WEEKLY WHINE

Because old horizons just suck

Things are happening at Pluto.

Well, not really. Things are happening here that have something to do with Pluto there.

You see, on SUN 15 MAY 2005, Stern et al used HST to spot two moons orbiting Pluto. We like to call them "new" moons, but it's not like S/2005 P1 and S/2005 P2 just suddenly showed up on Pluto's doorstep and said, "Hey, can we orbit you for a while?" and Pluto responded, "Sure! Do you want any of Charon's old stuff that doesn't fit him any more?"

But still, it'll be very interesting when the New Horizons spacecraft [named for the infamous elementary school in Wilmington, NC, USA] finally lifts off in a couple of weeks. If not for Congress, the mission [or one of its various guises like Pluto-Kuiper Express] would have flown by Jupiter already.

But who are we to complain?* And who are you to listen to us? Let's just agree that since no spacecraft has approached Pluto yet, this will be lots of fun and very educational. So let's review some of the things we want to learn.

MASS AND RADIUS

What, you think that's easy? Fine. Tell us Pluto's mass and radius to six figures.

See, we can watch Pluto and Charon orbit each other from here, which gives us a good idea of their total mass [about 1.46 × 10²² kg]. But it's harder to tell how many of those kilograms go to which object. It's also kind of hard to determine their diameters. So, the obvious solution is to go there and see.

ATMOSPHERIC COMPOSITION

In Charon's case: none. The occultation of 2UCAC 2625 7135, a magnitude 14 star, by Charon on MON 11 JUL 2005 suggests that it has a tenuous atmosphere at best, though you'd expect that given its size. As for Pluto, two other occultations in the last twenty years showed that it's got an atmosphere. But we suspect that it's rapidly thinning as its nitrogen and carbon monoxide freezes onto the surface. So that's why the scientific community was in such a rush to get to Pluto before there's no more atmosphere left.

SURFACE COMPOSITION

If we don't hurry up, frozen nitrogen and carbon monoxide. Seriously, though, we expect it to be made up mostly of ices, like Triton and some of the other large moons of the outer planets.

BRIGHTNESS

This is why we're not sure how big Pluto really is. We can see how much light it reflects, but we have to know the albedo – how much of the sunlight that hits it bounces back into space. Once we know that, we'll be happy.

SURFACE MAP

Start thinking now about the themes for surface features on Pluto and Charon. How about names of Disney characters for Pluto? That will be very fun for future settlers, won't it? "Yeah, I live in the base on Cruella Peak. But I'm thinking of building a habitat on Pongo Planitia."

* Answer: We're GoobNet. That's all we do here.