Building on yesterday's theme, we have close encounters with space-rocks all the time. Here's your round-up of recent past, upcoming future, and newly-discovered things that aren't hitting us.
Yesterday at 7:20 PST, 2014EF moseyed by at 0.4 lunar distances, then snuggled up to the moon less than three hours later. In between those two approaches at 8:34 PST, 2014DO7 strolled through our orbit, although at 27.4 lunar distances, it's wasn't even interesting enough to get reflexive panic attack from the most spastic of news organizations. (Technically, all these times are really Barycentric Dynamical Time, the solar system's time zone. I've translated into Pacific Standard Time by subtracting 8 hours, but it's really 8 hours, 34 seconds. Now you know my dirty, dirty lies.)
Remember how several of you commented that it's not unusual for us to only spot these rocks after they've whizzed past? Well, astronomers got their first peek at 2014EC yesterday, getting in just enough observations to plot its probable orbit just over 38 hours before its closest approach, within 0.2 lunar distances today at 1:29 pm PST. That's only the first of our visitors for Wednesday — minutes later at 1:40 pm, 2000 EE14 will stroll past at a luxuriant 64.6 lunar distances away, followed by 2014 DH10 at 4pm at a still nicely roomy 29.1 lunar distances.
EC2014 will be coming so close to the Earth today that the labels overlap in a tiny, indecipherable mess. Screenshot from the JPL Small Bodies Browser, a website that sounds mysteriously NSFW but isn't.
At 0.4 lunar distances, 0.2 lunar distances, 2014EF and 2014EC are going to be genuinely close. Worse, with limited observation data on 2014EC, we could be wrong about its orbital parameters. Yet, I'm still totally confident that neither of them are going to kill us. Why? Both are in the 5 to 15 meter diameter range. That's not an asteroid, that's a space-pebble! They're so small, they don't even count in the list of the roughly 20 near-Earth objects we'll encounter each year.
The orbital parameters report that both asteroids are moving at a respectable pace (15 km/s). Going for a worst-case scenario of a maximum diameter (15 m) iron asteroid hitting dead-on at 90 degrees (a glancing blow would be far more likely with an orbital miscalculation), an asteroid that small would explode nearly 2 kilometres up in the atmosphere. The air blast would be nasty — over 100 dB of noise, and winds topping out at 195 m/s (435 mph), damaging bridges, shattering windows, and blowing down trees. Any rock fragments would rain down, creating a crater field in the immediate vicinity. That's it. That's the very, very worst 2014EC could do to us. (Dear impact calculator: I love you. Thank you for all your tasty data.)
Actually, it's 2000 EE14 that scares me, and makes me very glad we've been tracking it for a several years. We know it's orbit within less than a second: it's going where we think it's going. That makes me breathe easier, because EE14 is somewhere between 1 and 2 kilometres diameter. That's big enough that if this time when I head over to the impact calculator, I use nice, friendly-to-humans assumptions of a medium-density rock and a glancing blow (alas, still at 15 km/s — we know that from observations already), that sucker would create a massive, complex impact crater 10 kilometres across and half a kilometre deep. Barringer Crater in Arizona is only 1 kilometre across!
Barringer Crater, also known as Meteor Crater, is a pipsqueek 1 kilometre diameter compared to the 10 kilometre pit we'd enjoy if EE14 crashed into us. Image processed by the Earth Observatory.
It's not just the crater that would be problematic. That sucker would produce a magnitude 7.7 earthquake, and an air blast so intense that on the opposite side of the planet, a full 20,000 kilometres away, people would still hear a 40 dB growl. Ok, fine, that isn't very loud (bird calls are 44 dB), but to still be able to hear the impact, unaided, on the far side of the planet is impressive. A fine coating of dust would blanket the planet, which can lead to all sorts of trickle-down climatic effects, screwing with the (relatively) good thing we've got going on. Sure, it's not a planet-killer, but it'd certainly make for an extremely bad day for a large chunk of people. Good thing it's not going to happen this orbit, or from the looks of it, on any close approach it will make to us, our moon, or any other planet, for the next 200 years.
A big rock, one on order of a kilometre across like EE14, hits the Earth approximately once every 10 million years. I, for one, am very glad that today we aren't beating those odds for spectacular death. At least, not today...
Need more asteroid goodness? Astro Bob has more information on observing 2014 EC. Keep track of close approaches by Near Earth Objects on the JPL site, or by following @AsteroidWatch on Twitter.
Correction: An earlier version of this article listed the velocities as 15 m/s, not 15 km/s. Thanks to engineer Eric for teasing that there's nothing respectable about crawling around in a 15 m/s orbit! Orders of magnitude: the matter.