We’ve talked often in these pages about Near Earth Objects (NEOs) and the potential danger posed not just by them but by objects from much further out in the Solar System if they were to take an Earth-crossing trajectory. But it’s also true that NEOs have a certain allure even if they are potentially dangerous. They’re close enough to consider a manned mission, and even a small 2-kilometer sized metallic NEO could contain rich metals and minerals worth trillions of dollars. Of course, what metals markets would do if we suddenly had access to such an object is another matter. And mining an NEO, not a new concept, is still on the impractical side.
But Hexi Baoyin (Tsinghua University, Beijing) and colleagues are proposing a possible solution. The temporary capture into Earth orbit of an NEO by creating a small velocity change could allow a relatively low-cost trajectory to the object that would provide mining opportunities. And indeed, various asteroid deflection schemes from solar radiation to nuclear explosions are available in the literature, most considered in terms of saving our planet from an impact. The authors of this new paper (thanks to Phil Mowatt for the tip) have set about identifying what it would take to capture an NEO to Earth orbit, using as their case in point a periodic comet called 39P/Oterma.
It’s an interesting object, this Oterma, one that sometimes is captured by Jupiter for one to several orbits. Call it a ‘temporary moon.’ In the same way, the authors believe that ‘a small velocity increment’ would be enough if exerted in the right place to cause the temporary capture of a NEO in Earth orbit. They acknowledge that the method would work only for small NEOs, based on our current technology, with the larger ones being too heavy for significant change to their orbital energy.
How to cause the desired effect? The authors look at alternatives from nuclear explosions and kinetic impactors (impulsive) to Yarkovsky effect, focused solar, gravity tractor, mass driver, pulsed laser and space tug (slow push) before settling on one from the first camp:
Considering the required impulsive velocity increment is not so small and the diameter of NEOs is relatively large, there are two impulsive capture methods available, kinetic impactor and nuclear explosion, but they are never tested or applied. Among them, the nuclear explosion method may not be proper one for the mentioned small NEO, because the nuclear explosion can release a very large amount of energy, the result may be a fragmentation of the target NEO. So the kinetic impactor is often considered as a better maneuver means especially for the NEOs smaller than 50 meters in diameter.
So we’re talking about a space probe or projectile that would hit the NEO at high velocity and change its orbit. A possible candidate is the smallish asteroid 2008EA9, but the list of candidates is growing as our surveys continue. The new orbit would be a temporary one but would allow a prolonged period of study and, possibly, exploitation of resources there. All of which jogged my memory of Carl Sagan’s work with JPL’s Steven Ostro on precisely these matters. One paper devoted to the problem was “Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations” (citation below). Two matters come to mind in relation to it, the first being the need to deal with space debris over the long haul, which Sagan and Ostro handle thusly:
Sooner or later human civilization must confront the asteroid/comet collision hazard or become extinct. Dealing with interplanetary collision hazards over a period of centuries or millennia will naturally take our spacefaring society further out into the solar system — if for nothing else, to improve surveillance of incoming comets. As technology advances and the life-span of our species (and its successors) lengthens, a slow outward transition from interplanetary travel towards cometary source regions and interstellar spaceflight seems conceivable.
That’s a ‘meme’ that Centauri Dreams has been working with for the past seven years, that interstellar flight will grow organically out of the need to extend infrastructure outwards in the Solar System rather than through an interstellar project mounted Apollo-like on its own. The second issue, though, is much more troubling. Sagan and Ostro again:
… altering the trajectories of objects in nearby interplanetary space can introduce perils on timescales much shorter than the average intervals between natural impact catastrophes… Thus, interplanetary collision hazards may act as a kind of sieve, simultaneously requiring civilizations to become spacefaring and to institute stringent controls on the misuse of orbit-engineering technology. These joint constraints may or may not be so severe as to truncate the longevity of spacefaring civilizations below the timescales for civilization-ending impacts themselves. One way or another, interplanetary collisions constitute a unique, exogenous environmental factor in the natural selection of long-lived civilizations.
I’m thinking that Sagan and Ostro had the matter precisely right. Whether through simple error or the calculated decision to use a small NEO as a weapon, the dangers of asteroid deflection for research and mining seem not to merit the risk. I’ll buy the notion that getting to an asteroid with robotic probes or manned missions makes sense as we continue to assess the potential threat they may pose, but let’s reach them without trying to tug them into new trajectories. As Sagan and Ostro noted some time ago, we’re about at the point where we have the technology to alter an asteroid orbit. And as Sagan wrote in Pale Blue Dot (1994), “If we’re not careful, many nations may have these capabilities in the next few decades. What kind of world will we then have made?”
The paper is Baoyin et al., “Capturing Near Earth Objects,” accepted for publication in Research in Astronomy and Astrophysics (Chinese Journal of Astronomy and Astrophysics). Preprint available. The Sagan and Ostro paper is “Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations,” JPL TRS 1992+, available online. See also Sagan, “Dangers of Asteroid Deflection,” Nature 368, Issue 6471 (1994), p. 501.