A balancing rock on Rosetta’s comet?

A balancing rock on Rosetta’s comet?
May 19, 2015
by Deborah Byrd in Blogs » Science Wire, Space

In close-up images via the orbiting Rosetta spacecraft, the rock looks poised like a ballerina, with only a tiny fraction of its surface touching the ground.

Scientists from the Rosetta spacecraft’s OSIRIS team – that is, its scientific imaging team – said this week (May 18, 2015) that they’ve discovered what appears to be a balancing rock on the larger lobe of Comet 67P/Churyumov-Gerasimenko. The spacecraft has been orbiting this comet since August, 2014, and will stick with it at least until the comet’s perihelion, or closest point to the sun, in August, 2015.

The close-range images from Rosetta show a group of three boulders on the comet’s surface. The largest one, with a diameter of approximately 30 meters (100 feet) appears perched on the rim of a small depression. Like balancing rocks found on Earth, this rock on Rosetta’s comet seems to have only a very small contact area with the ground.

Balancing rocks touch the ground with only a small fraction of their surface. They often look as if they may tilt or topple over any moment. You can see balancing rocks in Australia or the U.S. Southwest. These boulders are sometimes thought to have riden within glaciers to their current locations. Or, sometimes, wind and water eroded softer material surrounding the rock to turn them into balancing rocks.

But how a balancing rock came to be on Comet 67P/Churyumov-Gerasimenko – which presumably has no glaciers or wind as we experience it on Earth – is not entirely clear. It’s true that, as icy comets draw near their closest points to the sun that binds them in orbit – as 67P will this August – they become warmer and increasingly active. Some of their ices heat up and sublimate to become gas. This process releases dust grains that had been trapped in the ice. The dusty gas from a comet’s icy nucleus forms a glowing cloud around the comet called its coma, from a Latin word for hair.

More
http://earthsky.org/space/a-balancing-rock-on-rosettas-comet?utm_source=EarthSky+News&utm_campaign=05962b6665-EarthSky_News&utm_medium=email&utm_term=0_c643945d79-05962b6665-393525109