Balanced Rock in Arches National Park in Utah has cousins on comet 67P/Churyumov-Gerasimenko. Three boulders — the largest of which is roughly 30 meters across — are barely in contact with the comet’s surface, researchers report May 18 on the Rosetta blog. The resolute rocks showed up in images taken by the Rosetta spacecraft, which has been orbiting comet 67P since August.
Balancing boulders on Earth are either deposited by glaciers or carved by wind and water erosion — none of which exist on a comet. Researchers speculate that the comet’s boulders might have been relocated by surface material slipping and sliding after being heated by the sun.