How Meteorites Fit Into the Search for Alien Life
A recent discovery has injected hope into the search for extraterrestrials
NASA announced Monday that their researchers have found the strongest evidence yet that the components of DNA can be made in space. "People have been discovering components of DNA in meteorites since the 1960's, but researchers were unsure whether they were really created in space or if instead they came from contamination by terrestrial life," said Dr. Michael Callahan, lead author on a NASA-funded study just published in the Proceedings of the National Academy of Science. "For the first time, we have three lines of evidence that together give us confidence these DNA building blocks actually were created in space."
One way to read Callahan's statement is the way that the Daily Mail did. "We could be aliens after all, claims Nasa study looking at meteorites from outer space," reads the British tabloid headline. However, the new knowledge about our maybe-extraterrestrial origins will surely shed new light on earlier research into whether or not meteorites will lead the way to discovering alien life. Past research has indicated that other building blocks of life--amino acids and nucleobases mentioned in the latest NASA study--exist in meteorites, but scientists have always argued over whether these building blocks in fact came from the meteorites themselves or are in fact a result of earthly contamination, despite not always looking much like earthly building blocks.
One such case made international headlines in 1996 when scientists discovered showed bacteria-like structure on a meteorite discovered in Antarctica. Now known as ALH84001, the meteorite is thought to have come from Mars. The news that the rock contained signs of ancient life was big enough that Bill Clinton gave an address on White House's South Lawn commending the scientists' discovery. "Even as it promises answers to some of our oldest questions, it poses still others even more fundamental."
In March of this year, a similar discovery sparked a firestorm of controversy when another NASA scientist boldly declared that he'd found alien bacteria (pictured right) on a 200-year-old meteorite discovered in France. Richard B. Hoover inspected the Orgueil meteorite and two others of the same class under an electron microscope and found evidence of fossilized bacteria. It resembled a type of blue-green algae that exists on Earth, but because of some odd attributes of the meteorite, Hoover says it could not have come from Earth.
"The exciting thing is that they are in many cases recognizable and can be associated very closely with the generic species here on Earth," Hoover said at the time his paper was published in The Journal of Cosmology. "There are some that are just very strange and don't look like anything that I've been able to identify, and I've shown them to many other experts that have also come up stumped."
But when Hoover's discovery and the earlier ALH84001 discovery went under peer review, both were discredited. Hoover, at least, drew scorn from his colleagues. Meteorite expert Harry "Hap" McSween and Rosie Redfield led the way in debunking both claims, pointing out that just because meteorites look "strange" doesn't mean that they're alien. "These guys make some stupid announcement completely ignoring all the rules of biology and then get all the publicity," McSween told the Associated Press.
But the latest discovery stacks evidence in favor of meteorites supporting biological life. Even if it's not quite the headline-grabbing "we are not alone" story that Hoover was perhaps a little too quick to claim, it does add to the burgeoning body of knowledge around the origin of life as well as the possibility of life on other planets. That is, until the critics find time to disprove everything.
"But that's the way science is," said Seth Shostak of the SETI Institute in California. "People make claims that often don't hold up. That's the nature of science."