Although scientists have always agreed that comets are composed mostly of water ice, the type of ice - amorphous or crystalline - has been a matter of contention. Now, using data obtained from ESA's Rosetta spacecraft around the atmosphere of comet 67P/Churyumov-Gerasimenk, scientists from the Southwest Research Institute (SwRI) have discovered signs of a crystalline form of ice called clathrates, which could help us better understand solar system formation.
"The structure and phase of the ice is important because it tells us a lot about how and where the comet may have formed," said Adrienn Luspay-Kuti, lead author of the paper and a research scientist in SwRI's Space Science and Engineering Division. "If the building blocks of 67P were predominantly crystalline ices and clathrates, then 67P likely agglomerated from chunks of ice closer to the sun.
"The protosolar nebula closer to the sun experienced higher temperatures and more turbulence where crystalline ices could form as the nebula cooled," she added. "More pristine amorphous ices likely dominated the colder outskirts of the rotating disk of dust and gas that surrounds the core of a developing solar system."
Amorphous water can trap large amounts of volatile compounds, which are all released at once when warmed. Conversely, clathrates, which are crystalline in structure, contain gas molecules, and the volatiles that they contain in water create stable structures.
These structures release gases at certain temperatures depending on the gaseous volatile that is contained within the clathrate. Upon examination of the Rosetta spacecraft data, the team found an outgassing pattern that suggests comet 67P's nucleus contains clathrates.
"Without direct sampling of the nucleus interior, evaluating the composition of the coma provides the best clues about the ice structure and, as a result, the possible origin of cometary nuclei," said Luspay-Kuti. "Thought to closely reflect the composition of the building blocks of our solar system, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. These small icy bodies help us understand the big picture."
Using mass spectrometer data from the comet's southern atmosphere - referred to as its coma - the team compared the data to that from the flyby of Hartley 2, a comet considered to be similar in origin to 67P, in order to find correlations.
If the search for correlations reveals that comet 67P and Hartley 2 formed closer to the sun, as the presence of clathrate ices suggests, the data could be used to shed light on our current models of solar system formation.
The findings were published in the April 8 issue of Science Advances.
