Asteroids are less pristine than comets because they have often been exposed to heat and the effects of liquid water. But these effects can create dramatic new organic complexity. Scientists have known for decades that meteorites called chondrites, which come from asteroids, contain an amazing variety of organic molecules. The Murchison meteorite, which hit Australia in 1969, contains more than 96 different amino acids. Life only uses about 20. Osiris-Rex and Hayabusa2 have confirmed that the asteroids Bennu and Ryugu are as complex as these meteorites. And at least some of this complexity appears to have predated the asteroids themselves: A preliminary analysis The results of the Bennu sample indicate that it retained organic material, including polycyclic aromatic hydrocarbons, from the protoplanetary disk.
The chemistry of life?
Organic molecules on the early Earth have taken a remarkable new step in complexity. She somehow they organized themselves into something living. Some hypotheses about the origin of life on Earth assume a starter set of organic material from space. For example, the “PAH world” hypothesis postulates a primordial soup stage that was dominated by polycyclic aromatic hydrocarbons. The first genetic molecules emerged from this mud.
More generally, understanding how complex organic materials form in space and end up on planets could give us a better idea of whether life arose on other worlds. If the raw materials of life on Earth originated in the interstellar medium, the material of life would have to be present everywhere in the universe.
Currently, such ideas are largely untestable. But as life itself represents a new level of organic complexity, astrobiologists are looking for complex organics 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 to one of those moons, Europa, in October. Both will use onboard instruments to scan the atmosphere for organic molecules, as will the future Dragonfly mission to Saturn’s moon Titan.
Nevertheless, it is difficult to determine whether a particular organic molecule whether it is a biosignature or not. If scientists found sufficiently complex organic molecular arrangements, 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 is inherently complex. Compounds thought to be biosignatures have been found on lifeless rocks, such as the dimethyl sulfide that Hänni’s team recently identified on 67P.
