Painted Planet: Mercury's Surface May Be Darkened by Comet Dust

 / Updated  / Source: NBC News

Breaking News Emails

Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

The dark surface of Mercury may have an unusual origin: a billion-year paint job by passing comets. "It's long been hypothesized that there's a mystery darkening agent that's contributing to Mercury's low reflectance," said Lawrence Livermore National Laboratory's Megan Bruck Syal, co-author of a study published in Nature Geoscience. "One thing that hadn't been considered was that Mercury gets dumped on by a lot of material derived from comets."

Matter found in the comet craters created by firing high-carbon compounds into a simulated planetary surface.
Matter found in the comet craters created by firing high-carbon compounds into a simulated planetary surface.NASA / Ames / Brown Unviersity

Such cosmic passersby would likely start to break up that close to the sun, shedding a great deal of carbon into the neighborhood. Over billions of years, that constant bombardment would render the surface of Mercury as much as 3 percent to 6 percent carbon by weight. The comet chunks would also impact at great speed — the researchers tested the result of this using the NASA Ames Vertical Gun Range, a special cannon that can fire objects at stellar velocities (as much as 16,000 mph) to simulate events like meteorite strikes. They found that simulated comet pieces produced a thin coating of embedded carbon that absorbed light much the way Mercury's surface does.

A planetwide layer of this could very well be the source of Mercury's darkness, said co-author Peter Schulz of Brown University: "It appears that Mercury may well be a painted planet."

IN-DEPTH

SOCIAL

-- Devin Coldewey

Breaking News Emails

Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.
MORE FROM news