Finding Ass-roids

Okay, that title is unnecessarily crude, but fuck it. What follows is a video showing the number of asteroids that have been discovered since 1980.

Can you figure out which little dot is the earth? Here’s a hint: it’s the one going around the sun (err…which one is the sun, I wonder).

One thing you might notice is the sudden burst of discoveries at right angles to the earth right near the end of the video. I’m guessing those are discoveries made by the WISE satellite, which launched in December of 2009. The WISE satellite (Wide-field Infrared Survey Explorer) is an infrared survey satellite that is always pointed 90 degress from the sun and earth…exactly where all those asteroids are being found.

One thing that might be making you a bit nervous is the sheer number of asteroids that we can see by the end. With so many of ’em, the chances of being hit by one must be really high, right? Well, not really. Here, I’ll let my very close and personal friend whom I’ve never met, Phil Plait, explain why that is (from this post at his blog Bad Astronomy):

The distance between Mars and Jupiter is a bit roomier than depicted in the video. Remember, Mars is about 220 million km (130 million miles) from the Sun, and Jupiter is about 800 million km (480 million miles). That’s a whole lot of real estate: almost 2 quintillion square kilometers (670 quadrillion square miles)! Written out, that’s 2,000,000,000,000,000,000 square kilometers.

Yeah, a whole lot of real estate.

And that assumes those asteroids all lie in the same plane. In fact, many of their orbits are tilted, so we’re really dealing with volume. Even allowing that they may move above or below the plane of the solar system the paltry amount of a million kilometers, that means there’s really 2 septillion cubic kilometers: 2,000,000,000,000,000,000,000,000 cubic km! The volume of the Earth is only about a trillion cubic kilometers, so we’re talking a volume of space that could fit a trillion Earths in it!

Methinks we need not worry quite so much.

It’s Literally Nothing

Reflection Nebula NGC 1999
Source: Hubblesite.org

I’ve seen this image several times, and thanks to a lot of Terry Pratchett books and a bit of pareidolia, I always thought that this looked kind of like a silhouette of the Great A’Tuin emerging from the mists of  another universe. Still too far away and obscured by clouds to make out the elephants and the disc, you can nevertheless make out the head and the beginning of his shell. And of course the sun that orbits his mighty body is the cause of the back-lighting.

Now, quite apart from the fantastic image that I created in my own head, I always just figured that the silhouette was actually created by some kind of dense dust cloud getting in the way of the light behind it. The shape was surely an accident of history and all the dust and gas thrown off by some star or galaxy formed what looks to me like a giant turtle, and what must look to others like an amorphous blob, or as Phil Plait, the Bad Astronomer himself, says “it’s always reminded me of a Shuttle Orbiter”.

Then Phil Plait pointed out that things are not as they seem.

Herschel finds a hole in space
Source: European Space Agency

This is an image of a slightly larger area of the sky viewed in the infrared. You shouldn’t be able to tell by looking at this image exactly where the original image was because it shouldn’t look even remotely the same. The dark clouds of dust and gas that usually cause what look like empty spaces in…um…space block the visible spectrum of light, but they are usually still hot, and so glow in the infrared. A’tuin should be glowing just like everything else in this image. And yet I can see clearly that he is part of the green blob at the top of the image. Why is that?

It turns out that it’s not glowing because there’s nothing there to glow. A’tuin still appears in the image because he was literally never there to begin with. The silhouette was never a silhouette at all, but a whole different kind of black hole. It’s a big area of nothingness in the middle of that bright cloud of somethingness.

This is why I love science. How quickly and completely does our universe change with just a little bit of information! Things that we could clearly see and thought we understood turn out to not only be different than we thought, but may in fact turn out to have never actually existed in the first place!