The planets and moons of our solar system are constantly being shelled by particles hurdled away from the sun. On Earth, this has barely any impact, aside from the intriguing northern lights, in light of the fact that the dense climate and the magnetic field of the Earth shield us from these solar wind particles. Be that as it may, on the Moon or on Mercury things are extraordinary: There, the highest layer of rock is progressively dissolved by the effect of solar particles.
According to a new study by the TU Wien, the effects of solar wind bombardment are in some cases much more drastic than previously thought.
Prof. Friedrich Aumayr from the Institute of Applied Physics at TU Wien said, “The solar wind consists of charged particles – mainly hydrogen and helium ions, but heavier atoms up to iron also play a role. These particles hit the surface rocks at a speed of 400 to 800 km per second and the impact can eject numerous other atoms. These particles can rise high before they fall back to the surface, creating an “exosphere” around the Moon or Mercury – an extremely thin atmosphere of atoms sputtered from the surface rocks by solar wind bombardment.”
Because of the composition of the exosphere that allows deduction of the chemical composition of the rock surface, scientists more likely to take part in studying it. Additionally, in October 2018, ESA will send the BepiColombo probe to Mercury, which is to get data about the land and concoction properties of Mercury from the structure of the exosphere.
In order to obtain precise information of the effects of the solar wind on the rock surfaces, scientists investigated the effect of ion bombardment on wollastonite, a typical moon rock.
Paul Szabo, PhD student in Friedrich Aumayr’s team said, “Up to now it was assumed that the kinetic energy of the fast particles is primarily responsible for atomization of the rock surface. But this is only half the truth: we were able to show that the high electrical charge of the particles plays a decisive role. It is the reason that the particles on the surface can do much more damage than previously thought.”
“When the particles of the solar wind are multiply charged, i.e. when they lack several electrons, they carry a large amount of energy which is released in a flash on impact. If this is not taken into account, the effects of the solar wind on various rocks are misjudged. Therefore, it is not possible to draw exact conclusions about the surface rocks with an incorrect model from the composition of the exosphere.”
Protons make up by far the largest part of the solar wind, and so it was previously thought that they had the strongest influence on the rock. But as it turns out, helium actually plays the main role because, unlike protons, it can be charged twice as positively. And the contribution of heavier ions with an even greater electrical charge must not be neglected either.
For this study, high-precision measurements were carried out with a specifically developed microbalance at the Institute of Applied Physics. At the Vienna Scientific Cluster VSC-3 complex computer simulations with codes developed for nuclear fusion research were carried out in order to be able to interpret the results correctly. The Analytical Instrumentation Center and the Institute for Chemical Technologies and Analytics of the TU Vienna also made important contributions.
The results have now been published in the planetology journal “Icarus“.