It’s good to see asteroid deflection occasionally popping up in the news, thanks to the efforts of people like former astronaut Rusty Schweickart, whose efforts as co-chairman of the Task Force on Planetary Defense of the NASA Advisory Council are complemented by his work for non-profits like the B612 Foundation. Schweickart is worried about the potential consequences of even a small asteroid impact, pointing to the Tunguska event of 1908, in which 800 square miles of Siberian forest were flattened in the kind of strike that occurs every 200 to 300 years.
Bigger asteroids are, obviously, a far greater danger, and while they’re much rarer, they do have the capability of wiping out entire species, as may well have occurred some 65 million years ago in the destruction of the dinosaurs. In his recent New York Times article, Schweickart notes what we need to do:
With a readily achievable detection and deflection system we can avoid their same fate. Professional (and a few amateur) telescopes and radar already function as a nascent early warning system, working every night to discover and track those planet-killers. Happily, none of the 903 we’ve found so far seriously threaten an impact in the next 100 years.
Nonetheless, asteroids demand a constant vigilance. Schweickart continues:
Although catastrophic hits are rare, enough of these objects appear to be or are heading our way to require us to make deflection decisions every decade of so.
A deflection capacity is something NASA needs to be looking at, and the report of the Task Force on Planetary Defense urges that financing for it be added to the NASA budget. Schweickart believes that $250 to $300 million, added annually over the next ten years, would allow our inventory of near-Earth asteroids to be completed and a deflection capability to be developed, after which a maintenance budget ($50 to $75 million per year) would keep us tuned up for potential deployment.
Underscoring the need for a deflection capability is the work of Elisabetta Pierazzo (Planetary Science Institute), whose forthcoming paper in Earth and Planetary Science Letters focuses on two impact scenarios, 500-meter and 1-kilometer asteroids hitting a 4-kilometer deep ocean. What Pierazzo finds is that an ocean strike could deplete the Earth’s protective ozone layer for several years, resulting in a spike in ultraviolet radiation levels that would, among other things, make it more difficult to grow crops (not to mention its effects on other life forms).
Pierazzo and team’s atmospheric simulations show a global perturbation of upper atmosphere chemistry, as water vapor and compounds like chlorine and bromide alter the ozone layer to create a new ozone hole. Adds Pierazzo:
“The removal of a significant amount of ozone in the upper atmosphere for an extended period of time can have important biological repercussions at the Earth’s surface as a consequence of increase in surface UV-B irradiance. These include increased incidence of erythema (skin reddening), cortical cataracts, changes in plant growth and changes in molecular DNA.”
Ultraviolet radiation intensity can be expressed by the ultraviolet index (UVI), which indicates the intensity of UV radiation at the surface, with the higher numbers tending toward damage to skin and eyes. While a UVI of 10 is considered dangerous, resulting in burns to fair-skinned people after short exposure, values up to 18 are occasionally recorded at the equator. The highest recorded UVI is 20, recorded at a high-altitude desert in Puna de Atacama, Argentina.
Modeling a strike by an asteroid that hit at latitude 30 degrees north in the Pacific Ocean in January, Pierazzo’s simulations show that a 500-meter asteroid impact would result in a major ozone hole, boosting UVI values to over 20 for several months in the northern subtropics. A 1-kilometer asteroid would drive the UVI in certain areas to a sizzling 56, while boosting UVI values over 20 within a 50-degree latitude band north and south of the equator for about two years. The affected band’s northern end would include Seattle and Paris, while its southern end reached New Zealand and Argentina.
“A level of 56 has never been recorded before, so we are not sure what it is going to do,” adds Pierazzo. “It would produce major sunburn. We could stay inside to protect ourselves, but if you go outside during daylight hours you would burn. You would have to go outside at night, after sunset, to avoid major damage.”
We always tend to depict asteroid impacts in terms of their direst consequences as a way of illustrating the magnitude of the threat. But it’s chastening to learn that even a survivable impact like those Pierazzo and team have modeled would create serious environmental damage even if loss of life could be prevented. All this assumes, too, an asteroid that strikes in the ocean (the most likely scenario). There’s no question that building up our planetary defense against such impacts is the best insurance we could create, stopping potential impactors before they near our planet.
The paper is Pierazzo et al., “Ozone perturbation from medium-size asteroid impacts in the ocean,” in press at Earth and Planetary Science Letters (abstract). Jeremy Hsu’s article on this work in LiveScience is excellent.
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500m diameter bolides (producing an ~10km crater) appear to strike approx. every 100,000 years(1). So anatomically modern humans have survived 2(?) and H. Sapien, perhaps 4, or 5, strikes of this magnitude?
1) French B. M. (1998) Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite
Impact Structures. LPI Contribution No. 954, Lunar and Planetary Institute, Houston. 120 pp.
