Researchers Say Two More Mars Meteorites Show Signs of Life
(From the May/June 1999 issue of StarDate magazine)
Microscopic life inhabited Mars for much of its 4.5 billion-year history and may still exist on the planet today, according to a team of scientists that has studied several Martian meteorites. But the report is likely to come under intense attack over the next few months as other scientists examine the same rocks.
In 1996, a team led by David S. McKay of NASA's Johnson Space Center reported that Martian meteorite ALH 84001 contained evidence of ancient microscopic life, including organic molecules, magnetic minerals, and extremely small spheres and tubes that look like fossilized bacteria.
At the Lunar and Planetary Science Conference in Houston in March, McKay reported that his team has found similar evidence in two other meteorites from Mars: Nakhla, which is named for the Egyptian town where it fell to Earth in 1911, and Shergotty, which fell in India in 1865.
Because both meteorites are much younger than ALH 84001, they suggest that microscopic life continued to flourish on Mars for billions of years. Nakhla is 1.3 billion years old and Shergotty is only 165 million years old, compared with about 4.5 billion years for ALH 84001.
(Scientists identified the Martian origin of all three meteorites by examining the ratios of different forms of oxygen found in tiny bubbles inside the rocks. The ratio provides a unique chemical fingerprint for each planet in the solar system. The rocks were blasted into space in powerful collisions between Mars and asteroids.)
After the 1996 announcement, other scientists studied pieces of ALH 84001, and most of their findings refute the evidence of McKay's team.
But two recent reports seem to strengthen the case for ancient microscopic life on Mars:
• Mars Global Surveyor images show that early Martian volcanoes were more active than scientists had expected. The volcanoes would have pumped more carbon dioxide into the Martian atmosphere, trapping energy from the Sun and making Mars both warmer and wetter than thought.
• University of Queensland researchers discovered microscopic organisms on Earth as small as the possible fossils seen in the Martian meteorites. Critics of the ALH 84001 findings noted that the smallest microbes on Earth were about 100 times larger than the meteorite fossils. But the Queensland scientists found colonies of bacteria beneath the seabed off the coast of Australia that are the same size as the fossils -- about 20 to 150 nanometers (less than 0.00001 inch).
While the debate over the new meteorites takes wing, NASA plans to develop a small airplane to soar over Valles Marineris, a canyon system that stretches a quarter of the way around Mars. If it receives final approval, the craft could reach Mars on December 17, 2003 -- exactly 100 years after Orville and Wilbur Wright conducted the first controlled, powered human aircraft flight on Earth.
Engineers are working on designs with large, thin wings to provide as much lift as possible in the thin Martian atmosphere. The wings would fold up inside a small capsule for launch and the cruise to Mars, then unfold as the capsule dropped into the Martian atmosphere.
The aircraft would cover more than 1,000 miles before running out of fuel. Its cameras would be able to photograph features on the ground as small as baseballs, and a tail-mounted video camera would beam a view of both the airplane and the Martian surface below back to Earth. -- — Damond Benningfield
|
  |
Contact StarDate | About StarDate | Friends of McDonald | Sign up for Sky Tips
