shackleton crater
August 24, 2014

Lunar Soil Evolution Changed By Solar Storm Sparking

Eric Hopton for - Your Universe Online

They are the darkest and coldest places on the surface of the moon, but deep in the craters of the polar regions, electrical activity may be creating a kind of “sparking” that has driven changes in lunar soil evolution. New information about these areas could lead to greater understanding of planetary surfaces in the solar system.

To the scientists studying data from the Lunar Reconnaissance Orbiter (LRO), the moon is a giant laboratory. In June 2009, NASA launched an Atlas V rocket from Launch Complex 41 at Cape Canaveral. On board was the LRO, equipped with a range of 7 instruments designed to capture data from the moon environment. One of these was the CRaTER – the Cosmic Ray Telescope for the Effects of Radiation. CRaTER’s main purpose was to study the lunar radiation environment and its biological impacts.

After a four and a half day journey, LRO entered into orbit around the moon and began its long period of exploration. LRO has been a rich source of data for scientists back on Earth. Researchers at the University of New Hampshire (UNH), supported by NASA’s Solar System Exploration Research Virtual Institute (SSERVI), were particularly interested in the stream of information from CRaTER which detects high-energy particles including SEPs (solar energetic particles).

SEPs are born in solar storms and then “stream through space and bombard the moon.” When CRaTER detected SEP activity, the UNH team began to wonder what effect they may have on the ground. They hypothesized that when the SEP stream hits the soil in the frozen craters of the lunar poles, some of which have areas of permanent shadow where temperatures can be as low as minus 400 degrees Fahrenheit, electric charges can “build up faster than the soil can dissipate them.” This could, say the UNH team, lead to sparking.

The next step was to build a computer model of this process. In addition to data from CRaTER, they fed in information from the Electron, Proton, and Alpha Monitor (EPAM) on the Advanced Composition Explorer (ACE). Running the program confirmed their hypothesis was feasible and 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.” The results have been published in the Journal of Geophysical Research-Planets.

Sparking, also known as “electrostatic breakdown,” could result in a process of “breakdown weathering” in which soil grains are gradually fragmented. As electric charges accumulate in the soil they are suddenly released as sparks and vaporize tiny channels. Large solar storms may lead to repeated sparking which in turn could lead to bigger and bigger channels. The process might theoretically fragment the soil particles so much that they are effectively broken up into their distinct constituent minerals.

The researchers now hope for confirmation of their computer modeling by looking for actual evidence of lunar soil sparking from some of the other instruments on the LRO. As Timothy Stubbs, co-author of the report puts it, “If breakdown weathering occurs on the moon, then it has important implications for our understanding of the evolution of planetary surfaces in the solar system.”

Image 2 (below): This illustration shows a permanently shadowed region of the moon undergoing subsurface sparking (the "lightning bolts"), which ejects vaporized material (the "clouds") from the surface. Subsurface sparking occurs at a depth of about one millimeter. Image not to scale. Credit: Andrew Jordan/UNH


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