# Asteroid update: size doesn’t matter

Contributed by
Mar 25, 2008

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!