Martian Meteorite Measurements Give Information on Planet Evolution

http://www.yale.edu/opa/newsr/04-10-25-01.all.html

Yale University News Release

CONTACT: Janet Rettig Emanuel 203-432-2157 or

For Immediate Release: October 25, 2004

Martian Meteorite Measurements Give Information on Planet Evolution

New Haven, Conn. -- Scientists in the department of Geology and
Geophysics at Yale University have devised a method to precisely date
the timing and temperature of a meteorite impact on Mars that led to
ejection of a piece of the planet into space and its eventual impact
on Earth.

Meteorites are the main source of mass exchange between planets and
carry with them characteristic clues about the nature and history of the
planets or planetesimals where they originated, the impacts that
dislodged them, and the time they spent in space.

Kyoungwon Kyle Min, postdoctoral fellow in geology, reported an
innovation for determining the timing and temperatures of ancient
impacts that liberate meteorites from extraterrestrial bodies such as
Mars.

To measure both the age and thermal history of the piece of Martian
rock, Min assayed the natural radioactive decay of uranium and thorium
to the gas helium in these meteorites, and combined it with knowledge of
how temperature affects helium loss over time. This (U-Th)/He dating
method, used on single grains of minerals in the "Los Angeles" Martian
meteorite gave a far more accurate picture than the conventional method
of analyzing chunks of meteorite. The "helium age" of about three
million years corresponds with the estimated cosmogenic space exposure age.

According to co-author Assistant Professor Peter W. Reiners, "The three
million-year age of this meteorite is also important because other
meteorites we're working on, including some Martian ones, are several
hundred million to billions of years older. These methods allow us to
better understand both the timing and dynamics of ancient impacts on
other planets, and how these events relate to interplanetary material
transfer."

Scientists have long looked at meteorites to answer the question of
whether there is now, or once was, life on Mars. They now can compare
data from meteorites with the observations of space vehicles to learn
more about past activities on the surface of Mars.

Stefan Nicolescu and James Greenwood from Yale University co-authored
the study supported by a grant from the National Science Foundation.

Citation: Geology: 32, 677-680 (2004)

# # #