Scientists from the French National Center for Scientific Research (CNRS) have discovered that the majority of the ice buried inside comet 67P/ Churyumov-Gerasimenko is in crystalline form, meaning that its origins were likely the protosolar nebula and it is likely the same age as the solar system. The team made the findings using the Rosina2 instrument aboard the European Space Agency's (ESA's) Rosetta spacecraft.
The nature of ice on comets has been the center of much debate, with scientists divided into two groups: those that believe that their ice is crystalline and those that believe their ice is amorphous. Crystalline ice consists of water molecules arranged in a standard pattern, whereas amorphous ice contains water molecules that are disordered.
Using the Rosetta's Rosina mass spectrometer instrument, the team measured amounts of molecular nitrogen (N2), carbon monoxide (CO) and argon (Ar) in comet 67P's ice. Afterwards, they compared the findings to the data gained from laboratory experiments on amorphous and crystalline ice.
The ratios of N2 and Ar found in the comet corresponded to gas hydrates, a type of crystalline ice that can trap molecules of gas in its water molecules. Furthermore, the amount of Ar was approximately one hundred times smaller than the amount that is typically trapped in amorphous ice. Both findings support the hypothesis that the ice in the comet has a crystalline structure.
The results are important because they pave the way for a new way of determining the age of comets. In the case of 67P, gas hydrates are made up of crystalline ice that formed in the protosolar nebula, which stimulated the early solar system, meaning that it must have originated at the same time as the solar system.
In addition, the crystalline structure of comets also reveals that the protosolar nebula possessed levels of heat and density that allowed it to vaporize the amorphous ice that originated from the interstellar medium.
The team's work will help scientists create more accurate scenarios regarding the formation of gas on giant planets and their moons, a process that requires large amounts of crystalline ice.
The findings were published in the March 8 issue of The Astrophysical Journal Letters.
