It holds court quietly in the night. Our nearest astronomical neighbour – the Moon – has long been the subject of fiction, fantasy and serious studies. It balances our rotation, affects our tides and even plays a role in both human and animal behavior. The Moon shines not with its own light, but the reflected light of the Sun. Now a combination of spacecraft and computer simulations shows it reflects a lot more than just light… the Moon is crackling with electricity which affects the solar winds!
Unlike an Earthly-wind, solar winds are a flow of electrically charged gases called plasma. Moving at speeds of near a million miles per hour, these plasma “winds” are continually being generated by our Sun. When a more disturbed, heavy or fast stream encounters Earth’s magnetic field, it can cause magnetic and radiation “storms” known to disrupt satellites, power grids and electronic communications. However, Earth is protected by its own magnetic shield which surrounds it. This deflects the solar winds and creates a bow shock that stretches tens of thousands of miles across the day side of Earth. When solar winds crash into it, they are slowed from supersonic to subsonic speed.
Our Moon isn’t so lucky. It doesn’t have a global magnetic field to shield it. “It was thought that the solar wind crashes into the lunar surface without any warning or ‘push back’ on the solar wind,” says Dr. Andrew Poppe of the University of California, Berkeley. Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the Moon’s presence “upstream” in the solar wind. “We’ve seen electron beams and ion fountains over the Moon’s day side,” says Dr. Jasper Halekas, also of the University of California, Berkeley.
According to the news release, these phenomena have been seen as far as 10,000 kilometers (6,200 miles) above the Moon. Their presence causes turbulence in the solar wind ahead of the Moon, resulting in quiet 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. “With ARTEMIS, we can see the plasma ring and wiggle a bit, surprisingly far away from the Moon,” says Halekas. ARTEMIS stands for “Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun”.
“An upstream turbulent region called the ‘foreshock’ has long been known to exist ahead of the Earth’s bow shock, but the discovery of a similar turbulent layer at the Moon is a surprise,” said Dr. William Farrell of NASA’s Goddard Space Flight Center in Greenbelt, Md. Farrell is lead of the NASA Lunar Science Institute’s Dynamic Response of the Environment At the Moon (DREAM) lunar science center, which contributed to the research.
Just what could cause this disturbance in the force? According to computer simulations, a complex electric field is caused by both the sunlight and solar wind. This near-the-surface lunar feature can erupt in electron beams by speeding up electrons zapped away from the Moon’ surface from the Sun’s ultraviolet radiation. What’s more, similiar computer generations show that ions in the solar wind can also impact ancient magnetic fields located in isolated regions of the lunar surface. When this occurs, the ions are reflected back into space – creating a fountain effect. This ionic display is positively charged hydrogen atoms – the “most common element in solar wind.”
“It’s remarkable that electric and magnetic fields within just a few meters (yards) of the lunar surface can cause the turbulence we see thousands of kilometers away,” says Poppe. When exposed to solar winds, other moons and asteroids in the solar system should have this turbulent layer over their day sides as well, according to the team.
“Discovering more about this layer will enhance our understanding of the Moon and potentially other bodies because it allows information about conditions very near the surface to propagate to great distances, so a spacecraft will gain the ability to virtually explore close to these objects when it’s actually far away,” said Halekas.
Original Story Source: NASA Solar System News Release.