The Seeds of Life: First amino acid found on a comet

An amino acid called glycine has been found in dust collected by the Stardust spacecraft, which flew by Comet Wild 2 in 2004 (Illustration: NASA/JPL

An amino acid has been found on a comet for the first time, a new analysis of samples from NASA's Stardust mission reveals. The discovery confirms that some of the building blocks of life were delivered to the early Earth from space.

Amino acids are crucial to life because they form the basis of proteins, the molecules that run cells. The acids form when organic, carbon-containing compounds and water are zapped with a source of energy, such as photons – a process that can take place on Earth or in space.

Previously, researchers have found amino acids in space rocks that fell to Earth as meteorites, and tentative evidence for the compounds has been detected in interstellar space. Now, an amino acid called glycine has been definitively traced to an icy comet for the first time.

"It's not necessarily surprising, but it's very satisfying to find it there because it hasn't been observed before," says Jamie Elsila of NASA's Goddard Space Flight Center, lead author of the new study. "It's been looked for [on comets] spectroscopically with telescopes but the content seems so low you can't see it that way."

Raw materials
Comets and asteroids are thought to have bombarded the Earth early in its history, and the new discovery suggests they carried amino acids with them.

"We are interested in understanding what was on the early Earth when life got started," Elsila told New Scientist. "We don't know how life got started ... but this adds to our knowledge of the ingredient pool."

Jonathan Lunine of the University of Arizona agrees. "Life had to get started with raw materials," he told New Scientist. "This provides another source [of those materials]."
The amino acid was found in samples returned to Earth by NASA's Stardust mission, which flew by Comet Wild 2 in 2004 to capture particles shed by the 5-kilometre object.