Mercury may contain diamonds beneath its unusually dark crust, according to research by scientists at Sun Yat-sen University in Zhuhai, southern China.
Diamonds may exist in nano form under the surface of Mercury. Photo: Earth.com
The team said their observations and models suggest that the graphite content that gives Mercury its distinctive color may be much lower than previously estimated, suggesting that diamonds and other forms of carbon may exist. If previous estimates of the amount of carbon on the planet's surface are correct, a large portion of the element could be present in other forms, but tiny diamonds and amorphous carbon have no crystalline structure. The study, published in the journal Nature Astronomy on January 4, builds on previous research in the United States using data collected by NASA's Messenger spacecraft, the first spacecraft to orbit Mercury.
Mercury is the smallest planet in the Solar System, only slightly larger than the Moon. It is also the closest planet to the Sun, at an average distance of 77 million km from Earth, and the least studied because it is difficult to reach. The Messenger probe took nearly 11 years to get close to the planet, entering orbit around Mercury in 2011 and ending its mission in 2015.
In 2016, a team from the Johns Hopkins University Applied Physics Laboratory determined that carbon is likely responsible for Mercury’s dark color, reflecting its geochemical composition and a key clue to the planet’s origin and evolution. The carbon originated deep below the planet’s surface, within an ancient graphite-rich crust that was later buried by volcanic material, according to a US study published in the journal Nature Geoscience.
However, the latest research suggests that the carbon detected by the Messenger mission “may not exist entirely in the form of graphite.” The study’s results suggest that much of the carbon on Mercury is in forms other than graphite and was not completely expelled from the mantle during the crystallization of the magma ocean. According to the paper, the carbon on Mercury is mainly in the form of nanodiamonds due to long-term metamorphism or amorphous carbon due to graphite weathering. Graphite is the most stable form of carbon on Mercury’s surface. Under extreme pressure and temperature below 3,000 degrees Celsius, it can transform into diamond.
Lead researcher Xiao Zhiyong, a professor at the School of Atmospheric Sciences at Sun Yat-sen University, said that much of Mercury's graphite could have transformed into other forms of carbon after more than 4 billion years of weathering. "If Mercury's basal crust is composed of graphite, we can imagine that the continuous evolution over 4.65 billion years with countless collision, merging and destruction events would have caused most of the early graphite to undergo changes and become other forms of carbon, including diamond," Xiao explained.
Xiao is looking forward to the findings of a second mission to Mercury, scheduled to arrive at the planet in December 2025. The high-resolution data collected by the probe could help scientists identify and study meteorites on Earth that originated on Mercury. According to Xiao, meteorites from Mercury could serve as direct evidence of the planet’s surface composition until samples are collected.
The European-Japanese BepiColombo mission is set to launch in 2018. It will be the second mission to orbit Mercury and the most advanced, according to the European Space Agency. The Japan Aerospace Exploration Agency said that after entering orbit, the probe will observe the planet's characteristics such as its magnetic field and plasma environment.
An Khang (According to Nature )
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