Lifeboat Foundation

part 1: Tunguska
part 2: Bigger than Tunguska
part 3: Big…and Really Big
part 4: Impacts and Probabilities
part 5: Nemesis

part 6: Recommendations

An asteroid impact ended the dinosaurs. Another one could end us. Something, as the saying goes, should be done! But what? Undeniably, as the Association of Space Explorers, the “international professional organization of astronauts and cosmonauts” puts it, “…protracted debate …can lead to inaction; evacuation of the impact site may then be our only option.” Evacuation is however a legitimate plan, one which could result in economic damage but zero loss of life. Yet there are competing strategies as well. Their economic costs and technical feasibilities should be debated first, assessed next, plans laid, and any necessary preparations made.

The asteroid problem needs to be understood. That means discovering those with potentially dangerous impacts, and tracking them, so that impacts can be predicted many years in advance. That will give the required lead time for planning effective action. Such discovery projects are called “Spaceguard” surveys, after sci-fi great Arthur C. Clarke’s Project SPACEGUARD in his 1973 novel Rendezvous with Rama. Nineteen years later in 1992, NASA, the US space agency, released its “Spaceguard Survey: Report.” Still later, section 321 of the NASA Authorization Act of 2005 set the goal of discovering and characterizing 90% of NEOs (near Earth objects) at least 140 meters across by 2020. This objective seems a likely to be achieved a few years late. No matter — it is far more important to achieve it, than to achieve it precisely on time.

Knowing the dangerous asteroids is only chapter 1 of the story. Mitigating their threat is chapter 2. Some methods for neutralizing the danger a asteroid poses only work temporarily (e.g. centuries, millennia or more). These involve pushing it out of the way, no piece of cake considering that a rocky asteroid 100 feet in diameter could easily be around 600,000 tons (metric: 30 meters and 560,000 metric tons), millions of miles away, and flying at 20,000 mph (or about 6 miles/sec, reducing your commute time to under 2 seconds for a 10-mile trip if you don’t stick your hand out the window). You can’t just contract the local towing company to get it out of the way.

A variety of pushing strategies have been devised, some more starry-eyed than others.

· Land on the asteroid and install multiple mirrors positioned to simultaneously focus sunlight onto a specific area. Enough mirrors doing this would be able to heat up a spot enough to boil off material. The boiled off vapors would fly into space, pushing the asteroid little by little in the opposite direction, the same principle by which a rocket engine spews exhaust in one direction to push the ship the opposite way. (That’s in accordance with Isaac Newton’s 3rd Law: a force in one direction has an equal counter-force in the opposite direction.)
· As before, boil off material, but this time using a powerful laser (indeed the laser could be solar powered). The laser could not be on Earth because the beam would spread out too much over the vast distance, so space travel is still required.
· Hover a spacecraft near the surface of the asteroid rotating beneath it. Gravity will try to pull the spacecraft toward the asteroid, but at the same time pull the asteroid toward the craft (Newton’s 3rd law again). It is like when you step on the scale, thinking the Earth is pushing you down onto it but probably not realizing that you are pulling the Earth upward the same amount.
· Land spacecraft on the asteroid, then use an engine on the craft to push the asteroid. Sharp fellow, Newton.
· Absorbing and reflecting light create small amounts of force. For example, when the sun is directly overhead, it pushes on a square mile of the Earth’s surface with a weight of several pounds. Light pushes a perfectly reflective surface twice as hard as a pure black (absorptive) surface. Also all bodies emit thermal radiation, more at high temperatures and less at low. This produces a small amount of thrust — the Yarkovsky effect, named after Russian railroad employee Ivan Yarkovsky, 1844–1902 (asteroid 35334 Yarkovsky is also named in his honor). For these reasons, painting part or all of an asteroid surface black or white/silvery can gradually affect its orbit enough to get it out of harm’s way.

Although a weak force for a long enough time can do the job, a strong force for a short time can too. Explosions are a good way to produce strong, short forces.
· Detonate conventional explosives near, on, or under the surface of an asteroid.
· Nuclear explosives are stronger, hence more effective, and are feasible with current technology. They can also break up and destroy an asteroid instead of just pushing it. We should try it.
· Smash a spaceship into the asteroid to give it a push. For relative speeds measurable in miles/sec., the collision will be an intense explosion.

