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Veteran Astronomer Joins JPL Exoplanet Team

Karl Stapelfeldt. Image credit: NASA/JPL
Karl Stapelfeldt.

From Pat Brennan, JPL

Like many a planet-struck high-school student, Dr. Karl Stapelfeldt watched the Voyager spacecraft make their historic Jupiter flybys in 1979—and first became aware of NASA’s Jet Propulsion Laboratory. He even wrote a letter from his home in Florida asking how to get a job there.

And Stapelfeldt did make his way to JPL, first as a graduate student researcher and later as an employee working on a variety of projects: The WFPC2 camera for the Hubble Space Telescope, NASA’s Spitzer Space Telescope, and a proposed mission called the Terrestrial Planet Finder. Now, after a four-year stint at the Goddard Spaceflight Center in Greenbelt, Maryland, where he was chief of the Exoplanets and Stellar Astrophysics Laboratory, Stapelfeldt is returning to JPL.

A specialist in direct imaging of extrasolar planets—that is, planets circling stars other than our sun—Stapelfeldt will become the chief scientist for NASA’s Exoplanet Exploration Program, an arm of the NASA Astrophysics Division, helping to design state-of-the-art instruments for future space missions.

His timing couldn’t be better. JPL scientists are working on a new generation of space telescopes that should, in the years ahead, capture actual images of planets orbiting distant stars.

Stapelfeldtbrings expertise and a long list of goals and ideas to his new position. Hetook a few moments recently to talk about the big picture and provide a previewof coming attractions.

Q. What are the goals of NASA’s Exoplanet program for the next decade?

A. For a long time the program'sgoal has been to fly missions that can discover Earth-like planets around otherstars, and measure the properties of their atmospheres. Such planets might havewater on their surfaces, they might be habitable, perhaps even have life. Let'sfind out! The program manages NASA's current exoplanet-related projects anddevelops the technologies needed for future missions to observe the mostaccessible targets, the stars in the sun’s immediate neighborhood.

Thefirst exoplanet was only found 20 years ago, and since then we have detectedrelatively few exoplanets by way of direct imaging. To the layperson the mostnatural way to discover something is to actually see it. But for the most part,the exoplanets discovered so far are only known indirectly by the wobble oftheir host star, or dimming of the star as the planet passes in front. Theindirect methods have been great—they’ve told us so many amazing things—butimaging is still our ultimate goal. It has the potential to find Earth-sizedplanets around stars like the sun, and measure their (atmospheric) spectra veryclearly.

Inthe next 10 years a major first step is going to happen. We’ve been trying formore than a decade to get an imaging mission going. The first one will be theWFIRST (Wide-field Infrared Survey Telescope) mission that is starting now, andwill be launched by the mid 2020s. That mission will carry an exoplanet imageron it, for the first time flying a dedicated instrument for this purpose. Withthe WFIRST instrument we intend to show that our approach to the problem willwork in flight, and also get a taste of the science results that can come fromit. So in the mid 2020s we should be seeing the reflected spectrum ofJupiter-like exoplanets, or even down at Neptune size—though not at Neptune’sdistance from the sun.

Q. What is the next bigstep after that?

A. The WFIRST mission isnot going to get us the goal I mentioned before: imaging Earth-like planets,and finding out if they are habitable and if they have water and possibly life.To accomplish that we need, really, a major new observatory. NASA is about tostart a series of major mission studies, two of which will explore our optionsfor that observatory. The Exoplanet Exploration Program Office here willsupport those studies. Eventually the 2020 Decadal Survey of Astronomy andAstrophysics will evaluate those studies and hopefully recommend one of them togo forward.

Thenew observatory may be designed to block the starlight using the WFIRSTapproach of an instrument held inside the telescope—a coronagraph— oralternatively use a different approach to blocking starlight, a starshadefloating far in the distance along the sight line to the target star. Thesemethods would be developed to the level where we could see a planet 10 billiontimes fainter than the target star.

Q. What is your visionfor the program?

A. We need achievable andaffordable options for space missions that can make progress in this problem,and get the whole national science community lined up behind them.

Thisis really the intersection of astrophysics and planetary science. We’re usingthe tools of astronomers—telescopes and their attached instruments—to extendplanetary science to other solar systems. We want to get planetary scientistsand astronomers together in this enterprise.

Ihope to catalyze Goddard and JPL cooperation on this common goal. And followingthe precedent of Hubble, get other countries to join with us to achieve thesechallenging goals. I’d like to see an international effort.

Thepublic is very excited by this problem of exoplanets. We see imaginary worldsall the time in science fiction. The missions we will be developing can take usfrom imagination to knowing what’s really out there. Exoplanet science combineskey scientific questions with the public’s general enthusiasm for exploration.

Q. How did you first getinterested in science and astronomy?

A. I was like many littlekids affected by what I saw on television, both the reality of the Apolloprogram and the visions in science fiction. Both were inspiring. I havekindergarten drawings that show what was in my mind at the time. My dad got mea telescope at the right age and I just read all I could about this stuff.

I’vealways been interested in where planetary science and astrophysics cometogether. During my graduate years, we didn’t know of any exoplanets. The nextbest thing at that time was circumstellar disk material in orbit around a star—gasand dust clouds that might form a planetary system, or might be leftover fromforming it. I started in my research career studying them.

Q. What science questionintrigues you the most?

A. I would like to be ableto understand the complete evolution of a planetary system, just as a geologistwould like to see every stage in the evolution of a continent or a mountain.Knowing the processes that govern the formation, maturation, and eventualdestruction of planetary systems is a prerequisite for understanding theprevalence of life in the universe.

Q. Any advice to youngpeople considering a career in science or astronomy?

A. I think it’s one of themore rewarding things one could do. You’re pursuing knowledge for its own sake,especially in astronomy. It’s not one of the more practical things. The kind ofsatisfaction you get out of it is not really connected to financial reward; it’sunderstanding our place in the universe.

Awhole bunch of NASA folks 40 years ago worked hard to make the Hubble telescopea reality, to get it started. I was lucky to be in position for the payoff fromtheir efforts—to enjoy using that machine when it began operating on-orbit. Sofor young people, the message is that NASA right now is working to define yourtelescope, the telescope you will use when you are a researcher. So go tocollege and graduate school and become that researcher, so that you can takethis machine and do great things with it.