Surprising dunes on comet Chury

February 22, 2017
Surprising dunes on comet Chury
Left, an image of comet Chury showing outgassing of water vapor, which entrains dust. Right, the neck region, between the comet's two lobes. Various types of relief can be seen, including the dunes, at bottom left (circled in red), in the sandy region. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

Surprising images from the Rosetta spacecraft show the presence of dune-like patterns on the surface of comet Chury. Researchers at the Laboratoire de Physique et Mécanique des Milieux Hétérogènes (CNRS/ESPCI Paris/UPMC/Université Paris Diderot) studied the available images and modeled the outgassing of vapor to try to explain the phenomenon. They show that the strong pressure difference between the sunlit side of the comet and that in shadow generates winds able to transport grains and form dunes. Their work is published on 21 February 2017 in the journal PNAS.

The formation of sedimentary dunes requires the presence of grains and of winds that are strong enough to transport them along the ground. However, comets do not have a dense, permanent atmosphere as on Earth. Nonetheless, the OSIRIS camera on board the Rosetta spacecraft showed the presence of dune-like forms approximately ten meters apart on 67P/Churyumov-Gerasimenko. They are found on the lobes of the comet as well as on the neck that connects them. Comparison of two images of the same spot taken 16 months apart provides evidence that the dunes moved and are therefore active.

Faced with this unexpected finding, the researchers show that there is in fact a wind blowing along the comet's surface. It is caused by the between the sunlit side, where the surface ice can sublimate due to the energy provided by the sunlight, and the night side. This transient atmosphere is still extremely tenuous, with a maximum pressure at perihelion, when the comet is closest to the Sun, 100 000 times lower than on Earth. However, gravity on the comet is also very weak, and an analysis of the forces exerted on the grains at the 's surface shows that these thermal winds can transport centimeter-scale grains, whose presence has been confirmed by images of the ground. The conditions required to allow the formation of dunes, namely winds able to transport the along the ground, are thus met on Chury's .

This work represents a step forward in understanding the various processes at work on cometary surfaces. It also shows that the Rosetta mission still has many surprises and discoveries in store.

Explore further: Image: Rosetta's shadow crosses Comet 67P/Churyumov–Gerasimenko in daring encounter

More information: Pan Jia et al. Giant ripples on comet 67P/Churyumov–Gerasimenko sculpted by sunset thermal wind, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1612176114

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5 comments

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cantdrive85
1.4 / 5 (11) Feb 22, 2017
It's called an ionic wind which creates these dunes, the fanciful pressure gradient is but another failed guess by the plasma ignoramuses.
Frosted Flake
5 / 5 (1) Feb 22, 2017
Interesting photo here. Notice date.

astrowatch.net/2015/01/rosetta-data-reveals-more-surprises.html
gkam
2.4 / 5 (8) Feb 22, 2017
The surprise is not the dunes but the giant sandworms.
Captain Stumpy
4.1 / 5 (9) Feb 22, 2017
failed guess by the plasma ignoramuses
@nazi sympathizing eu cult member
so then where is your study validating your claim?

the scientists actually provide evidence for their claim, as well as build upon what is known and validated (past science)

whereas you made a claim that is not proven nor substantiated by anything
you can't even provide supporting evidence to demonstrate your ionic wind is capable of doing anything at all... and you've historically been proven to be lying when you claim the failure of MS Astrophysicists and their knowledge of plasma physics

if you can't prove it with reputable evidence from a peer reviewed source, why do you continue to repeat your lies?

who are you trying to convince? yourself?
or do you get points for pushing your pseudoscience?
jonesdave
5 / 5 (7) Feb 22, 2017
It's called an ionic wind which creates these dunes, the fanciful pressure gradient is but another failed guess by the plasma ignoramuses.


Lol. Where are you getting the ions from? In case the last 30 plus years of results from this mission and others have passed you by, then I'm afraid that I have to inform you that the outgassed species are neutral. They don't become ionised until they are some distance from the nucleus. There are three mechanisms that can cause this; photoionisation, charge exchange and electron impact ionisation.
So, for the hard of thinking; no ions = no ionic wind.
Only one ignoramus here, far as I can see.

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