The European Space Agency's mission to investigate Comet 67P has uncovered evidence of organic compounds considered to be some of the building blocks of life.
The finding supports a theory held by many that life on Earth might have been kicked off by such compounds delivered courtesy of a comet strike, researchers suggest.
The Philae lander delivered to the comet's surface by the Rosetta spacecraft discovered 16 "carbon and nitrogen-rich" organic compounds, including four never before detected on comets, ESA scientists say.
Some of these compounds "play a key role in the prebiotic synthesis of amino acids, sugars and nucleobases," all of them key ingredients for the beginnings of life, they say.
The discovery of the organic compounds came during 60 hours of scientific investigation Philae conducted immediately after it landed, before it eventually went silent because it was not receiving sufficient sunlight on its solar panels.
During that time, it discovered dark grains of material around a millimeter wide, apparently consisting of complex organic molecules.
"This is fundamental," says lead scientist for the Philae lander Jean-Pierre Bibring. "We didn't know that."
The results were included in a number of studies published in a special edition of the journal Science.
"The existence of such complex molecules in a comet, a relic of the early Solar System, imply that chemical processes at work during that time could have played a key role in fostering the formation of prebiotic material," the ESA said on its Rosetta mission website.
As scientists ponder how life began on Earth, the discovery takes on even more importance, says Laurence O'Rourke, a system engineer for the Philae lander.
"If you apply energy to such organic compounds ... like a comet hitting a planet ... it could lead to the creation of amino acids which make up proteins, which are the basis of life itself," he says.
Philae has not remained completely silent; it awoke and began transmitting data up to the Rosetta spacecraft as the comet moved closer to the sun and more sunlight began reaching the lander's solar panels.
On July 9, there were 12 minutes of uninterrupted transmissions between the lander and the spacecraft orbiting the comet, but Philae has been out of touch and silent since then.
Still, the lander is a "robust machine," O'Rourke says, and mission scientists remain hopeful there may be chances of reestablishing contact.
"There's no way we can say the lander is dead," he says.
