I began researching this post believing that Apophis (with its April 13, 2029 close approach) was our best opportunity to capture the resources of an asteroid for humanity and the space program.
Soon I realized that the selections are bountiful (or frightening, depending upon your point of view).
NASA maintains several valuable web sites and services, including
- the Potentially Hazardous Object list (over a thousand) at http://neo.jpl.nasa.gov/orbits/ (where you can display an orbit animation)
- the Small Body Database Browser at http://ssd.jpl.nasa.gov/sbdb.cgi which lists 3,000+ comets and 400,000+ asteroids
- the Near Earth Object Program at http://neo.jpl.nasa.gov/
- The Sentry Risk Table at http://neo.jpl.nasa.gov/risk/ listing PHOs in order of threat. Apophis is currently #4, not based upon 2029 or 2036 but the 2068 approach.
As I described in my post Capturing Apophis, these objects are far too large for us to simply man-handle. We must use finesse, or more precisely, we must use the gravitational influence of a body such as the Earth to do most of the work for us. We can nudge small to medium size bodies a bit given months or years of head start. So, we need objects that pass close by, perhaps within the orbit of the Moon.
Plus, I’m interested in objects we can capture in my lifetime.
Here is a list of potential asteroids. Their distance of closest approach is given in Earth radii (1 Er = 6400 km). For reference, the Moon averages 60 Er (Earth radii) away. This list is in order of close approach date.
- 2005 YU55 passes at 25 Er on 8-Nov-2011. It’s 120 meters across, masses 3 million tons. I wish it passed later – it would make a wonderful practice asteroid but we’re not likely to be able to launch a deflection mission in time.
- 2008 UV99 passes at 7.16 Er on 30-Mar-2019, is 400 meters wide and masses 87 million tons.
- 2001 FB90 passes at 13 Er on 24-Mar-2021, is 349 meters wide and masses 58 million tons.
- 2007 RY19 passes within 0.89 Er on 12-Mar-2024, is 110 meters wide, masses 1.8 million tons.
- 2001 CA21 passes at 6.41 Er on 9-Oct-2025, is 677 meters wide and masses 422 million tons.
- 2001 WN5 passes at 37.5 Er on 26-Jun-2028, is 780 meters wide, massing 646 million tons.
- Apophis 99942 passes at 5.86 Er on 13-Apr-2029, is 270 meters across and masses at least 25 million tons.
- 2007 FT3 passes at 22 Er on 03-Oct-2030, is 340 meters wide, masses 54 million tons.
- 2009 UN3 passes at 19 Er away on 09-Feb-2032, is 919 meters wide massing just over a billion tons.
Note that the sizes are estimates based upon the apparent brightness of the asteroid. None of these have been imaged and measured. The masses are estimates based upon a spherical body of that size with a density of 2.6 tons per cubic meter (partly porous). A solid body would mass more, nickel-iron much more.
This list is not exhaustive, and some of these asteroids may be moving too fast (or not have suitable advance rendezvous orbits) for our purposes. But all 9 of these pass close enough to the Earth that their subsequent orbits are changed by the Earth’s gravity, and a relatively small nudge can be used to control a gravitational slingshot and choose its subsequent path. Some may require multiple slingshots and many elapsed years before they can be parked in a suitable orbit, but even the smallest of these (2007 RY19 at 1.8 million tons) contains enough resources to pay for the effort many times over.
There are many other asteroids from which to choose. A number of asteroids are in horseshoe or spiral orbits near the Earth, and may make suitable low delta-V rendezvous targets. Many more are easier to reach (in terms of required delta-V) than the surface of the Moon. Some of these are nickel-iron asteroids, others may be extinct comets containing huge amounts of ice. One estimate is that 6% of asteroids may be extinct comets.
We need better observations of all of the above objects. If one were a carbonaceous chondrite or an extinct comet, its value would be immensely greater due to the high content of carbon and water – the stuff of life. If one was nickel-iron then that, too, would have extra value. But all asteroids have great value once they’ve been captured into a stable Earth orbit, as all of them contain oxygen, silicon, magnesium, and iron.
Clearly, we don’t need to fight over these trillion-dollar resources. There are enough potentially valuable asteroids to share.