Global Catastrophic Risks (now slightly outdated with a 2008 publication date) has a chapter on comets and asteroids.
It estimates that an impactor with a diameter of 1 or 2 kilometers would be “civilization-disrupting” and 10 kilometers would “have a good chance of causing the extinction of the human species”. So that’s what the “big” means in this context.
We can estimate the population of possible impactors via impact craters, telescopic searches and dynamical analysis. Using these techniques, “[i]t is generally thought that the total population of near-Earth asteroids
over a kilometre across is about 1100.” But there are other classes of impactors with greater uncertainty-comets and Damocloids. “Whether small, dark Damocloids, of, for example, 1 km diameter exist in
abundance is unknown—they are in essence undiscoverable with current
search programmes.”
This sounds like a plausible reconciliation of the apparently conflicting claims. OpenPhil is specifically talking about near-earth asteroids where we do indeed have fairly accurate estimates. The NASA employee referenced by MacAskill may be referring to the larger class of all possible impactors where uncertainly is much greater.
No idea really. The chapter reports “The best chance for discovery of such [dark Damocloid] bodies would be through their thermal radiation around perihelion, using infrared instrumentation on the ground (Rivkin et al., 2005) or in satellites.” Rivken et al. 2005 is here.
Global Catastrophic Risks (now slightly outdated with a 2008 publication date) has a chapter on comets and asteroids.
It estimates that an impactor with a diameter of 1 or 2 kilometers would be “civilization-disrupting” and 10 kilometers would “have a good chance of causing the extinction of the human species”. So that’s what the “big” means in this context.
We can estimate the population of possible impactors via impact craters, telescopic searches and dynamical analysis. Using these techniques, “[i]t is generally thought that the total population of near-Earth asteroids over a kilometre across is about 1100.” But there are other classes of impactors with greater uncertainty-comets and Damocloids. “Whether small, dark Damocloids, of, for example, 1 km diameter exist in abundance is unknown—they are in essence undiscoverable with current search programmes.”
This sounds like a plausible reconciliation of the apparently conflicting claims. OpenPhil is specifically talking about near-earth asteroids where we do indeed have fairly accurate estimates. The NASA employee referenced by MacAskill may be referring to the larger class of all possible impactors where uncertainly is much greater.
Thanks, super helpful!
Do you happen to know how promising it could be to work on innovating on new methods of discovery and tracking things like Damocloids?
An unknown number of those guys being out there is scary :-/
No idea really. The chapter reports “The best chance for discovery of such [dark Damocloid] bodies would be through their thermal radiation around perihelion, using infrared instrumentation on the ground (Rivkin et al., 2005) or in satellites.” Rivken et al. 2005 is here.