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The comet 67P/ Churyumov-Gerasimenko is indeed a binary object !

11 October 2021

A new study conducted by researchers from Paris Observatory - PSL at the Laboratory of Space Studies and Astrophysics Instrumentation on the Rosetta space mission reinforces the hypothesis that comet 67P/Churyumov-Gerasimenko is a binary body formed by the low-speed collision of two distinct objects during the very early phases of the formation of the Solar System. The results are published in the journal Astronomy & Astrophysics on September 22, 2021.

Researchers continue to analyze the extraordinary data harvest of the Rosetta space mission, which was the cornerstone of the European Space Agency (ESA) space exploration program dedicated to small bodies. Rosetta observed comet 67P/Churyumov-Gerasimenko (hereafter 67P) for almost 2 years, allowing to study for the first time the evolution of the surface of a cometary nucleus.

A new study led by researchers from LESIA (Laboratoire d’études spatiales et d’instrumentation en astrophysique) focuses on the detailed analysis of the geomorphology, surface changes, and characterization of the water ice exposed on the Wosret region, located on the small lobe of the comet.

Left: the southern hemisphere of comet 67P with the names of regions indicated. Wosret occupies most of the southern hemisphere of the small lobe. Abydos, which is part of this region, is the final landing site of the Philae lander. Right: RGB color image, from the OSIRIS instrument, showing Wosret and Anhur. There are many bright spots on Anhur - with blue spectra - associated with exposed water ice on the surface, while there are very few on Wosret. Both regions are very active, eroded and exposed to the same solar flux.

Wosret, on the small lobe of the comet...

This region, like others in the southern hemisphere, is one of the most active and eroded, as it is illuminated during the perihelion passage when the solar flux is most intense.

Despite the fact that Wosret is very active, with over 40 sources of cometary activity identified, very little surface change has been identified. To wit:

  • A cavity about 30 m long and 6 m deep,
  • A thinning of its dust layer of about one meter on a limited surface,
  • A loss of total mass estimated at 1.2 million kilograms.
  • Water ice exposed on the surface very limited: observed on areas less than 2 m2.

...vs Anhur and Khonsu, on the large lobe

On Anhur and Khonsu, two regions of the comet’s large lobe - subject to the same high illumination conditions as Wosret and also highly active -, many morphological changes were observed:

  • Mass losses ranging from 50 to 170 million kilograms,
  • A higher abundance of frost and water ice.
For more details, see:
⭐ Fornasier et al. 2019, Astronomy & Astrophysics, Volume 630, id.A13 ;
⭐ Hasselmann et al. 2019, Astronomy & Astrophysics, Volume 630, id.A8,

Hypothesis reinforced

The comparison between regions of the two lobes - subjected to intense solar fluxes and exposing the most primordial and least altered layers of the comet - has allowed to highlight that the material of the small lobe of the comet has different physical and mechanical properties than that constituting the large lobe.

This material is more consolidated, less fragile and without volatile matter, at least for the most superficial layers.

What to remember:
These results reinforce the hypothesis, formulated on the basis of the study of cometary nucleus stratification by Massironi et al, (2015, Nature, 526, 402), that comet 67P is a binary body formed by the low-velocity collision of two distinct objects, which occurred during the very early phases of Solar System formation.

Reférence

S. Fornasier, J. Bourdelle de Micas, P. H. Hasselmann, H. V. Hoang, M. A. Barucci and H. Sierks. Small lobe of comet 67P: Characterization of the Wosret region with ROSETTA-OSIRIS. Astronomy & Astrophysics 653, A132, 14p.
Published online: 22 September 2021
DOI: https://doi.org/10.1051/0004-6361/202141014
Open access : https://www.aanda.org/articles/aa/pdf/2021/09/aa41014-21.pdf

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