[meteorite-list] Spitzer Finds a Flavorful Mix of Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 2 Sep 2010 11:26:22 -0700 (PDT)
Message-ID: <201009021826.o82IQMnn020091_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-283

Spitzer Finds a Flavorful Mix of Asteroids
Jet Propulsion Laboratory
September 02, 2010

New research from NASA's Spitzer Space Telescope reveals that asteroids
somewhat near Earth, termed near-Earth objects, are a mixed bunch, with
a surprisingly wide array of compositions. Like a pinata filled with
everything from chocolates to fruity candies, these asteroids come in
assorted colors and compositions. Some are dark and dull; others are
shiny and bright. The Spitzer observations of 100 known near-Earth
asteroids demonstrate that the objects' diversity is greater than
previously thought.

The findings are helping astronomers better understand near-Earth
objects as a whole -- a population whose physical properties are not
well known.

"These rocks are teaching us about the places they come from," said
David Trilling of Northern Arizona University, Flagstaff, lead author of
a new paper on the research appearing in the September issue of
Astronomical Journal. "It's like studying pebbles in a streambed to
learn about the mountains they tumbled down."

After nearly six years of operation, in May 2009, Spitzer used up the
liquid coolant needed to chill its infrared detectors. It is now
operating in a so-called "warm" mode (the actual temperature is still
quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of
Spitzer's infrared channels, the shortest-wavelength detectors on the
observatory, are working perfectly.

One of the mission's new "warm" programs is to survey about 700
near-Earth objects, cataloguing their individual traits. By observing in
infrared, Spitzer is helping to gather more accurate estimates of
asteroids' compositions and sizes than what is possible with visible
light alone. Visible-light observations of an asteroid won't
differentiate between an asteroid that is big and dark, or small and
light. Both rocks would reflect the same amount of visible sunlight.
Infrared data provide a read on the object's temperature, which then
tells an astronomer more about the actual size and composition. A big,
dark rock has a higher temperature than a small, light one because it
absorbs more sunlight.

Trilling and his team have analyzed preliminary data on 100 near-Earth
asteroids so far. They plan to observe 600 more over the next year.
There are roughly 7,000 known near-Earth objects out of a population
expected to number in the tens to hundreds of thousands.

"Very little is known about the physical characteristics of the
near-Earth population," said Trilling. "Our data will tell us more about
the population, and how it changes from one object to the next. This
information could be used to help plan possible future space missions to
study a near-Earth object."

The data show that some of the smaller objects have surprisingly high
albedos (an albedo is a measurement of how much sunlight an object
reflects). Since asteroid surfaces become darker with time due to
exposure to solar radiation, the presence of lighter, brighter surfaces
for some asteroids may indicate that they are relatively young. This is
evidence for the continuing evolution of the near-Earth object population.

In addition, the fact that the asteroids observed so far have a greater
degree of diversity than expected indicates that they might have
different origins. Some might come from the main belt between Mars and
Jupiter, and others could come from farther out in the solar system.
This diversity also suggests that the materials that went into making
the asteroids -- the same materials that make up our planets -- were
probably mixed together like a big solar-system soup very early in its
history.

The research complements that of NASA's Wide-field Infrared Survey
Explorer, or WISE, an all-sky infrared survey mission also up in space
now. WISE has already observed more than 430 near-Earth objects -- of
these, more than 110 are newly discovered.

In the future, both Spitzer and WISE will tell us even more about the
"flavors" of near-Earth objects. This could reveal new clues about how
the cosmic objects might have dotted our young planet with water and
organics -- ingredients needed to kick-start life.

Other authors of the paper include Cristina Thomas, also from Northern
Arizona University; Michael Mueller and Marco Delbo of the Observatoire
de la C??te d'Azur, Nice, France; Joseph Hora, Giovanni Fazio, Howard
Smith and Tim Spahr of the Harvard-Smithsonian Center for Astrophysics,
Cambridge, Mass.; Alan Harris of the DLR Institute of Planetary
Research, Berlin, Germany (DLR is Germany's space agency and stands for
Deutsches Zentrum f??r Luft- und Raumfahrt); Bidushi Bhattacharya of the
NASA Herschel Science Center at the California Institute of Technology,
Pasadena; Steve Chesley and Amy Mainzer of NASA's Jet Propulsion
Laboratory, Pasadena, Calif.; Bill Bottke of the Southwest Research
Institute, Boulder, Colo.; Josh Emery of the University of Tennessee,
Knoxville; Bryan Penprase of the Pomona College, Claremont, Calif.; and
John Stansberry of the University of Arizona, Tucson.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer
Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology, also in Pasadena.
Caltech manages JPL for NASA. For more information about Spitzer, visit
http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer .

JPL manages the Wide-field Infrared Survey Explorer 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

2010-283
Received on Thu 02 Sep 2010 02:26:22 PM PDT