Contact: Lee Tune,
1-301-405-4679
[EMAIL PROTECTED]
UM-Led Team Finds Oldest Known Asteroids
March 20, 2008
COLLEGE PARK, Md. -- Using visible and infrared data collected from
telescopes on Hawaii's Mauna Kea, a team of scientists, led by the
University of Maryland's Jessica Sunshine, have identified three
asteroids that appear to be among our Solar System's oldest objects.
Evidence indicates that these ancient asteroids are relatively unchanged
since they formed some 4.55 billion years ago and are older than the
oldest meteorites ever found on Earth, say Maryland's Sunshine and
colleagues from the City University of New York, the Smithsonian
Institution, and the University of Hawaii. Their findings are published
in this week's edition of Science Express.
"We have identified asteroids that are not represented in our meteorite
collection and which date from the earliest periods of the Solar
System," said Sunshine, a senior research scientist in the University of
Maryland's department of astronomy. "These asteroids are prime
candidates for future space missions that could collect and return
samples to Earth providing a more detailed understanding of the Solar
System's first few millions of years."
In the Beginning
At the beginning of the Solar System, there was just a disk-shaped cloud
of hot gas, the solar nebula. When gasses on the edge of the early
nebula began to cool, the first materials to condense into solid
particles were rich in the elements calcium and aluminum. As the gasses
cooled further, other materials also began to condense. Eventually the
different types of solid particles clumped together to form the common
building blocks of comets, asteroids, and planets. Astronomers have
thought that at least some of the Solar System's oldest asteroids should
be more enriched in calcium and aluminum, but, until the current study,
none had been identified.
Meteorites found on Earth do contain small amounts of these earliest
condensing materials. As seen in meteorites, these bright white ancient
materials, the so-called calcium, aluminum-rich inclusions, or CAIs, can
be as large as a centimeter in diameter. Scientists, in fact, long have
used the age of CAIs to define the age of the Solar System.
"The fall of the Allende meteorite in 1969 initiated a revolution in the
study of the early Solar System," said Tim McCoy, curator of the
national meteorite collection at the Smithsonian's National Museum of
Natural History. "It was at that time scientists first recognized that
the remarkable white inclusions -- later called calcium, aluminum-rich
inclusions-- which were found in this meteorite, matched many of the
properties expected of early Solar System condensates.
"I find it amazing that it took us nearly 40 years to collect spectra of
these [CAI-rich] objects and that those spectra would now initiate
another revolution, pointing us to the asteroids that record this
earliest stage in the history of our Solar System," said McCoy.
Sunshine and McCoy, with colleagues Harold Connolly, Jr, City University
of New York; Bobby Bus, Institute for Astronomy, University of Hawaii,
Hilo; and Lauren La Croix, Smithsonian Institution, used the SpeX
instrument at the NASA Infrared Telescope Facility in Hawaii to look at
the surface of asteroids for evidence of the presence of such early bits
of high-temperature rock. In particular, they looked for spectral
"fingerprints" indicative of the presence of CAIs. Because different
minerals have different reflective properties, the spectrum, or color of
light reflected from a surface, reveals information about its
composition enabling telescopic compositional analysis.
In their paper, Sunshine and colleagues quantitatively compare the
spectral signatures of asteroid surfaces and CAIs in meteorites from the
Smithsonian's National Museum of Natural History collection. "Several
CAI-rich asteroids have been identified that contain 2-3 times more CAI
material than any known meteorite," Sunshine said. "Thus it appears
ancient asteroids have indeed survived, and we know where they are."
This research was supported by NASA and the National Science Foundation
(NSF).
Making a Deep Impact on Space Exploration
University of Maryland scientists and engineers are at the forefront of
many efforts to explore our Solar System and the universe beyond it.
Maryland astronomers have led or participated in many Solar System
missions, including: Deep Impact and its current follow-on mission
EPOXI; the Dawn mission to study dwarf planet Ceres and asteroid Vesta;
and the NEAR spacecraft that in 2000 became the first to orbit, and then
land on, an asteroid.
Scientists of the university's space physics group have built sensors
for some 13 spacecraft, including the two Voyager spacecraft, now
exploring the outer edge of the Solar System; the Cassini mission
(Saturn); the Ulysses probe to the solar poles; and near-Earth missions
such as Geotail and the Solar Anomalous and Magnetospheric Particle
Explorer (SAMPEX).
The University of Maryland's Space System Laboratory works to make
humans more productive while working in space by designing tools and
suits for astronauts; creating robotic systems capable of assisting
astronauts in space and studying how the human body works in space. To
simulate the weightless environment of space, the laboratory uses its
neutral buoyancy facility, the only such facility located on a college
campus.
# # #
------------------------------------------------------------------------
"Ancient Asteroids Enriched in Refractory Inclusions," J. M. Sunshine1*,
H. C. Connolly, Jr.2, 3,4, T. J. McCoy5, S. J. Bus6, and L. M. La
Croix5,7
1Department of Astronomy, University of Maryland, College Park, MD
2Department of Physical Sciences, Kingsborough Community College of the
City University of New York, Brooklyn, NY
3Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ
85721, USA
4Department of Earth and Planetary Sciences, American Museum of Natural
History, New York, NY
5Department of Mineral Sciences, National Museum of Natural History,
Smithsonian Institution, Washington, DC
6Institute for Astronomy, University of Hawaii, Hilo
7Department of Geological Sciences and Engineering, University of
Nevada, Reno NV
Science contact-
Jessica M. Sunshine
1-301-405-1045
[EMAIL PROTECTED]
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