Rosetta’s Comet Smells Bad As It Fizzes Into Life

The world has been enjoying some nice images of Comet 67P/Churyumov–Gerasimenko, but what does it smell like? Well according to the Rosetta probe’s instruments, pretty bad, like a mix of horse dung and rotten eggs.

The revelation comes as new pictures of the comet’s icy head show it to be becoming more active, sending jets of dust shooting out into space. Swiss scientists got a whiff of how the comet must smell by using an instrument called the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA).

Since early August it has been sniffing its fumes with its two mass spectrometers. They show that the chemistry in the coma, or atmosphere, of the comet is surprisingly rich already even though it is more than 400 million kilometres (250 million miles) from the Sun.


Jets of dust are imaged spewing from the comet’s head on 10 October by Rosetta’s OSIRIS camera. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/ INTA/UPM/DASP/IDA

The comet is showing a gradual, but clear, increase in activity, as can be seen in the latest images provided by the OSIRIS team. Images obtained a few months ago showed distinct jets of dust leaving the comet, these were limited to the “neck” region of the twin-lobed comet. More recently, images obtained by Rosetta’s scientific imaging system, OSIRIS, show that dust is being emitted along almost the whole body of the comet.

“At this point, we believe that a large fraction of the illuminated comet’s surface is displaying some level of activity,” says OSIRIS scientist Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research (MPS) in Germany. The ROSINA team thought that at these vast distances from the Sun, its relatively low intensity would only release the most volatile molecules via sublimation, namely carbon dioxide and carbon monoxide.article image

However, ROSINA has detected many more molecules. A report in September listed Water (H2O), Carbon monoxide (CO), Carbon dioxide (CO2), Ammonia (NH3), Methane (CH4) and Methanol (CH3OH). In a new report released yesterday, it was revealed that ROSINA has also detected Formaldehyde (CH2O), Hydrogen sulphide (H2S), Hydrogen cyanide (HCN), Sulphur dioxide (SO2) and Carbon disulphide (CS2)

As Kathrin Altwegg, principal investigator for ROSINA, put it: “The perfume of 67P/C-G is quite strong, with the odour of rotten eggs (hydrogen sulphide), horse stable (ammonia), and the pungent, suffocating odour of formaldehyde. This is mixed with the faint, bitter, almond-like aroma of hydrogen cyanide. Add some whiff of alcohol (methanol) to this mixture, paired with the vinegar-like aroma of sulphur dioxide and a hint of the sweet aromatic scent of carbon disulphide, and you arrive at the ‘perfume’ of our comet.”


High resolution mass spectrum from ROSINA’s Double Focusing Mass Spectrometer (DFMS), taken on 10 October at a distance of 10 km from the comet centre. The plot shows the detection of hydrogen sulphide and the heavier isotope of sulphur, 34S, which is a fragment of all sulphur bearing species. Image credit: K. Altwegg, University of Bern

The density of these molecules is very low. The main part of the coma is made up of water and carbon dioxide, mixed with carbon monoxide, but detailed analysis of this mixture and how it varies as 67P/C-G grows more active will allow scientists to determine the comet’s composition.

Further work will show how 67P/C-G compares with other comets, for example by revealing differences between comets originating from the Kuiper Belt (like 67P/C-G) and comets that hail from the distant Oort Cloud that surrounds the Solar System (like Comet Siding Spring, which recently flew past Mars). The goal is to gain insights into the fundamental chemical make-up of the solar nebula from which our Solar System and, ultimately, life itself emerged.

While 67P/C-G’s overall activity is clearly increasing, the mission’s designated landing site on the smaller lobe still seems to be rather quiet. However, there is some indication that new active areas are waking up about one kilometre from the landing site. These will allow the lander’s instruments to study the comet’s activity from an even closer distance. Landing on a Comet – The Rosetta Mission. Credit: DLRde  Source: SEN


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