Seminar: Origin of Mercury's exosphere: from Mariner 10 to BepiColombo
The solar system’s innermost planet Mercury has very special physical and chemical characteristics, which go back to its origin. Besides the planet`s high average density, which was known since the Mariner 10 flybys in 1974–1975, the MESSENGER spacecraft 2008–2015 discovered that Mercury’s surface is volatile-rich and has a very high K/Th ratio and a surface abundance of potassium which is above Earth’s value but below chondrites. Moderately volatile lithophile elements like Si, Ca, Al, and Mg are chondritic. Additionally, to these surprising discoveries, substantial H2O-ice deposits were detected within the permanently shadowed craters at the polar areas. Different formation theories will be discussed and from the MESSENGER findings, the most likely ones addressed. Compared to Venus, Earth or Mars, Mercury has not been able to retain its atmosphere and only a thin collision less exosphere surrounds the planet. This thin gaseous envelope consists of silicates that are released from the surface by various processes that will be identified and discussed. Like Earth’s Moon, Mercury’s surface can be directly exposed to solar radiation, the solar wind and the ambient plasma (ions and electrons), as well as to meteoroid fluxes. Direct exposure to these exogenic sources has important consequences for the formation and evolution of planetary surfaces, including altering their chemical makeup and optical properties and generating a neutral gas exosphere. After a brief discussion on the surface release processes and reactions review of species so far discovered from Earth and previous spacecraft the expected measurements of exospheric neutrals and ion densities with instruments on board of ESA’s BepiColombo spacecraft will be discussed.
recording: www.youtube.com/watch