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The Moon Affects the Solar Wind

June 10, 2012; 6:30 AM ET

With the moon as the most eye-catching body in the nocturnal sky and the primary cause of an unseen pull that creates ocean tides, many primeval cultures thought it could also affect our health or state of mind thus the word "lunacy" has its origin in this belief. Now, an aggregate of spacecraft and computer simulations is introducing the idea that the moon does indeed have a far-reaching, unobservable influence, but not on us, on the sun, or more specifically, the solar wind.

The solar wind is a slender stream of electrically conducting gas called plasma that's constantly blown off the surface of the sun in all directions at around a million miles per hour. When a particularly speedy, compressed or unsettled solar wind collides with the Earth's magnetic field, it can produce magnetic and radiation storms that are capable of interrupting satellites, power grids and communication systems and also cause the light shows that we call the northern and southern lights. The magnetic "bubble" surrounding Earth also pushes back on the solar wind, creating a bow shock tens of thousands of miles across over the day side of Earth, where the solar wind slams into the magnetic field and abruptly slows from supersonic to subsonic speed.

Unlike Earth, the moon is not surrounded by a global magnetic field. Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the moon's presence "upstream" in the solar wind.

According to NASA, "These phenomena have been seen as far as 6,200 miles above the moon and generate a kind of turbulence in the solar wind ahead of the moon, causing subtle changes in the solar wind's direction and density. The electron beams were first seen by NASA's Lunar Prospector mission, while the Japanese Kaguya mission, the Chinese Chang'e mission, and the Indian Chandrayaan mission all saw ion plumes at low altitudes. NASA's ARTEMIS mission has now also seen both the electron beams and the ion plumes, plus newly identified electromagnetic and electrostatic waves in the plasma ahead of the moon, at much greater distances from the moon.

Computer simulations help explain these observations by showing that a complex electric field near the lunar surface is generated by sunlight and the flow of the solar wind. The simulation reveals this electric field can generate electron beams by accelerating electrons blasted from surface material by solar ultraviolet light. Also, related simulations show that when ions in the solar wind collide with ancient, "fossil" magnetic fields in certain areas on the lunar surface, they are reflected back into space in a diffused, fountain-shaped pattern. These ions are mostly the positively charged ions (protons) of hydrogen atoms, the most common element in the solar wind."

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