Beneath the surface: Exploring the composition of Philae’s comet, Part 2

Comet 67P/Churyumov-Gerasimenko, the destination of the ESA’s Rosetta probe and Philae lander, has a dust-to-ice level of 0.4 to 2.6 and a very high porosity of 75 percent to 85 percent, according to one of several studies published Thursday in a special edition of the journal Science.

Wlodek Kofman of the French National Centre for Scientific Research (CNRS) and his colleagues used the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) instrument to direct electromagnetic signals through the nucleus of the comet.

No scattering pattern was detected in the signals, indicating that the interior of 67P/C-G is likely homogenous or uniform throughout. Furthermore, they reduced the size of uncertainty over Philae’s final landing site down to roughly 21-by-34 square meters, and found that the average permittivity (resistance of the electrical field) is about 1.27.

Comets not ruled out as source of Earth’s organic compounds

A separate study led by Fred Goesmann of the Max Planck Institute for Solar System Research analyzed the 67P/C-G’s composition using the Cometary Sampling and Composition (COSAC) instrument, which was made to identify organic compounds in the comet in order to determine if comets delivered materials crucial to chemical and biological evolution to the Earth.

COSAC, which is a mass spectrometer designed to analyze organic molecules on the surface of the comet following Philae’s touchdown, took a reading in what the authors refer to as “sniffing” mode 25 minutes after first contact. It detected a total of 16 organic compounds – including four never before seen in a comet (methyl isocyanate, acetone, propionaldehyde, and acetamide).

In an email, Dr. Goesmann told redOrbit that his team’s interpretation of the mass spectrum was “surprisingly unsurprising.” While he said that the findings probably did not reveal all that much about the origins of life, the detections of organics on a comet suggests that is such material were to “fall onto a planet in the right environment, emerging life could make use of it.”

“As far as I am aware,” he added, “the two main theories about the development of complicated organic chemistry on Earth are: A. hot springs in deep oceans and B. external delivery by comets or meteorites.” His team’s findings indicate that the latter option “should not be ruled out.”

Studying materials preserved from the early solar system

Finally, in related research conducted by Ian Wright of The Open University’s Department of Physical Sciences and his colleagues, Philae’s Ptolemy instrument was used to analyze Comet 67P/C-G’s organic compounds. Wright’s team analyzed mass spectra taken by Ptolemy roughly 20 minutes after the lander’s initial touchdown to determine its chemical content.

The instrument, which measures stable isotope ratios, found regular mass distributions indicative of the presence of a radiation-induced polymer on the comet’s surface. Specifically, Ptolemy was able to detect signs of compounds with additional -CH2- and -O- groups, suggesting the presence of a radiation-induced polymer on the surface.

Furthermore, Wright and his co-authors report that these measurements may indicate an absence of benzene and other aromatic compounds, a lack of sulfur-bearing species, and an extremely low concentration of nitrogenous material on the comet. Since the properties of cometary material are indicative of the physical and chemical conditions during their formation, the study basically provides a look at materials preserved from the formation of the solar system.

“In the history of the Solar System, there was a moment in time when a bunch of abiological compounds somehow got together in the right configuration to initiate the origin of life. You can’t study that process on Earth because it has gone to completion,” Wright told redOrbit. “In order to gain an insight into what these things might have looked like, you need to go and study a surviving remnant from a time before this took place. Comets offer just that possibility.”

Image: Lander position at Agilkia, the initial site. (Credit: J. Biele et al.)