The Positives and Negatives of Trying to Mine on Electrically Charged Asteroids

Pulling off a manned mission to an asteroid is one of the most popular spaceflight goals of the 21st century. But not surprisingly, landing on an errant space rock millions of miles from Earth presents an intimidating array of challenges.

One of the less obvious hurdles that must be cleared, for example, is gaining a better understanding of the electrical environment around asteroids. While the Earth's magnetosphere is able to fend off the harsher effects of the Sun's highly-magnetized wind and radiation, asteroids don't have the luxury of a protective magnetic shell.

Accordingly, when sunlight strikes an asteroid, negatively charged electrons are forced from the surface, resulting in the sunny side of the rock having a positive electric charge. At the same time, the solar wind pummels the asteroid with its own highly-charged stew of ions and electrons. The negatively-charged electrons crowd into the shadowy areas of the asteroid before the more massive positive ions have an opportunity to fill those voids. This results in the dark areas of an asteroid having an overall negative charge.

This complex interplay of negative and positive charges could present many hazards to astronauts, and future missions will require more sophisticated tools to select safe landing sites. Fortunately, researchers funded by the Solar System Exploration Research Virtual Institute (SSERVI) have developed a new computer model capable of mapping the electrical environment with unprecedented precision.

"Our model is the first to provide detailed, two-dimensional views of the complex interaction between solar activity and small objects like asteroids," said project leader Michael Zimmerman of Johns Hopkins University in a NASA statement.

One of the model's biggest innovations is its wandering focus. Classic “grid-type” models divide their attention equally to all geographical regions, whereas Zimmerman's “tree code” model constantly shifts its attention to areas that are experiencing more complex activity.

"Our model can calculate a solar activity-asteroid interaction in a few days," said Zimmerman. "It would probably take a few weeks—or a supercomputer—for a grid-type model to do the same at high resolution."

These simulations may prove invaluable in protecting astronauts from dangerous surface conditions. But could there also be a positive side to the odd electrical properties of asteroids? After all, many companies are gearing up to mine asteroids for raw materials. Could electrical power be harnessed from these objects as well?

“The answer is 'it depends,'” plasma physicist and SSERVI principal investigator William Farrell told me. “As it turns out the voltage differences we are discussing, up to ~1000 volts, are large. However, the overall current flow in the solar wind charge particle flux is relatively small (like a few micro-Amps/square meter).”

“Since power is voltage times current, the power in the environmental solar wind at a few hundred meters scale is relatively small," he said. Indeed, Farrell suggests it might not even be a Watt of power, saying, "you would need a very large collector to really boost up the power.”

So while tapping an asteroid's electricity may be quixotic at this point, the new computer model will be able to do more than isolate hazardous areas. “One of the reasons we're visiting asteroids is because they are relatively pristine remnants from the formation of the solar system, so they give clues as to how the planets formed and life originated," Farrell said in NASA's statement.

“However, spacecraft release gases (like water) that ionize, and these spacecraft-emitted ions likely will contaminate the surfaces of the asteroids we want to study. This new asteroid model will allow us to estimate the degree of ion collection and contamination over various regions," he added.