Scientists have presented their initial observations of Comet 67P/Churyumov-Gerasimenko in seven articles published Thursday in the journal Science. Among the more surprising finds: images of ripples and dunes on the comet's surface, unexpected given that the comet lacks an atmosphere (and therefore wind) and experiences very little gravity.
Above: High-resolution data show evidence of dune-like structures, via Thomas et al.
Nicolas Thomas, a professor of experimental physics at the University of Bern in Switzerland and lead author of the paper documenting the comet's morphological diversity, speculated for the New York Times:
"You have to ask yourself, is that possible?" said [Thomas, who] said that back-of-the-envelope calculations indicated that it might be plausible, with the jets of gas and dust acting as wind and the particles held together through intermolecular attraction known as the van der Waals force instead of gravity. "You can convince yourself you can make them move," Dr. Thomas said. "It's plausible, at least at the moment." convince yourself you can make them move," Dr. Thomas said. "It's plausible, at least at the moment."
Some of the dune-like structures can be seen in the image at the top of this post. Below, images acquired in the Hapi region show ripple structures (which aren't uncommon here on Earth, or Mars, for that matter), rocks with wind tails, and rocks with moats, which Thomas' team says "provide further support for localized gas-driven transport":
"Features in the Hapi region show evidence of local gas-driven transport producing dune-like ripples (left) and boulders with 'wind-tails' (right) – where the boulder has acted as a natural obstacle to the direction of the gas flow, creating a streak of material 'downwind' of it. The images were taken with the OSIRIS narrow-angle camera on 18 September 2014." Image and Caption Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/ DASP/IDA
More on the first round of Rosetta's results at the NYT.