Soil From Mars May Be Tested For Signs of Life
Since the completion of the human genome project, biologists have been fanning out to study the genetics of virtually every imaginable life form: armadillo, potato, slime mold, various fungi, and many, many others. To this list, Harvard biologist Gary Ruvkun would like to add extraterrestrial life.
Of course, it’s impossible to study the genetics of something that hasn’t been found. But then that, Ruvkun says, is the whole idea.
With preliminary funding from NASA, Ruvkun is working on a sensor designed to test the soil of Mars for DNA. Ruvkun hopes that the sensor his team is working on, the first part of a project he has dubbed the “Search for Extraterrestrial Genomes,” will be a part of a Mars lander mission in the next decade.
The project represents a sharp break from the reigning philosophy of life detection: avoiding an earth-centric view of what life might look like. In the 1970s, for example, the Viking lander conducted tests for signs of chemical changes that might be associated with life, without assuming life there would be exactly as it is on earth.
Instead, inspired by evidence that microbes can shuttle between planets aboard meteors, Ruvkun argues it is most likely that any life on Mars would be related to life on Earth and thus have roughly similar DNA. The project is an example of jackpot science — long odds, huge potential payoff — and will eventually present NASA with a difficult philosophical decision.
“I admire the ideas,” said Andrew Knoll, a professor of natural history at Harvard University who is involved with Mars exploration. “But the opportunities to actually land on Mars over the next 20 years appear to be limited, and there is going to be a lot of competition to fly.”
The allure of the project has attracted a high-profile team of scientific talent. Ruvkun, a professor at Harvard Medical School and Massachusetts General Hospital, is a highly respected geneticist. One active team member is Maria Zuber, head of MIT’s department of earth, atmosphere, and planetary sciences and considered one of the world’s top designers of scientific instruments for space exploration. Also involved is Nobel Prize winner Walter Gilbert, a professor of biology at Harvard, and a number of other leading figures.
The project’s prospects depend on a bit of deep history. About 4 billion years ago the planets experienced a period of intense bombardment. Meteors came crashing down to the surface, ejecting more rocks into space, some of which came crashing down onto other planets. Life on Earth appeared very quickly after the bombardment — too fast, Ruvkun believes, to have evolved on its own.
The bombardment, Ruvkun believes, could have brought life to Earth from somewhere else. And if life on earth came from somewhere else, then perhaps it also came to Mars from “the same somewhere else,” Ruvkun says. Martian rocks have been found on earth, and an analysis of one of them revealed that portions of its core never experienced superheating as it fell to earth, showing that meteors could be viable shuttles for life. At the same time, research has shown that there are microbes that have adapted to almost unbelievably extreme environments — including the radioactive cores used on nuclear power plants and the hot, crushing depths of deep-sea ocean vents. Astronauts on the Apollo 12 mission found microorganisms that survived for years in the camera of a craft sent to the moon’s surface.
The team is building a sensor that uses PCR, a technique that allows for the detection of incredibly minute quantities of DNA, to look for portions of two genes that have been found in all life whose genes have been sequenced. They play a crucial role in assembling protein, a central function in living things. If life on Mars has a common origin with life on Earth, Ruvkun reasons, then it will probably share these genes.
Still, the idea is a gamble – a “jackpot experiment,” as Ruvkun calls it. It would yield a positive result only if there were life on Mars that is related to life on earth. This has brought some skepticism among other scientists, who argue that it does not make sense to look for DNA before testing for more general signs of life.
“It would not be my first choice,” Norman R. Pace, a biologist at the University of Colorado, Boulder, said in an e-mail. Pace specializes in using DNA techniques to find microorganisms.
Building such a device will be a tremendous challenge: Space, power, and weight all come at an extreme premium on space missions. It will be especially challenging, Zuber said, to ensure that fluids inside the device flow reliably — a requirement for PCR to function — even though it is operating in the extreme Martian environment. The team is still far from having a device ready for flight and has not been approved for flight by NASA, Zuber and Ruvkun said.
An even bigger issue, Ruvkun said, is overcoming the risk of contamination – that the team will find microbes that hitched a ride aboard the same Mars lander that brought the experiment. The team is working on a number of engineering solutions to the problem, but there is also a biological answer. If the team finds DNA, they could compare it to the same two genes found in earthbound organisms. This would allow them to place the new DNA in the family tree of life. If it appears closely related to something on Earth, then it’s probably contamination, but if it appears to be a distant cousin, then the history of life will have to be rewritten.
Many scientists doubt that there is anything currently living in the harsh Martian environment. But Ruvkun does not count himself among the pessimists.
“Never bet against life,” he said.