What lies beyond the edge of the solar system? Does life exist on other planets? Why is the universe constructed the way it is? Drawing on new insights and technologies, scientists are probing these unknowns in ways that were unimaginable just a few years ago. This month, DISCOVER presents a three-part investigation of the astonishing results. First up: In conjunction with the National Science Foundation, Caltech, and the Thirty Meter Telescope, DISCOVER brought together four leading astronomers to describe their studies of wayward comets, alien worlds, black holes, and the expanding universe. The panel discussion was held at Caltech’s Beckman Auditorium and moderated by DISCOVER’s Bad Astronomy blogger, Phil Plait. The four-part video from the panel is included in the two-page article below; to see video interviews with the four panelists, see the homepage for the event.
Also see the other articles in the three-part package on what's out there in the universe:
▪ The Biocentric Universe Theory: Life Creates Time, Space, and the Cosmos Itself
▪ A Scientist's Guide to Finding Alien Life: Where, When, and in What Universe (to be published tomorrow)
Phil Plait: When each of you started your research, you were trying to answer some big questions. Can you explain those initial questions and tell us if you have different big questions now?
Saul Perlmutter: I couldn’t imagine being as lucky as I was, to be able to study whether or not the universe is going to last forever and whether it is infinite or finite. In 1998, when we discovered that the expansion of the universe isn’t slowing down—it’s speeding up—we realized this could tell us something fundamental about how physics works. Now we’re hoping that the explanation for why the universe is accelerating might address questions like “How do you tie gravity into the other forces in physics?” In that sense, the questions have really changed, but they’re still in the same category of fundamental, deep questions that I love.
Debra Fischer: One of the questions in the beginning was “Are there other planets out there?” When the first extrasolar planets were found, they seemed so different from those in our own solar system, so the question quickly morphed to “How does our solar system compare with other solar systems?” The one thing they turn out to have in common—and this is still not completely appreciated—is that in solar systems with multiple planets, these multiple planets fill all the gravitationally stable niches around the star. I used to wonder why our solar system didn’t have more planets, but then people who run solar system simulations tried to drop more planets in and found that all the other planets became gravitationally unstable. We started out with a solar system where many planetesimals were forming, and that evolved into a system where all the stable niches are filled. To me that’s one of the most exciting discoveries in this field.
Mike Brown: One thing that I did not set out to study initially, but which has become important, is that most of the objects we find in the outer solar system are quite small. You hear about the big ones, such as Eris [the largest known body beyond Neptune], because it led to the very justified death of Pluto as a planet...
Plait: Hey!
Brown: ...but for a lot of the very important science, it’s the small objects that really matter. The small ones are little particles that sit in the outer solar system, and they’re gravitationally swept around by planets. The analogy I like is that these objects in the outer solar system are the blood splattered on the wall after some horrendous murder. I love this analogy—it’s disturbing, but I love it. As Debra just suggested, there might have been additional planets that used to be here in our solar system [but were ejected due to gravitational instability]. The bodies have all been removed. I like to study the blood that’s left around. I didn’t know that this was where the field was going when I started. I thought I was just very interested to know what are the largest things out there. Is there something bigger than Pluto? What can we say about the outer solar system? But as you go farther and farther, you realize the richness of everything you’re finding and how it preserves this forensic record of what happened in the distant past.
Andrea Ghez: I didn’t know astronomy was so gory!
Plait: Yeah—how do you follow an answer like that?
Ghez: The question that I started off with was, I thought, very simple. It was just “Is there a massive black hole at the center of the Milky Way?” But one of the things I love about science is that you always end up with new questions. What happened with my research is that the stars we studied to prove that there was a black hole turned out to be very young. Young stars have absolutely no right to be next to a black hole because a black hole should shear them apart. We have no idea how these stars formed. So that’s one of the major questions we’re trying to address today: “How do baby stars form next to this completely inhospitable object?”
Plait: One of the advantages of being a blogger is that I get to read about the kinds of research people are doing today and think about how much things have changed since I was a kid. I used to look at dingy pictures of galaxies and planets in Time Life books. And now we have these gorgeous pictures from Hubble and Keck. So that leads me to the next question: How have changes in technology in the past few years helped you in searching the limits of your knowledge about what you study?
Brown: Is there anybody in this audience who does not own a digital camera? Almost everybody has a digital camera—in your cell phone, at home, or somewhere. This is one of the few things in my field where commercial technology has done an incredible job of trickling down to astronomers. The same technology that’s in your digital camera has led to people like me being able to take pictures of wide swaths of the sky at a time. This seems trivial, the fact that you can have a better camera every year, but for me it has been transformative.
