Meteorites are less ancient than comets, often bearing the effects of heating and liquid water. But these effects can create 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 that fell in Australia in 1969 contains over 96 different amino acids. Life only uses 20 or so. Osiris-Rex and Hayabusa2 confirmed that the Bennu and Ryugu asteroids are as complex as those meteorites. And at least some of this complexity seems to have arisen before the planets themselves: a Preliminary analysis The Bennu sample suggests that it has retained organic material, including polycyclic aromatic hydrocarbons, from the protoplanetary disk.
The chemistry of life?
Organic molecules on the early Earth took a new, remarkable step in complexity. that Organized itself somehow In a living thing. Some hypotheses for the origin of life on Earth involve a starter kit of organic material from space. The “PAH world” hypothesis, for example, posits a state of primordial soup dominated by polycyclic aromatic hydrocarbons. The first genetic molecules emerged from this slurry.
More generally, understanding how complex organic matter forms in space and ends up on planets can give us a better idea of whether life has arisen on other worlds. If the raw materials for life on Earth formed in the interstellar medium, then the ingredients for life must be everywhere in the universe.
For now, such ideas remain largely unsustainable. But because life itself represents a new level of biological complexity, astronomers are looking for complex organisms as a potential biosignature, or sign 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 to one of those moons, Europa, in October. Both will use onboard instruments to search the atmosphere for organic molecules, as will the future Dragonfly mission to Saturn’s moon, Titan.
Yet it is difficult to determine whether a given organic molecule is Bio-signature or not. If scientists were to collect enough complex organic molecules, it would be enough to convince at least some researchers that we have found life on another world. But as comets and planets show, the inanimate world itself is complex. Compounds considered biosignatures have been found on inanimate rocks, such as the dimethyl sulfide Haney’s team recently identified at 67P.
