According to a new study, Mercury’s dark surface was produced by a steady dusting of carbon from passing comets
A new study, which was conducted by the researchers from the Brown University in Rhode Island, has explained the Mercury’s dark, barely reflective surface.
Astronomers have long been baffled by Mercury’s dark surface. Mercury is much darker than its closest airless neighbor, our Moon. Airless bodies are known to be darkened by micrometeorite impacts and bombardment of solar wind, processes that create a thin coating of dark iron nanoparticles on the surface.
Megan Bruck Syal, postdoctoral researcher at Lawrence Livermore National Laboratory who conducted the research at the Brown University, said, “It’s long been hypothesized that there’s a mystery darkening agent that’s contributing to Mercury’s low reflectance. One thing that hadn’t been considered was that Mercury gets dumped on by a lot of material derived from comets.”
According to the research, when comets approach Mercury and the Sun, they often start to break up. The dust that comes off these comets could be composed of up to 25% carbon by weight. This means that the planet would be exposed to a steady bombardment from these comets.
The researchers used a model of impact delivery and micrometeorite flux at Mercury to predict how often cometary material would hit the planet, how much carbon would stick to it and how much would be sent off back into space. The researchers found that Mercury’s surface should be between 3-6% carbon.
The researchers used a 14ft cannon to stimulate celestial impacts by firing projectiles at 16,000mph. They launched projectiles in the presence of sugar, which mimics the organics in comet material. The intense heat of the impact burns the sugar and releases carbon. The researchers then fired this onto material mimicking lunar basalt – the rock that makes up the dark patches of the moon.
They found that tiny carbon particles became embedded in the impact, reducing the amount of light reflected by the target material to less than 5% – about the same as Mercury’s darkest patches.
“We show that carbon acts like a stealth darkening agent. It appears that Mercury may well be a painted planet,” added Prof Peter Schultz, a co-author from Brown University on Rhode Island.
The findings were published in the Nature Geoscience journal.