[meteorite-list] NPA 06-25-1981 Meteorites...Martian fragments, McSween

From: MARK BOSTICK <thebigcollector_at_meteoritecentral.com>
Date: Tue May 17 17:00:21 2005
Message-ID: <BAY104-F17360F489578B2F62C7701B3160_at_phx.gbl>

Paper: Syracuse Herald Journal
City: Syracuse, New York
Date: Thursday, June 25, 1981
Page: A-11, National

Meteorites indicate Martian fragments

By PATRICK YOUNG
Newhouse News Service

     WASHINGTON - Scientists studying four rare meteorites believe they may
be looking at stony fragments from one of Earth's neighboring planets -
probably Mars.
     Dating techniques show rocks in three of the meteorites formed between
600 to 1.2 billion years ago when molten lava cooled. This is the youngest
rock ever found in such visitors from outer space. Dating efforts are
continuing on the fourth, an 18-pounder found in the Antarctic less than two
years ago.
     The four meteorites are classified as Shergottites, and they are the
only ones of their kind scientists know about. Dating them has proved
difficult because of their history.

Shock effects

     "They suffered a lot of shock effects from being ripped from their
parent body," says Harold McSween of the University of Tennessee in
Knoxville, who has studied all four meteorites. How they were blasted free
remains unknown.
    New evidence indicates the meteorites originated on some sizable body, a
finding that has surprised scientists. "Before this we thought all
meteorites came from the Asteroid Belt," McSween says.
     The Asteroid Belt is a ring of material ranging from dust grains to
planetoids orbiting the sun between Earth and Mars. Meteorites from there
date back 4.6 billion years, the time of the solar system's formation.
     Researchers say it is unlikely the type of conditions that formed the
Shergottite meteorites existed in the Asteroid Belt within the last 1.2
billion years.
     "We think we understand how melting could occur on a small body 4.6
billion years ago, but not 1 billion years ago," McSween says. "That leaves
two alternatives. One they all came from a planet; two, we don't understand
melting on small bodies."
     Rocks returned by the Apollo astronauts rule it out as the meteorite's
source, and other factors seem to rule out Mercury and Venus.

Volcanic acitivity

     But the right conditions may well have existed on Mars. Volcanic
activity still occurred on the planet at least 500 million years aog, and
some scientists think Mars may still be active.
     Researchers have also compared the chemical composition of the
Shergottite meteorites to soil studies curried out by the two Viking
spacecraft that landed on Mars in 1976. The Martian surface is rich in
sulfur and chlorine, which may be left from volcanic eruptions. If these
two chemicals are subtracted, the composition of Mars and the meteorites is
remarkably alike.

(end)

Meteorites referenced include: Shegotty, Zagami, ALH 77005, and Yamato
793605.
Received on Tue 17 May 2005 05:00:16 PM PDT