Thu, 09 Jun 2011 08:50 UTC
A meteorite found in B.C. contains evidence that asteroids are production sites for molecules such as amino acids that form the building blocks of life, a new study says.
"What we're saying is that amino acids are actually the result of the geology happening on the asteroid," said Chris Herd, the planetary geologist at the University of Alberta who led the study published Thursday in Science.
"It's like a little factory. It's taking even more primitive molecules that are coming in from space and doing them up a bit."
He added that the warmer temperatures in the asteroid and the presence of water and possibly certain minerals provide a better environment than interstellar space for certain chemical reactions. Those reactions are needed to produce organic molecules, a class of carbon-based chemicals that living things are largely made of.
Meteorites are pieces of asteroids that fall through the Earth's atmosphere and land on the surface. They have been suggested as possible original sources for some of the molecules necessary for life on Earth.
Their composition depends on what materials came together to form that particular asteroid, Herd said. Only some contain organic molecules.
The meteorite studied by Herd and his team landed as a few dozen fragments on the snow covering Tagish Lake, which spans northern British Columbia and Yukon, in the winter of 2000.
It is a rare type of meteorite called a carbonaceous chondrite that is known to contain organic molecules such as amino acids. "They constitute a few per cent of meteorites that are known," Herd said.
Uniquely pure meteorite
Factors that make the Tagish meteorite unique are that it was never contaminated with organic molecules from Earth because it landed on snow, it was never touched by human hands and it was kept frozen since its collection, preserving the organic molecules inside it.
Herd led a Canadian consortium in 2006 that bought the meteorite fragments from the man who collected them, providing an opportunity to study them in more detail.
One of the first things he noticed is that some fragments looked different than others.
"Some of them were kind of dark, very black, almost sooty with dust coming off. Others were more of a salt-and-pepper look," he said.
A detailed analysis showed that the meteorite contained a much wider variety of organic chemicals than seen on other meteorites and that different kinds and amounts of organic molecules corresponded to different appearances of the rock.
An analysis showed the types of chemicals and the appearance of the rock depended on how much water had percolated through as ice on the asteroid melted during its early history, 4.5 billion years ago. Herd said that suggested there was active organic chemistry happening on the asteroid, producing and later destroying different types of compounds.
"These things preserve different stages of the alteration by water," Herd said. "That is really remarkable. There's no other meteorite like that."
The study answers a key question about whether organic molecules found on some meteorites come from interstellar space, Herd said: "This is strong evidence you're forming them on the asteroid itself."