Dr. Drake Deming, former Chief of Goddard Space Flight Center’s Planetary Systems Laboratory, currently serves as Senior Scientist with NASA’s Solar System Exploration Division where he specializes in detecting and characterizing hot Jupiter extrasolar planets. Dr. Deming was named recipient of the 2007 John C. Lindsay Memorial Award, Goddard’s highest honor for outstanding contributions in space science, for his work in developing a way to detect light from extrasolar planets and use it to measure their temperatures.
NASA Tech Briefs: What is the Solar System Exploration Division’s primary mission within NASA and what types of projects does it typically handle?
Drake Deming: Our primary mission is to study planetary science in the context of NASA’s space mission program. In this case planetary science also includes planets orbiting other stars.
NTB: You began your career in education teaching astronomy at the University of Maryland. What lured you away from academia to pursue a career with NASA?
Deming: Research, and the opportunity to do cutting-edge space-based research.
NTB: Had you always planned to move in that direction, or was it after you had started your career that NASA entered the picture?
Deming: I had always planned to move into research.
NTB: Much of your research over the years has focused on trying to detect and characterize so-called “hot Jupiter” extrasolar planets. What are “hot Jupiter planets, and what can we learn from them?
Deming: Hot Jupiters are giant planets, like Jupiter in our own solar system, but they’re in much closer to their stars. Not only are they much closer than Jupiter in our solar system is, but they’re much closer even than our own Earth. What we can learn from them is quite a bit, because they’re in so close to the star they’re subject to strong irradiation from the star, so the dynamics of their atmosphere is very lively, the circulations are very strong, so we can learn about the physics of their atmospheres. Also, they are subject to tremendous forces from the star; they’re subject to tidal forces, which may play a role in inflating their sizes. So, we can learn about their internal structure, and we can learn a lot about planets from studying hot Jupiters because they’re an extreme case.
NTB: Why are extrasolar planets so hard to detect?
Deming: They’re so hard to detect because, so far, we cannot spatially resolve them from their parent stars, so we have to study them in the combined light of the planet and the star. That means it’s a small signal riding on top of a large noise source – in this case, the star.
NTB: You are the principal investigator on a program called EPOCh, which stands for Extrasolar Planet Observations and Characterization. Tell us about that program and what you hop to accomplish with it.
Deming: Well, we have just concluded our observing with EPOCh. We have over 170,000 images of planet-hosting stars, and when we get these images we don’t resolve the planet from the star. We use the images to do precise photometry. These are bright stars that have planets that transit in front of them, and the geometry of the transit tells us quite a bit about the planet. It tells us the radius. We can examine the data to see whether it has rings or moons. We can look for other, smaller planets in the system that may transit. And in favorable cases our sensitivity extends down to planets the size of the Earth, so we’re searching for smaller worlds in these systems.
NTB: You’re also the Deputy Principal Investigator for a mission called EPOXI…
Deming: Yes. That’s the same as EPOCh. EPOXI is a combination of EPOCh and DIXI (Deep Impact eXtended Investigation). DIXI is the component of EPOXI that goes to Comet Hartley 2, and that’s now ramping up because EPOCh is finished.
NTB: What is that mission designed to accomplish?
Deming: Well, I’m not involved in that, but it’s designed to image a comet nucleus. It will use the imaging capability of the Deep Impact flyby spacecraft to image another comet. The original Deep Impact mission released an impactor into a comet nucleus and actually blew a crater in it. Of course, the impactor is no longer available to us because it was used up, but still, a tremendous amount can be learned by imaging another comet nucleus for comparative purposes.
NTB: That was the Temple 1 comet, right?
Deming: That was the Temple 1 comet.
NTB: EPOXI spent most of the month of May observing a red dwarf star called GJ436 that is located just 32 light years from Earth, and it has a Neptune-size planet orbiting it. What did you learn from those observations?
Deming: We’re still very intensely analyzing those data, but what we hope to learn is whether there’s another planet in the system, and in this case our sensitivity extends down to Earth-sized planets, so we’re looking for another planet that may have left a small signature in the data as it transited the star. If we can find that, there’s a good chance that that planet might even be habitable. Because our period of observation extends for more than 20 days, and because this is a low-luminosity red dwarf star, the habitable zone in that system is in close to the star where the orbital periods are on the order of 20 days. So we have sensitivity to planets in the habitable zone in this case.
