[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 |
StumbleUpon del.icio.us Yahoo MyWeb |