A real sea-change that’s happened in the last ten years is the discovery of extra-solar planets, which has suddenly made planetary science respectable among astrophysicists. They suddenly see it as an exciting field.
I think it’s very ironic that, if you look at what’s going on with extra-solar planets right now, the techniques that are being applied and the kind of data that are being obtained, it’s very reminiscent of the situation in planetary science at the time that I came here. You’re getting just crude data—just the tip of the iceberg is beginning to emerge, and it’s not clear where it’s all headed.
It’s going to be a very long time before we get spacecraft data back from extra-solar planets, of course, but that discovery is one of the things that’s revolutionized planetary science. The environment right now is like it was a century ago when people didn’t know exactly how stars work, and where they got their energy and how they evolved. We are in a similar state of ignorance about planetary systems, how they are formed and how they evolve.
I now have a student and a post-doc working with me, Brian Jackson and Rory Barnes, and we’re looking at extra-solar planetary systems. Something like 240 of these have been discovered, and we can start to look at what they have in common, what are some of the broad issues, what orbital characteristics and kinds of interactions are there; so we can look at a population and sort stuff out. That, I think, is going to be really crucial in terms of understanding how planetary systems formed and stuff.
So we’re looking at extra-solar planetary systems, turning out quite a few papers about them, and I think the kinds of things we’re finding do have implications for how the planets formed. I think that that’s going to morph into looking more carefully at planet formation. I’ve written a couple of seminal papers back a quarter of a century ago about planetary accretion, how they grew in the first place, so I think the information we have about extra-solar planets is going to reap this effect.
Gilda Ballester, and a graduate student as well who left for France recently, discovered a spectral feature in the absorption spectrum of a [extra-solar] planet that wasn’t known before. It turned out to be, as near as we could tell, due to the absorption of atomic hydrogen in an excited state. Well, to get atomic hydrogen into that excited state you have to heat it up, and it turns out the upper atmosphere of this planet is hot as the dickens; it’s about five thousand degrees Kelvin. That’s about the temperature of the surface of our Sun. That’s why it has this absorption. So she did the first measurement of the temperature in a planetary atmosphere in another solar system, which is quite a thing.
That’s probably the one of the directions that the Lunar Lab will want to go into, extra-solar planets. NASA is talking about missions, not to actually visit extra-solar planets because we can’t do that, but missions that will get outside of the Earth’s atmosphere so you can make measurements of various aspects of these things. Probably there’s going to be people getting in on those, and that’s a direction for us to go in.