Turning Pixels into Planets

By Dr. Jon Jenkins; Carl Sagan Center for the Study of Life in the Universe, SETI Institute, and Gail Jacobs

Dr. Jon Jenkins of the SETI Institute is the Analysis Lead for NASA's Kepler Mission. He heads up a group of about two-dozen scientists and programmers who designed and built the software that is the brains behind this dramatic search for other worlds. With a photometric precision of 20 parts per million, Kepler is able to discover planets that are the same size as the rocky, inner orbs of our own solar system. By making an inventory of such worlds, Kepler will answer one of the most intriguing questions in astrobiology: are Earth-size planets abundant or rare?

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Describe your role as Analysis Lead for the Kepler Mission.
As the Analysis Lead for NASA's Kepler project, I'm responsible for designing and building the science pipeline that processes the raw photometric data we get from the Kepler spacecraft. We measure the brightness of the 165,000 stars we're continuously monitoring in order to detect instances where the planet crosses in front of the disc of its star. These events are known as transits. In essence, the team is looking for very tiny solar eclipses where the planet comes in between us and its star and casts a shadow in our direction.

Briefly tell us about your research project.
Kepler is all about detecting small planets around Sun-like stars. The goal is to determine the frequency and distribution of Earth-size planets around these stars. We are especially interested in those small planets we consider to be in the habitable zone of their stars - that range of distance for which the surface temperature would be between the freezing and boiling points of water so liquid water could pool on the surface.

An Earth-size planet's radius is about 1/100 the size of a Sun-like star. We're looking for one part per 10,000 drop in brightness caused by this tiny planet blocking a small fraction of the light from the star. In order to confirm our findings, we need to observe at least three transits - three times when the star is blocked by the body of the planet crossing in front of it. This can take several years. The time interval between these transits tells us what the orbital period of the planet is, and the fractional drop in brightness tells us the size of the planet relative to its star.

Diagram showing relative sizes of all confirmed Kepler planet discoveries as of February 2, 2011, and comparison with Earth and Jupiter. Image credit: Sam Quinn, The Harvard Smithsonian Center for Astrophysics

Since we've classified these stars, we know what their masses are, roughly how big they are, and how hot they are. Using Kepler's laws of planetary motion, for which this mission is named, we can take the orbital period, the time interval between transits, and the mass of a star to provide us with an estimate of the distance of the orbit of the planet from the star. This gives us the size of the orbit. If we know how hot and big the star is, we can then predict the temperature of the planet. That's what allows us to determine if the planet is likely to be in or near the habitable zone. Catching these planetary shadows will help us to identify the essential properties of the planets.

We also want Kepler to help us better understand planetary formation in general. That's why we're observing not just a large number of stars but also a large variety of stars - from the cool M-Dwarfs to the hot Late-A stars.

How long have you been working on this project?
I began working on this project in May 1995, and Kepler was launched in March 2009. Kepler was proposed four times to NASA's Discovery Program, beginning in 1994. We were selected for flight in December 2001. This tells you how long these processes can take. The proposal cycle alone is over a year. Usually these competitions have as many as 40 proposals competing for two launch opportunities at most. In our case, it took well over a year to be selected.

With Kepler halfway through its current mission and returning amazing data, what are your days like now?
I began as the person on point for the technical development and I did a lot of the engineering and science design and analyses. Now, I spend most of my time leading and providing guidance and oversight to some fairly large teams of engineers and scientists who built the production line software and science pipeline servers and put all the hardware together.

Now that we've got real flight data, I also spend much of my time writing papers, giving talks, or reading and reviewing other people's papers. Kepler is phenomenally productive. We've got wonderful data coming down and are making incredible discoveries. We now have the first 120 days of data out to the public. At the same time, we released a paper describing over 1200 planetary candidates we've identified in that data. We're talking about 10 planetary candidates being discovered per day. It's challenging to keep up with all the data that's coming to us at such an incredible pace!

What is the coolest thing about your project?
The Kepler Project is going to allow us to answer a question I've been asking all my life - "Are we Alone?" When I was a child, I would lie on the grass in the summertime, look up at the stars, and wonder if there were other beings on those stars looking up into their night sky in our direction, wondering the same thing. We're taking a small step closer to answering that ultimate question. "Are there other worlds out there?" has been asked since the early Greeks, so we've been wondering about what the skies may hold for at least 2,000 years. What could be cooler than being in a position to answer a question that has been asked for so long without the possibility of being answered?

