By Dr. Murthy S. Gudipati, Principal Scientist, JPL/Caltech
The region where comets were formed – far away in the coldest places in our Solar System – harbors the "primordial material" that was left unaltered since before the planets formed. The nuclei of comets may store matter that is older than our Solar System, from more than 4.6 billion years ago.
There were potentially a large number of comets that were sent in every direction due to Jupiter and Saturn, the giant gas planets. Many of these gravitationally scattered comets and asteroids should have landed on Earth with velocities sometimes as fast as a few tens of kilometers per second, distributing their contents everywhere – in the oceans, on the surface, and in the atmosphere. Scientists believe that the first traces of life on Earth began around the same time (about 3.8 billion years ago), indicating a possible connection of asteroids and comets to the origin of life. It is hypothesized that matter made in interstellar ice grains – stored unaltered in comets and delivered to Earth by impacts – may have helped to trigger the origin of life on Earth.
Almost a decade ago, laboratory simulations on analogs of interstellar ice grains – similar to this primitive material stored in comets – showed that a wide range of complex organics are made from simple ices containing molecules such as water, ammonia, methanol, carbon dioxide and carbon monoxide that are also the major components of a comet. These complex organics included amino acids such as glycine.
Parallel to this development, amino acids have been detected in some meteorites. The Stardust mission captured glycine, the simplest of the amino acids, at comet Wild 2 among several other organics in its aerogel matrix. Very recently ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) directly detected glycine along with methylamine and ethylamine in the coma of Comet 67P/Churyumov-Gerasimenko (Altwegg et al. Science Advances, 27 May 2016 DOI: 10.1126/sciadv.1600285).
This observation by Rosetta/ROSINA ends one era of confirming the synthesis of some of life's essential molecules in space and opens up another era of enquiry: how these lifeless molecules may have transformed into the first forms of life on Earth.