It's difficult for Dante Lauretta to describe what he's hoping to find on asteroid 1999 RQ36. But there's a good reason for that.
"We don't exactly know what we'll find until we get there," he says. "But we're looking for really carbon-rich viable material that normally doesn't survive passage to the surface of the Earth on a meteorite. We're looking for things that humans haven't ever seen."
Lauretta is the deputy principal investigator for NASA's recently announced OSIRIS-REx mission. It's an appropriately cinematic name for what he and his colleagues are trying to do. Namely, they're hoping to find the origins of life on Earth in space.
I know what you're thinking. You're thinking, "OMG, panspermia!" And you're wrong. That's not really the right way to describe the concept Lauretta and principal investigator, Michael J. Drake, are trying to prove.
The theory of panspermia is about life that already exists—tiny bacteria that travel through the cosmos and then plummet to Earth on a falling star. It hypothesizes that organisms could survive in the cold reaches of space and accidentally immigrate to our planet, where they become Life As We Know It. When you think about panspermia and talk about "the origins of life on Earth," the emphasis is on the "Earth." For research on that, you want the Living Interplanetary Flight Experiment.
OSIRIS-REx, on the other hand, is about the origins of life, which happens to be, from our perspective, on Earth.
It's a mandate that feels, at once, a little disappointing ("So, what, no aliens then?") and astoundingly ambitious. OSIRIS-REx is trying to answer the questions that panspermia just sort of shrugs at. How did life form? What prompted organic molecules to stick together, form chains, and become the proteins that build everything from us, to plants, to tiny bacteria? Drake and Lauretta have a theory for that, and they think they'll find evidence to support it on asteroid RQ36.
Like a Rock
Today, NASA describes RQ36 as a near-Earth asteroid. But the point, for Drake and Lauretta, is that this wasn't always the case. At least, that's what they think. Because RQ36 is one of the near-Earth asteroids that could, potentially, hit our planet at some point in the far future, it's been studied extensively by other researchers. Thanks to that telescope data, scientists have learned a few things about this little object in space. They know that it is likely to be less of a rock than a rubble pile—a cluster of debris, bound together by its own gravity. They also know that rubble is dark. Very dark. From spectrographs at three different telescopes, they've found that only 3% of the sunlight that hits the surface of RQ36 gets reflected back. It's the darkness that excites Drake and Lauretta.
"We really think that dark asteroids are possibly carbon rich. We suspect that they're either extinct comets, or asteroids that come from the outer main asteroid belt," Lauretta says.
If RQ36 comes from the far reaches of the asteroid belt, it could hold something special—simple organic molecules that haven't been heated and changed by the process of planet-making. Basically, it could provide a glimpse of the organic building blocks that were formed out of the birth of stars back at the dawn of our Solar System. We could be talking about amino acids humans have never seen before. Like the bacteria of panspermia, they might have fallen to Earth as part of a meteor, where they started to bond together and kick-started the development of life.
Dust to Dust
Although OSIRIS-REx will likely mark the first time humans send a probe to visit a dark asteroid and return with samples, Drake and Lauretta aren't the first people to come up with this idea. In fact, the European Space Agency even considered a similar mission, Marco Polo, that was aimed at doing basically the same thing. The key difference is that OSIRIS-REx has been approved for funding and will launch in 2016, while Marco Polo languishes.
It's also possible that the theories about dark asteroids will turn out to be wrong. One of the interesting things about OSIRIS-REx, according to Dante Lauretta, is that it will give astronomers an opportunity to test the accuracy of the assumptions they make based on spectrograph data. In particular, asteroid RQ36 is considered a small object—about 580 meters in diameter. That makes it difficult to collect clear spectrographic information. So far, nobody's found direct evidence of carbon on the asteroid, Lauretta said. There's a risk that OSIRIS-REx will have more to teach us about the way we study the stars than about the origins of life.
And, even if it does bring back previously unseen molecules, OSIRIS-REx will still leave some questions hanging. For example: If the molecules of life came from space, how did they survive the trip to Earth?
The whole reason no human has ever seen the molecules OSIRIS-REx is looking for is that those molecules aren't likely to make it through our atmosphere unchanged. There's reason to suspect that they could, under the right conditions. But it's really an open question that's difficult to answer without knowing what, exactly, the molecules in question are.
"We don't really know how they would have survived to the surface of the Earth in the early days," Lauretta says. "There are models for the survival of compounds from an impact, where some fraction could survive. But they don't survive as intact samples. Instead, they would fragment into tiny dust particles. The idea is that those dust particles would be something that could start to form life."
Published 9:08 am Thu, Jun 9, 2011