We're very fortunate to live at a time that places us on the cusp of this major discovery of other worlds similar to Earth - worlds that could have liquid water, life, or even intelligent beings pondering the same questions as you and I.

Kepler team at NASA Ames Research Center presents a plaque to Nichelle Nichols (Lieutenant and Commander Uhura of Star Trek). Plaque reads: "Kepler - NASA's First Missions Capable of Finding Earth-size Planets...To Nichelle Nichols."
Photo credit: NASA Kepler mission

Professionally, what are the most rewarding aspects of your job?
Watching the Kepler mission grow from a tiny seed into a large enterprise and working with thousands of other people to make this dream come true is the most rewarding aspect of my job. Kepler is changing our fundamental understanding of the Earth and our place in the universe. The Kepler mission has offered me a very big and extremely exciting opportunity. I've been able to take on a critical role because the nature of the job has been so broad in terms of all the things we have to achieve to make this mission a success. I think it's been a very unique opportunity and my background has allowed me to make these contributions, which has been extremely rewarding. I was in the right place at the right time and I had the right background to solve this suite of problems.

One of the most rewarding aspects of this project so far has been seeing results many people, including me, didn't expect to see so soon. In this initial slate of planetary candidates, about a third of the stars that host planetary candidates host multiple transiting planet candidates. About 20% of our planetary candidates are in systems where multiple planetary bodies appear to be transiting their star. I didn't expect to see that so early in this mission.

Tell us a bit about Kepler 11.
Kepler 11 is the planetary system that just seems to keep on giving. It has six planets, and the five innermost planets are in orbits that fall well within the orbital distance between Mercury and the Sun. It's only the sixth planet that is outside Mercury's orbit, but not outside Venus' orbit. It's an extremely compact system. It's similar in flatness to the solar system, but our own solar system is much more spread out than Kepler 11's system of planets. If you were to scale this planetary system to the size of an old LP record in terms of the tilts of the orbits, then it would be no thicker than that old LP record. With regard to the five innermost planets, you can scale that system down to a Compact Disc, and the tilts of the orbital planes and their orbits would be no thicker than a Compact Disc to hold all those planets.

Kepler-11 is a small, cool star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in this artist's conception of a simultaneous transit of three planets observed by NASA's Kepler spacecraft on August 26, 2010.
Image credit: NASA/TimPyle

These very flat systems are fully consistent with our classic model of how planetary systems form. A protoplanetary disc, basically a disc of dust and gas, collapses and becomes flatter and flatter and spins faster and faster. The innermost part of that disc collapses gravitationally to form the central star, or the sun. Fragments then clump together in the outer part and those fragments stick together and collide and stick to grow and create the planets.

We're seeing that nature appears to really love making systems of planets; not just solitary planets around solitary stars. We're also seeing a large variety of other extremely exciting science discoveries being made in the data that have nothing to do with planets themselves. For example, even in the earliest data sets, we saw evidence for Doppler boosting, which is a relativistic effect that was predicted but never before observed. Essentially this is sort of the Star Wars effect, when you engage to go faster than light and the star field collapses to a point in front of you. It's a very small effect because these stars are certainly not going anywhere close to the speed of light; but Kepler's photometry is so good, we're able to see it easily.

How is Kepler helping scientists "hear" the song of stars?
Stars are like bells - they ring. They are big balls of fluid and gas so they tend to oscillate. The Kepler Asteroseismic Science Consortium that is associated with Kepler has over 400 asteroseismologists -- astronomers who study the interiors of stars by studying their pulsations and oscillations. Stars have what are known as starquakes, which are similar to earthquakes and can excite oscillations or acoustic modes in the stars. When stars are singing songs as they oscillate and pulsate, they actually change their shape. This shape change causes an apparent change in brightness, which we can measure very well. As we study the brightness variations in time, we can essentially hear the songs of the stars. By then studying the tones, or the notes the stars are singing, we can learn about the star's interior structure and work from models to estimate the size and the age of the star.

The variations in brightness an be interpreted as vibrations, or oscillations within the stars, using a technique called asteroseismology. The oscillations reveal information about the internal structure of the stars, in much the same way seismologists use earthquakes to probe the Earth's interior.
Image credit: Kepler Asteroseismology Science Consortium webcast of 2010 Oct 26

Learning more about stars is important for Kepler in terms of planetary discovery. We can use this data to estimate the size of our brighter stars that host planetary candidates and can measure the radius to 1%, which is far greater than through any other means available to us today. These stars are 600 to 3000 light years away. We see only a point source, yet we're able to measure that point of light to 1%. That's pretty exciting!

