Space weathering on inner planetary surface analogues induced by swift multicharged heavy ion bombardment

Silicates are ubiquitous in space. They dominate the surfaces of the inner rocky planets (Mercury in the case of the Solar System), the Moon, and asteroids, forming the major part of the non-volatile material. The physical and chemical properties of the rocky surfaces are determined not only by their initial composition but also by the processes occurring on them. Here we discuss one of these processes; irradiation by energetic cosmic particles that induces many effects among which structural changes and sputtering, the latter contributing to the formation of exospheres. In the current work we report the results of experiments conducted on anorthite, jadeite and nepheline silicates that have been irradiated with energetic heavy ions with the aim to better understand the interaction of galactic cosmic rays, solar wind, and solar energetic particles with planetary and small body surfaces. The sputtering effects induced by energetic (MeV/u) multicharged heavy ions (e.g., Rh-105 and Ba-140) were analyzed by the PDMS-TOF-SIMS technique (plasma desorption mass spectrometry - time-of-flight secondary ion mass spectrometry). Positive and negative secondary ionic species are identified: Na+, K+, Al+, Ca+, SiO2-. Ejection of (SiO2)(n)(-) and (AlSi)O-m(-) cluster series are also observed. Less frequent, negative ion yields are one order of magnitude less than positive ones, or greater, which is the case for nepheline, with 0.671 ions impact 1 for positive and 0.126 ions impact(-1) for negative ions. The results concerning ejection of ionic species show, for instance, that the Na+/K+ ratio is similar to 2.5, which is in very good agreement with that observed in the Hermean exosphere found to be similar to 2.3.

Automated summary

Silicates are widely present in space and play a significant role in the surfaces of planets and small bodies. Irradiation by energetic cosmic particles induces structural changes and sputtering effects, affecting the physical and chemical properties of planetary surfaces. Experimental studies on irradiated silicates provide insights into the interaction between galactic cosmic rays, solar wind, solar energetic particles, and planetary surfaces.