<p>I heard on the radio, courtesy of Garrison Keillor (sp), that today marks the anniversary of a meteor passing with 500,000 miles of Earth back in 1979 (may have the wrong year).</p>
<p>Apparently, this meteor was the size of a “mountain” and had it hit Earth it would have made a crater the size of the District of Columbia.</p>
<p>The most troubling aspect is that its impact would have had the effect of “40,000 hydrogen bombs” detonating!!! That is an unbelievable amount of devastation! Would ANY life on Earth survive it?!</p>
<p>My question is: What plans, if any, have been made to ensure that such a catstrophe doesn’t happen? I realize of course that if an errant PLANET or similar object was headed our way there would be nothing we could do, but with our technology could we not handle lesser threats from space?</p>
<p>Oh, and please spare me the Chicken Little jokes. ; )</p>
<p>Actually, asteroids–which is what the OP is referring to–have passed within the orbit of the moon, approx. 240,000 miles. The “within the orbit of the moon” has become a rule-of-thumb benchmark for assessing danger for large objects. Asteroids are the biggest threat…speaking of planet-sized objects, absent a Phillip Wylie WHEN WORLDS COLLIDE scenario where some detached planets come whirling into the solar system from the deep beyond, is remote to an extreme probability…and very few asteroids have orbits that intersect with Earth’s. Most, oddly enough, occupy the asteroid belt in the region between the orbits of Mars and Jupiter where, depending on your chosen flavor, a planet either never formed or one formed and then broke up…I think the former theory is the one with greatest credence these days but I admit not to having read on the subject for 2-3 decades. </p>
<p>There are some indications that the inner solar system may have been “cleaned out” of errant asteroids by now. Certainly at one time they were far more prevalent…just look at the moon’s surface for evidence. And it was a hella big something that hit Tycho, that’s fer sure. Not to mention that the Gulf of Mexico is probaby the fossil remnant of a strike by a Very Large Object.</p>
<p>In terms of damage, anyone in the local area would not have a good day. But the larger consequence would be climatic, a precipitous cooling of the Earth due to the kicked up dust (or water vapor) in the atmosphere in some combination aborbing/reflecting the sun’s heat. The cool weather after the explosion of Krakatoa in the early 1800’s would be a pimple on an elephant’s butt in comparison. Such a phenomenon as been linked to the disappearance of the dinosaurs and 90 percent of the then-extant species at the time of the K-T boundary between geologic eras…Cretaceous and…umm. (Sorry, I’m doing this all from memory.) Would be an ironic way to control the now rapid global warming.</p>
<p><em>Doing</em> something about a predicted impact is something else. Some SF writers have written stories about this, though I can’t recall any good ones off the top of my head. Simply trying to blast it with a salvo of nuclear warheads wouldn’t do much. First, there’s the problem of outfitting suitable rockets to boost the payload to a speed beyond Earth escape velocity…ordinary ICBM’s won’t suffice. Then, even if you break a large mass into bits, the central path of those bits is still going to be an impact on Earth. Off the top of my head, you need a deep space mission to intercept the problem asteroid and then mount thrusters with sufficient force to tweak the asteroid’s track so that it will miss Earth…this is a non-trivial problem.</p>
<p>Thanks, TheDad, asteroids it is then!
Speaking of diverting the incoming asteroid’s path with “thrusters”, what about using nuclear warheads, sufficiently removed from posing a problem for Earth, to exlode at a distance that would effect such a diversion without blowing it up into smaller yet still problematic fragments?</p>
<p>There have been a number of suggestions with regard to dealing with an asteroid. One would be solar sails, admittedly I’m not sure how these work, but I think it uses the force of light energy or maybe solar wind (j/k, unless it’s actually right). A sail would be put on the asteroid to push it out of it’s path. I think a professor at Cornell has been working with these at least theoretically. Some others have said that by merely flying a space shuttle or satellite near the asteroid would provide enough of a gravitational force to deflect an asteroid. Another would be to simply, as someone else said, strap a rocket to it.</p>
<p>Bombing an asteroid would break it into pieces, and tracking the pieces would be almost impossible, so some may still hit earth.</p>
<p>Of course it’s a great threat, but be comforted in the fact that most asteroids can be spotted years before predicted collisions.</p>
<p>Leanid, exploding a nuclear warhead in “front” of the asteroid would do very little…there’s no significant medium in space for a shock wave to propogate in and the force of the explosion itself would be negligible.</p>
<p>Garland…those are among the movies that I avoid like the plague though I think I read the parody of at least one of them in “MAD Magazine.”</p>
<p>Bing, a solar sail would theoretically work, but it takes a long time for the thrust to build to an appreciable level. Especially when you consider that the light pressure would be minimal the further out you go in the solar system, which is where you’d intercept an Incoming. </p>
<p>Seat of the pants intuitive guess says that an inbound object at the orbit of Mars would take about the same amount of time to get here as an Earth-originated probe would take to get to Mars…so, that’s what, about 21 months? Not a lot of time to detect, plan, and then execute a preventative action. Notwithstanding that we can currently barely reach the orbit of the moon with any sort of manned operation and the control factor on a robotic operation, e.g., the “comet scooper” that just returned to Earth, is very dicey…witness the number of lost Mars probes, roughly 1 in 3.</p>
<p>Ceres, the largest asteroid, is something like 480 miles long. Scale drops rapidly and the lethal size for a strike on Earth is probably something in the 1-5 mile size range. </p>
<p>Which is why a lot SF scenarios about invasions of Earth are silly. If you really want to overwhelm Earth, send in half a dozen asteroids to wallop the planet, stand back and wait 200 years for the dust to settle and climate to stabilize, and then walk in and pick up the pieces. No fuss, no muss. A bio-engineering assault with tailored bacteria or virii might be quicker, I suppose.</p>
<p>Ah. Thanks, Coureur. I hate the brain cramps that prevent me from accurately accessing memory, particularly stuff I haven’t browsed through in a while. It’s so bad that a couple of weeks ago I was talking to a woman who seemed really really familiar and then it suddenly hit me that I was at the breakfast table and it was TheMom.</p>
<p>Thedad: agreed, just wanted to point out that they’d been done already. Coming from a family of amateur astronomers, we find the real life stuff way more interesting.</p>