In 2004, astronomers identified Apophis, a 270-meter asteroid heading in our direction. Although NASA initially feared that the odds of Apophis striking Earth in 2029 were 1-in-37, they have since calculated that the asteroid will pass no fewer than 29,450 km above Earth's surface. There is an extremely small chance that Apophis could hit us on a later pass — a 1-in-250,000 in 2036 and a 1-in-330,000 in 2068.

However, Anatoly Perminov, director of the Russian Federal Space Agency, has said that Russia is very concerned about the possibility of a collision with Apophis, and is considering a plan to change the asteroid's course. However, he is a bit vague on his reasons for fearing an impact:

"I don't remember exactly, but it seems to me it could hit the Earth by 2032," Perminov said.

"People's lives are at stake. We should pay several hundred million dollars and build a system that would allow to prevent a collision, rather than sit and wait for it to happen and kill hundreds of thousands of people," Perminov said.

The Space Agency is talking about sending a spacecraft to intercept Apophis, although this won't be an Armageddon scenario. The plan isn't to blow up the asteroid, but to physically push it off course to prevent a close encounter with Earth. Perminov says that, once the project is finalized, NASA, the ESA, and the Chinese space agency will be invited to join the mission.

Russia may send spacecraft to knock away asteroid [Mail via reddit]

Currently, NASA has been able to detect roughly 83 percent of the estimated 940 Near-Earth asteroids that are at least one kilometer in diameter. If such an asteroid were to enter our atmosphere, it could bring with it sun-blocking dust and radical climate change even before it makes an impact. But astronomers are growing more concerned with the more numerous smaller asteroids, whose impact could flatten trees — as happened in Siberia where many astronomers believe a comet or asteroid exploded in 1908 — shatter cities, and cause unpredictable waves of coastal flooding. Because of their size, these asteroids are difficult to detect, and astronomers fear one could strike the Earth with little or no warning.

In 2005, the United States Congress charged NASA to detect at least 90 percent of these smaller asteroids by 2020, but a report from the US National Research Council reveals that achieving that goal will require far more equipment than is currently allotted to asteroid detection. The report indicates that new facilities need to be built, with equipment capable of detecting fainter asteroids and covering a wider range of the cosmos. A better system will need to be developed for detecting asteroids that are particularly close to Earth, rather than simply creating a catalog of near-Earth asteroids, and a telescope would need to be placed at another vantage point in space to detect asteroids coming from the sun.

The NRC is unsure what the cost of these systems would be, but panel leader Irwin Shapiro of the Harvard-Smithsonian Center for Astrophysics believes it is essential to our continued safety:

"There is no free lunch," Shapiro agrees. But he adds, "We're talking about investing in an insurance policy."

Earth could be blindsided by asteroids, panel warns [New Scientist]

Researchers reported this week in Proceedings of the National Academy of Sciences that they found have found shock-synthesized diamonds — known to result from impact events — in the Arlington Canyon on Santa Rosa Island in California, and have previously found similar diamonds in the Greenland Ice Sheet. The placement of the Arlington Canyon diamonds coincide with North America's oldest known human remains — from the Clovis people, who went extinct nearly 13,000 years ago — and the disappearance of the pygmy mammoth from Santa Rosa. This fits with the team's earlier speculation that a comet strike led to a mass mammalian extinction across North America:

In 2007 researchers theorized that a comet set off continental fires that led to the mysterious disappearance of the Clovis people and the extermination of 35 mammal genera, including mammoths, mastodons, ground sloths and camels. The team documented a "black mat" of charcoal throughout North America that contains high levels of iridium, magnetic spheres, and nano-diamonds, which are consistent with such an airburst.

However, the hypothesis remains controversial, and other geologists and archeologists are reluctant to buy the diamonds as evidence of a comet-induced die-off, especially given the absence of an impact crater.

Did a Comet Cause a North American Die-Off around 13,000 Years Ago? [Scientific American]

NASA's list of potentially hazardous asteroids (PHAs) currently numbers 959. That's 1,000 asteroids that astronomers pretty much know are going to get closer than 7.5 million kilomters to Earth, about 20 times the distance from here to the Moon. Five of those are expected to come between Earth and the Moon over the next century.

