Microsummary: we are on the right track!
The latest estimates of the NEO size distribution by Alan W Harris retain the shape of previous estimates, a power law with a pretty steep exponent and an unexplained ‘dimple’ where there are too few 10-100 m NEOs.
Donald Yeomans showed that the impact flux from comets is small compared to Near Earth Asteroids (NEAs) (less than a percent). Satelite surveys have produced a flood of data (check out this animation or my graphs) and we have good reason to think we have already seen a sizeable fraction of the NEAs that would be serious global catastrophic risks (GCRs) - and they are in orbits that are safe for at least the next century. This has really reduced the expected risk.
The mandate from the US Congress wants a 90% completion by 2020 for the big (>140) NEAs, which might be tough unless there is some extra push (ideally a Venus orbit satelite or more time at the Large Synoptic Survey).
The LSS will be able to catch a lot of 45 m objects 1-3 months out, and people are starting to seriously look at finding smaller objects on their “death plunge” just before they hit Earth. They pose just local risk (if any at all) but as the GCR risk is retired their relative risk go up. Mark Boslough showed that some of them might produce pretty destructive airbursts. This domain also deals with the “we are going to be so successful that we are going to put ourselves out of business” problem - we are 10 times more likely to save lives by including imminent impactors in the next surveys, although the number of lives saved might be smallish.
Obama’s call for a manned NEO mission is a tough challenge, mainly because the best objects from a mission technical perspective (low deltav etc) might be smaller than the spaceship! Overall, NEO missions are maturing but the Japanese seem to be a decade ahead with Hayabusa and Hayabusa II.
Deflecting asteroids with kinetic impactors looks pretty good, but a lot hinges on the porosity of the asteroid. A fluffy asteroid just absorbs the impact, while a “hard” asteroid will eject a plume of debris that gives an extra push. Unfortunately we have no way of measuring the porosity, so plenty of talks investigated models and ways of estimating it.
Gravity tractors are wimpy, but seem to be fairly close to a realistic technology. They are pretty useless for deflecting an asteroid away from Earth, but enough for preventing it from going through a keyhole. This makes them a pretty ideal supplement for any mission. Flotillas of tractors can be more effective than single tractors. Paul W. Chodas also showed that there are “Jabbas”, robust states of an orbit that are hard to budge.
Nuclear deflection looks like it is workable, but it is definitely a last resort and mainly useful for imminent hits. Some serious issues about how to avoid dispersing loosely held together impactors. The main problem is getting the warheads to the impactor in time and to have them detonate at the right standoff distance.
Erick Ball described a real “Armageddon” scenario where a 5 km long periodic comet discovered ~290 days out could be deflected if mankind really got its act together - something we all felt was doubtful. Several other deflection methods (laser ablation, robotic rockthrowing, ion beam shepherds, painting to cause Yarkovsky effect deviations…) are investigated but not ready from prime time. Another problem is that NEOs seem to be quite different from each other, and methods that work for one type might need to be tweaked for other types.
Organisationally, things are moving forward. NEO study and defense is becoming more and more organised in the big space agencies, the UN and the US government. Some interesting notes from Frans von der Dunk on the legal aspects: check out the report “Legal Aspects of NEO Threat Response and Related Institutional Issues.”
In particular, the ‘responsibility to protect’ might apply here, requiring states to have capabilities to deal with NEO risks. There are also an interesting possible tradeoff between sharing information and doing missions in an open manner and avoiding liability: if damage occurs in the course of a NEO response states might not be held liable as long as the mission is within parameters set by proper mandate international community groups.
My own talk was about the issue of cognitive bias and rationality in impact mitigation. Basically, our biases are interfering with both the public, decisionmakers and the research community, and overcoming them is an important part in public relations, explaining the situation and doing the research. Not all of them are bad for the impact risk community: the preference for hard numbers really helps it in the “competition” with softer risks. But availability bias (it has never happened, never will) and scope neglect (a million dead are just
statistics) make many decisions rather irrational.
statistics) make many decisions rather irrational.
There are also problems with planetary defence being a public good, being long-term (it might be rational to put off doing things for a while, since tech is advancing - but this easily leads to putting off doing things too long; the “sweet spot” might be a decade, about a political lifetime) and discounting the future too heavily.
However, I think the impact community are an example to all of us dealing with other existential risks. They are doing a pretty good job. They have managed to 1) demonstrate the existence of a risk and quantify it, 2) convinced enough decisionmakers to fund preliminary investigation, 3) built a lively interdisciplinary community devoted to the risk and mitigation (with an inflow of new students carrying on and developing the thinking). Other risk communities may do well to study how they did it.
And finally, a great motto: “There ain’t no such thing as a free launch.”
Link: Article ("Anders Sandberg on Progress in Mitigating Asteroid Impact Risks")