“A deflection capacity is something NASA needs to be looking at, and the report of the Task Force on Planetary Defense urges that financing for it be added to the NASA budget.”
This is overdue; it is my wish that this issue does not become overly politicized as global warming and evolution have been. Fantasy? There are those influential people who point to English translations of ancient documents from the Middle East and proclaim such possible catastrophes to be fulfillments of ‘prophecy’.
We live in an age of increasing importance of science and technology. Educating the public about these matters is desirable. The implications of the recent impacts visible (by amateur telescopes, no less) on Jupiter are a case in point. Very simply: this can be Earth, but the resulting damage would be proportionately greater… potential extinction levels. There used to be bumper stickers which read “Extinct is Forever”. That applies to all biology…
I think the most significant effect of a major impact would be the collapse of agriculture during the time it takes for the atmospheric debris kicked up by the impact settles. This is believed to be several months.
It would be interesting to see how “big” (ignoring speed atm) an asteroid has to be before the economics of the situation say it would be in our benefit to deflect said asteroid. IE … Graph the cost of clean up based on size of impactor against cost of deflection mission based on size of impactor.
Also interesting is that one would have to calculate the cost of the clean up in the future when it might be easier to clean up, but you would have to calculate most of the clean up cost now when it is surely more expensive.
^^^ the musings of a reader
I would support ongoing funding for detection but not for deflection.
Large asteroids are potentially devastating but also the most easily detected. When detected, even if they are targeting Earth, would likely be decades to centuries before doing so. Developing planetary defenses now would probably be wasteful since technology and space-based infrastructure will be so much different at that time.
Let’s not forget that evacuation is a legitimate response to an asteroid threat. A Tunguska-sized object will likely be detected several days out giving plenty of opportunity for evacuation. Phil’s cost/benefit comment is relevant at this point. Say a Tunguska has a 5% chance of destroying urban infrastructure. How much would that clean-up cost versus a reliable deflection mission for object discovered a few days out? Although that’s calculable, I’m skeptical about the case for spending money now for a deflection mission of an unknown object of unknown size at unknown distance out.
Would be interesting (someone has probably done this already) to calculate/produce an equation that describes to a high degree of certainty the point at which we HAVE to do something about an impactor that has a chance of hitting earth or the moon. I include the moon because if the impactor is large enough, we could have a problem on earth and also if there are colonists…
Off the top of my head here would be a bunch of variables such as:
size of impactor
type of impactor
likely hood of hitting earth or moon
when it is likely to hit
economic situation on earth
cost of intervention
type of intervention
Would make for an interesting modelling project…
I would tend to agree, although I would not object too strongly if the money was spent if it encouraged the advances in propulsion and other technologies along the same lines that the Space Race did. We are going to get there eventually, and even now, assuming the threat was not too imminent, we would likely be able to mount a successful deflection effort, if it was deemed necessary.
“[Former NASA astronaut Thomas] Jones spoke at the European Space Agency’s operational center in Darmstadt, Germany, where former NASA astronauts and scientists from space agencies across the globe pushed for international space agencies to band together to address the issue from within the U.N.
“Jones and his colleagues proposed that a group involving the world’s space agencies be established to pool resources to prevent such an asteroid’s impact and to better inform the public of the possible threat.”
For those interested in such events, I would like to recommend the following book: Tsunamis: the Underrated Hazard by Australian geo-physicist Edward Bryant (http://www.amazon.com/Tsunami-Underrated-Springer-Geophysical-Sciences/dp/3642093612/ref=sr_1_2?ie=UTF8&s=books&qid=1288390902&sr=8-2), which deals with many of the issues associated with ocean impacts that are significant in scope. Technical at times, the book is also a marvelous history (make sure you read the appendices), fully engaging in its writing and quite scary, in a sober sort of way. The book was originally published in 2001, I believe, and is by far the best book on the subject I have ever encountered. This is an unfortunately expensive re-issue so you may want to visit a university library. My copy is not for sale.
This whole issue just highlights the unserious was in which we approach problems.
We are short term planners for the most part.
And I second the comments about the danger of asteroid threats getting politicized like “Global Warming.” You can count me as a skeptic on that issue, but I’m open to serious discussion. If irrefutable facts are there after tampering and “data enhancement” is removed then it is prudent to have a grown-up discussion as to how to mitigate and balance the “cure” with the real economic impact/pain suffering it may induce.
Instead we have people that make movies and millions of dollars on “Climate Change” and literally jet-set around the globe like the leaders of cult accepting awards and promoting media and nothing substantial gets done. All players are deionized, but many make a huge living off it. Lets hope the problem is small or not even real because no serious analysis and mitigation approach will be tried.