What do you currently consider your biggest challenge?
There are so many challenges. The biggest challenge may be to deal with the fact that because the instrument is such an exquisitely sensitive photometer, it is very sensitive to its thermal state. Kepler is in its own orbit about the Sun, so environmentally it's in a very stable, benign environment and that's what enables us to reach a photometric precision of approximately 20 parts per million in 6 ½ hours. That allows us to find very small planets like the Earth. Nevertheless, as the Sun rotates around the barrel of the spacecraft from the spacecraft's point of view, we see thermal changes in the structure that cause the shape of the telescope to change. Over time, this causes the focus to change.

If these shape changes were all that was going on, it wouldn't be overly problematic. However, the spacecraft, although designed to be thermally isolated from the instrument, has boxes and components attached to its side that need to have their temperature conditioned, or kept within certain temperature limits. Heaters on those components cycle on and off to maintain those limits. We see signatures of that cycling in the science data, and those small heat load fluctuations are getting into the telescope and changing its shape by a very small amount. We can trim a lot of those parameters remotely, but there are certain limits to how much we can control. We could easily see in the data the signature of this heater going on and off, causing the distance to move by 1 millionth of a meter. What makes this challenging is we're looking for very small signatures - a one part per 10,000 change in brightness. What would normally be something we could disregard for most instruments is important, in this case, to achieving our ultimate goal of determining the frequency of Earth-size planets in our target sample. We see lots of opportunities to improve how we process the data but we have to rank and prioritize these opportunities and focus our energies on getting the most out of the science.

Why should the general public care about your research?
I think this project and the question it may answer resonate well with the public. People are extremely excited about Kepler and want to learn more about it. I think people really want to know the answer to the question, "Are we Alone?" That's why they're so interested in Kepler and SETI. Our discoveries can give us perspective about our place in the universe. There are 200 billion stars in the Milky Way galaxy. We're on one very small, typical planet; it would indeed be surprising if we were the only example of an Earth-like planet around a Sun-like star. There's no reason to believe there aren't a lot of other "earths" out there. Until you make an observational measurement and prove that there are others, however, we don't really know if we are alone.

This artist's concept illustrates the two Saturn-sized planets discovered by NASA's Kepler mission. The star system is oriented edge-on, as seen by Kepler, such that both planets cross in front, or transit, their star, named Kepler-9. This is the first star system found to have multiple transiting planets. Image credit: NASA/Ames/JPL-Caltech

I think people do care about this ultimate question and they really want to know what's going on out there. As scientists, we want to know whether our solar system is typical. So far, it's been our only example of a planetary system with rocky bodies in it. Kepler is the first mission to unequivocally detect and discover a rocky planet. That rocky planet is in a 20-hour orbit but we're not in a position yet with our current data to expect to have discovered an Earth-size planet in an Earth-like orbit. Because the orbital period is a year, we'll need at least three year's worth of data before we can even begin to answer that particular question.

How can the Kepler data impact future space missions?
Kepler's potential impact is to revolutionize our understanding of planetary formation and the frequency of planets and systems like our own solar system. That provides important answers for future NASA missions, like Terrestrial Planet Finder. That mission's sole purpose is to image planets near their stars and actually do spectroscopy to look for biomarkers in the atmospheres of these planets. It won't be able to look nearly as deep as Kepler; and there are three competing architecture designs for this mission. The architecture design decision will depend in no small part on the answers Kepler provides in terms of the abundance of Earth-size planets in the habitable zones of their stars.

We need Kepler to answer this question of abundance before we can move on to the next phase, which is characterizing these planets. Kepler does not allow us to determine whether there is liquid water or atmosphere on these planets; at least not for the small rocky ones. But it does provide us with the crucial information necessary to go onto that next step of designing the Terrestrial Planet Finder and other successive missions that will answer these next level questions.

How did you come to join the SETI Institute?
I joined the Institute on April 1, 1992. I was working on data for the Magellan Orbiter and remote sensing of planetary atmospheres using the Pioneer Venus Orbiter, which was managed out of NASA's Ames Research Center. I was awarded a guest investigator grant and the SETI Institute was recommended to me as a place to come to support me in my research.

