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Author Q&A: A retrospective look at the Spitzer Space Telescope

10 February 2021

Astronomers Michael Werner and Peter Eisenhardt talk about their book on the recently retired IR observatory and what to expect from its successor, the James Webb Space Telescope.

Werner and Eisenhardt.
Peter Eisenhardt (left) and Michael Werner (right) worked on the Spitzer Space Telescope for more than three decades. Credit: Robert Hurt

The Spitzer Space Telescope was deactivated a little over a year ago after more than 16 years exploring the IR emissions of active galactic nuclei, stellar and planetary nurseries, and more. For Michael Werner and Peter Eisenhardt, Spitzer was the mission of a lifetime; both scientists worked on the project for more than 30 years. Their recent book, More Things in the Heavens: How Infrared Astronomy Is Expanding Our View of the Universe, provides an overview of the observatory’s scientific achievements for a broad audience. In Physics Today’s February issue, astronomer Edward L. Wright calls the book a “well-written account” of the telescope’s triumphs. Werner and Eisenhardt recently spoke to Physics Today via email to discuss the book and their experiences working on Spitzer.

PT: When did you begin working on what eventually became Spitzer? What were your roles on the project?

WERNER: I started working on Spitzer—then called the Shuttle Infrared Telescope Facility (SIRTF)—in 1977, when Dave Rank from the University of California, Santa Cruz, and Fred Witteborn from NASA’s Ames Research Center asked me to chair a group studying photometric instruments. At the time, I was on the physics faculty at Caltech. After I was denied tenure, I took a job at NASA Ames, which was then responsible for SIRTF. I was named project scientist and chair of the science working group in 1983, and I have held that position ever since, migrating to the Jet Propulsion Laboratory when SIRTF moved in 1990. I was responsible for assuring the scientific integrity of the mission.

EISENHARDT: I began working with Mike in 1987. Along with John Stauffer and Witteborn, we formed the science team. Our job was to make sure everyone understood what we wanted Spitzer to do. At the time, the concept was to launch SIRTF into low-Earth orbit using the space shuttle and retrieve it every few years to replenish its supply of liquid helium.

We were already thinking about launching SIRTF into a higher, 70 000-km-altitude orbit, with less IR loading from Earth, but Johnny Kwok at JPL came up with an even better idea: an Earth-trailing solar orbit. I served at one time or another as instrument scientist for each of Spitzer’s three instruments before settling on the Infrared Array Camera (IRAC).

I was shocked to hear that Stauffer passed away recently. He was a leading stellar astronomer and an unsung contributor to Spitzer’s success.

PT: What was the most surprising result produced by Spitzer? What do you think its legacy will be?

WERNER: The most surprising result was certainly the identification of the TRAPPIST-‍1 system of exoplanets, which consists of seven Earth-size planets orbiting a faint red star barely larger than Jupiter. They are closer to the star than Mercury is to the Sun.

Spitzer’s legacy is twofold. First are the large, systematically observed data sets that are already being used to study all manner of astronomical problems. Second are the important technological advances demonstrated by Spitzer, most notably the use of passive cooling, which kept the telescope temperature below 27 K even after the cryogens were depleted.

NGC 1333.
Spitzer’s IR eyes helped astronomers explore star-forming regions such as NGC 1333, which is located about 1000 light-years away in the constellation Perseus. Credit: NASA/JPL-Caltech

EISENHARDT: I agree that Spitzer’s exoplanet results were the least anticipated. I’ve also been quite surprised by the relative ease with which Spitzer helped discover galaxies at redshifts of 8 and even 11 (that is, between approximately 400 and 650 million years after the Big Bang); we’d been hoping before launch to reach redshift 5 at best.

One legacy is Spitzer’s survey of regions that will be mapped by the European Euclid mission; those surveys will then point the James Webb Space Telescope to the seeds of reionization in the early universe. More broadly, we now know the history of cosmic star formation thanks largely to Spitzer’s measurements of star formation and the buildup of stellar mass over cosmic time.

PT: Why did you want to write More Things in the Heavens? What was the objective of the book?

WERNER: Spitzer was my life’s work. It succeeded beyond anybody’s wildest expectations and returned fantastic results in many areas of science. I was eager to share them—and our great images—with a general readership.

PT: Is there a favorite moment that comes to mind, during your time working on Spitzer, that wouldn’t make the cut in a scientific paper?

WERNER: Walking through the “rocket garden” at Cape Canaveral, where launch vehicles used by previous space scientists point upward at the sky, I had a feeling of kinship with those early pioneers. I realized that they, like our team, were pursuing the basic human desire to explore and learn. It was a mystical experience.

EISENHARDT: My friends and family—including my 78-year-old mother—watched from Jetty Park pier as Spitzer launched at 1:30 in the morning, passing around a jug of Carlo Rossi wine in celebration. We stayed up the rest of the night and swam in the Atlantic at dawn.

PT: What should readers know about what goes into planning an intricate mission like Spitzer?

WERNER: The first thing needed is a clear set of scientific requirements, which are then turned over to the engineering teams. Continued back-and-forth discussion between the science and engineering teams is critical during this phase. And for scientists, engineers, and managers alike, there is no substitute for hands-on experience. There is much more to missions like Spitzer than following a cookie-cutter recipe.

EISENHARDT: It really is complicated. On Spitzer, we emphasized informal peer reviews at lower levels of the team, where people felt freer to discuss design issues. We were fortunate that Spitzer’s science working group included several pioneers in IR space astronomy who were not shy about asking questions. Finally, Mike always took time to explain to everyone working on Spitzer how our work specifically connected to advancing our understanding of the universe, and I tried to follow his example.

PT: Spitzer’s successor in the IR spectrum will be the James Webb Space Telescope. What should we expect?

WERNER: We can anticipate great advances in many of the areas pioneered by Spitzer and the Hubble Space Telescope. These include more detailed studies of exoplanet atmospheres and probes of the distant universe in search of the earliest stars and galaxies.

EISENHARDT: Assuming it has no major technical problems, Webb’s incredible sensitivity and formidable spectroscopic capabilities will reveal temperatures, compositions, and dynamics of stars and galaxies that Spitzer could only barely detect in images.

PT: What are you working on now?

WERNER: I am working on a paper describing the engineering results from Spitzer, which will be of great interest for the design of future space-based IR telescopes. In the retirement half of my life, I am learning watercolor painting.

EISENHARDT: I’m working on a paper compiling optical spectroscopic measurements of about 200 hot, dust-obscured galaxies, or hot DOGs, which include some of the most luminous galaxies in the universe. I’m also helping with the development of the Near-Earth Object Surveyor, which we hope will launch around 2025. And I’m part of NASA’s science team for the European Euclid mission, planned for launch next year.

PT: What have you been reading?

WERNER: I am reading an excellent book by James McBride called Deacon King Kong. But I cannot resist mentioning my favorite book of the past year, The Book of Eels by Patrik Svensson, which combines natural history, the history of science, and the experience of growing up in a truly amazing way.

EISENHARDT: I spend some time each night reading books with my autistic daughter. We’re currently working through Sidney Lanier’s translation of Thomas Malory’s Le Morte d’Arthur.

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