As soon as NASA's recent press conference was over, a number of science organizations posted web sites focusing on the possibility of the existence of ancient life on Mars. Because there are so many sites to choose from, we checked them out and have provided a guide to some of the best. We hope you will first read our main story, which summarizes NASA and Stanford University press releases and includes Real Audio interviews with several Exploratorium scientists. But if you're looking to go in-depth to the question of whether life existed on Mars, these web resources below are certainly worth checking out too.

TODAY@NASA

FAS Space Policy Project

Sky & Telescope

NASA AMES: Life on Mars

Mars Meteorites

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Was There Life on Mars?
A NASA-sponsored scientific team has announced that a meteorite from Mars shows evidence that life once existed on that planet. The world's scientific community eagerly awaits publication of the August 16 issue of Science magazine, which will feature the group's official report.

The meteorite, found twelve years ago in Antarctica, has yielded clues indicating that simple, one-celled organisms may have thrived on Mars--the only planet in our solar system besides Earth considered likely to have harbored life--billions of years ago.

The evidence, which the research team emphasizes is "circumstantial," consists of organic compounds, unusual mineral compounds often produced by microscopic life on Earth, and microfossils similar to those of our planet's smallest bacteria.

The Other Wet Planet

About 3.5 to 4 billion years ago, when scientists believe Mars was warmer and held surface water, some water may have seeped underground. Carbonate minerals may have formed when living organisms and carbon dioxide from the Martian atmosphere interacted.

PAHs and mineral compounds believed to be formed by microscopic life were found near concentrations of this carbonate. The meteorite also yielded fossil structures similar to the smallest terrestrial microscopic fossils.

The research team, which includes a contingent from Stanford University, gave several reasons for its conclusion that the meteorite did not acquire these clues to life after its arrival on Earth. First, no other similar meteorites have indicated such evidence. Second, the PAHs were concentrated deep inside the meteorite; they would be located primarily on its crust, with smaller amounts closer to its center, if the fragment had acquired them on Earth. Finally, the life that produced these clues predate similar life-forms here.

The Rock That Fell to Earth

The 4.2-pound (nearly 2 kg) meteorite was found during an Antarctic scientific expedition in 1984, but it was identified as coming from Mars only in 1993. Scientists believe that the rock fragment, which is about 4.5 billion years old, was ejected from the surface of Mars when a comet or asteroid struck the planet about 15 million years ago. After millions of years in space, the meteorite then fell to Earth, lying in Antarctica for 13,000 years before its discovery.

Scientists checked the meteorite with a laser mass spectrometer for polycyclic aromatic hydrocarbons (PAHs), a class of organic molecules common on Earth. The instrument blasts a pinpoint area with an infrared laser for scant millionths of a second at a temperature of more than 100 million degrees per second, which harmlessly detaches molecules from the target surface. Then, another laser pulse--this one consisting of ultraviolet light--ionizes molecules. (Ionization separates an electron from each molecule, creating a positively charged molecule.)

The spectrometer then measures the ionized molecules' speed to calculate their mass, allowing researchers to identify the compounds more accurately than by other methods. Earlier techniques were not sophisticated enough to detect microfossils and other clues as small as those in this fragment.

What Do We Do Now?

Scientists around the world will immediately study the NASA team's conclusions, but it may be several years before they reach definitive conclusions. In the meantime, the new spectrometer technology will inspire a new look at many other meteorite fragments. On a grander scale, this discovery may inspire a resurgence in interest in space exploration.

"What's New" asked Exploratorium scientists Linda Shore, Paul Doherty, and Charles Carlson to comment on this discovery. The following interviews require the RealAudio player and 28.8 modem connection or better. Click on a scientist to listen to the interview.

If you need the RealAudio player, click here to download it.