June 5, 2006

Part III: Astrobiology

Taking the Galactic Planetary Survey
Gregory Laughlin, University of California, Santa Cruz
35 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)

There are two distinct possibilities: either we are alone in the Universe,
or we are not. Both are equally terrifying.
— Arthur C. Clarke

The complaint leveled against astrobiology has remained the same for forty years now: astrobiology is an area of study without a known subject. George Gaylord Simpson famously wrote in an issue of Science (v.143, p.769) in 1964: "this 'science' has yet to demonstrate that its subject matter exists!"

Yet even should the discovery of a second, independent genesis of life elsewhere in the universe remain decades away, astrobiology will still nonetheless profoundly change of our views of the evolution of life on Earth. Geology was the science that informed and transformed evolutionary thought during Darwin's time. Comparative planetology, although it is a new field of inquiry, will do the same during ours.

Speculating on the evolution of life in the universe has always been a risky business, and one not always highly regarded. Two hundred and fifty years ago, when the first thoughts that the formation of the planets must have occurred by secular (natural) means in the two competing cosmogenies of Buffon and Laplace, rather than as part of a supernatural command, the ideas were met with at best only tepid enthusiasm.

Indeed Thomas Jefferson, our most intellectual and erudite president, wrote fifty years later, in 1804, "Dreams about the modes of creation, ... [are] too idle to be worth a single hour of any man’s life."

Almost certainly Simpson and Jefferson would now change their minds when confronted with the possibilities of the discoveries that await us. Life, up until recently, has always been a property unique to the planet Earth. It really hasn't been considered in any other context.

But we are now beginning an extraordinary new voyage of discovery: we are beginning to take a galactic survery of planets, at least in our very small region of the Milky Way. Because of this, we are beginning to get a sense of the diversity of planetary systems possible.

So far the results have appeared less than promising. The planetary systems we're finding would seem incapable of supporting life in general, and certainly not the kind of life we see here on the Earth. But those results have been greatly biased by the detection technologies we've devised so far.

In this lecture, Greg Laughlin describes four of the technologies that are currently being employed: astrometry, radial velocity measurements, direct imaging and transiting. The first three methods only work well for large planets, but the third, planetary transits in front of their host star does present us with the opportunity to detect Earth-sized planets, if we are lucky enough to be aligned with the remote star in its plane of its ecliptic. Moreover, it does not require the massive observational equipment that the first three methods need.

The chance of discovering transiting planets using this method is high enough that since Greg gave this lecture, he and Tim Castellano, of NASA Ames, have formed transitsearch.org, a mechanism designed to recruit amateur astronomers in the search. Because increasing numbers of amateurs are now able to acquire affordable telescopes with CCDs and computers, amateurs can play an important role in monitoring extrasolar planets for possible transits, a step crucial to detection follow-up. A modest 8- or 10-inch telescope is all that's necessary for such work.

— Wirt Atmar

About the Speaker

Greg Laughlin's research interests are in theoretical astrophysics, with an emphasis on numerical simulations. Current areas of investigation include:

• The dynamics of extrasolar planets: Over seventy extrasolar planets have been detected, and more systems are being detected every month. By studying the long-term orbital evolution of the new systems, we can gain insight into their formation, and thus obtain a better understanding of how our own solar system fits into the galaxy's inventory of planets. Other projects include an ongoing observational search for planets around high metallicity stars (in collaboration with Debra Fischer and Geoff Marcy at UC Berkeley), and the coordination of a detection network for transiting extrasolar planets.

• The hydrodynamics of self-gravitating disks: This work is mainly geared toward understanding the growth and saturation of spiral density waves in protoplanetary disks. Spiral instabilities are a key mechanism for eliciting the transport of angular momentum through nascent planetary systems, and thus are very important to an overall understanding of planet formation.

• Stellar evolution: Research topics in this area include the luminosity functions of white dwarfs and low mass stars, the metallicity distribution of stars in the solar neighborhood, the evolution of low mass red giants, and the stellar evolutionary consequences of the giant planet — stellar metallicity connection.

• The long-term evolution of the Universe: In a collaboration with Fred Adams of the University of Michigan, we are studying processes which unfold over timescales greatly exceeding the Hubble Time. These include galactic evolution, the effects of proton decay, and processes involving black holes.