Two articles – available here and here – published in the journal “Nature Astronomy” report the results of as many analyzes of data collected by ESA’s Rosetta space probe which reveal the presence of compounds such as ammonium salts on the comet 67P/Churyumov-Gerasimenko. A team of researchers led by Kathrin Altwegg of the University of Bern, Switzerland, analyzed the data trying to understand the reasons for the scarcity of nitrogen on the comet, concluding that its presence is actually difficult to detect because a part is tied to ammonium salts. These salts are among the building blocks of molecules that include some precursors of life such as urea and glycine, already found on the comet. Another team discovered in the data traces of aliphatic compounds, considered essential for life on Earth, on the comet.
The mission of the Rosetta space probe ended on September 30, 2016 with its crash on the surface of the comet 67P/Churyumov-Gerasimenko. Over the course of a few years it made many detections of the materials present in the coma that formed when the comet approached the Sun enough to cause the sublimation of some materials present on its surface.
In some cases, Rosetta got close to the point of ending up inside the coma, a maneuver not without risks because it created orientation problems for the probe, interfering with its position detection systems and with the communication systems with the Earth. Despite this, it managed to successfully conduct some flybys, in September 2016 even less than two kilometers from the nucleus.
In particular, the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument made it possible to detect compounds never found before even on the comet 67P/Churyumov-Gerasimenko. A considerable amount of ammonia was also found in the coma and according to Kathrin Altwegg, who is also this instrument’s principal Investigator, it can be attributed to the presence of ammonium salts. Both ammonia and these salts have a much higher evaporation temperature than ice and on comets it’s in solid form. This made it impossible to measure those compounds and they needed to perform a series of lab analyzes to prove their presence.
Nora Hänni of the ROSINA instrument team, co-author of one of the two articles, explained that she and her colleagues found traces of five different ammonium salts: ammonium chloride, ammonium cyanide, ammonium cyanate, ammonium formate and ammonium acetate. This indicates that nitrogen is probably present in amounts on comets but above all in ammonium salts, building blocks for more complex molecules such as urea and glycine.
The article on aliphatic compounds offers the results of another analysis, this time of data collected by the VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) instrument, which was used to examine the nucleus of the comet 67P/Churyumov-Gerasimenko. The examination of several million infrared spectra detected by VIRTIS allowed to discover clear signs of hydrogen and carbon chains that form aliphatic compounds, the first time they were discovered on a comet nucleus.
Andrea Raponi of the Italian National Institute of Astrophysics, first author of this article, explained that the origin of materials such as aliphatic compounds is crucial for our understanding not only of the solar systems but of the planetary systems of the whole universe. That’s because they’re compounds considered essential for life as we know it.
An interesting discovery is expressed by Fabrizio Capaccioni, also of the Italian National Institute of Astrophysic, VIRTIS principal investigator, who explained that the nucleus of the comet 67P/Churyumov-Gerasimenko has a composition similar to the interstellar medium. This means that it contains materials that existed before the solar system formation and got captured during its formation after they ended up in the protoplanetary disk that formed it.
Investigations into the comet 67P/Churyumov-Gerasimenko keep on offering really interesting results, also confirming that many compounds that contributed to the birth of life forms on Earth may have come from comets. This adds to the results reported in an article published in the journal “Monthly Notices of the Royal Astronomical Society” on the similar origin of phosphorus. In short, confirmations of the link between life and comets and also of the link with ancient stars.
