Scientists have long wondered what caused the darkness of the planet Mercury’s surface. A previous theory imagined that the dark surface could have been caused by carbon dust that littered the surface during the impact of comets. However, that theory has been challenged by a newer one that proposes Mercury’s surface was at one time encrusted in graphite.
Perhaps in the very earliest days of its existence, Mercury contained a gargantuan, hot magma ocean. Over time, as the closest planet to the sun aged and cooled, graphite could have risen to the surface, hardening into a very dark crust that encased the surface, the Washington Post reports.
Larry Nittler of Carnegie Science and deputy principal investigator of the MESSENGER mission has played a very important part in this exciting new discovery, as the co-author. Nittler says that though previous theories were on the right track, the spacecraft MESSENGER, which has orbited Mercury, has given vastly greater insight and evidence into the planet’s surface history.
“The previous proposal of comets delivering carbon to Mercury was based on modeling and simulation. Although we had prior suggestions that carbon may be the darkening agent, we had no direct evidence.”
After analyzing information from the Messenger’s voyage, scientists learned the darkest parts of the surface also contained the highest concentration of carbon. Interestingly enough, they believe the carbon to be in the form of graphite, which is the material used to make pencil lead.
The darkest areas of Mercury’s surface seem to be in the craters formed from the impact of comets and other space objects. This evidence leads them to believe that the graphite, which once possibly encrusted the entire surface, now lies well below the surface.
— Jason Major (@JPMajor) March 7, 2016
According to Epoch Times, Messenger was able to shoot pictures of the surface of Mercury from only 6 miles away, as compared to previous photos, which were taken at 120 miles away from the surface. The up close and personal shots allowed scientists to note the carbon deposits.
Johns Hopkins research scientist, Patrick Peplowski, noted the following regarding the discovery of the new evidence indicating Mercury had a graphite surface.
“A process of elimination led prior researchers to suggest that carbon may be the unidentified darkening agent, but we lacked proof. Imaging data suggested that weight-percent levels of carbon, likely in the form of graphite, would be required to darken Mercury’s surface sufficiently.”
Johns Hopkins planetary geologist, Rachel Klima, weighed in on the topic as well.
“Experiments and modeling show that as this magma ocean cooled and minerals began to crystallize, minerals that solidified would all sink with the exception of graphite, which would have been buoyant and would have accumulated as the original crust of Mercury.
“If we’ve really identified the remains of Mercury’s original crust, then understanding its properties provides a means for understanding Mercury’s earliest history.”
Scientists reveal the secret behind Mercury’s unusually dark surface: An ancient graphite crust may be the culprit. https://t.co/Gs8zUzXu8R
— Teddy Backers (@TBackers) March 7, 2016
Unfortunately, Messenger is no longer sending its research data back home, as it finally ran out of fuel, completing its mission, reports the Mirror. The special spacecraft performed a superb job in getting so close to the surface of the planet, and in sending such detailed information that scientists can now theorize with greater confidence that the surface was at one time encased in graphite.
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