Electric sparks may have altered properties of lunar soil

Scientists have found that high-energy particles from uncommon, large solar storms penetrate the Moon's frigid, polar regions and electrically charge the soil, a finding that may change our understanding of the evolution of planetary surfaces in the solar system.

Researchers from the University of New Hampshire and NASA found that over the eons, periodic storms of solar energetic particles may have significantly altered the properties of the soil in the Moon's coldest craters through the process of sparking.

The study, published in the Journal of Geophysical Research-Planets, proposed that the sparking process has possibly changed the very nature of the Moon's polar soil, suggesting that permanently shadowed regions, which hold clues to our solar system's past, may be more active than previously thought.

"Decoding the history recorded within these cold, dark craters requires understanding what processes affect their soil," said Andrew Jordan of the UNH Institute for the Study of Earth, Oceans, and Space, lead author of the paper.

"To that end, we built a computer model to estimate how high-energy particles detected by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument on board NASA's Lunar Reconnaissance Orbiter (LRO) can create significant electric fields in the top layer of lunar soil," Jordan said.

The scientists also used data from the Electron, Proton, and Alpha Monitor (EPAM) on the Advanced Composition Explorer (ACE).

CRaTER, which is led by scientists from UNH, and EPAM both detect high-energy particles, including solar energetic particles (SEPs). SEPs, after being created by solar storms, stream through space and bombard the Moon.

These particles can build up electric charges faster than the soil can dissipate them and may cause sparking, particularly in the polar cold of permanently shadowed regions - unique lunar sites as cold as minus 240 degrees Celsius and known to contain water ice.

"Sparking is a process in which electrons, released from the soil grains by strong electric fields, race through the material so quickly that they vaporise little channels," Jordan said.

Repeated sparking with each large solar storm could gradually grow these channels large enough to fragment the grains, disintegrating the soil into smaller particles of distinct minerals, Jordan and colleagues hypothesise.