What first sparked your interest in science and astronomy in particular?
My parents both worked at the Kennedy Space Center. My dad was an engineer who worked on the Mercury and Gemini programs and then on Apollo for awhile. I grew up on Merritt Island watching launches of Apollo and later the shuttle. I was always very interested in space science, but it wasn't something I set out to do when I went to college. My doctorate is in electrical engineering. Some roommates knew of a professor in Electrical Engineering who was doing research for NASA. They introduced us and that's how I came to work on planetary science. But it was a natural fit, and I was very excited by that opportunity. I was able to spend a couple of summers as an intern at the Kennedy Space Center writing software that monitored Space Lab II. Those two summers were a lot of fun because I got to go on unofficial tours of the shuttle. As we were integrating Space Lab into the shuttle, we had the opportunity to walk all around the shuttle and look inside the cargo bay from inspection cat walks that went over the shuttle. It was quite a thrill!

Did you feel a sense of sadness with the shuttle program coming to an end?
There is a little bit of sadness but I'm looking forward to the space program doing more than just being in lower orbit. We've been limiting ourselves far too long to low-Earth orbit.

What motivates you?
Doing something nobody else has ever done before. I think that's the principal motivation of most scientists and engineers. It's either to see something that nobody has ever seen before, to discover or learn something nobody has even known before, or to design and build something to perform some service that no one has ever been able to do before.

As a youth, were there any books that influenced your career?
I read a lot of science fiction. The first science fiction book I read was Have Space Suit -- Will Travel, by Robert Heinlein. I quickly got lured into reading lots of science fiction as a child, which continued through college.

If you were speaking to a group of teens about your career, what would you tell them?
Engineering remains a great career. Throughout my career, I've not fit in anywhere, in some sense. I basically operate in the intersections between different fields. I think that allows me to make very unique contributions wherever I am because I can bring knowledge and techniques from electrical engineering and signal processing to bear on astronomical questions of great interest. Working with astronomers, astrophysicists and geophysicists, I can help identify and develop new solutions to the problems we're facing, and I've learned a lot of science along the way. Strong mathematical tools and background can give you a lot of flexibility to engage in different areas of science; and electrical engineering uses a lot of those types of tools and techniques. Some of the most interesting and exciting activities going on in science today require a multidisciplinary approach, and we need people with broad sets of experiences and backgrounds to be able to solve these problems.

In terms of choosing a career in general, I would advise people to choose something you love to do because you're going to be spending a lot of time doing it. I think it would be very sad to spend half your waking days doing something you really don't want to do. For me, the money is of secondary importance. I'd rather do something I love instead of doing something simply to give me the financial resources to do what I love to do.

Who do you admire and why?
I admire Frank Lloyd Wright. I think I draw inspiration from him because he was an incredible visionary who dreamed of things nobody had ever done before and brought them to life. He was very concerned about designing buildings that fit in with their natural surroundings. And he didn't limit himself to just the building; he also designed the furniture and, in fact, went into such details as designing his wife's dresses to fit in with the home décor. Walking inside a building Wright designed is like being in a temple in the sense that it is really awe-inspiring.

The Kepler mission has provided me with an opportunity to have my own vision and see it through - from inception to fruition. This has been an incredibly broad and extremely detailed mission that has covered a spectrum of science and engineering. I'm thrilled to have been involved from the beginning point at which a photon becomes an electron and it gets counted on the CCD all the way through the design of the flight software to the design and development of all the processing and analysis software that can allow us to do whatever is necessary - including reconstruct the pointing of the spacecraft so Kepler can do everything it was designed and built to do - to ensure the Kepler team can turn these pixels into planets and discover what age-old questions we can finally answer.

If you had a one-year sabbatical to learn something entirely new, what would it be?
With all the data coming down, we're learning something new every day, so I'm totally absorbed in the learning process already.

What's in store for you in the future?
I hope there continues to be a lot more data from Kepler and a lot more planets. It looks promising. I've learned quite a bit about managing a really large and complex project. Kepler requires a lot of organization and process and systems engineering management to make this project come together. Every piece has to fit together with all the other pieces so that at the end you have something that does what you need it to do. And it has to be done all together and on schedule. As a co-investigator on a proposed Explorer class mission that would involve an all-sky transit survey, I know I would really enjoy taking the lessons I've learned from Kepler and applying them to a new mission. That would be a lot of fun as well as scientifically very rewarding.

Learn more about Jon and his amazing research in his full interview.