Asteroid 2012 DA14 may have gotten this close to us, but most 'potentially-hazard asteroids' do not
Asteroid 2000 EM26 passed by the Earth late on Monday night, coming to within about 3.4 million kilometres (or nearly nine times the distance between us and the moon). This 270-metre-wide asteroid was discovered on March 5th, 2000, and the orbit that scientists traced for it shows that it travels between just outside the orbit of Mercury, to between the orbits of Earth and Mars (making it an Aten asteroid). It's been doing so every nine months or so, for an extremely long time (possibly going as far back as the early days of the solar system) and it's still doing so now. So it hasn't posed any impact risk in the past, and it actually doesn't pose any impact risk in the foreseeable future either (at least out to the year 2200 so far). It hasn't even shown up on NASA JPL's Sentry Risk Table.
Now, if 2000 EM26 actually did hit Earth, its size and speed could produce an impact with the force of up to the equivalent of a 200 megaton bomb. That's pretty significant, considering that the largest nuclear bomb ever detonated was somewhere around 50 megatons. For this reason, and because it does come somewhat close to us (in a cosmic sense) it's considered a 'potentially-hazardous asteroid' by those that monitor near-Earth objects. Despite that label, our orbits are out of sync enough, and are just off-kilter from one another enough, that there's really no chance that it will hit us.
Scientists always watch these big asteroids as they whiz by us, though, to get even better tracking information, and produce even better orbital paths for them. Plus, it's always good to check in on these things. With the number of asteroids flying around out there, Earth really is flying around in a cosmic shooting gallery. If 2000 EM26 were to hit another big asteroid out there, either could be nudged into an orbit that's more hazardous to us. So, getting updates will help us protect ourselves.
As for finding new asteroids, there are plenty of observers on the ground, and NASA's NEOWISE satellite looks for asteroids using their heat. NEOWISE principle investigator Amy Mainzer talks about the program in this video:
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Two more big asteroids are set to fly by us later this week. Asteroid 2014 BR57 is a roughly 71-metre-wide space rock that will pass us on Thursday. It's less than a third of the size of 2000 EM26, but it flies by at around half the distance that the larger rock did — 1.7 million kilometres or around 4.4 'lunar distances' (LD). Asteroid 1995 CR, which is another 200+ metre-wide rock, swings by on Friday, but it's also another one that passes at a very safe distance — around 3 million kilometres or 7.7 LD. We've had some startling events just in the past year, though, with the close pass of 2012 DA14, the Chelyabinsk meteorite explosion just a year ago, and even the meteor that apparently exploded west of Montreal back in November.
Right now, there's only one asteroid that we know if that still ranks as any kind of potential impact threat — asteroid 2007 VK184. This roughly 130-metre-wide Apollo asteroid is listed as a 1 (one) on the Torino Impact Hazard Scale, due to a 1 in 1,750 chance that it will hit the Earth on June 3rd, 2048. That ranking on the scale means that scientists are watching this one, and will likely demote it to a 0 (zero) on the scale with future observations. One opportunity is coming up on May 23rd of this year, when 2007 VK184 crosses our orbit at a point well-ahead of us — a nice safe distance of about 25 million kilometres. Getting more information about it during that close-approach will tell us if we really need to worry about early June 2048, and 2007 VK184 could be a great target for us to test out asteroid deflection strategies!
(Image courtesy: Getty)
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