One Proposal to Relieve a Warming Planet: An Umbrella Made of Asteroid

Take that, space mirrors! Scientists have a new way to shield us from the sun.

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The latest form of solar shield: an asteroid whose dust is stabilized beyond Earth through gravity's pull (Charlotte Lücking, based on images from ESA and NASA)

Average global temperatures will likely rise by 2 to 11.5 degrees by the end of the century, the UN's Intergovernmental Panel on Climate Change has declared. There is, of course, a very straightforward way to prevent this: reduce our carbon emissions. But for a host of reasons -- economic, cultural, political, and generally human -- implementing that solution is pretty much the opposite of straightforward. As the months and years march on, we're faced with the more and more likely proposition that we will be unable to change our ways until it's too late for the change to make a difference.

So scientists have been coming up with ideas that might buy us some time while we get our environmental act together. Some of their proposals are, at this point, basically the stuff of science fiction -- like, for example, the plan to geo-engineer plankton blooms, via marine iron fertilization, to absorb some of the excess carbon dioxide we've emitted into the atmosphere. Or to use pipes to stimulate water mixing within the world's oceans -- thus bringing the nutrient-rich waters of the sea's depths to the surface and stimulating the growth of those algae blooms. Or to cool the Earth by shielding it with mirrors (a single, enormous one, per one proposal, or tons of tiny ones, per another) that would deflect the sun's light away from us and back into space.

Recently, though, scientists in Scotland put forward a new proposal -- this one involving, yep, an asteroid. The idea, from researchers at the University of Strathclyde's Advanced Space Concepts Laboratory, goes like this: We locate a suitably sized asteroid. We harness it into a position near Earth. And then we blast its surface to create a cloud of dust, which the asteroid's own gravitational pull would suspend around it, encompassing Earth at the same time.

Insert Bruce Willis joke here.

The scientists estimate that the resulting dust cloud would be large enough to block out 6.58 percent of the solar radiation that reaches Earth -- enough not to halt global warming, but at least to slow it. "We can buy time to find a lasting solution to combat Earth's climate change," researcher Russell Bewick puts it. "The dust cloud is not a permanent cure, but it could offset the effects of climate change for a given time to allow slow-acting measures like carbon capture to take effect."

This isn't the first time asteroids have been proposed as agents of geoengineered solar filtering. Dust-as-sunshade is actually a fairly longstanding idea in the field of geoengineering. The insight the Strathclyde team had, though, was that an asteroid's own gravitational forces could assist in the job, creating a cloud that would be far enough away from Earth's atmosphere to act as a remote filter but close enough to benefit from the asteroid's pull. Instead of the dust simply dispersing into space, it would be kept intact as a kind of exo-atmosphere.

The key would be to maneuver the asteroid to Lagrangian point L1, a location -- about four times the distance from the Earth to the moon -- where the gravitational pull of the sun and the Earth are in balance. (The most likely candidate for this fanciful form of geoengineering, the scientists suggest, would be 1036 Ganymed, the largest near-Earth asteroid.) The asteroid, once in place, would be fitted with a "mass driver," a kind of electromagnetic catapult that would provide the power both to move the asteroid into position and to blast the cloud of dust, once created, from its surface.

If all this sounds as science fiction-y as its fellow proposals ... that's because, effectively, it is. Though everything the team suggests is theoretically possible -- and though a distant dust cloud is much more appealing than sunshades that would fully block out the sun -- the impediments are, of course, many. The expense. The political will. The general inadvisability of experimenting with an extraplanetary environment that we're just starting to get to know. The danger that comes with trying to, you know, harness an enormous asteroid.

Then again, Planetary Resources -- "the asteroid mining company" -- will soon start living up to its tagline; so the risk will be there either way. The dust cloud proposal, the Strathclyde team says, would also be much less expensive than, say, solar mirrors. And it's nice to know, regardless, that as we humans keep failing to cool a warming planet through a relatively simple proposition -- behavioral change -- scientists are working toward high-tech alternatives on our behalf. If we keep polluting, there could always be a way to halt, if not reverse, the damage we do. It's just that it might involve blowing up an asteroid.