Although Mercury is the closest planet to Earth and all other planets in the Solar System according to average times, it is one of the planets that receives the least attention. We can say that the biggest reason for this lack of interest is Mercury, which lasts 59 Earth days and is a scorched planet with temperatures reaching 430°C during the day, which does not offer a good welcome to its guests. Even if we don’t consider the lack of atmosphere, it can easily be said that this is not a planet you would want to visit.
But this planet still has very interesting features. For example, in 1974, NASA’s Mariner 10 mission flew past the planet and discovered evidence that the planet was shrinking.
This evidence came from mile-high cliffs known as “steps” across the planet. These arise from faults beneath the rocks, called “thrusts,” as the planet contracts due to thermal cooling.
Mercury is shrinking due to thermal contraction of its interior
“As Mercury’s interior shrinks, its surface (the crust) has less and less space to cover,” David Rothery, Professor of Planetary Earth Sciences at the Open University and author of a new paper investigating the planet’s contraction, wrote in a piece for The Conversation. “It responds to this by developing ‘thrust faults,’ where a piece of land is pushed onto adjacent land,” he explains, “This is similar to the wrinkles that form on an apple as it ages; But while the apple shrinks because it dries, Mercury shrinks because of the thermal contraction of its interior.”
In 2014, it was estimated that the planet had shrunk by approximately 7 kilometers. On Mercury, it’s possible to get a pretty good idea of when this shrinkage occurred by looking at the many impact craters that cover its surface. Although some craters have become shorter due to the planet’s contraction, there are craters on the steps as well, meaning that the impact that caused them occurred after the fault altered the planet’s crust.
Based on this information, astronomers concluded that the steps are approximately 3 billion years old. But in the new study, the team found evidence that as Mercury continues to cool, the planet’s shrinkage is not over yet.
Open University PhD student Ben Man found “grabens” (depressions) on steep slopes, where land falls between two faults, a sign of stress.
Stretching may seem surprising on Mercury, where “the crust is generally compressed,” Rothery explains, “but Man realized that these grabens would form if a thrust slice of the crust was twisted as it was pushed into adjacent land. “If you try to bend a piece of toast, it may crack in the same way.”
Because these grabens are not completely covered by debris from impacts from meteor impacts on Mercury, the team estimates that the stretching and collapse occurred less than 300 million years ago, providing evidence that the planet’s contraction still continues today.
The study was published in Nature Geoscience.
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