The dust fountains of the moon

Throughout history there have been people who have reported seeing flashes of light on the surface of the moon. Reports were of large balls of light, colored sparks, or a local glow that appeared for a few seconds and then disappeared.

As the landing of an unmanned vehicle on the moon became a more frequent affair, the scientific interests increasingly outweighed the political ones. There were still victory symbols and signals, but the cameras had improved, communication with the spacecraft had improved, and science had taken the front seat on every mission. One of the interesting discoveries was made by the American Survivor 7 spacecraft. When Sorbior's cameras were aimed at the horizon and photographed the setting sun, they caught a strange and unexpected glow: rays of light that still shone even after the sun had already disappeared over the mountains.

Throughout history there have been people who have reported seeing flashes of light on the surface of the moon. Reports were of large balls of light, colored sparks, or a local glow that appeared for a few seconds and then disappeared. Astronomers tended to dismiss these reports. Some have suggested that meteorite impacts are a possible cause of these flashes of light, but the frequency of reports has not matched the estimated frequency of meteorite impacts on the Moon. Even when William Herschel, one of the leading astronomers of the 18th century, said that he saw three points of light in a dark area of ​​the moon, the other scientists still refused to believe that there was a real phenomenon here.
The turning point came in 1963. Two cartographers, James Greenacre and Edward Baer, ​​reported seeing bright red dots on the moon. Both of these explorers had a reputation as extremely precise scientists, people who were meticulous about the point of iodine in every measurement, as thorough mapping work requires. This report could no longer be easily ignored. The phenomenon of lights on the moon began to receive a lot of attention in the scientific community. Survivor 7's discovery that the mysterious glow is related to the setting sun on the lunar horizon provided the critical clue to solving the puzzle: dust.

The lunar dust, like that on Earth, is able to accumulate a large amount of static electric charge. On the surface it is exposed to a constant bombardment of particles from space. On the side facing the sun, high-energy photons hit the atoms and eject electrons from them. The electrons have a negative electric charge and without them the dust grains become more positive. Two grains with the same electrical charge repel each other, so some of the dust begins to float on the surface. The resulting result is a kind of dust fountain: charged particles float high, hundreds of meters and maybe even kilometers above the ground, then fall back down, are repelled again, fly up and come back again. The lunar dust jets prove that the moon is not a static and unchanging environment as it was initially thought.

This phenomenon also occurs on the dark side of the moon, but there the external factor is not photons but negative ions that the Earth's magnetic field throws towards the moon. The ions charge the dust grains with a negative and not a positive electric charge - but the principle is the same: the dust grains repel each other, float and rise like sandblasters. And what happens on the line between day and night? On the day side the grains are positively charged. On the night side - negative charge. The moon becomes a kind of huge battery - all that is missing is just a plus and minus marking. The grains on both sides are attracted to each other and a horizontal convection of dust is created between the day and night zones, as if an imperceptible wind carries them above the surface. We cannot see the dust flux because the grains are very small, but when the sun's rays pass through this flux - they break and create a sudden and surprising glow, which the Apollo astronauts also saw with their own eyes later.

Even on Earth we know fine sand and tiny dust grains - but on the moon, these small grains become one of the most significant threats to astronauts and their equipment. The water and winds on the earth wear away the small grains, sanding and rounding them. This erosion does not exist on the moon, therefore the dust grains on the surface of the moon are dense with sharp corners. This spiky structure allows the moon dust to stick to almost any surface. It sticks to bearings, lenses and measuring devices and wears them out. It covers solar panels and prevents them from turning sunlight into electricity, and even prevents astronauts from holding their tools.

The lunar dust is very thick and is everywhere. Some of the Apollo spacecraft had to land 'blind' because their jets kicked up so much dust that visibility outside the spacecraft dropped to zero a few tens of meters above the surface. When the astronauts returned after a wander outside, the spaceship was full of dust. When they took off back to Earth and air filled the spaceship, some of the grains were released and floated in the cabin - this was a real nuisance and maybe even a serious health problem in the long run.

Soviet engineers also experienced the danger of dust. In the XNUMXs, when it was clear that the Soviet Union was giving up on manned exploration of the moon, the Russians sent mobile robots as a replacement. The Soviet engineers had to solve for the first time a series of problems that the Americans would encounter only decades later, in the robotic missions to Mars. One of the problems was the long delay in communication between the robot and the control station on Earth: every command sent to the robot reached it only a second and a half later, and another second and a half passed before a response was received. Controlling the robots was a real nightmare for the operators: the front-facing cameras transmitted a single image every few seconds, and even then visibility was highly dependent on the angle of the sun above the horizon and the confusing shadows it cast on the craters.

In 1970, the first robot, Lonkhod 1, managed to travel ten kilometers on the lunar surface. Lonkhod 2 went into operation three years later, and the project managers were very clear about what would be considered an achievement in the mission: more kilometers than Lonkhod 1, of course. They had no intention of jeopardizing the safety of the ride in order to approach rocks or craters, so the scientists were not even allowed to enter the robot's control room. Lonkhod 2 did manage to travel 37 kilometers before it was struck by bad luck: one of the operators got confused, and the robot went into a deep crater. In an attempt to get out of the crater, the side of the vehicle rubbed the walls of the crater. On the control panel, the operators saw a sharp drop in the power of the electric current received from the solar panels, and immediately understood what had happened: dust from the crater walls fell on the solar panels and covered them. The engineers also knew that the real problem was much more serious.

During the lunar night, the solar panels were closed and folded into the robot to reduce exposure to the low temperatures. The dust that was sitting on the boards penetrated into the guts of the robot and settled on the radiator, cooling in Hebrew - the part that is supposed to cool the robot during the lunar day, when the sun hits it mercilessly. The moon dust is an excellent heat insulator: it covered the radiator like a blanket and prevented it from cooling the systems. Indeed, when the sun returned to the sky, the temperatures inside the robot began to climb and climb. Everyone understood that Lankhod 2 was a 'dead walking robot' and that it was only a matter of time before its delicate electronics would overheat and burn. The scientists tried to urge the managers to let the robot enter a crater that looked geologically interesting. 'If we are to die,' they said, 'at least we shall die the death of heroes.' But the managers refused and squeezed out of Lonkhod 2 a few more meters of travel before Shab Chaim. The robot is still standing in the same place where its wheels stopped, but if you see it - don't touch it, it's not yours. An American businessman bought it about fifteen years ago at an auction for several tens of thousands of dollars.