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In the Now Guru
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There isn't any--yet. There's been some interesting speculation: tales of extinct Martian civilizations, the supposed canals, the infamous "face" on Mars. But none of that would stand up in court.
Most of the evidence we do have relates to water, a key component of life (at least as we know it). Before Opportunity and Spirit started digging up water-washed rocks, earlier probes had observed patterns of erosion that suggested the presence of ancient lakes and rivers. And Mars's polar regions may contain significant amounts of water in frozen form. There's even evidence that more exists, trapped in the Martian soil.
Strangely, the most compelling evidence of life on Mars comes from here on Earth. In 1996, scientists discovered organic molecules on a 15-million-year-old Martian meteorite that landed in Antarctica. These molecules suggest that some kind of microbial life may once have called Mars home. But the study's conclusions are controversial. Some scientists think the molecules could have an Earthly origin; others suggest they could have come from non-biological sources.
What's life like on Mars, if there is any?
Mars is mild compared to some planets, but life there would definitely need sunscreen, anti-oxidants, and mittens. The problem is the Martian atmosphere. Mars does have one, which is a bonus, because life can't exist in a vacuum. But it's thin and inhospitable. It's composed mostly of carbon dioxide, with only trace amounts of oxygen. Other compounds in the atmosphere promote oxidation, a chemical reaction that's very destructive to life.
Then there's the issue of sunburn. Mars gets a decent amount of light, which is crucial for photosynthesis. But the Martian atmosphere is too weak to provide protection from the damaging solar energy that comes with it. The result is a cosmic bombardment of lethal radiation many times more powerful than what we get here on Earth. And for all that radiation, Mars is still a pretty cold place, about -81° Fahrenheit (-63° Celsius) on average. On a warm day, it can feel like spring on Earth. But most of the time, in most places, Mars makes Antarctica look tropical.
When will humans land on Mars?
Well, the trip is no picnic. Even with Mars at its closest, it's a 35-million-mile journey to get there. That's more than 150 times farther than the Apollo astronauts had to go to land on the moon. At that distance, even a fast trip would take about six months. (Opportunity and Spirit launched last June and arrived in January.)
Still, even before the Bush administration announced its interest in Mars, many knowledgeable scientists had been advocating for sending humans there. It will be tricky, for sure. Scientists will have to overcome issues with intense solar radiation, fuel and life-support system limitations, and several other hurdles long before anyone packs a suitcase. And it's tough to say when those things will happen.
If Mars turns out to be a dead end, where else can we look for life?
How about Europa?
One of Jupiter's moons, Europa, may be an even more likely spot than Mars for little green microbes--at least living ones. In the end, it's all about the water. Mars probably doesn't have enough left to support life. Europa, on the other hand, is swimming in it.
Jovian probes show that Europa has an icy surface of unknown thickness. Under the ice, gravitational tides likely maintain a warm ocean several miles deep. The presence of a weak magnetic field around Europa even suggests that this water is a nice, conductive, salty blend ideal for supporting life. Europa's surface temperature only gets up to about -234° F (-148° C). But the completely frozen surface may actually help, by protecting the liquid interior from life-destroying forces like radiation and oxidation.
So when can we expect a manned mission to Europa? No time soon. NASA's Galileo probe examined its icy surface in the 1990s, but it had to slingshot around Venus to get there, and that trip took four years--one way. Dave Bowman and the HAL 9000 computer may have flown to Jupiter in 2001, but in reality, it'll be more like 2101 before people land on Europa to look for life.
Christopher Call studied marine science at Boston University, where he did research at the Marine Biological Laboratory in Woods Hole, Massachusetts. Later, he earned a master's degree in biology from Loyola University in Chicago, where he studied the invasion of the zebra mussel into the Great Lakes ecosystem. Today, he teaches biology and environmental science at Elmhurst College and dives with dolphins at Chicago's Shedd Aquarium.
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03-12-2004 11:43 PM
