Asteroids are less ancient than comets, which often bear the effects of heat and liquid water. But these effects can generate dramatic new biological complexity. For decades, scientists have known that meteorites called chondrites, which originate from asteroids, contain an astonishing variety 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 it seems that at least some of this complexity originated before the asteroids themselves: A preliminary analysis The Bennu sample shows that it has retained organic material, including polycyclic aromatic hydrocarbons, from the protoplanetary disk.
Chemistry of life?
Organic molecules on the early Earth took a new, remarkable step up in complexity. They somehow organized myself Into something living. Some hypotheses for the origin of life on Earth involve a starter kit of organic materials from space. The “PAH world” hypothesis, for example, posits a stage of the primordial soup that was dominated by polycyclic aromatic hydrocarbons. The first genetic molecules emerged from this solution.
In general, by understanding how complex organisms form in space and end up on planets, we can get a better idea of āāwhether life has arisen on other worlds. If the raw materials for life on Earth formed in the interstellar medium, then the stuff of life should be everywhere in the universe.
For now, such ideas remain largely untestable. But because life itself represents a new level of biological complexity, astrobiologists are looking for complex organic materials as potential biosignatures, or signs of life, on other worlds in our solar system.
The European Space Agency's Juice mission is already on its way to study Jupiter and its three icy moons, and NASA's Europa Clipper mission launched toward one of those moons, Europa, in October. Both will use onboard instruments to search the atmosphere for organic molecules, as will a future Dragonfly mission to Saturn's moon, Titan.
Yet it is difficult to determine whether any given organic molecule biosignature or notIf scientists find a sufficiently complex organic molecular combination, it would be enough to convince at least some researchers that we have found life on another world. But as comets and asteroids show, the inanimate world itself is complex. Compounds considered biosignatures have been found on lifeless rocks, such as the dimethyl sulfide Hanni's team recently identified on 67P.