On the Impending Asteroid Impact

I’m primarily a stellar astronomer, but if you look back at my previous blog posts you’ll notice I spent a lot of time talking about stuff within the Solar System. Partly that’s because it’s been a really great couple of years for space exploration, full of gorgeous images and fascinating science, partly because it’s the passion that got me into astronomy in the first place, and partly because it’s the stuff that impacts us directly.

So let’s talk about the asteroid that’s going to impact us directly.

The object has the oh-so-clinical provisional designation WT1190F and is destined to hit the Earth’s atmosphere on Friday, November 13th. It is not expected to do any damage, and any surviving pieces will land somewhere near Sri Lanka.

Most sources are reprinting the first few lines of the AOL article about the topic, which is great except that the logline (“Researchers have discovered some space junk hurtling toward Earth, and they aren’t exactly sure what it is.”) is immediately contradicted by the fact that we DO have a pretty good idea what it is, and we did before the article was posted. Here’s ESA’s Near Earth Asteroid Tracking page, with an article dated from October 22, 5 days BEFORE the AOL article. I can’t get a direct link to just the article in question, so I’ll summarize it for people who are looking at this in the future.

WT1190F was found by the Catalina Sky Survey on October 2nd, 2015. It’s been observed enough to conclude that a.) it’s quite tiny – about 7 feet long (roughly the size of LeBron James), b.) it’s been in a 3-week-long orbit around the Earth (just inside the 4-week-long orbit of the Moon), c.) it’s going to impact the Earth about 100 kilometers south of the coast of Sri Lanka at around 6:20 UT on November 13, 2015, and d.) not only it it small, it’s much less dense than rock, as if it’s a hollow rocket booster. Or maybe Space Jam 2 is going to feature the most incredible slam dunk of all time.

In further summary, 1.) it’s harmless, and 2.) it’s probably one of ours. Short of actually identifying which space mission the booster is from (which I’m sure someone is working on), I don’t know that we’ll get any more information than that.

This is only going to be the second time in human history that we’ve tracked an “asteroid” that later hit the Earth – an object that burned up over Sudan in 2008 was the first time, and this might not even count if it’s really just some of our own space debris. We’ve seen that lots of times.

But wait! I hear you say. Didn’t an asteroid just pass the Earth on Halloween? Well, yes. Actually, this sort of thing happens all the time. If you check the JPL Close Approaches page, you can see there’s usually one or two asteroids passing us every day. Of course, this list takes a very broad view of “close approach”, as most of the passing asteroids pass more than ten times farther away than the Moon. Basically, if the Earth is in a shooting gallery, it’s an incredibly tiny target being aimed at by very poor marksmen.

But do we need to care about asteroids in general? Well, yes. An asteroid killed the dinosaurs. A 100 meter impact would have the force of a couple nuclear weapons. The Tunguska Event was probably caused by a 30-60 meter asteroid (and that’s what JPL’s Close Approach tracker is watching for), the Chelyabinsk meteor event was probably on the lower end of 20 meters in size… There are search efforts being made to find all the asteroids larger than 100 meters, and that’s how we know about 700,000 asteroids. “Spooky” the Halloween Asteroid (2015 TB145) was fairly notable for being over 600 meters in size, which is large enough to make a 6-mile-wide crater (the size of downtown Chicago) if it hit… we thought we were already tracking all of those, but it was first noticed on October 10, 2015. Why? Because it’s in an unusual comet-style orbit (and is probably a comet that ran out of ice aeons ago).

What can I say, the solar system is still plenty exciting. And we can enjoy these latest spectacles safe in the knowledge that these are not dangerous.


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