Spitzer Finds a Flavorful Mix of Asteroids

Feature September 2, 2010


Spitzer Finds a Flavorful Mix of Asteroids

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-283&cid=release_2010-283

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 piñata 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 Côte 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 für 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 .

#2010-283

Whitney Clavin 818-354-4671
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

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