Ten years ago, the European Space Agency's Rosetta probe pulled up alongside a dusty, icy lump the size of a mountain. The probe would follow its quarry, a comet called 67P/Churyumov-Gerasimenko, for two years as onboard instruments caught and analyzed the dust and gas streaming away from the comet. Scientists sought hints about how our solar system came to be -- and about the origin of one class of molecules in particular.

Organic molecules -- compounds containing carbon -- abound on Earth, especially in the bodies of living things. They're often called the building blocks of life, and for good reason: Carbon atoms can chemically bond to four other atoms and easily form long, stable chains that serve as "carbon backbones" for complex biological molecules.

The Rosetta mission and others have shown just how ubiquitous organic molecules are in space, too.

"Rosetta really changed the view," said Nora Hänni, a chemist at the University of Bern who has been analyzing data from the probe. When Hänni and her colleagues processed just one day's worth of the probe's data in 2022, they uncovered 44 different organic molecules. Some were very complex, containing 20 atoms or more. Rosetta caught whiffs of glycine, one of the amino acid building blocks of proteins. And more recently, Hänni used Rosetta data to identify dimethyl sulfide -- a gas that, on Earth, is only known to be produced by living organisms.

What Rosetta did for comets, Japan's Hayabusa2 and NASA's Osiris-Rex are doing for asteroids. In 2020 and 2023, respectively, the two missions scooped up samples of the asteroids Bennu and Ryugu and returned the samples to Earth. Scientists have been sifting through the material ever since, and they find that both asteroids sport plenty of organic molecules. Ryugu alone contains at least 20,000 kinds, including 15 different amino acids.

"It's just everything possible from which life could emerge," said Philippe Schmitt-Kopplin, an organic geoscientist at the Technical University of Munich.