Science

Signs of nearby life

Not exactly little green men, but microbes may have left their mark on rock from Mars

Mark Nichols March 12 2001
Science

Signs of nearby life

Not exactly little green men, but microbes may have left their mark on rock from Mars

Mark Nichols March 12 2001

Signs of nearby life

Science

Not exactly little green men, but microbes may have left their mark on rock from Mars

Mark Nichols

In 1877, Italian astronomer Giovanni Schiaparelli reported spotting canali on the surface of Mars, leading other scientists to speculate that a race of intelligent, canal-building beings lived there. Planetary experts know today that the lines on Mars’s surface are natural features. Yet there is an enduring fascination with the notion that life might exist on Earth’s planetary neighbour—and not only among science-fiction writers. In the latest thrust in a smouldering controversy that flared five years ago, American scientists last week published findings that they claimed provide “compelling evidence” that life existed on Mars 3.5 billion years ago. They argued that chains of crystal embedded in a Martian meteorite found in Antarctica could only have been formed by biological processes. “As far as I’m concerned,” declared Imre Friedmann, the NASA scientist who led the study, “Martian bacteria were in this meteorite. When you put all the elements together, there can be no other explanation.”

If the latest claims about the Martian rock known as ALH84001 are accurate, the implications are awesome. That could mean biological life emerged twice in the solar system shared by Earth and Mars, enormously increasing the chances of life—even intelligent beings—existing elsewhere in the vastness of the universe. And if bacteria once thrived on Mars, they might survive there today, even though the planet is drier and colder than in the distant past. Still, initial reaction suggested that even scientists who believe life could well have developed on Mars remain deeply skeptical about the NASA group’s claims. “My feeling,” said Jaymie Matthews, an astronomer at the University of British Columbia in Vancouver, “is that they could be right. But we need a smoking gun—evidence that everyone can agree with—and I don’t think we’ve got it yet.”

One of the few things scientists in both camps agree on is that ALEI84001 almost certainly originated on Mars, since gases trapped inside it closely resemble samples taken from the surface of Mars by unmanned U.S. spacecraft in 1976. Scientists think the 1.8-kg rock was formed roughly 4.5 billion years ago, then flung into space by an asteroid that struck Mars 15 million

years ago. Eventually, the meteorite was captured by Earth’s gravity and plunged into the Antarctic, where scientists found it in 1984.

It remained a litde-known curiosity until August, 1996, when NASA scientists announced that they had found evidence of Martian life inside the meteorite. But other scientists argued that the evidence advanced by the NASA group did not prove bacterial life had existed on Mars. Some critics suggested the meteorite might have been contaminated by Earth-based bacteria during its years in the Antarctic.

The latest paper, published in the journal Proceedings of the National Academy of Science, focuses on chains of tiny magnetic crystals, called iron magnetite, inside ALH84001, which they argued could only be of biological origin. Similar chains of material are found in Earth bacteria, which use them as navigational guides. These crystals must have originated on Mars, they added, because they are embedded in Martian material. The fact that the rock apparently contained large numbers of bacteria, the researchers added, meant microbial life must have once been widespread on Mars.

Other scientists found the arguments less than convincing. “It’s not conclusive,” said Norman Murray, a University of Toronto astrophysicist, who noted that magnetite crystals might not always be biological in origin. “It’s possible,” he added, “to imagine them being formed by some other process.” An irony of the debate over ALH84001 lies in the stream of tantalizing images beamed to Earth since September, 1997, by NASAs Mars Global Surveyor, which hint at the possibility of water existing beneath Mars’s barren surface. If it does, some scientists think there is a slim chance that, regardless of what ALEI84001 may or may not prove, microbial life could exist today somewhere inside the Red Planet.