Mercury, the Sun's innermost planet, is one of the darkest major bodies in the solar system. It reflects less than 10 percent of the sunlight that strikes its surface. A recent study suggests that passing comets could coat Mercury with carbon-rich molecules, darkening the surface. This 2015 image of Mercury from the Messenger spacecraft features a wide, deep basin known as Rembrandt. [NASA/JHUAPL/CIW]
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A couple of brilliant planets highlight the early morning sky right now. Venus, the “morning star,” is well up in the east at dawn, with Jupiter to its lower left.
The two worlds look so bright for several reasons. One of them is that they really are bright — they reflect most of the sunlight that strikes them back out into space.
The planet Mercury stands much lower in the sky — just a few degrees above the horizon. It looks much fainter than the other two — in large part because it is faint. In fact, Mercury is one of the darkest major bodies in the solar system.
A recent study says that Mercury may be darkened by debris from passing comets — carbon-rich material that forms a thin film atop Mercury’s volcanic surface.
Many comets break up as they get close to the Sun, releasing large amounts of dust into space. Much of that material consists of carbon-rich compounds.
The study found that some of those compounds may slam into Mercury. As they do so, they break up, liberating carbon molecules. Some of those molecules may then embed in Mercury’s surface — darkening the Sun’s closest planet.
Look for Mercury just a whisker above the crescent Moon in the glow of twilight early tomorrow. The planet will be at its farthest point from the Sun in our sky in a few days. It’ll grow a bit brighter over that period as well, making it easier to spot. After that, it’ll quickly drop back toward the Sun — and vanish in the twilight.
Script by Damond Benningfield, Copyright 2015