Honestly, the first thing that governments should do before funding asteriod deflection efforts is to stockpile food, water, and fuel that can keep a country going for a full year without oil/mining, and agriculture. I think the United States used to do that decades ago, but most of that old cold-war policy has been dismantled. Unseriousness prevails yet again.
My guess is that a stand off blast of a 100 megaton to 1,000 megaton nuclear device could be effective at deflecting a 5 kilometer to 10 kilometer asteroid.
We would need to optimize nuclear weapons designs to make the device easily transportable to orbit and launched on an intercept with the asteroid.
Now, one metric ton of fusion fuel will yield about 180 megatons and so 5.5 metric tons of fusion fuel, assumming 100 percent or even 90 percent burnup will get us to 1,000 megatons.
The Russian Tsar Bomba was a 100 megaton design which some say could have been fueled up to 150 megatons without much trouble. The device fueled at a level of 59 megatons was heavy at about 27 metric tons, but the device was neither optimized nor produced by a long duration R&D effort. It was something ginned up in a relatively quick and inexpensive crash program to assert the military industrial prowess of the U.S.S.R.. The device was light enough however to be air dropped by a prop driven plane.
The device was essentially a fission-fusion device of a 59 megaton yield monster, but could have been easily fueled way up by an enclosing U-238 (no not a U-235) jacket. The neutrons from the hydrogen fusion would have been used to split the U-238 atoms.
U-238 or U-235 both have a yield of about 22.5 megatons per metric ton.
Given the ability of the space shuttle to lift some 30 metric tons or more, and the Saturn V having lifted over 100 metric tons, it is simply no stretch to consider that we could assemble and loft a 1,000 megaton monster to do a stand off blast near an asteroid.
Now some folks will say that the momentum delivered to the asteroid by such a blast would not amount to much, and ordinarilly that would be the case. However, by vaporizing and superheating a thick surface layer of the asteroid by the blast, much more momentum can be imparted to the rock than would otherwise simply because of the decompressional forces of the expanding gas or plasma layer away from the rock.
I think we need to rethink the treaty banning nuclear explosions from space but in the context of blasting space rocks instead using such devices on our fellow humans.
A high yield nuclear device is compact, and relatively simple in mechanical structure although manufactured to very precise tolerances.
All this talk about attaching large sails to a large asteroid, attaching huge nuclear thermal rockets, mass drivers, or hitting the rock with KE projectiles, would work as well, but such systems are needlessly complex, and thus might fail in the time of a 1 year emergency warning window.
Several decades ago the science fiction magazine Analog had an article “Gian Meteor Impact”, that pointed out a sea strike would be worse, generally, than a land strike because more of the energy was captured by the environment. A sea strike will vaporize a lot of water, and that turns into weather. Not to mention the tsunami generated.
We need to develop a deflection system in the near future, because we don’t know when we’ll need one, developing one forty years from now does us no good, if we need it in fifteen.
On how to best deflect an asteroid by nuclear explosion:
I think the best location for a bomb blast is well below the surface, maybe as far as halfway to the center. That way, the full energy of the blast is utilized to knock off a substantial part of the asteroid to one side, as reaction mass for a good push to the rest of the body. In effect, part of the asteroid will become propellant with a giant crater as the engine nozzle. There will be a clear dichotomy between material blasted out of the crater and material remaining, with almost nothing continuing at the original trajectory.
It would require a landing and drilling mission, but any old warhead would probably work off-the-shelf for the actual bomb. We’d want to send three independent missions, just to make sure we don’t lose because of bad luck…
A 475 kiloton warhead such as the U.S. Navy’s W-88 produces one heck of alot of energy. If converted to kinetic energy with even 50 percent efficiency, the mechanical energy would be the equivalent energy of a projectile traveling at 2.8 kilometers per second having a mass of 237,500 metric tons. This works out to a projectile traveling at 28 meters per second having a mass of 2,375,000,000 metric or a projectile with a mass traveling at 2.8 meters per second with a mass of 237,5000,000,000 metic tons. For the case of 1.4 meters per second, we could effectively shove an asteroid out of the way having a mass of 1 trillion metric tons which works out to be a silicate type of asteroid with a diameter of about 5.8 miles.
This rock would effectively travel (1.4)(31,000,000) meters or 42,400 off its initial course if the asteroid was one year away from impact. This is about 6.5 times the radius of Earth which should be adequate.
Those good o’l Navy nukes might come in handy.
If the U.S. did not want to get involved in sending nukes into space, our friends on the other side of the Atlantic such as Russia, the U.K, France, and China might be able to help here.
Italian doomsday: killer asteroids in 1958
Asteroid impact threats have become a staple of both major motion pictures and made-for-TV sci-fi movies in recent years. Dwayne Day discovers that the theme also was the subject of an obscure Italian movie from the late 1950s.