Meet Kenneth and Juliette, possibly some distant relatives of yours. Image: ESA/Rosetta/MPS for COSIMA Team

With only a few days left before it’s scheduled to crash-land on the surface of Comet 67P, the Rosetta spacecraft is still yielding amazing discoveries. And I’m not just talking about lost comet landers.

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Scientists now report that Rosetta detected complex organic molecules in the dust surrounding its comet. This strengthens the argument that the building blocks of life itself may have come from icy space rocks.

Complex organic molecules—mixtures of mostly carbon, hydrogen, and oxygen that form the basis of our biology—have been hinted at on comets before, most notably during fast flybys of Halley’s comet. But Rosetta is the first mission to actually catch dusty organic particles escaping the surface of such a body, affording scientists a detailed look at their composition.

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Two of those dust grains, curiously nicknamed Kenneth and Juliette, are the subject of a scientific paper published this week in Nature. Captured in May and October of 2015 and analyzed with Rosetta’s on-board mass spectrometer, each of these wee grains contains carbon-based molecules bound together in very large structures, similar to the organic matter found in carbonaceous chondrite meteorites here on Earth.

“Our analysis reveals carbon in a far more complex form than expected,” Hervé Cottin, a co-author on the new study, said in a statement. “It is so complex, we can’t give it a proper formula or a name!”

Comparison of the spectra determined for Kenneth and Juliette with the composition of organic matter in a chondritic meteorite found on Earth. Red lines indicate cometary dust grains while black lines indicate the meteorite. Image: ESA/Rosetta/MPS for COSIMA Team

The finding is significant for a few reasons. For one, it builds off early discoveries made by the Philae lander in the hours before its batteries went dead on Comet 67P’s surface. While Philae only sniffed very light, gaseous organic compounds known as volatiles, the new analysis focused on large, solid particles, which indicate more complex organic chemistry.

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Second, scientists have long debated whether the organics found in meteorite samples come from space, or whether these rocks were contaminated after crash-landing on a biological planet. The discovery of similar molecules in space itself strengthens the argument that the carbon-based stuff we see in meteorites came from beyond Earth.

Finally, Rosetta’s discovery offers a tantalizing glimpse of what’s to come from NASA’s OSIRIS-REx asteroid sample return mission. A first-of-its kind attempt to grab a scoop of dirt from a space rock and bring it back to Earth for analysis, OSIRIS-REx is expected to give us a detailed look at the makeup of the rogue bodies buzzing our planet’s backyard. That mission launches today, by the way—so even as we say goodbye to Rosetta, expect plenty more on whether all of the Kenneths and Juliettes out there are your distant ancestors in the years ahead.

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[Rosetta Blogs]