Mercury It may not have shrunk as much as scientists previously thought, potentially solving the mystery posed by the planet’s continuing earthquakes.
Mercury is the smallest and inner world in the solar system, and it was a mysterious planet until NASA DELIVERY COURIER The spacecraft became the first probe to orbit Mercury in 2011. The only other visits it has received were flybys made by NASA’s Mariner 10 probe nearly 50 years ago, although a new Japanese-European mission called BepiColombo will arrive at planet at the end of this decade.
Sailor 10 revealed that Mercury was covered in large, rugged faults, or cliff-like structures that look like giant steps in the landscape; Using data from MESSENGER, the scientists calculated that these scarps can reach 600 miles (1,000 kilometers) long and more than 1.8 miles (3 km) high.
Related: Photos of Mercury from NASA’s Messenger spacecraft
Fault scarps arise when rocks come together, one side up from the other, along faults or fractures in a planet’s crust. The most accepted model of the origin of Great Mercury fault scarps is that they are essentially wrinkles that formed when the interior of the planet cooled over time. The cooling caused Mercury to shrink and, in turn, shrink its crust like the skin of a raisin.
Previous research suggested that Mercury may have “supercontracted” up to 8.7 miles (14 km) in diameter. In new research, Thomas Watters, a planetary scientist at the National Air and Space Museum in Washington, DC, estimates that the planet contracted by no more than 1.2 to 2.5 miles (2 to 4 km).
Watters analyzed orbital imagery and topographic data from MESSENGER to develop a model of the shrinkage of Mercury. It only incorporated landforms with clear evidence that they were physically connected to deep-seated contractive faults on the planet, as opposed to more superficial features that were less likely to have direct links to the contraction of Mercury.
Still, these new findings suggest that “Mercury has retained more of its primordial inner heat than previously thought,” Watters said. This discovery could help explain why MESSENGER found small rugged faults less than 50 million years old, which scientists believe are evidence that Mercury can still rumble with earthquakes, or “Mercury earthquakes“: The extra heat can help keep Mercury geologically active.
These new estimates go against conventional wisdom, which holds that the smaller the body, the faster it cools and becomes geologically inactive, Watters noted. “Mercury is showing us an alternative evolutionary path,” he said. “Small rocky planets can retain their inner heat and experience less global shrinkage overall. This slow cooling can drive very recent and even current tectonic and seismic activity on Mercury.”
Mercury may have maintained its primordial heat due to the insulating effect of a thick “megaregolith,” that is, a layer of fractured bedrock beneath its regolith, or dust, soil, and rocks on the planet’s surface. Although Mercury should have cooled since its formation, this porous layer that it developed over time may have prevented a significant amount of this heat from seeping up and out, a bit like insulating foam does in houses.
“The bark of Mercury, like the bark of Moon, it has been fractured greatly and deeply over billions of years by giant impacts, “Watters explained. This fractured porous rock” has probably greatly inhibited internal cooling. “
“If small planets like Mercury, and even smaller bodies like the moon, can retain their inner heat and remain geologically active after billions of years, then we can expect small rocky exoplanets to follow the same evolutionary path,” Watters added. (TO Study 2019 found that the moon can still experience earthquakes due to effects like contraction, as well as tidal forces from Earth’s gravitational pull).
Detailed watters your findings January 14 in Communications Earth & Environment magazine.
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