. WISE has not found an asteroid yet
that would be too dark for detection by visible-light telescopes on the
ground.

"We're beginning the process of sorting through all the objects we're
finding so we can learn more about their properties," said Mainzer. "How
many are big or small, or light versus dark?"

WISE will also study Trojans, asteroids that run along with Jupiter in
its orbit around the sun and travel in two packs -- one in front of and
one behind the gas giant. It has seen more than 800, and by the end of
the mission, should have observed about half of all 4,500 known Trojans.
The results will address dueling theories about how the outer planets
evolved.

With its infrared vision, WISE is good at many aspects of asteroid
watching. First, infrared light gives a better estimate of an asteroid's
size. Imagine a light, shiny rock lying next to a bigger, dark one in
the sunshine. From far away, the rocks might look about the same size.
That's because they reflect about the same amount of visible sunlight.
But, if you pointed an infrared camera at them, you could tell the dark
one is bigger. Infrared light is related to the heat radiated from the
rock itself, which, in turn, is related to its size.

A second benefit of infrared is the ability to see darker asteroids.
Some asteroids are blacker than coal and barely reflect any visible
light. WISE can see their infrared glow. The mission isn't necessarily
hunting down dark asteroids in hiding, but collecting a sample of all
different types. Like a geologist collecting everything from pumice to
quartz, WISE is capturing the diversity of cosmic rocks in our solar
neighborhood.

In the end, WISE will provide rough size and composition profiles for
hundreds of near-Earth objects, about 100 to 200 of which will be new.

WISE has also bagged about a dozen new comets to date. The icy cousins
to asteroids are easy for the telescope to spot because, as the comets
are warmed by the sun, gas and dust particles blow off and glow with
infrared light. Many of the comets found by WISE so far are so-called
long-period comets, meaning they spend billions of years circling the
sun in the frigid hinterlands of our solar system, before they are
shuttled into the inner, warmer parts. Others are termed short-period
comets -- they spend most of their lives hanging around the space near
Jupiter, occasionally veering into the space closer to the terrestrial
planets. WISE's measurements of these snowy dirtballs will allow
scientists to study their size, composition and density. Measurements of
the comets' orbits will help explain what kicks these objects out of
their original, more distant orbits and in toward the sun.

WISE will complete one-and-a-half scans of the sky in October of this
year. Visit http://wise.astro.ucla.edu to see selected WISE images
released so far.

JPL manages WISE for NASA's Science Mission Directorate, Washington. The
principal investigator, Edward Wright, is at UCLA. The mission was
competitively selected under NASA's Explorers Program managed by the
Goddard Space Flight Center, Greenbelt, Md. The science instrument was
built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft
was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science
operations and data processing take place at the Infrared Processing and
Analysis Center at the California Institute of Technology in Pasadena.
Caltech manages JPL for NASA. More information is online at
http://www.nasa.gov/wise and http://wise.astro.ucla.edu .

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

2010-176