I think the public is becoming more and more interested in our work. I can see it over my career very easily, never mind over the four hundred years of astronomy. I think technology has led to the development of tools that can make the public access what we’re doing much more easily. So if the public has any interest through the web, through getting a telescope of their own, through podcasts, through documentaries like this one people can find out what’s going on in astronomy and they can dig very deep. And I think people find that it is really relevant to the topics they are thinking about. Everyone asks me “Is there other life in the universe?” and with the Keck telescope finding planets we’re in a great position to have a dialogue on that topic. Is the universe expanding? Yes, people are amazed at that. The fact that the expansion is accelerating. People really relate to this, and I think we’re going to see this only increase over time as people can perhaps watch what we’re doing at the telescope even every night. So I think this is a great time to celebrate the connection between astronomy and the public.

Because I advocate keeping Pluto as a planet and because I use the characteristics of the object to define it, then I would have to accept the fact that our solar system has more planets than you were taught in grade school. If Pluto is a planet, then several other objects that have been found out in the Kuiper Belt where Pluto orbits which are as big as Pluto, maybe a little bigger, maybe a little smaller, should also be planets. I don’t personally have a problem with that. I think it’s actually exciting that we can find more planets in our own solar system. I think it gets kids more interested. Maybe they could grow up and find another planet in our solar system.

My hero in science, like a lot of people is Albert Einstein. I think I just admire the way that he was able to do so much himself working as a single person rather than as a big team and also the way he completely changed our conception of very basic things like space and time. That said, I’m really actually very interested in the teams of people and the activity around finding new planets and discovering whether there’s life on them. This is what’s happening now and so although Einstein really opened up our conceptions of the universe, my own focus is really more about a little more practical thing which is, are we alone? So people who are looking for extraterrestrial intelligence, people who are searching for earth-sized planets, people who are trying to understand astrobiology are kind of my heroes right now too.

It was about 15 years ago that we began to get the first direct observations of objects around other stars that were either planets or at least weren’t stars. In fact, it was the same year in 1995 that a breakthrough occurred in both of these areas. So nature makes stars. We know that. We knew that it made planets in our solar system but we didn’t know for a fact that it made planets any where else, although as I said, we had all of this evidence that it probably did. And then there’s the possibility of making objects that are in between stars and planets. These are called brown dwarves. They would be massive enough that they have nuclear fusion which is what stars do and planets don’t. But they’re not so massive that they can shine for a long time with a stable luminosity like stars do. So those are called brown dwarves. And in both cases, but especially with planets, they’re not going to be very bright at all. In fact, we would have a very difficult time seeing them until we have different instrumentation.

With brown dwarves, they’re not as bright as stars, but at least you might have a hope of finding them if they were reasonably close to us. So people were searching for both kinds of objects and in 1995 there were breakthroughs on both fronts. We were able to image the first brown dwarves directly so they were bright enough and close enough that we could get an image of it in the telescope, measure its spectrum and prove that it wasn’t really a star. And at the same time the first planets were detected around other stars. We couldn’t see those planets. As I said, they’re much too faint. What we could see was the effect of the planet on the stars. If it’s a massive planet and it’s orbiting the star, it will pull the star a bit and we can measure the motion of the star even if you can’t see what’s pulling it. We have ways of deducing what the object pulling on the star is and people were able to show that these were planets that they were seeing; the indirect effects of planets.

I work on brown dwarves so I came to this debate from the upper mass end of things and began to form opinions about how we should define planet. I’ve written an article on this in which I call out the fact that the word planet is actually defined in several different arenas which unfortunately don’t have much to do with each other and that’s part of the reason that this is a confusing argument.

So some people want to define planet by what the object actually is, that is physical characteristics of the planet so that should be probably mass-based or have something to do with what kind of object it is and nothing else. This is how we define stars for example. Others would like to define planet by what its circumstances are. That is to say should planets have to be orbiting stars and if they are orbiting stars should they be orbiting alone or can they have a bunch of things orbiting with them. These are all sort of circumstances in which the object finds itself but are used by some to help define the word planet. You can see that doesn’t really have anything to do with what the object itself is, it has to do with its circumstances.

The third arena which doesn’t have anything to do with the first two is - how did I make this object? This is the one where astronomers like to argue about the most. I think the public is less interested in that question but it’s generated a lot of the argument in the astronomical community. That is to say, when I made this object did I make it by a process that looks a lot like the way I make stars. If I did that then they don’t want to call it a planet. We imagine planets as getting built up, as I said, by the accumulation of dust into larger bodies and then the accumulation of those bodies all the way up into a planet. So a substantial fraction of the astronomical community would like to actually use that as the definition of a planet. If you built it up that way it could be a planet. If you did it another way, it can’t be a planet. Unfortunately the observations so far suggest that when you get into the mass range of planets that Jupiter is in for example, it looks relatively likely that you actually can build such objects up both ways. So you can see that part of the community wants to give those two things different names and part of them who want to use circumstances or characteristics would like to give them the same name so my own opinion is we should stick as much as possible to the characteristics of the object and not worry so much about circumstances. So I would be in favor of calling Pluto a planet and not kicking it out because of a circumstance that it has some company with it. But others disagree.

That brings me to the fourth arena of planet definition which is just culture. And that’s where you the public come in. People are not going to accept the definition of planet that doesn’t feel right to them. And so astronomers don’t really have complete freedom to define the word planet. We really have to pay attention to what people think about planets. So things haven’t gotten fully settled because we have these four different arenas in which people argue about the definition.