Blogs / Bad Astronomy

Just a quickie update on the asteroid naming thingy:

Michael Stackpole and Rebecca (well, A Real Girl for Rebecca) have posts on their asteroids. They mention their asteroid designation numbers — all asteroids get a number and a name, hence 165347 Philplait — which means I can look up their characteristics too!

I wish I hadn’t. Of the four (including PZ’s), mine is smallest.

Figures.

Rebecca’s is about 4.3 kilometers in diameter, and Michael’s is about 1.7 km across. Mine is 1.3, PZ’s is 2.6.

Sigh.

Anyway, I described how the diameter is estimated in my last post, but specifically there is a parameter called the absolute magnitude, which describes how bright the asteroid would be if it were 150 million kilometers from both the Earth and the Sun and the side of the rock facing us was completely lit by the Sun. This geometry is actually impossible (the Earth needs to be between the asteroid and the Sun for this to happen, so the asteroid can’t be the same distance to both at the same time!), but it’s just a definition. Once you know the absmag and assume an albedo, you can calculate the asteroid diameter. I used astronomer Dan Bruton’s calculator webpage for this, once I got the absmag from the bottom of the JPL Small-Body orbit diagram page (the links for those are above and in my last post).

I checked my numbers twice and I’m still smallest. Reality can be cruel.

Still, I did happen to see that of all four, mine gets closest to the Sun in its orbit, and hence closest to Earth. That makes it the easiest to get to, so I’ll probably get mine colonized first. It’s smaller, with lower gravity, making it easier to land on (really dock to) as well. That’s something.

I also see that Rebecca’s has the widest orbit; I can think of any of a half-dozen jokes I could make, any one of which would get me emasculated the next time I see her so I’ll refrain — and you should too, I’d wager.

Seriously though, I’m totally chuffed by this. Congrats to my trio of extraterrestrial compatriots as well. And Jeff Medkeff, the co-discoverer of the quartet, has posts up about them: mine, Rebecca’s, PZ’s, and Michael’s, as well as a general post about with an overview of the situation. Thanks Jeff!

It is with great honor and no small amount of pride to announce that the asteroid 2000 WG11 shall henceforth be known as asteroid 165347 Philplait.

That’s right: I now have an asteroid named after me.

My friend, fellow astronomer, fellow skeptic, and fellow blogger Jeff Medkeff discovered the asteroid in 2000. It was given the preliminary designation of 2000 WG11, and Jeff had the privilege of naming it, and the short version is he decided it was my time.

The asteroid is about 1.3 km (0.8 miles) across, making it rather small as asteroids go. Because of that (and its current distance of 450 million kilometers) it’s a bit faint, shining right now at about magnitude 21. That’s within reach of a 12" telescope with a nice CCD detector on it, but you won’t be seeing this with your birdwatching binocs.

I don’t have any images of it… yet. It’s listed in the Minor Planet and Comet Ephemeris Service; put "Philplait" into the big text box and it will give you the coordinates of the asteroid (it’s currently in the constellation of Aries). You can see where it is in the solar system on the JPL Small Body Database Browser. Here is the map for today:

As you can see in the map, it’s a main belt asteroid, orbiting the Sun between Mars and Jupiter. It can’t impact the Earth (too bad, since that would be pretty good publicity for Death from the Skies!; I’d sell a million books — plus, the headlines would read "Philplait to Destroy the Earth!" which is awesome). If it could hit us, it would have an impact yield of at least 35,000 megatons, which is a lot, and could easily be a lot more (I’m assuming here that the minimum impact speed is 11 km/sec, Earth’s escape velocity; it could in fact be much higher). This probably would not cause an extinction level event for humans, but it wouldn’t be fun either. The asteroid that wiped out the dinosaurs was from a rock more then 8 times the diameter of 165347 Philplait^* and 500 times the mass.

To give you an idea of the asteroid’s size, it has more than 200 times the volume of Hoover Dam. Assuming that it’s made of rock, it has a mass of about 2 quadrillion grams, or about 2 billion tons. If it’s metal it’ll be about twice that massive.

The orbit is mildly eccentric, which means it’s not a perfect circle. It gets as close as about 300 million km from the Sun and as far as 400 million km (180 to 240 million miles). This keeps it well outside the orbit of Mars and well inside Jupiter’s. It’s a nice, safe, rock.

I would say having this rock named after me is a singular honor, but in fact it isn’t: three other skeptics join me in the asteroid belt: Rebecca Watson, Michael Stackpole, and, yes, PZ Myers.

Now, I know my readers, and I know what you’re thinking: whose asteroid is bigger, mine or PZ’s? I asked Jeff that as well, but first I need to take a little diversion into sizes of asteroids.

Asteroids in the main belt are in general too small and too far away to see them as anything other than unresolved dots. So we can’t measure their size directly. Instead, it’s inferred. Imagine two asteroids at the same distance from us, but one is bigger than the other. Since it has more surface area, it reflects more sunlight, and will appear brighter to us. However, the reflectivity of the asteroid also determines its brightness: a shiny white asteroid will be a lot brighter than one the same size that’s soot black. The reflectivity of an asteroid is called its albedo. Something that reflects 100% of the incoming light has an albedo of 1, while something pitch black would have an albedo of 0.

So the size of an asteroid is calculated using its distance and assuming an albedo. On average, asteroids have an albedo of about 0.15, so that’s what usually assumed. It’s also assumed that the asteroid is a sphere, which may not be true. In fact, only asteroids hundreds of miles across are spherical, so one a mile across can be any sort of weird shape.

So assuming the asteroid has an albedo of 0.15 and that it’s round, it’s about 1.3 kilometers in diameter. It could be shinier and smaller, or darker and bigger, or elongated and bigger, or or or. Until we go there and take a look we won’t know.

Having said all this, I’ll note that all things being equal, PZ’s asteroid (153298 Paulmyers) is twice the diameter of mine. Sigh. Figures. However, I’m not insulted. In fact I think PZ is overcompensating for something. Still and all, we don’t really know how big they are, but his being bigger is the safe way to bet.

Even if I must share this honor with PZ (and there better be a species of squid named after me soon to make up for this) it is still a great one. I wonder… some time in the distant future, will some astronaut mine this asteroid? Will it be someone’s home, or will it be just another rock among billions, silently orbiting the Sun?

Either way, this is totally amazing. It’s a little slice of immortality, and one I am truly touched to receive.