Do we know how many big asteroids could impact Earth?
post by Milan_Griffes
score: 31 (13 votes) ·
This is a question post.
Will MacAskill discussing asteroids with Joe Rogan, starting around 1:24:00 in this recording –
Rogan: When you think about how big that thing was, that killed the dinosaurs 65 million years ago, and that there are hundreds of thousands of those things floating around in space.
MacAskill: I was asking some people at NASA, just two days ago actually, how many of them we've managed to identify – cause they're serious about scanning the skies to find them all...
I thought we had it covered. I thought this was something where NASA was like "Yeah yeah, we know where all the earth-killers are."
And their response was like "No, we have no idea. We don't know how many of them are out there, and so we don't know [what proportion] we've managed to track."
That was in 2017. It cuts against this 2013 Open Phil report (a) which states:
Unlike other GCRs (e.g., nuclear war), asteroid risk is extremely quantifiable: scientists have estimated the number and size of near-earth asteroids and are able to track how many have been discovered.
I'm inclined to follow MacAskill here, as the Open Phil investigation is based on public sources and NASA may have incentive to overstate their handle on the problem in public-facing communications.
But I haven't looked into this closely. Has anyone in EA thought about asteroid risk, recently?
(It looks like this isn't totally neglected – the B612 Foundation was set up to "to protect Earth from asteroid impacts." I haven't poked them enough to know how good their stuff is.)
answer by cole_haus
· score: 8 (2 votes) · EA
Global Catastrophic Risks (now slightly outdated with a 2008 publication date) has a chapter on comets and asteroids.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
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.
comment by Milan_Griffes
· score: 2 (1 votes) · EA
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 :-/
comment by cole_haus
· score: 3 (2 votes) · EA
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.
answer by agdfoster
· score: 4 (3 votes) · EA
Don’t know much about this but I thought you could estimate a ballpark for the total frequency by looking at craters on moons and mars.
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