The universe is full of complex organic molecules

Asteroids are less pristine than comets and have often suffered from warming and the effects of liquid water. But these effects can produce spectacular new organic complexity. For decades, scientists have known that meteorites called chondrites, which originate from asteroids, contain an astonishing diversity of organic molecules. The Murchison meteorite, which fell in Australia in 1969, contains more than 96 different amino acids. Life only uses 20 or so. Osiris-Rex and Hayabusa2 have confirmed that the asteroids Bennu and Ryugu are as complex as those meteorites. And at least some of this complexity appears to have arisen before the asteroids themselves: preliminary analysis of the Bennu sample suggests that it retained organic material, including polycyclic aromatic hydrocarbons, from the protoplanetary disk.

The chemistry of life?

The organic molecules of the early Earth took a remarkable new step in complexity. They somehow they organized into something alive. Some hypotheses about the origins of life on Earth involve a starter kit of organic material from space. The “PAH world” hypothesis, for example, postulates a primordial soup stage that was dominated by polycyclic aromatic hydrocarbons. From this mixture the first genetic molecules emerged.

Overall, understanding how complex organic compounds form in space and end up on planets could give us a better idea of ​​whether life has also emerged on other worlds. If the raw materials for life on Earth formed in the interstellar medium, the raw materials for life should be everywhere in the universe.

For now, these ideas remain largely untestable. But because life itself represents a new level of organic complexity, astrobiologists are searching for complex organic compounds as a possible biosignature, or sign of life, on other worlds in our solar system.

The European Space Agency’s Juice mission is already underway to study Jupiter and three of its icy moons, and NASA’s Europa Clipper mission launched toward one of those moons, Europa, in October. Both will use onboard instruments to search for organic molecules in atmospheres, as will the future Dragonfly mission to Saturn’s moon Titan.

However, it is difficult to determine whether a given organic molecule Is it a biosignature or not?. If scientists found sufficiently complex organic molecular assemblies, that would be enough to convince at least some researchers that we have found life on another world. But, as comets and asteroids reveal, the non-living world is complex in itself. Compounds thought to be biosignatures have been found in lifeless rocks, such as dimethyl sulfide that Hänni’s team recently identified in 67P.