MAVEN Observations of Periodic Low-altitude Plasma Clouds at Mars

Ion escape to space through the interaction of solar wind and Mars is an important factor influencing the evolution of the Martian atmosphere. The plasma clouds (explosive bulk plasma escape), considered an important ion escaping channel, have been recently identified by spacecraft observations. However, our knowledge about Martian plasma clouds is lacking. Based on the observations of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we study a sequence of periodic plasma clouds that occurred at low altitudes (similar to 600 km) on Mars. We find that the heavy ions in these clouds are energy-dispersed and have the same velocity, regardless of species. By tracing such energy-dispersed ions, we find the source of these clouds is located in a low-altitude ionosphere (similar to 120 km). The average tailward moving flux of ionospheric plasma carried by clouds is on the order of 10(7) cm(-2) s(-1), which is one order higher than the average escaping flux for the magnetotail, suggesting explosive ion escape via clouds. Based on the characteristics of clouds, we suggest, similar to the outflow of Earth's cusp, these clouds might be the product of heating due to solar wind precipitation along the open field lines, which were generated by magnetic reconnection between the interplanetary magnetic field and crustal fields that occurred above the source.

Automated summary

This study investigates periodic plasma clouds at low altitudes on Mars using observations from the MAVEN spacecraft. The heavy ions in these clouds are energy-dispersed and have the same velocity, originating from a low-altitude ionosphere. The characteristics of these clouds suggest they may be the result of heating due to solar wind precipitation along open field lines.