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Chemical Processes of Moon and Mercury Exospheres Simulated with Supercomputer in Tomsk
January 23, 2018 09:56


Scientist Rashid Valiev

Associate Professor of the Physics Department of the Tomsk State University, Rashid Valiev together with his colleagues from the Moscow State University and the TPU have simulated the chemical processes that take place in the surrounding space (exospheres) of the Moon and Mercury, the press service of the TSU reports. The research results are published in the journal Planetary and Space Science.
Scientists have proved that the presence of certain metal types in planetary exospheres is caused by meteorite bombardment.
At present, in the exospheres of the Moon and Mercury, atoms of alkaline and alkaline-earth metals are found: Li, Na, K, Mg and Ca. They were found with the help of spectroscopic instruments on satellites, as well as by means of telescopes on the Earth. There may be several reasons for the appearance of these metals in the exospheres, but the most probable is the meteorite bombardment. This version is also supported by the fact that during meteoritic showers the concentration of metals increases.
The study of the exosphere of the planets and celestial bodies of the solar system is one of the most important tasks of modern astrochemistry. In particular, it is for this purpose that the European and Japanese scientists plan to send the BepiColombo Satellite to study the exosphere of Mercury in 2018.

 "The fact is that when approaching the surface of celestial bodies, meteoroids develop a speed equal to several dozen km per second, and, therefore, have an immense kinetic energy, which, is released as heat when they are falling”, - Rashid Valiev explains. - After certain thermochemical reactions, oxides and hydroxides of these metals are generated and fly out at high speed. Under the influence of solar radiation, such molecules can disintegrate into separate components – thus the metal atoms appear in the exospheres of the celestial bodies of the Solar system”.

To test the hypothesis, scientists had to establish the time of photolysis - the collapse of a molecule into atoms under the influence of solar radiation. If the molecules fall apart quickly and do not have time to leave the exosphere, the hypothesis is correct. It is extremely difficult to study the photolysis processes under cosmic conditions or conduct such experiments experimentally. However, they can be simulated on supercomputers.
"We have created a physical model and deducted working formulas. Afterwards we coded a calculative software program. The main calculations were carried out using quantum chemistry methods on the supercomputer of the Tomsk State University”, - the scientist says.
Our results have confirmed that the source of atoms in the exospheres of the Moon, Mercury and, possibly, other celestial bodies of the Solar System is indeed photolysis with solar photons of the LiO, NaO, KO and MgO molecules”.
Later, Rashid Valiev and his colleagues plan to consider a whole series of molecules, including triatomic molecules, to finally confirm all the conclusions of this hypothesis. Now the team is presenting its results at scientific conferences.

Abstract from Photolysis of metal oxides as a source of atoms in planetary exospheres:
“The cross sections of photolysis of LiO, NaO, KO, MgO, and CaO molecules have been calculated by the use of quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides have the order of 10−17 cm2, and for alkaline earth metal monoxides these values are less on 1–2 orders of the magnitude. The lifetimes of photolysis at 1 astronomical unit are estimated as 5, 3, 60, 70, and 3,000 s for LiO, NaO, KO, MgO, and CaO, respectively. Typical kinetic energies of main peaks of photolysis-generated metal atoms are determined. Impact-produced LiO, NaO, KO, and MgO molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight while CaO molecule is more stable against destruction by photolysis. Photolysis-generated metal atoms in planetary exospheres can be detected by performing high-resolution spectral observations of velocity distribution of exospheric metal atoms”.




Author: Vera Ivanova

Tags: Russian scientists     

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