A new study has determined that solar particles “rejected” by the lunar surface are helping astronomers better understand how the sun affects the moon.

The moon has virtually no atmosphere, so its surface is constantly being bombarded by solar wind, the charged particles flowing outward in all directions from the sun. Some researchers think the solar wind could be what creates water on the moon.

“Conceptually, protons which come from the solar wind get absorbed by the surface (of the moon), and they may interact with oxygen, which is in minerals there to produce water and hydroxyl,” said Mr. Stas Barabash, of the Swedish Institute of Space Physics in Kiruna. “Much more research is needed to prove or disprove this idea,” he added. But, according to a report in the National Geographic News, data from India’s Chandrayaan-1 moon probe show that one out of every five protons that impacts the moon gets bounced straight back into space. Previously, astronomers had thought that virtually all solar particles that reach the moon are absorbed by the lunar soil.

Like taking photographs by capturing light bouncing off an object, Barabash and colleagues hope to make a new class of images by mapping where these rejected protons are bouncing off the moon. “This method provides a way to really see what happens when the solar wind impacts the surface,” Barabash said. When a proton bounces off the moon, it picks up an electron from the lunar surface and becomes a neutral hydrogen atom. “Because they are neutral, they are not affected by any electromagnetic forces and the (moon’s) gravitational force affects them so little that they continue moving straight forward,” Barabash said. Since the atoms are such straight shooters, they should provide a highly accurate picture of which places on the moon are being most affected by solar wind. For example, some pockets of the moon have local magnetic fields that shield them from solar wind. These areas wouldn’t absorb or reflect protons and so would show up in the new maps as dark spots. The method should also apply to other solar system bodies that have thin atmospheres, according to Barabash.