Astronomers used to find the planet Mercury unsettling, as they couldn’t figure out why it is so dark – darker than the Moon, even though it contains way less iron. But the mystery has been finally solved, as scientists shine some light on the mesmerizing past of the innermost planet in our Solar System.
The answer is rather simple: the dark color of Mercury is given by the fact that the planet is literally slathered in graphite – the very same carbon-based material we use in our pencils.
What’s more, the study featured today in Nature Geoscience explains that the patches of graphite found on Mercury’s surface could be the exposed remains of a massive carbon crust, which in turn is the result of an ancient lava ocean.
Lead study author Patrick Peplowski, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory, said the discovery was “really a huge surprise” for the researchers involved.
The hypothesis that Mercury’s surface may be so dark because of carbon first emerged about a year ago, discarding the theory that iron or titanium or other typical darkening agents could be involved in the mystery.
With the help of model simulations, astronomers showed that Mercury’s early history could’ve been battered with comets rich in graphite. But their models needed confirming, which finally came in the form of NASA’s MESSENGER mission.
MESSENGER is the first space probe to provide astronomers with detailed geologic data from Mercury’s surface. The information collected between 2011 and 2015 showed clear and direct evidence for the presence of graphite on the planet.
Study co-author Larry Nittler, who is also the Deputy Principal Investigator on the MESSENGER mission, said in a statement that MESSENGER’s Neutron Spectrometer was used to “spatially resolve the distribution of carbon and found that it is correlated with the darkest material on Mercury.”
According to the data – gathered in the final days of MESSENGER’s mission as it was performing low-altitude flyovers – Mercury’s surface could contain a few percent carbon, but more than other planets in our Solar System.
And opposed to the previously held belief, MESSENGER’s data shows that comets are not responsible for the high graphite percentage; instead, indigenous carbon that came from deep within the planet.
Authors also noted that the huge dataset delivered by MESSENGER will take years to analyze, and this discovery is only a fraction of the information brought back to Earth.
Image Source: Messenger