President Obama threw out an intriguing idea during a speech about the future of the US space program earlier this month:
Early in the next decade, a set of crewed flights will test and prove the systems required for exploration beyond low Earth orbit. And by 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the Moon into deep space. So we’ll start -- we’ll start by sending astronauts to an asteroid for the first time in history.
Obama was almost certainly referring to a Near Earth Object or NEO. As the name suggests, NEO's are a class of asteroids or comets that periodically come close to or intersect earth's orbit. There are no firm plans to visit an NEO, but they're a logical choice for the next destination. If planets and moons are the New Worlds of the solar system in the modern age of discovery, NEO's are its midway islands.
Aside from the resources and safe harbors NEOs represent, conveniently floating around interplanetary space, it would be good to learn more about them. Because, from time to time, one of them hits the earth. Usually with devastating results. In 1989 a space rock 300 hundreds yards across passed through the exact spot earth had been in just six hours earlier. Makes you think of disaster flicks.
In movies the heroes watch, eyes wide, as the apocalyptic fireball streaks overhead and strikes the distant horizon with a mighty flash, before they flee or take shelter with various degrees of success. In real life, if you saw a 300 yard rock burn in, even if it did hit just over the horizon twenty miles away, it would be the last thing you'd ever see. Because your retinas would be sizzling in their sockets like tiny fried eggs. Not that that would matter, much, the impact fireball would be so much brighter than the sun that it would burn any exposed skin to cinders while your clothes and hair burst into flame.
The ground wave would arrive in a few seconds with the force of an earthquake, followed in another minute or so by a wall of super-heated air and debris -- from splintered glass to SUVs -- traveling 500 mph. After that the ejecta blasted out of the impact zone into high, lazy, suborbital arcs would start raining down in earnest from the edge of space, an artillery barrage of thousands of white-hot meteors the size of beach-balls. For miles around the glowing crater it would get so hot that even asphalt driveways would burn like oily rags.
A 300 'yarder' is not a dino killer, not even close. The most destructive, direct effects would be confined to a region smaller than Kansas. But it would kick up enough dust, gas, and smoke to dim the sun and quickly drop temperatures the world over. It's unclear how long that would last, how cold it would get, or how resilient our global agricultural and economic systems would turn out to be in the wintry aftermath.
About 7000 NEOs have been cataloged, they vary from dozens of yards to and several miles in size. A typical one might come within a million miles of earth's orbit now and then, and be made of nickel and iron, rock, or mixes of tar-like organic chemicals and volatile ices. Either way it's valuable stuff.
A 300 'yarder' made of nickel and iron would represent billions to trillions of dollars in metal. An NEO made of organic material and ices of carbon dioxide and water would also be a goldmine; water is one of the most valuable substances we can find in space. We drink it, we grow food with it, we run hydraulics and generators with it, and we can use water to make rocket fuel or breathing air. Even one made of boring slaggy stone over laid with loose gravel would contain useful elements, and we can dig out spacious living quarters and shelters against unpredictable and potentially deadly solar storms. Another great thing about exploring and exploiting NEOs is their gravity, it's so weak there would be none of the headaches of landing and taking off on the moon or Mars. It would be more like pulling a boat up to a dock and tying off lines to keep from floating away.
If humans last long enough, sooner or later we're going to need to know how to deflect NEOs away from earth. Until then they're probably the most promising way to start building a scalable network in space. We can reach NEOs now with unmanned missions, and in the near future with manned spacecraft not too much more advanced than Apollo. We can use the materials they provide to transform them into supply depots, giant interplanetary space stations and, eventually, construction platforms and staging areas to expand the network to the rest of the solar system.
Inhabited NEOs would change the night sky, an earthbound stargazer looking up might see dozens of new streaks among the ancient stars, artifacts of billowing gas and dust from off-world communities and industries teased into feathery comet-like tails by the solar wind. We might eventually learn to nudge them into orbits that periodically pass close to various planets and large asteroids; hugely useful for dropping off and picking up cargo or people. And one day our descendants might even ride ships the size of small worlds right out of the solar system, setting sail at last on the vast ocean of interstellar space. That all might take centuries to unfold, perhaps millenia, but like any long journey, it all begins with one small step.