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New report suggests that Mercury's crust is thinner, denser than imagined



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Researcher and scientist Michael Sori believes that the crust of Mercury could be thinner and denser than previously thought. If the result is true, it would make the already strange Mercury a little bit weirder orbiting in a unique 3: 2 spin-orbit resonance, in which the planet spins around its axis exactly twice, it's about the sun. It has the least axial tilt, but the largest orbital eccentricity known in the solar system; The distance of Mercury from the sun in perihelion (the position of the planet when it is closest to the sun) is only 66 percent of its distance at aphelion (the point farthest from the sun).

One of the biggest curiosities of mercury is the dimension of its core, coat and crust. On Earth (the densest planet in the solar system), the iron-rich core of the planet accounts for 15 to 17 percent of its mass. On Mercury, the nucleus is 55-60 percent of the planet's total mass, and it is believed to be a solid inner iron core and a liquid outer iron core. Unlike Mars and Venus, Mercury has a global magnetic field, even though it is only about 1.1 percent as strong as Earth's. But why is the core so much of the planet – and what does the thin crust actually consist of?

There are several theories why Mercury – the smallest planet by radius – has such a dense core. One argument is that Mercury was hit by massive impacts that destroyed most of the planet's original surface. It is believed that the late heavy bombardment that took place between 4.1 and 3.8 years ago was caused by the orbital migration of the gas giant planets and a tremendous amount of asteroids known as the Trans-Neptunian Belt. In the following diagram, the innermost planet is Jupiter, followed by Saturn, Neptune and Uranus – with Uranus and not Neptune as the remotest planet of the Solar System.

This simulation shows the outer planets and the planetesimal belt: a) early configuration before Jupiter (green) and Saturn (orange) achieve 2: 1 resonance; b) Scattering of planetesimals into the inner solar system after the orbital shift of Neptune (dark blue) and Uranus (light blue); c) After the ejection of planetesimals by planets. Photo credits: Wikipedia user Astromark

The gravitational interactions between the trans-Neptunian belt objects and the gas giants have largely freed the belt from smaller objects. Some of them would have crashed into the sun, some were ejected from the solar system, and some were fired on trajectories that hit Mars, Earth, Venus, and Mercury. One theory is that Mercury was originally 2.25x larger than its current mass, but was hit by an object that is about 1/6 of its own size (or just over one-third the size of the current planet). The impact tore away the Mercury crust and left the core.

Another theory is that Mercury, the planet closest to the Sun, is partially vaporized by the enormous amount of energy emanating from the star that is still emerging. As the protosun contracted into its current form, temperatures on the mercury could reach up to 10,000 K, more than enough to vaporize rocks and lighter elements. A third explanation is that Mercury never accreted lighter particles because the strong solar wind of the sun swept them away before the planet could form. The space probe MESSENGER, whose mission ended in 2015, found traces of minerals that should have been destroyed by a massive impact, which may make the third statement sound right.

According to Sori, his findings indicate that the Mercury crust is only 16 miles thick with a higher density than aluminum. He notes that our measurements of the Mercury crust have been revised for a long time – initial estimates, based on data from Mariner 10, showed a crust 62-186 miles thick. Later measurements with more precise spaceships exacerbated them to about 21 miles. But Sori, who used various techniques to analyze the data returned by Messenger, believes that the Mercury crust was primarily formed by volcanic activity and that it is similar to the moon as the percentage of silicate material that has been converted into crust , The Moon and Mercury are superficially similar to the naked eye, as they both lack an atmosphere or geological processes that would transform impact craters, some of which are billions of years old but still visible to the naked eye. Erosion and plate tectonics on Earth make it difficult to identify such ancient impact craters on our own planet.

Originally it was believed that mercury had turned about 11 percent of its silicates into crust, raising the question of why Mercury is "better." as the moon (about 7 percent of the silicates of the moon are found in the crust). Sori's work, if proven, would lower the amount of Mercury silicate in the crust to about 7 percent-identical to the Moon. There are two theories about how the crust could have formed on planets. Either the crust is lighter material that literally floats on the igneous ocean below (flotation crust), or it is the last remnant of the magma ocean that once covered the planet, with additional deposits of eons of volcanic activity. Mercury's last major episodes of volcanic activity are dated to 3.5B years, though periodic explosive volcanism may have continued after.

Soris's theories should be confirmed or refuted by the arrival of BepiColombo, a joint mission between ESA and Japan's Aerospace Exploration Agency. The joint mission consists of the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO) and will investigate the magnetic field, the magnetosphere and the internal structure of Mercury. BepiColombo is scheduled to launch in October of this year and arrive at Mercury by December 5, 2025. It takes years to reach Mercury, as spacecraft trying to reach their orbit must approach the planet at very high speeds without missing the target and being caught by the sun.


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