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| At a recent McGill panel discussion, distinguished scientists weighed in on the hot topic of astrobiology, a new field concerned with looking for signs of life on other planets.
So why, with all the planets out there, did the speakers talk mostly about Mars?
"Mars is the most likely planet to tell us about life on earth," says Christopher McKay, a planetary scientist at NASA's Ames Research Center. "It is the closest planet to Earth, and its distance from the sun means that it is in a continually habitable zone."
Although the unmanned Viking space probe that visited Mars concluded that there was nothing on the planet capable of consuming nutrients, the red planet could have sustained life in the very distant past. Its atmosphere contains carbon dioxide and other essential gases, "and millions of years ago, it was very much like Earth. There was a lot of water, judging from the dead lakes and rivers on the planet today."
The similarities to Earth make it an irresistible lure.
"That's why we're sending more ships to Mars than all the other planets combined. Mars reminds us of ourselves, and there's nothing we find more interesting to study."
So far, all rock samples from Mars have been volcanic rock, such as meteorites (see below), "but what we really need is sedimentary rock, which might contain fossils," says McKay.
"Still, fossils would not answer the crucial question: If Mars had life, did it have a different origin or genesis from that of Earth? If not, life on Mars could have been from Earth. For example, a rock containing fossils could have been dislodged from Earth by a meteor, and eventually found its way onto Mars."
While scientists are more fascinated by Mars' past than its present, McKay posed the question, "Does the planet have a future?
"That would depend on heating it up. We know how to warm up a planet; we're doing it now. It's probably not a good idea on Earth, but it would be crucial on Mars, which is cold and frozen." In other words, global warming could be a form of terraforming for a future colonization of our closest neighbour.
One way of studying the possibility of life elsewhere is to examine Earth analogues, usually the coldest places on the planet.
"Certain places in the Arctic and Antarctic are analogous to the target systems," said McGill geography professor Wayne Pollard, "such as Mars and Europa (a satellite of Jupiter with an icy crust)."
Pollard himself will be risking frostbite in the Canadian Arctic when he goes into the field at the McGill Arctic Research Station in April.
Michael Meyer, a discipline scientist for astrobiology at NASA's Office of Space Science, agreed that Earth itself could teach us more than distant planets.
"We're planning to go look for life on other planets, but we don't know squat about life on this planet... By exploring extreme environments on Earth, we can learn the thermal limits of life, which will give us clues to the evolution of life elsewhere."
Biology professor Graham Bell, the director of the Redpath Museum, warned that any expedition to Mars to bring something back alive will have difficult challenges to solve. He pointed out that space probes to Mars were carefully sterilized, to ensure that anything they brought back was not simply from Earth.
"But if humans go to Mars and come back with Martians, how do we know? If they bring fossils back, then we know that it is from Mars. But if it is a living organism on a petri dish, it would be embarrassing to admit that we can't be sure, that maybe one of the astronauts coughed at the wrong time."
In that kind of quandary, scientists could do DNA analysis, "but it would probably just look like the DNA structure of something on Earth. The only way we could be sure is if it was radically different from anything that we see on Earth."
Assuming it becomes more economically and practically feasible, deciding to send people to Mars will still pose dilemmas. In a nutshell, according to Bell, "the decision to go to Mars is the decision to pollute."
The forum was part of the Astrobiology Lecture Series, presented by the departments of Earth and Planetary Sciences, Anatomy and Cell Biology and Geography. The series is funded by grants from the Beatty Memorial Lectures Committee, the Faculties of Arts, Science and Medicine, and the Canadian Space Agency.