Though strange-sounding, the strategy would make use of a real-world phenomenon known as the Yarkovsky effect, named for the Russian engineer who discovered it in 1902. The effect results from the fact that asteroids heat up as they bask in the sun’s light.
“The coat of paint would be a very thin, almost like a Saran Wrap layer,” said aerospace engineer David Hyland of Texas A&M, who leads a team that has been studying this method for several years. “If we push it in the right direction, we can get the asteroid to cease crossing Earth’s orbit and completely eliminate the threat.”
Asteroids make fairly frequent flybys of our planet, with one of the latest Earth-grazers being 2012 DA14, which on Feb. 15 will pass closer to our world than some satellites orbit. Though small objects enter the atmosphere all the time, the odds of a large asteroid hitting the planet are thankfully small. There was some concern that 325-meter-long asteroid Apophis could impact in 2036 but recent observations have put the probability of this potentially catastrophic event at less than one in 10 million.
Still, the thought of an ecosystem-annihilating rock from space, like the one that killed the dinosaurs 66 million years ago, is unnerving. Scientists have long thought about ways to mitigate the hazard of a civilization-destroying asteroid and developed many different techniques to deflect any killer rocks, including shooting it with lasers, ramming it with a spacecraft, or blowing up a nuclear bomb on its surface. Now a team of researchers wants to launch a mission to test the effects of painting an asteroid in order to repel it.
The Yarkovsky effect works by changing the amount of light an asteroid gives off. As an asteroid rotates, the surface that has been heated by the sun moves away to face space and radiates infrared photons. Though massless, these photons carry away small bits of momentum from the asteroid, essentially generating a tiny rocket thrust in one direction. The effect is very slight but over time can noticeably change an asteroid’s orbit. By making an asteroid lighter or darker, and therefore changing the amount of radiation it absorbs, we could turn up or down this miniscule rocket thrust. It’s a long haul-technique, requiring years, decades, or even centuries of advanced notice to alter an asteroid’s trajectory.
Researchers have considered using the Yarkovsky effect to drive off dangerous asteroids for several decades, though Hyland and his collaborator’s proposal is among the most detailed investigations. Last year, a graduate student at MIT suggested using paintballs to deflect an asteroid but Hyland said that ordinary water- or oil-based paints wouldn’t work in space. When exposed to a vacuum, these substances would vaporize, “basically exploding,” he said. Paintballs would have to be tough enough to not explosively decompress yet weak enough to splatter on the asteroid’s surface instead of merely leaving hundreds of tiny craters.
Instead, Hyland suggested using a dry powder with an electrical charge. The solar wind – a river of charged particles constantly flowing out from the sun – bathes everything in the solar system and should give an asteroid a small positive charge. A satellite could come up to the asteroid and shoot paint through a tribocharging gun. No, that’s not some misspelling of turbocharging but rather what happens when you force particles through a narrow tube where they rub against the walls and pick up extra electrons, becoming negatively charged. Once bathed in ultraviolet light from the sun, the paint particles would melt together to cover the asteroid with a new color. Hyland and his collaborators are hoping to get funding for a mission that could launch in 2021 to rendezvous with the formerly worrisome asteroid Apophis to test their spray-paint method. The researchers have collaborated with NASA and the King Abdulaziz City for Science and Technology(KACST), which runs Saudi Arabia’s space research institute, to design a satellite. Hyland is currently working to secure a launch date for their first hardware tests either on the International Space Station or in low-Earth orbit in late 2014 or 2015.
The proposal is interesting and worth investigating but “it needs a demonstration to show that it actually works,” said geologist Jay Melosh of Purdue University.
Melosh noted that while asteroid surfaces should be positively charged in principle, scientists don’t actually know the electric field in the vicinity of such objects because no asteroid-encountering spacecraft has ever carried instruments to study this. Researchers would also need to gather detailed information about the axis on which an asteroid spins before attempting to move one with paint.
Melosh is a co-author on a 2010 study called “Defending Planet Earth” that looked at different asteroid deflection techniques. Because it could only be used on fairly small asteroids whose potential for destruction is known well ahead of time, the report ranked slow-push methods, like using the Yarkovsky force, below other techniques like exploding a nuclear warhead on an asteroid or ramming it with a giant impactor.
The spray-painting method doesn’t allow for detailed fine-tuning and would probably only work with a few specific asteroids, such as Apophis, said former astronaut Rusty Schweickart, co-founder of the B612 Foundation, which aims to protect Earth against deadly impacts. “The problem is that Apophis is not that typical and what you’ll need for most deflections is a precise orbital change,” he said. A gravity tractor that pulls an asteroid into a specific orbit would be more useful for the majority of cases.
Hyland understands the limitations of his proposed method. “This is not going to be the sole method of asteroid deflection,” he said. “And I think we need as many tools in our tool box as we can get.”
One advantage of the method is the risk of screwing things up catastrophically is relatively low. Because it works so slowly, it would give scientists plenty of time to rejigger their calculations and try again. Unlike the nuclear or ramming options, moving an asteroid snail’s pace also means that it can’t fall into the wrong hands and be used as a weapon of mass destruction – you’ve got ample time to deflect a bullet that takes years to hit you.
Instead of work on something that could be weaponized, Hyland said “it’s nice to collaborate on a project that, who knows, might one day save the Earth.”
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