Rusty Schweickart, Apollo 9 Astronaut, Responds About Asteroid Threats
By Russell “Rusty” Schweickart, Chairman and Co-founder, B612 Foundation and Apollo 9 Astronaut
Editor’s Note: Rusty Schweickart contacted me with a correction and clarified the probability of asteroid impacts.
Editor: On the first point, my earlier post Fly-by on Feb.15,2013: What can asteroid 2012DA14 tell us about fundraising? incorrectly indicated that asteroid Apophis could have a possible 5.1 megaton impact in 2029 (2.7% chance which subsequently declined). Correction: 510 megatons, not 5.1.
Schweickart: 510 MT would cause regional devastation; e.g. the SF Bay Area or the NYC, CT, NJ metropolitan area. As to lethality… it depends entirely on where it hits…
Apophis hitting in the ocean would cause a moderate sized tsunami… on land (again) a regional disaster (BUT NOT planetary). DA14, like the Tunguska object, would cause local devastation… at Tunguska 800+ sq. miles of forest were instantly destroyed and set fire. Were it directly over any city (very unlikely) it would have destroyed everyone in that city. For planetary scale impact the generally accepted minimum size is 1 km in diameter or larger. Such objects only hit with a frequency of ~ once per million years. Tunguska events about once per 300 years. Apophis events once per 100,000 years.
Editor: If the Cretaceous–Paleogene extinction was the most recent 65 million years ago, then have we had 65 million-year spins with the Earth being extremely lucky? Are we (statistically) overdue for one of these?
Schweickart: Regarding the Cretacous Period extinction… the Chicxulub object was ~10 km in diameter and the frequency of impact for objects of that size is ~1/100 Million Years. So 66 Million Years have passed… but there are no objects which we know of that large which have any probability of impacting. Objects that large are easily seen and NASA’s Spaceguard system has essentially fully cataloged all objects that size. The issue is with smaller objects…
The Chelyabinsk object falls in the far left bar… 1% discovered… and frankly no one even dreams of being able to inventory that cohort. However the next bar up… the 30-100 meter bin… which is the Tunguska size and up, we also have less than 1% (more like 0.5% actually) in our database.
It is these objects and larger that B612’s Sentinel telescope will be looking for. In the 6.5 years of operation we expect to end up with well over 90% of 140 meter objects and up to 50% of 40 meter objects. The total number of objects we expect to discover in the 6.5 years is > 500,000. Our current total is just under 10,000.