So we'll have a few close shaves but nothing to worry about, right? Not so fast. The total number of PHAs and comets astronomers think are out there is probably more like 20,000. That means we've mapped about 5% of the objects that stand a good chance of hitting us. So take the future part of this chart as a best-case scenario. The past five close encounters, however, show just how vulnerable we are:

1) The Comet of 1491. This one must've scared the hell out of some folks. At a little less than four times the distance to the moon, this was the closest pass ever recorded at the time, and no one knows for sure how big it was. Little did our ancestors know how much more interesting things would get.

2) Tunguska, 1908. One of the most famous Earth lcose calls of all time, it was also a pipsqueak. For a long time scientists believed a comet perhaps 60 meters in diameter exploded over Siberia with a force of as much at 30 megatons, or about 2,000 times more powerful than the atomic bomb dropped on Hiroshima, though nothing solid ever hit the planet. All those pictures of flattened forest certianly look impressive, but last year, scientists re-crunched the numbers and found that the comet oculd've been as small as 30 meters, and the blast just 5 megatons. In other words, much smaller objects can do way more damage than we ever thought before. Gulp.

3) The Great Daylight Fireball of 1972. The name says it all — it doesn't get much closer than this. Size estimates range from 3 to 14 meters in diameter, depending on whether it was ice or rock. Whatever it was, the object called US19720810 burned through the atmosphere from Utah to Canda for about a minute and a half. Luckily, the space rock struck a glancing blow — had it hit Earth directly, it could've blasted us with 1/2 a Hiroshima worth of energy.

4) 2004 FH and 2004 FU162. At 30 meters in diameter and made of solid rock, 2004 FH would be a thumper of Tunguska proportions if it ever hit home. In the right (or wrong) place, it could detroy a city. As it was, it passed 43,000 kilometers above Earth on on March 18, 2004.

Three weeks later, FU 162 came whizzing along. Astronomers basically discovered it at bascially the same time as the 6-meter in diameter rock soared just 6,400 kilometers above Earth's surface.

5) Comet Hyakutake. Now we're getting into civilization-threatening territory. At 2 kilometers in diameters, this comet only got within about 40 lunar distances to Earth in 1996. Compared ot our other close calls, that's pretty comfortable, but considr this: it was discovered less than two months before its closest pass. Had it been on a collision course with Earth there's almost nothing we could've done other than brace for the millions dead, massive climate disruption, crop failure, 500-foot high tsunami...you get the idea.

FUTURE:

6) 1999 AN10. In a little less than 20 years, our usually quiet Earth-Moon system is going to have a lot of visitors. In August 2027, AN 10 is going to get about one lunar distance from Earth, and we'll get a chance to see just how big this bad boy is. Estimates range from 1/2 to 2 kilometers in diameter, plenty large to leave a dent in humanity if it ever gets closer.

7) 2001 WN5. Just six months after AN10 comes a callin' WN5 will get even closer, just about splitting the difference between Earth and the Moon. At 700 meters in diamters, this asteroid has a got potential for major dmaage, but current odds of impact are rated a negligible.

8) 99942 Apophis. By far the most famous of the end-bringing objects we know about in our solar system, astronomers thought for a while that this 270 meter-wide rock had an almost 3% chance of hitting us. Since then, odds have been lowered to 1 in 43,000 that it could slam into Earth in 2029. But if it passes through a gravitaitonal keyhole — a tiny region in space that could tweak its orbit ever so slightly — an impact could still happen on April 13, 2036.

9) 2005 WY55. Just 200 meters wide, astronomers think this asteroid could still pack a wallop. Right now it's scheduled to get within about 75,000 km of Earth, but impact odds are big enough to kep in mind — currently they're rated at around 1 in 70,000. If our number comes up on that faeful dayin May 2065, look out — blast yield estimates from this rock range to 1100 megatons.

10) 2000 WO107. Depending on how well humanity holds up under climate change, bird flu, and all the other things that could potentially kill us off, we might be able to look up and see WO107 zoom by in December 2140. The 400 meter-wide rock isn't scheduled to hit us — it should get about half way between Earth and the Moon — but if calculations are off by even a little bit (and all of the future examples here have some uncertainty) we could care a lot.

Sources: NASA's Near Earth Object Program, Harvard List of PHAs

Additional research by Nivair H. Gabriel. Image by Stephanie Fox.