(ORDO NEWS) — Mercury has a tail, almost like an old large comet, whose tail flies millions of kilometers from the planet and glows with a faint orange-yellow light.
All thanks to the position of the planet: Mercury is the innermost planet in our solar system. At such a distance, the small, dense, rocky world is constantly bathed in solar radiation and exposed to the blows of the solar wind.
Since Mercury has a low mass – about 5.5% of the mass of the Earth – it is not particularly strong in terms of gravity. And its magnetic field is not particularly strong: only 1 percent of the earth’s.
Consequently, the planet does not have what we could reasonably call the atmosphere. Rather, it has a thin exosphere made up mostly of oxygen, sodium, hydrogen, helium, and potassium atoms that are lifted up by the solar wind and the bombardment of micrometeoroids. This exosphere is gravitationally tied to the planet, but too diffuse to behave like gas.
All this suggests that the surface of Mercury is poorly protected from solar radiation and solar wind.
We know that solar radiation exerts pressure. We even used this pressure to propel a spaceship equipped with a sail, like the wind moves ships on water. This radiation pressure is what gives comets their tails.
Here's Mercury and its sodium tail on June 4 through a 60 mm refractor and a 589.3/1.0 nm bandpass filter. The trailed star to the lower left is HIP 31650. pic.twitter.com/jlbKu5B3Oo
— Qiсһеng Ζһаng (@aciqra) June 14, 2020
As the comet approaches the Sun, the ice inside them begins to sublimate, raising dust, leaving the comet’s body. The pressure of solar radiation pushes this dust into a long tail, while gas is formed by magnetic fields embedded in the solar wind; That is why comet tails always rush away from the Sun – the tail does not generate movement, but their proximity to the star.
Mercury has ice, but its tail is not made of it. The main ingredient is sodium atoms; they glow when ionized by ultraviolet radiation from the Sun in a process similar to what drives the auroras on Earth.
Nov 10, 2020:
That’s not a comet but the tail of our inner planet Mercury ”seen“ from my backyard. This stacked image was exposed through a custom-made Sodium filter. The horizon is from the first exposure.#mercury #spica #yellow #sodium #sodiumtail #spica #astronomy #science pic.twitter.com/vjpK3RAkeA
— Dr. Sebastian Voltmer (@SeVoSpace) November 15, 2020
As a result, the planet looks like a comet with a tail, which, according to observations, moves at a distance of almost 3.5 million kilometers from the planet.
Sometimes, when the solar wind is blowing in the right direction, Venus has a tail-shaped structure of ionized oxygen. And the Earth’s Moon, naked and unprotected from the solar wind, also has a sodium tail, although it is not as large and lush as that of Mercury.
— APOD Bot (@APOD_Bot) July 8, 2020
But Mercury’s tail is special for a different reason. By studying it at different times in the planet’s orbit, we can learn about seasonal variations in the exosphere of Mercury and how events such as solar flares and coronal mass ejections affect the small planet.
This is a great example of how planets can be very different from each other – every planet in the solar system, even Uranus and Neptune, has its own characteristics. Each is a rare and precious person; learning how and why is a step towards understanding planets and planetary systems in the grand universe.
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