The Edge of Life
|A map of Chile’s Atacama Desert.|
Credit: Medical University of South America
Life – as we know it – needs water to survive. It doesn’t have to be a lot of water, at least not for microscopic life. Even in most of the world’s deserts, in regions where plant and animal life cannot subsist, bacteria and lichen manage to eke out an existence, clinging to life underneath or in the cracks within rocks.
These organisms have adapted to living in some of the harshest, most extreme conditions on the planet. But are there places on Earth that are so dry that nothing can live there?
That is one of the questions that a group of scientists studying Chile’s Atacama desert hope to answer during their three-year research project. In the process, they hope to develop better techniques for searching for evidence of life on Mars. Their research project, Life in the Atacama, is funded by NASA’s ASTEP (Astrobiology Science and Technology for Exploring Planets) program.
The Atacama is a vast desert, stretching for some 1000 kilometers (620 miles) south from Chile’s northern border with Peru. It is believed to be the driest place on Earth, receiving an average of only one-tenth of a millimeter (four-thousandths of an inch) of rain per year. Some parts of the Atacama haven’t seen rain for more than 400 years.
Chris McKay, of NASA’s Ames Research Center, is a member of the Life in the Atacama science team. The Atacama, McKay says, is "so dry that in that desert, unlike other deserts that we’ve studied, it’s possible to cross the boundary between life and death, between conditions that are suitable for desert bacteria and desert algae and conditions that are so extreme that they don’t appear to be there any more."
Not surprisingly, says McKay, water is the critical factor. "Most places on Earth, it’s hard to find a location where there’s not enough water [for life]. Even where there’s not enough water for plants, not enough water for humans, there’s still enough water for bacteria. Everywhere. There’s bacteria living in the hottest place in Death Valley – richly living, in fact.
|Hyperion, the prototype rover developed by Carnegie Mellon to search for signs of life.|
"We all understand intuitively that water is a limiting factor for life, but to find a place where the water is so low that, essentially, no organism has leaned how to live there – that’s interesting. One or two odd bacteria seem to pop up occasionally in these very dry places, but we don’t know what they are or how they got there."
The Life in the Atacama project will take three years to complete. Each year, researchers will travel to the highland desert. There they will deploy a prototype rover, Hyperion, developed by the Robotics Institute at Carnegie Mellon University (CMU). Hyperion’s goal: traverse the Atacama, searching for signs of life and mapping the boundaries between the habitable and the inhospitable. The first of these annual expeditions, a preliminary shakedown of the rover and its scientific instruments, took place in April of this year.
Nathalie Cabrol, who is with the SETI Institute and NASA’s Ames Research Center, heads the science team for the Atacama project. "We want to understand if the Atacama represents, really, a limit for life on Earth," says Cabrol. "Previous field experiments were mainly targeting the understanding of the geology and the climate of the field site," Cabrol explains.
The ASTEP research will take an important step forward in the use of robots to search explicitly for life. "What we are trying to do right now is basically to do robotic astrobiology. [We want] to understand better the notion of habitat and the notion of distribution of life," she says. To that end, one of the novel instruments onboard the Hyperion rover will use fluorescent dyes to look for some of life’s key molecules: nucleic acids, carbohydrates, lipids and proteins.
Although the Atacama project is in part an effort to understand the limits of life on Earth, it is also a training exercise of sorts for future missions to Mars. "The Atacama," says Cabrol, "has some very interesting parallels to Mars, in that, today, it’s a very arid place, but at the end of the last glacial maximum, about 12,000 years ago, it was a wetter place. And you had channels and you had lakes there. And now, the water is gone." So "life had to adapt in a very short period of time. And we want to understand, where did it go and how did it adapt – or if it didn’t."
|An artist’s representation of a Mars Exploration Rover.|
The plan for year three of the project calls for the Hyperion rover to operate independently in the Atacama for several months, traveling autonomously for hundreds of kilometers. (The soon-to-be-launched Mars Exploration Rovers (MERs), by comparison, will travel a total of less than one kilometer each.)
The advantage of the rovers on Earth, says McKay, is their stamina. "There’s nothing that they’re going to do in the Atacama that we can’t do better with graduate students." But not many graduate students would be willing to spend months on end trekking through the Atacama, stopping every few meters to sample the soil.
"If you have a robot that doesn’t care too much about staying in the desert and has the right capabilities to perform the task you are asking it to perform, it’s better," Cabrol adds.
If in the Atacama, robots are a convenience, on Mars, they are a necessity. "I can’t send a graduate student to Mars," says McKay. "We’re not going to be sending humans to Mars [any time soon]. So what we have to do is teach these machines to do a job that’s very easy for humans but very difficult for machines, which is to understand an environment that they’re in, understand where they are, understand what they’re seeing, and then to send that information back to Earth so that scientists, looking through the eyes and ears of the machine," can study the environment much as they would if they were able to go there themselves.
If the Life in the Atacama project is successful, scientists will come away with both a better understanding of limits of life on Earth and a better understanding of how to search for life on our neighboring desert world, Mars.