If mitigation fails, at least we should know when and where the impact will be as far ahead as possible. With a lead time of 100 years or more, an impact zone could be gradually evacuated at a deliberate pace. Even a major city could be moved or dispersed within 100 years without undue hardship. If Seoul had started moving 50 years ago to get out of range of North Korean artillery, they could be half done. With an impact warning only days or weeks in advance, emergency evauation would be needed. Some cities have such plans already. Houston’s hurricane evacuation plan, executed but badly for hurricane Rita in 2005, involved converting inbound lanes on major highways into outbound lanes, thereby doubling the amount of outbound roadway. All areas should be required to have plans and those plans should be tested to the degree feasible.

Since most of the Earth is covered with deep water, most asteroid impacts will in deep water. These cause tsunamis. The disastrous earthquake-linked 2004 Indian Ocean tsunami caused over 200,000 deaths. Legends of ancient, otherwise unrecorded tsunamis saved many Andaman Islanders from that disaster, because they recognized the signs of an incipient tsunami and ran for cover. Flood stories of many cultures, including our own (think Noah’s Ark), testify to the importance of maintaining both a worldwide tsunami warning system and emergency evacuation plans for all coastal communities, large and small.

Asteroid impact as an act of God gives pause, but what about as an act of mankind? If we learn how to push asteroids out of the way, it will become possible to push them into the way. An act of war! This could cause an impact mere decades away. As weapons, asteroids actually have some desirable qualities. Since the impact must be planned and engineered years in advance, evacuation could prevent deaths. Warfare without loss of life is better than the other kind, so with some trepidation I recommend going forward with research on asteroid warfare.

Finally, a couple of recommendations that are less earthshaking (literally). One is to check out some shooting stars. They are space rocks, too small to cause damage, that burn up high in the atmosphere, putting on brief but awe-inspiring shows. Shooting stars can and do happen on any night, but there are more during meteor showers. The Perseid shower peaks around Aug. 12–13, typically at a rate of dozens per hour. Meteor “storms” are meteor showers with particularly high rates, hundreds or at times even thousands per hour. The so-called “king of meteor showers” is the Leonid shower, peaking yearly on a night on or near Nov. 17–18, with peak rates that vary greatly over a 33-year cycle (because comet Tempel-Tuttle is the source of the Leonids and has an orbital period is 33 years). One can get an idea of how many shooting stars will be visible on what nights of what years and from what meteor showers at http://leonid.arc.nasa.gov/estimator.html. Cloudy, too much light pollution, or you don’t feel like going outside? Then view videos of shooting stars available online at sites like youtube.

Another thing you can do is hunt for micrometeorites. As discussed earlier, anyone can do it.

A final suggestion: check out an old impact site. This can be part of a fun vacation! For example, Meteor Crater in Arizona is commercially developed into a tourist attraction and is easily accessible from Interstate Highway 40. If you have more time and money, you can arrange a Tunguska site tour, see e.g. http://www.sibtourguide.com/tunguska.html. Such activities can help impress visitors with the awe-inspiring power of the universe.

References

Association of Space Explorers, the “international professional organization of astronauts and cosmonauts”: R. L. Schweickart, T. D. Jones, F. von der Dunk, and S. Camacho-Lara, Asteroid threats: a call for global response, 2008, Association of Space Explorers, http://www.space-explorers.org/ATACGR.pdf.

“…protracted debate …can lead to inaction; evacuation of the impact site may then be our only option.” Association of Space Explorers, www.space-explorers.org (document no longer online).

“Spaceguard Survey: Report.” D. Morrison, Spaceguard Survey: Report of the NASA international near-Earth object detection workshop, Jet Propulsion Laboratory, Cal. Inst. of Tech., Pasadena, CA, 1992, http://impact.arc.nasa.gov/downloads/spacesurvey.pdf (linked from http://impact.arc.nasa.gov/gov_nasastudies.cfm).

“This objective seems a likely to be achieved a few years late.” Near-Earth object survey and deflection analysis of alternatives (report to congress), National Aeronautics and Space Administration (NASA), 2007 http://neo.jpl.nasa.gov/neo/report2007.html.

“a rocky asteroid 100 feet in diameter could easily be around 600,000 tons (metric: 30 meters and 560,000 metric tons).” C. Q. Choi, Small asteroids pose big new threat, part (1b) of Tunguska revision, and a possible NEA impact on Mars, Dec. 21, 2007, News Archive, NASA, http://impact.arc.nasa.gov/news_detail.cfm?ID=179.

“A variety of pushing strategies have been devised, some more starry-eyed than others.” Near-Earth object survey and deflection analysis of alternatives (report to congress), National Aeronautics and Space Administration (NASA), 2007, http://neo.jpl.nasa.gov/neo/report2007.html.

“Explosions are a good way to produce strong, short forces.” ibid.