The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta

Abstract

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

Density and Charge of Pristine Fluffy Particles From Comet 67p/Churyumov–gerasimenko

“…The aggregates may be coated with a sticky organic material, observed on the surface of 67P's nucleus (Capaccioni et al 2015). This organic coating was observed on interplanetary dust particles collected in Earth's stratosphere (Flynn et al 2013); it can have a significantly higher tensile strength Kudo et al 2002) than is provided by van der Waals forces assumed in Equation (2).…”

Complex organics in space from Solar System to distant galaxies

“…Some particles in the Stardust sample have been identified to be of interstellar origin (Westphal 2014). A broad 2.9-3.6 µm feature detected by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS)on Rosetta is attributed to nonvolatile organic macromolecular materials on the nucleus of comet 67P/Churyumov-Gerasimenko (Capaccioni et al 2015).…”

Rosetta Studies of Comet 67P/Churyumov–Gerasimenko: Prospects for Establishing Cometary Biology

“…Spectroscopy carried out by the VIRTIS instrument on board the Rosetta spacecraft has revealed a surface overwhelmingly dominated by carbon bearing macromolecules exhibiting a broad integrated CH structure [5]. This spectral feature is said to be "compatible with opaque minerals associated with non-volatile organic macromolecular molecules" for which hypothesis some laboratory experiments are cited.…”

“…Spontaneous racemisation of aspartic acid appears to follow the same exponential law. Figure 7 shows the transmittance spectra of bacteria and diatoms in a sample of local river water obtained by S. Al-Mufti [5]. The similarity between the spectra in Figures 6 and 7 (red boxes) cannot go unnoticed.…”

“…Similar to other cometary nuclei, Comet 67P/C-G has low albedo of 0.06, characteristic of its largely carbonaceous surface and regolith [5]. It has large smooth areas like 'seas' surrounded by elevated rugged terrain ( Figure 2).…”