Asteroids are less pristine than comets, often suffering from the heat and impact of liquid water. But these effects can create dramatic new organic complexities. For decades, scientists have known that meteorites called chondrites, which originate from asteroids, contain an incredible diversity of organic molecules. The Murchison meteorite that fell in Australia in 1969 contained more than 96 different types of amino acids. Life only uses 20 or so. Osiris-Rex and Hayabusa2 have confirmed that asteroids Bennu and Ryugu are as complex as those meteorites. And at least some of this complexity appears to have existed before the asteroids themselves: A preliminary analysis of the Bennu sample suggests it retained organic material, including polycyclic aromatic hydrocarbons, from the protoplanetary disk.
Chemistry of life?
Organic molecules on early Earth took a remarkable new step forward in complexity. Surname somehow organized itself into something alive. Some theories about the origin of life on Earth involve an initial collection of organic matter from space. For example, the “PAH world” hypothesis postulates a phase of primordial mixtures dominated by polycyclic aromatic hydrocarbons. From this slurry, the first genetic molecules emerged.
In general, understanding how complex organics form in space and persist on planets can give us a better idea of whether life has emerged on other worlds. If the raw materials of life on Earth were formed in the interstellar medium, then the stuff of life would be everywhere in the universe.
Currently, such ideas remain largely untestable. But because life itself represents a new level of organic complexity, astrobiologists are hunting for complex organics as a biosignature or sign of life on other worlds. other worlds in our solar system.
The European Space Agency's Juice mission is on track 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 for organic molecules in the atmosphere, as will the future Dragonfly mission to Saturn's moon Titan.
However, it is difficult to determine whether a given organic molecule has one Is it a biological signature or not?. If scientists find sufficiently complex assemblages of organic molecules, that would be enough to convince at least some researchers that we have found life on another world. But as comets and asteroids reveal, lifeless worlds are complex in nature. Compounds thought to be biological signatures have been found on non-living rocks, like the dimethyl sulfide that Hänni's team recently identified on 67P.