Why is Mercury a planet

Mercury: a planet full of puzzles

Agency

Mercury is the least explored inner planet in our solar system. Because of its proximity to the sun, it is difficult to observe from a distance. And it is difficult for space probes to reach. Internationally, BepiColombo is regarded as one of the most difficult and costly missions in the exploration of the planetary system.

It is not without reason that the ESA mission bears the nickname of the Italian mathematician and aerospace engineer Giuseppe "Bepi" Colombo, who died in 1984. Most of what we know about the planet Mercury comes from three flyby of NASA's Mariner 10 probe in 1974/75, whose complex trajectory is based on Colombo's calculations. He also found out how Mercury's unusual period of rotation works: the planet rotates three times around its axis in two orbits of the sun.

Iron planet

So far, the planet closest to the Sun, of which not even half of its surface has been photographed, has posed many puzzles to scientists. Outwardly, it resembles our Earth's moon with its crater-riddled surface. Its interior seems to correspond more to that of the geologically dynamic earth. Mercury does not have an atmosphere comparable to that of Earth. Its “atmosphere” - hydrogen, helium, oxygen, sodium, potassium - is as thin as that of the Earth's moon.

Mercury is believed to have a huge iron core, estimated at 3,600 kilometers in diameter. Measured against its planetary diameter of 4880 kilometers, the iron core would take up three quarters. Like the earth, it has a magnetic field. But it is completely unclear whether this magnetic field is generated by dynamo-like processes in the planet's core - which would require an at least partially liquid core - or is caused by magnetized, ferrous rocks on the surface of Mercury.

No signs of active volcanism

The large number of craters per area - a measure of the age of the crust - suggests a very old surface, around 4 to 4.5 billion years old. The images show no signs of active volcanism, plate tectonics or other endogenous processes.

But there are also no traces of erosion that indicate the prolonged exposure to wind or water. Water ice, on the other hand, could exist in the interior of near-pole craters despite being close to the sun. Where there is eternal night with temperatures around minus 200 degrees Celsius, the water from the time the planet was formed could have been preserved.

To the origin of the earth

During his lifetime, Giuseppe Colombo could not answer the question of how the smallest planet in our solar system was formed and what it looks like inside.

BepiColombo should now clarify these and other questions:

  • What do the previously unknown parts of Mercury look like?
  • Why is the planet so dense?
  • Why does such a small planet have a magnetic field while Venus, Mars and the Moon have none?
  • How is this magnetic field generated?
  • Is Mercury Still Active?
  • Does it have a solid or a liquid core?
  • Are there really ice deposits in the polar regions?
  • Do northern lights occur - as they do on Earth?
  • Is the planet shielded by radiation belts?
  • What effects does the sun's radiation and particle bombardment have on the surface and the hardly measurable atmosphere of the planet?
  • Last but not least, BepiColombo should also check Einstein's theory of relativity using Mercury's orbit.

The target object, Mercury, is considered to be the key to the history of our solar system. Scientists therefore hope that the complex exploration of the innermost planet will also provide new insights into the genesis of our own blue planet. Perhaps BepiColombo will bring us up to the early planetary history of the earth?

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