NASA Discovers Asteroid Delivered Assortment of Meteorites
WASHINGTON -- An international team of scientists studying remnants of an asteroid that crashed into the Nubian Desert in October 2008 discovered it contained at least 10 different types of meteorites. Some of them contained chemicals that form the building blocks of life on Earth, and those chemicals were spread through all parts of the asteroid by collisions.Chemists at Stanford University found that different meteorite types
share the same distinct fingerprint of polycyclic aromatic
hydrocarbons (PAHs). These complex organic molecules are distributed
throughout the galaxy and form on Earth from incomplete combustion.
A research team from NASA's Goddard Space Flight Center in Greenbelt,
Md., found amino acids in strongly heated fragments of the asteroid,
where all such molecules should have been destroyed. Both PAHs and
amino acids are considered building blocks of life.
Before landing on Earth, the 13-foot asteroid was detected by a
telescope from the NASA-sponsored Catalina Sky Survey based at the
University of Arizona in Tucson. Hours prior to its demise,
astronomers and scientists around the world tracked and scanned the
asteroid. It was the first time a celestial object was observed prior
to entering Earth's atmosphere.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., created a search
grid and impact target area. The data helped Peter Jenniskens, an
astronomer at NASA's Ames Research Center in Moffett Field, Calif.,
and the SETI Institute of Mountain View, Calif., guide a recovery
team from the University of Khartoum in Sudan to search the desert
landscape. During four expeditions, approximately 150 students
recovered nearly 600 meteorite fragments weighing a total of more
than 23 pounds.
"Right from the start, the students were surprised to find so much
diversity in meteorite texture and hue," said Muawia Shaddad, an
astronomer at the University of Khartoum, who led the search effort.
"We estimate the asteroid initially weighed about 59 tons, of which
about 86 pounds survived the explosion high in the atmosphere."
Subsequently, scientists determined most of the fragments are a rare
type of meteorite called ureilites. Less than 10 of the nearly 1,000
known meteorites are ureilites. The recovery team made history when
they found the first-ever freshly fallen mixed-composition, or
polymict ureilite. The majority of the remaining fragments are
similar to the more common types of meteorites called chondrites.
Other Ames researchers showed the ureilite fragments contained widely
varying amounts of the minerals called olivine and pyroxene. Carnegie
Institute of Washington researchers found these minerals have the
full range of oxygen atom signatures detected in previous ureilites.
Scientists believe this is evidence all ureilites originated from the
same source, called the ureilite parent body. Astronomers theorize
the parent body experienced a giant collision approximately 4.5
billion years ago and caused iron-rich minerals to smelt into
metallic iron. However, the olivine and pyroxene didn't melt, which
allowed the oxygen atoms in them to stay in the same arrangement as
when they first formed.
Researchers at NASA's Johnson Space Center in Houston were able to
deduce that much of the ureilite parent body was reduced to fragments
measuring 30 to 300 feet during this giant collision. After the
catastrophic collision, scientists believe the material that ended up
making 2008 TC3 had a long history of violent collisions and impacts.
These later collisions ground the fragments down into the smaller
sand grain-sized pieces that gathered loosely together with many voids.
Researchers believe the amino acids were delivered to 2008 TC3 during
the later impacts, or formed directly from trapped gases as the
asteroid cooled following the giant collision. Other non-ureilite
types of meteorites also became part of the asteroid. To date, ten
different meteorite types have been identified, accounting for 20-30
percent of the asteroid's recovered remains.
"Asteroids have just become a lot more interesting," Jenniskens said.
"We were surprised to find that not all of the meteorites we
recovered were the same, even though we are certain they came from
the same asteroid."
Astronomers have known asteroids orbiting the sun frequently are
broken and reassembled during collisions, but until now they thought
little mixing occurred because asteroids, or impactors that broke
them apart, are usually very small. The research is featured in 20
papers published this week in an issue of the Meteoritical Society's
journal Meteoritics and Planetary Science. For information about NASA
and agency programs, visit:
http://www.nasa.gov
Source: NASA
