David Charbonneau

Ongoing planet searches continue to turn up new discoveries almost monthly, many of them far more strange than anyone had imagined. All of the planets discovered to date are gas giants, incapable of supporting life as we know it. But the detection of those elusive, small Earth-like worlds may be closer than you think, according to David Charbonneau, an authority on the search for transiting planets and an R.A. Millikan Postdoctoral Scholar in Astronomy at Caltech.

Last year, Charbonneau led a team that made the first direct detection of the atmosphere of a planet outside our solar system. Using the Hubble Space Telescope, the astronomers probed the atmospheric composition of the planet as it passed in front of its parent star, filtering light through its atmosphere.

Charbonneau also is working with Dr. John Trauger of the Jet Propulsion Laboratory to develop an instrument that may help astronomers find a slew of large planets orbiting nearby stars. The low-cost instrument combines a charged-coupled device, or CCD, with a standard 300-millimeter Leica camera lens. Their observations will be combined with those of similar instruments at two other locations, forming a planet-search network.

The network will look for large, gaseous planets as their fast orbits take them into the line of sight between the star and Earth in what is known as a transit. Astronomers will watch for the "wink" from the star as an orbiting planet partially blocks its light.

Charbonneau was interviewed on March 25 at JPL.

PlanetQuest: This new planet-search network could detect a number of new "hot Jupiters" (large, gaseous planets located close to their parent stars), adding to the catalogue of known extrasolar planets. What could we learn from finding more of these?

Charbonneau: The difference is that we're trying to study a significant number of those that pass in front of their stars. For such planets, we will be able to determine the mass and size. Then we can calculate density and infer their composition. So we'll get a better understanding of what these planets look like and what they are made of.

PQ: How many new planets do you expect the network will discover?

Charbonneau: If we find one, that would be great. But we hope to find as many as couple of dozen over two years.

PQ: When will the search begin?

Charbonneau: The two existing telescopes (in the network) are already observing the sky. We hope our new telescope will begin operating this summer.

PQ: Could the relatively low cost of these devices, which are made from off-the-shelf parts, put planet-finding within the reach of amateur astronomers?

Charbonneau: Amateurs could buy the hardware, but the real difficulty is that you need someone able to analyze the data. It requires several astronomers working around the clock. Perhaps in a few years, when we better understand how such a system can work ... I can foresee a scenario where it would be feasible to have amateurs participate in the search.

PQ: In November of last year, you and your colleagues announced the detection of sodium in a planetary atmosphere outside our solar system, using the Hubble Space Telescope. What did the findings tell us about this particular planet?

Charbonneau: The most interesting result is that we now know that we have a technique for studying the atmospheres of planets orbiting stars that are hundreds of light-years away.

With regard to the star HD 209458, we observed less sodium than predicted, and this might indicate the presence of high-level clouds that may have blocked some of the light.

PQ: Do you plan to use the Hubble again to study this planet or other extrasolar planets?

Charbonneau: The real hope is to use the Hubble to look for the fingerprints of other molecules in the planet's atmosphere, such as potassium. We also hope to gather data from the Keck Observatory in the infrared, looking for signs of carbon dioxide, methane and water vapor.

PQ: Aside from the Hubble, what other existing telescopes could be used to study the atmospheres of planets around other stars?

Charbonneau: Well, the Hubble is ideal because it is above the Earth's atmosphere. The Keck Observatory is also very powerful, enabling us to gather a great deal of data very quickly. Other large telescopes around the globe would be useful.

PQ: How long will it be before scientists might be able to study the atmospheres of Earth-like planets around other stars?

Charbonneau: That's much more difficult. We are close to being able to find Earth-like planets. But it may be decades before we are able to study their atmospheres.

PQ: How did you get interested in astronomy?

Charbonneau: I was always fascinated by the stars. Even when I was young, I would lie out in a field and look up at the stars. I became really interested when I started to learn about the scale of things. When I heard about Einstein's theory of relativity in high school, it seemed even more fascinating than just images. Those kinds of concepts pushed me toward astrophysics.

PQ: On a personal note, what do you like to do in your spare time?

Charbonneau: I find home beer-brewing very satisfying. I also like to go sea kayaking.


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