Of course, those data have our highest priority and we’re inspecting them very intensely. However, the data analysis process is very involved. We have a lot of sources of spacecraft noise that we have to discriminate against.
NTB: In July 2008, NASA’s Deep Impact spacecraft made a video of the Moon transiting – or passing in front of – the Earth from 31 million miles away. Why did that video generate so much excitement within the scientific community?
Deming: Well, I think it generated a lot of excitement both in the scientific community and outside of the scientific community because it’s really, I think, the first time that we’ve seen the Earth/Moon system from that particular perspective, from that specific perspective, where you see the Moon transit in front of the Earth. And there’s also, as we analyze those data, some realization that although it would be a relatively low probability that, if that were to occur for a planet orbiting another star and its moon transited in front of it, we could learn about the topography of the planet.
NTB: Do you think we’ll learn anything new about Earth from that video?
Deming: I think we’ll learn new things about the Earth as a global object, as an astronomical object. For example, one of the things we should start prominently seeing in the data is the sun glint from the Earth’s oceans, and this has been hypothesized as a way to detect oceans on planets orbiting other stars because that glint would be polarized. Although we don’t have any polarization capability, we can see that the glint sometimes becomes dramatically brighter and we’re trying to understand why that is. It may be because the glint is a specular reflection, probably from the Earth’s oceans, so by correlating that glint, the brightening of that glint with, for example, winds across the oceans and wave heights, we may find that smooth patches of ocean give us a particularly strong glint. So, if the glint were observed on an extrasolar planet, we could then infer from a variable polarization signal the presence of the glint and the presence of oceans.
NTB: It was discovered some time ago that Deep Impact’s high-resolution camera has a flaw in it that prevents it from focusing properly. This was a problem during its original mission when it was trying to study a crater made by an impactor on the comet Temple 1, but you were somehow able to use that to your advantage to study planets passing in front of their parent stars. Can you explain how that works?
Deming: That’s a big advantage for us because we’re not trying to image the planet. We’re only measuring the total photometric signal, so when the planet passes in front of the star we see a dip in intensity. That dip in intensity is, like, one percent. We’re doing very precise photometry, so that one-percent dip is actually the largest signal we see. We’re actually looking for much smaller dips due to smaller planets. Well, in order to measure that dip very precisely, we have to get a very precise photometric measurement, which means we need to collect a lot of light from the star. If we didn’t have the defocus, all of that light would be falling on one or two small pixels of the detector and they would immediately saturate. We’d have to constantly be reading them out and it just wouldn’t be practical. But by having a defocused image, we can spread the light over many pixels and use them to collect more light in a given readout. For each readout we collect many more photons from the stars.
NTB: Among your many accomplishments at NASA, you developed a way to detect light from extrasolar planets and use that light to measure their temperature. Can you explain how that technique works?
Deming: This was an observation with Spitzer. And it was also done concurrently by Professor David Charbonneau at Harvard. The Spitzer Observatory wasn’t really developed for that purpose. We just found that that it was particularly capable of that application, and what we did was we observed the systems that had transiting planets in the infrared where the planet is a significant source of radiation and we waited until the planet passed behind the star – and we could calculate when that would be – and then we saw a dip in the total radiation of the system. Since we knew the planet was passing behind the star at that time, the magnitude of that dip tells us the magnitude of the light from that planet. So, in that way we were able to measure the light from extrasolar planets. This has become a big topic of research for Spitzer. Spitzer has done this for many planets over many wavelength bands. It has been able to reconstruct, in kind of a crude way – but even crude measurements of planets orbiting other stars are very revealing and important – it’s been able to reconstruct the emission spectrum of some of these worlds orbiting other stars.
NTB: In 2007 you won the John C. Lindsay Memorial Award, Goddard’s highest honor for outstanding contributions in space science. What does it mean to you to have your name added to such a distinguished list of scientists?
Deming: Well, of course, I was very honored to receive this award. I was also very surprised because I had no indication, no hint, that this was coming.
NTB: Nobody tipped you off?
Deming: Nobody tipped me off. It was a complete surprise. I think the award speaks not to my own personal accomplishment but to the success of the NASA missions that enabled the measurements and all the people who designed and built the Spitzer Observatory. It wouldn’t have been possible to make those measurements without that facility.
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