WISE-ing up on NEO numbers

[Sam Fraser]

WISE Revises Numbers of Asteroids Near Earth (Each asteroid image represents about 100 actual objects)

http://www.nasa.gov/images/content/592665main_pia14734-43_946-710.jpg

New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. ... Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found.

The situation is different for the mid-size asteroids ... So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover. In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids...

http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html (make sure to click on images/illustrations for additional pages)

[JohnHunt]

In various news articles on this new finding, I have been unable to find out why there was th initial over-estimate. *I would be curious as to the reason.

I have long felt that the risk of a truly devastating asteroid strike has been over-stated more often than not. *Especially this is true in the popular media but also, I believe, by scientists.

I wouldn't presume that scientists had previously intentionally over-estimated the numbers of mid-sized asteroids. *I'll give them the benefit of the doubt and presume that it was simply lack of data which has now been corrected.

But even with this announcement, the lead investigator said that the estimated numbers of mid-sized asteroids was "somewhat" less than previously estimated. *A 40% reduction isn't "somewhat" less, it is quite a bit less. *For example, the remaining undiscovered asteroids between 500 and 1,000m just went from an estimated 50% to 20%.

I find it pretty comforting that we know that 80% of asteroids of this size are not on a collision course with the Earth. *Of course, the situation is even better for asteroids larger than this and, fortunately, asteroids smaller than 500m are less devastating (still a bad situation) than those larger. *Very rarely is evacuation mentioned when risks of asteroids are discussed in any setting.

When discussing whether we should send humans to an asteroid, almost always one of the rationales is that we need to do this in case we find that a big one is headed our way. *This is erroneous to the point of being dishonest for several reasons:
**1) we don't need humans to deflect an asteroid,
**2) we are rapidly finding and clarifying more and increasingly smaller asteroids. *Money would probably be far better spent building the next generation of WISE,
**3) We are now detecting asteroids of less than 10m days before they hit. *We would likely have months if not years of forewarning in order to evacuate. *Besides, we have no recorded instance of s person dying from an asteroid / meteor.

Yet, after having said all this, I still support our sending humans to an asteroid if we continue the Flexible Path simply because, if we venture further and further into deep space, why not visit an asteroid? *It would be sort of cool.

[sgeos]

I have long felt that the risk of a truly devastating asteroid strike has been over-stated more often than not. *Especially this is true in the popular media but also, I believe, by scientists.
It is an instant game over for everyone, so even if the event is unlikely it is worth a certain amount of attention. The most likely scenario is that civilization continues undisturbed until we can relatively easily deal with potential devastating asteroid strikes.

[Sam Fraser]

It is comforting to know all the NEOs large enough to cause planet-wide or continent-wide devastation have been found. Large comets are still a threat, since they can approach at much higher speeds with their kamikaze orbits from beyond the Oort cloud above or below the ecliptic. In many cases we'd only have a few months warning, another reason to develop space resources and become a multi-planetary species ASAP.

[Rhyshaelkan]

It is comforting to know all the NEOs large enough to cause planet-wide or continent-wide devastation have been found. Large comets are still a threat, since they can approach at much higher speeds with their kamikaze orbits from beyond the Oort cloud above or below the ecliptic. In many cases we'd only have a few months warning, another reason to develop space resources and become a multi-planetary species ASAP.

Quite so. Their small 20 km forms do not become apparent until they get on the near side of the asteroid belt. Then they start outgassing due to solar heating.

Doubtful that we will ever find them all. Thus it might be useful for a powersat to be able to swivel and focus its microwave array to blast incoming 10-100m asteroids detected by the PERMANENT Earth Shield radar(lidar) warning system. Blasted by several tera-watts of microwaves(the powersats in the constellation with a clear line of sight) we could avoid catastrophic damage to human settlements.

Only warning for targetable and focusable powersat microwave arrays are death beams from the sky :D But that is off-topic for this thread.

[JohnHunt]

It is comforting to know all the NEOs large enough to cause planet-wide or continent-wide devastation have been found.

Do you know this to be so? There are, statistically, about 70 asteroids larger than 1 km which are still undetected. I presume that these are on the smaller end of things and that there probably is no longer any undetected asteroid out there that is 10 km in size. But this is just my speculation and not anything that I have read. But even if a 2.5-10 km "dinosaur killing" asteroid were to hit the Earth, my belief is that our intelligent preparation means that most of civilization would survive both the strike and the aftermath. We would all be vegetarians and eating food grown under grow lights. While we would not thrive, at least we would survive.

[Sam Fraser]

You're right, JohnHunt, I can't know this with absolute certainty. We shouldn't get too complacent, but I think the asteroid impact threat is a bit hyped. Same with the cometary impact threat. While a comet could hit us from above or below the ecliptic at even higher speed than a NEO with magnitudes more kinetic energy and potential for planetary devastation, it's also a remote possibility. I'm hoping when the sheer number of NEOs big and small passing quite close to Earth becomes firmly established the desire and momentum to visit them and do something useful with them will grow.

[RaresH]

Nice diagram Sam! Whatever the revised figures any data that gets us a better understanding of the count and composition of neo's is good in planning security, economic, and scientific exploration. I'm more interested in the economic potential, however neither is necessarily mutually exclusive.