June 23, 2008
Is There Extreme Life On Mars?
Microbes flourish on Earth in many extreme environments -- from the Atacama Desert in Chile, to the hot springs of Yellowstone National Park, to the sunless sea bottom vents in Pacific.
Could exotic life like this exist in the frigid arctic plains of Mars?
NASA's Mars Phoenix has been poking its long arm into the sticky soil and collecting scoops of Martian dirt to both bake in a test oven and examine under a microscope.
Phoenix turned up a lead last week when it uncovered what scientists believe are ice flecks in one trench and an icy layer in another. Scientists hope experiments by the lander will reveal whether the ice has ever melted and whether there are any organic, or carbon-containing, compounds.
"We're looking for the basic ingredients that would allow life to prosper in this environment," chief scientist Peter Smith of the University of Arizona in Tucson has said in describing the mission's goal.
The discovery of extreme life forms, also known as extremophiles, in unexpected parts of the Earth in recent years has helped educate scientists in their search for extraterrestrial life.
"It's very suggestive that there are lots of worlds that may support life that at first glance may look like fourth-rate real estate," said Seth Shostak, an astronomer at the SETI Institute, a nonprofit dedicated to the search for extraterrestrial intelligence.
If there was life on Mars, scientists speculate it would likely be similar to some extreme life on Earth -- microscopic and hardy, capable of withstanding colder-than-Antarctica temperatures and low pressures.
"It's going to be microbes. It's not going to be a little green men," said Kenneth Stedman, a biologist with the Center for Life in Extreme Environments at Portland State University.
The Phoenix does not carry instruments capable of identifying fossils or living things. It does, however, have a set of ovens and a gas analyzer that will heat soil and ice and sniff the resulting vapors for life-friendly elements. Its wet chemistry lab will test the pH, or acidity, of the soil much like a gardener would. And its microscope will examine soil granules for minerals that may indicate past presence of water.
The range of conditions in which life can survive has been expanded with recent discoveries of micro-organisms trapped in glaciers and rocks or living in volcanic vents and battery acid-like lakes. These conditions on Earth mirror the harsh environments found on Mars and other parts of the solar system.
Most researchers agree life likely cannot develop on the Martian surface, which is bombarded by lethal doses of radiation. But satellite images have revealed a softer side, spying hints of a vast underground store of ice near the red planet's polar regions. Last week, Phoenix hit what's thought to be an ice layer 2 inches below the surface.
A more sophisticated spacecraft would be needed to determine if life was ever there or is present now.
The twin Viking missions in 1976 is the last time NASA looked for organics. It sampled soil near the Martian equator but turned up empty.
This time, scientists chose to dig in Mars' far north region because they think it's an analog to Earth's polar regions, which preserves life's building blocks and sometimes even life itself in ice.
Researchers have shown microbes on Earth can be inactive in a deep freeze for thousands of years and resuscitated under the right conditions.
Three years ago, NASA researchers announce they revived bacteria that were apparently dormant for 32,000 years in a frozen pond in central Alaska. Penn State University scientists said earlier this month they were able to grow in the lab an ultra-small species of bacteria trapped in Greenland glacier under high pressure and low oxygen for at least 120,000 years.
"There's a lot of amazing things that survive in the cold environments," said Jennifer Loveland-Curtze, a senior research associate at Penn State.
Scientists are plumbing the depths of Earth for clues to possible life that may exist elsewhere in the universe.
"We need to continue to try to understand what's going on with the extremophiles here on Earth," said Stedman of Portland State University. "The more we learn how extremophiles here are functioning, the more that will inform any kind of future mission."
On the Net: