Mercury has been found to have a dark side, with graphite, a crystalline form of carbon commonly found in pencils, being the source of the mysterious dark colouration of the planet’s surface.
This intriguing discovery suggests that the planet’s geological history may be more complex than previously thought, as the presence of graphite indicates processes that could involve significant volcanic activity and the interaction of solar winds with the surface materials.
Furthermore, researchers are exploring how the unique environmental conditions on Mercury, characterised by extreme temperatures and a lack of atmosphere, contribute to the formation and retention of these dark, graphite-rich regions.
This ongoing investigation not only enhances our understanding of Mercury’s surface composition but also raises questions about the potential for similar materials to exist on other celestial bodies in our solar system.
The study, published this week in Nature Geoscience, was led by a team from the Johns Hopkins University Applied Physics Laboratory in the US, which analysed measurements collected by NASA’s Messenger spacecraft as it went through its final orbits of Mercury.
The findings not only test theories of early planetary formation but may also explain the amount of carbon here on Earth.
Remains of a Primordial Crust
The surface colour of planetary bodies is often an indicator of the elements that make them up. For example, the distinctive rusty red appearance of Mars can be attributed to iron oxide, which gives the planet its characteristic hue and is a result of extensive geological processes that have occurred over billions of years.
Similarly, other planets and moons exhibit varying colours due to their unique compositions and surface conditions; for instance, the icy surfaces of Europa reflect a bright white, suggesting the presence of water ice, while the vivid hues of Jupiter’s atmosphere reveal a complex mix of gases and chemical reactions.
Understanding these surface colours not only helps us identify the elemental makeup of these celestial bodies but also provides insight into their geological histories and the potential for past environmental conditions that may have supported life.
It had previously been believed that the iron and titanium were typically responsible for the dark colouration on planetary surfaces. However, Mercury is quite dark, but lacks high enough concentrations of those elements to account for its colour.
“Mercury’s surface was significantly darker than we could account for based on our understanding of Mercury’s surface chemistry,” said Dr Patrick Peplowski, from the Johns Hopkins University Applied Physics Laboratory, and lead author on the study.
The investigation into the dark colouration of Mercury revealed that this phenomenon is primarily attributed to the presence of carbon. Analysing the data transmitted to Earth by the Messenger probe, researchers established that Mercury possesses higher levels of carbon than any other planet or their moons, thereby elucidating the cause of its unusually dark surface.
The discovery of carbon on Mercury was an unexpected one, so much so that none of the instruments on Messenger was designed to detect the element. Instead, Peplowski and his colleagues had to use multiple instruments to identify the carbon.
Need for continued planetary exploration
The discovery provides exciting support for a fascinating theory about Mercury’s formation. Remarkably, carbon-rich material has been found beneath the younger volcanic materials that now shape Mercury’s vibrant surface.
This suggests that early Mercury’s original carbon-rich crust may have been formed from graphite that floated to the top of a global magma ocean. These primordial “floating crusts” provide a rare perspective on early planetary formation.
“This is interesting because the original crusts of the other planets were destroyed long ago by processes like volcanic resurfacing, plate tectonics and erosion,” Peplowski told The Conversation.
The carbon we see today may be the remains of that ancient, 4.5 billion-year-old crust. However, there are still questions about how the planetary crust was originally formed and why carbon was found around some craters but not others.
There is a lot of follow-on work to be done. Future missions to Mercury might benefit from instrumentation specifically designed to map carbon to follow up on this result. The next planetary exploration of Mercury could provide further answers, with the European Space Agency launching the BepiColumbo probe to Mercury next year. It has an entirely new suite of instruments that can add to our understanding of carbon on Mercury.
Planetary Puzzles
Dr Helen Maynard-Casely, an Instrument Scientist from the Australian Nuclear Science and Technology Organisation, who was not involved in the study, said the study sheds light on some longstanding mysteries in planetary science. She added that the theory they study suggests that how Mercury evolved shares many similarities with the early formation of the Moon.
“The early crust of the Moon was made of lighter minerals. It is thought these were stripped off the Earth. In terms of planetary formation, these minerals are like froth on a coffee. Then, as the surface of the Moon has evolved, impacts and lava flows have brought the darker material onto the faces of the Moon,” she said.
What they’re discovering is that this intriguing, darker material on Mercury represents the remnants of the early frothy material, showcasing the planet’s dynamic history. Graphite shines brightly in contrast to the other materials on Mercury, suggesting that it rose to the top during the exciting early moments of the planet’s formation, forming the very first crust of Mercury as it was cooling down.
But throughout the life of Mercury in the solar system, repeated impacts had churned up the crust, leaving very little of the early surface intact. Maynard-Casely says that the discovery came as a surprise and may change our view on how the solar system was formed, and the current model of predicting the presence of carbon, including here on Earth.
Carbon has always been a complex element for us to fully understand, even right here on Earth, and it’s truly a challenge to uncover the mysteries surrounding our carbon.
Many believe that a significant amount of carbon is concealed deep within the Earth’s interior, leaving us to wonder about the valuable minerals we might be overlooking. It’s heartening to see that there is a global effort underway to seek out these hidden treasures.
The knowledge of carbon’s significance on Mercury would bring those questions back to the forefront and reinvigorate discussions.
Reference: https://theconversation.com/discovery-of-carbon-on-mercury-reveals-the-planets-dark-past-55940
