The Seeds of Life?

Today’s news includes an amazing story from the Lunar and Planetary Science Conference 2022 being held this week about the samples taken from the asteroid known as Ryugu. These samples, about 5 grams of dusty rock, were collected by the Japanese space probe Hayabusa2 last year and were dramatically brought back to Earth last December. A large team of Japanese scientists have presented an preliminary analysis of the molecular content of the sample, which are very pristine snapshots of the constitution of the early Solar System when planets like the Earth were being formed. You may recall from previous posts that Ryugu looks like a big rubble pile of fragments, held together by their own gravity. Turns out that various elements like carbon, nitrogen and oxygen have been found in greater abundance than expected of asteroids of its type, suggesting that Ryugu itself drifted inward from the colder, outer regions of the Solar System. Otherwise, molecules containing such elements like water (H2O) or carbon dioxide (CO2) would have likely been evaporated (and be much less abundant) if Ryugu formed at its present distance from the Sun. Indeed, Ryugu’s highly fragmented appearance suggests it was the product of a collision with another asteroid a long, long time ago and perhaps it was this event that triggered its inward migration. Meanwhile, the molecular analysis has revealed the presence of 10 types of amino acids within the sample, which is really big news for those interested in understanding how life arose on the Earth.

Amino acids are particularly special molecules to biology because a subset of about 20 of them are the building blocks of proteins. Indeed, the team has found two biologicial amino acids, glycine and l-alanine, in the sample, as well as eight non-biological amino acids. The presence of these molecules in the Ryugu sample suggests that chemical processes in the disk out of which the Solar System formed could actually produce them naturally, and there was nothing special about Earth being a site where such chemical complexity could arise. Recall my post from a couple of days ago about how large molecules are being detected in the protoplanetary disks of young stars. Interestingly, the “chirality” in the Ryugu amino acids, that is the right-handed or left-handed sense in which the atoms are arranged in these molecule, is equal, suggesting extraterrestrial origins– all life on Earth strangely uses only left-handed amino acids but the Ryugu ones have left- and right-handed arrangements in equal amounts. Why life uses left-handed amino acids only remains a big mystery of biology. Note that amino acids have been seen previously in meteorites before and also on the Comet 67P/Churyumov-Gerasimenko by the Rosetta probe, but there’s a sense here with this discovery that pristine asteroids such as Ryugu, being relatively close to Earth, might have carried the seeds of life on this planet. Here’s links to the short paper one and paper two presented by the team this week.