Chandrayaan 2 observes solar outbursts inflating lunar exosphere
Scientists had long suspected that solar storms caused the tenuous exosphere of the Moon to inflate. The Chandrayaan 2 orbiter has directly observed the process for the first time.
Between 8 and 15 May 2024, the Sun erupted in a number of Coronal Mass Ejections (CMEs), clouds of charged plasma that were hurled outwards into the Solar System. These CMEs merged in interplanetary space, resulting in the strongest geomagnetic storm at the Earth recorded in two decades. The Chandra's Atmospheric Composition Explorer 2 instrument on board the Chandrayaan 2 orbiter observed for the first time the effect of CMEs on the lunar atmosphere, that is so tenuous and wispy that it is called an exosphere. The instrument registered an increase in particle density by an order of magnitude, which is in line with theoretical predictions of how space weather affects the Moon.
The lunar atmosphere is so thin that the gas atoms and molecules that make it up rarely interact with each other. The lunar exosphere is a surface-boundary exosphere, because the density of particles is low even at the surface. A number of processes produce the exosphere of the Moon, including interaction with the harsh solar radiation, meteorite impacts, solar wind and solar storms. All of these processes cause outgassing from the lunar surface, with the molecules and atoms becoming part of the lunar exosphere. The lunar exosphere is sensitive to even small variations in any of these factors, including CMEs from the Sun that bombard the surface with energetic particles.
Research informs future crewed missions
The outer core of the Earth, made up of a liquid ocean of iron and nickel produces a geomagnetic field that traps most of the energetic particles, preventing harmful radiation from the Sun or cosmic sources from reaching the surface. The Moon is devoid any such protection, and is directly exposed to solar fury. The May 2024 solar storms provided scientists with a valuable opportunity for studying the impact of severe space weather on the lunar exosphere. The research provides valuable insights for the design of future crewed missions to the lunar surface, as well as the level of protection necessary to shield spacefarers from extreme weather events, when it comes to the design of lunar habitats for a sustained human presence on the surface of the Moon. A paper describing the research has been published in Geophysical Research Letters.