Look up at our nearest neighbor , the moon , and you 'll see stark evidence of the dangerous neighborhood we live in . The Man in the Moon was sculpted by large-scale events , including many meteor and asteroid impacts . In 1994 , the comet Shoemaker-Levy 9 dove into Jupiter . The result was awesome . The impact caused a brilliant flash , visible in Earth telescopes , and left an ugly dark scar on Jupiter 's cold , gaseous surface . With the recent fly-by of a 1,000-foot-wide asteroid labeled 99942 Apophis , one of a class of space rocks referred to as `` near-Earth objects '' or `` Earth-grazers , '' scientists have revised their worst estimates of its chances of striking Earth . Current thinking is : We 're safe . For the next couple of decades . But this does not mean the danger is over . Far from it . Named after the evil Egyptian serpent god Apophis , lord of chaos and darkness -- and recently dubbed the `` doomsday asteroid '' -- it flies past Earth every seven years . This year , its 1,000-foot bulk approached to within 9 million miles . In 2029 , it will swoop in close enough to put some of our orbiting satellites in peril -- 20,000 miles . In that year , no doubt Apophis will arouse even more attention , because it will be visible in the daytime sky . In 2036 , it will probably pass by at a reassuring 14 million miles . Yet there 's always a possibility we do n't have these measurements exactly right . Something could happen at any point in Apophis ' orbit to modify its course , just a smidgen . A tiny collision with another object , way out beyond Mars ? What could change between now and 2029 , or during any orbit thereafter ? Apophis masses at more than 20 million tons . If it hit Earth , the impact would unleash a blast the equivalent of over a billion tons of TNT . That 's not an extinction event , but it could easily cause billions of deaths and months , if not years , of climate disruption . The potential risk is huge . And Apophis is far from alone . Life in our solar system has always been dangerous . As kids we learn about the Barringer Crater in Arizona , a relatively recent formation -- 50,000 years old -- caused by a rock weighing several times more an aircraft carrier . That impact released the equivalent of 20 megatons of TNT and left a crater 4,000 feet wide . Both Mars and Earth were long ago hit by planet-sized objects , one spinning off our Moon , the other shaping two distinctly different hemispheres on Mars . To this day , a steady rain of meteors falls on Earth -- some of them left-over pebbles and dust from worn-out comets , others from the `` asteroid belt , '' still others from big strikes on the Moon and Mars . Since oceans cover two-thirds of the Earth 's surface , it 's more likely debris will hit water than land . Scientists believe it was the blast of a 6-mile-wide asteroid off the coast of Mexico some 64 million years ago that changed Earth 's weather for years and hastened the departure of the dinosaurs . Ocean hits are worse than land hits , not just because of immense tidal waves , but because of the vast quantities of super-heated water vapor and dust that spread from the impact to shroud the entire Earth . In March 1966 , J.E . Enever published his ground-breaking article , `` Giant Meteor Impact , '' in the periodical Analog Science Fiction/Science Fact . Enever surveyed the available material on meteor and asteroid strikes , then published his own calculations and analysis of what such strikes could do , and have done , to the Earth , with cinematically vivid prose and equally terrifying physics . He was the first to put it all together and publish in a respected and widely available forum . Although geology was still reluctant to admit to any form of `` catastrophism , '' eschewing biblical explanations , many read and pondered ... seriously . In the decades since Enever 's article , writers , scientists , and engineers have proposed various ways to avert such disasters . Some have suggested we strap rocket motors to a threatening rock and nudge it away . A steady pulse of projectile `` paintballs '' could also do the trick . Others have suggested we use nuclear weapons to `` kick '' an asteroid from its orbit , or even to shatter it into smaller debris -- a rather dim idea that misleads us into believing a single bullet is worse than the blast from a shotgun . Our atmosphere provides little protection against meteors larger than a truck . Moreover , many asteroids are chunky masses of rock and dust loosely held together by very little gravity , like loosely packed peanut clusters . Attempting to attach a rocket to one of these might merely dislodge a few `` peanuts , '' leaving the rest to do the dirty work . Wrap one of these peanut clusters in a giant steel net , then drag it off its deadly course ? Intriguing , but for now -- like deploying tractor beams from the starship Enterprise -- it 's just so much super-science .
John Bear : Asteroid Apophis flew by this month and was much larger than expected . Named after an evil Egyptian serpent god , Apophis swings by every ten years . Bear : We can never be 100 % sure how close it will come or if events might change its course . If Apophis hit Earth , he said , the blast would be the equivalent of over a million tons of TNT .