UH team calls
Mars shard a
‘shocked rock’
UH researchers again
By Helen Altonn
dispute the theory that the
fragment signaled early
life on that planet
Star-BulletinUniversity of Hawaii scientists and two mainland research teams today announced discoveries toppling the idea of ancient life on Mars.
Findings of possible remains of ancient bacteria in a Martian meteorite by NASA scientist David McKay and Stanford University colleagues caused an international stir two years ago.
More likely it was a "shocked rock," UH planetary scientist Edward Scott said last May after research on a meteorite sample with associates Sasha Krot and Akira Yamaguchi.
More detailed investigations the past year confirm their earlier findings, Scott said yesterday.
A University of Tennessee and Case Western Reserve University collaboration, and a University of Arkansas group, also dispute the discovery of Martian microorganisms, for different reasons.
Reports by the three teams are among 19 papers on Martian meteorites by 50 scientists in six countries appearing in the current issue of Meteoritics and Planetary Science.
The famed rock under surveillance and debate is known as Allan Hills 84001, one of only 12 Martian meteorites ever identified on Earth.
It's believed an asteroid struck Mars about 16 million years ago and catapulted the potato-sized rock into space. Hills found it in an Antarctic ice field in 1984.
All evidence of life suggested by McKay's group was found in carbonate crystals in the rock, Scott noted.
He said last year his team had studied carbonates in a sample of ALH 84001 that appeared to have formed at high temperatures in an impact and couldn't be remains of living organisms.
The NASA group argued that the disk-shaped grains it studied were different than those Scott's team examined.
Using electron and optical microscopes, the UH team has since studied carbonates of all shapes and sizes in more than a dozen chips of the Martian meteorite.
Those shaped like disks were formed in the same way as those studied a year ago, with the same properties and chemical varieties, Scott said. "So there is no dispute that all carbonates were formed in the same way."
More detailed studies also support the UH scientists' view that the carbonates formed in the impact, he said.
Scott said evidence shows the carbonates grew rapidly from a hot fluid in the rock when the fractures were opened, then closed by impact. The grains are wide in the area where they started growing and narrow where the growing stopped, he said.
The University of Arkansas team suggests features described by McKay's group, rather than life-supporting, may be due to contamination on Earth or processes that commonly occur on the surfaces of minerals.
However, Arkansas researcher Derek Sears said, "Martian meteorite ALH 84001 and David McKay have shown that we must search carefully for signs of microorganisms in Martian rocks, and the hunt has only just begun."
Scott said his group wants to look at other Martian meteorites to see how its evidence fits other carbonates and minerals that form them.
Scott and Krot work in the Hawaii Institute of Geophysics and Planetology. Yamaguchi, formerly with the institute, is at the National Institute for Research in Inorganic Materials in Japan.
"We still want to know how the carbonates got there in the first place," Scott said. "If they did form from solutions, we would like to know how and why and what that tells us about the water on Mars.
"It doesn't look as though it has very much water because the rock is still very fresh -- the materials didn't get converted to clay," he added. "There is only a tiny amount of clay minerals."
So it's a puzzle how water got into the rocks. "Mars has no water flowing on the surface but evidence is that there was water," Scott said.
McKay, at the Johnson Space Center in Houston, couldn't be reached for comment.
"No one has said the data (by McKay's group) is incorrect," Scott said. It's a matter of how one interprets the shapes and how the carbonate compounds and particular minerals are formed, he said.
Even though evidence is building against life in the Martian meteorite, he added, McKay's group triggered an explosion of interest in possible life on Mars and elsewhere in the solar system.
"Not since astronauts landed on the moon has there been so much excitement about rocks from space," he said.
