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Questions and answers with John Asher Johnson

21 November 2016

The Harvard astronomer hopes to introduce future researchers to the search for planets outside our solar system.

John Asher Johnson. Credit: Jim Harrison
Credit: Jim Harrison

If you’re interested in exoplanets, you have almost certainly run across the work of John Asher Johnson. Johnson earned his BS in physics from the University of Missouri–Rolla (now called the Missouri University of Science and Technology) and his PhD in astronomy from the University of California, Berkeley. In 2012, Johnson’s team at Caltech discovered three exoplanets using data from NASA’s Kepler mission. He is currently a professor of astronomy at Harvard University.

In his book How Do You Find an Exoplanet?, reviewed in this month’s Physics Today, Johnson writes that “unlike many astronomers, my interest in the night sky didn’t begin until later in my life, well into my college education.” An impromptu trip to watch the Perseids meteor shower sparked Johnson’s interest in astronomy at age 21.

Future astronomers may well cite Johnson himself as the reason they became interested in exoplanets. How Do You Find an Exoplanet? lays out the four most common methods used to look for new worlds, in language geared toward intrigued but inexperienced undergraduate astronomers. Johnson’s book also gives the reader an engaging look at the history of astronomy, along with a glimpse into his own career path.

Physics Today recently caught up with Johnson to discuss the book.

PT: What motivated you to write this book?

JOHNSON: For a long time I’ve wanted an introductory book in exoplanets that I could hand to an aspiring undergraduate researcher that would quickly get her or him up to speed in the field. There already exist several excellent books at the popular science level and for graduate students, and I hope that this book fills an important niche and enables young researchers an accessible entry point to the field.

PT: Your book opens with the story of your first encounter with astronomy as an undergraduate. How did you decide that you wanted to focus your career on detecting exoplanets?

JOHNSON: I started my astronomy career thinking I’d study cosmology, with a specific focus on building instruments that would be launched on rockets or balloons. At the time, around 1999, exoplanets were brand new and not an established subfield of astronomy. Fortunately, I was pursuing my PhD at one of the few institutions that had researchers specifically focusing on exoplanets. I found the opportunity to find planets orbiting other stars irresistible. Once I learned that this was a viable career path, I immediately hopped on board.

PT: Your book discusses four methods for finding exoplanets: the Doppler technique, transit observations, microlensing, and direct imaging. Which method did you enjoy writing about the most? Were any methods particularly challenging to write about?

JOHNSON: I found the chapter on microlensing to be both the most challenging and most enjoyable. In fact, I enjoyed it because of the challenge. It was fun to first understand the foundational principles of the concept, which rely on general relativity and some very sophisticated math. Then I faced the task of breaking it down to a simpler Newtonian framework that better elucidated the basic physics of the problem. I learned the most from writing that chapter.

PT: At several points in the book, you explore the history of astronomy or the history of a particular astronomical technique. What do you think astronomy students (or astronomers) gain from knowing the history of the field?

JOHNSON: All new scientific discoveries rest on a foundation of previous successes and failures. It’s impossible to see a path forward without knowing whence you’ve come.

PT: What is your next project?

JOHNSON: I’d like to write a book that focuses on science as a human enterprise that is shaped by the broader culture in which it is situated. I feel like scientists too often believe in the myth that science takes place in a bubble, insulated from society. The fact is that all scientists are influenced by their personal history and the history of their broader society, and the state of the field today is intimately tied to the ways that humans create and re-create culture. Looking back and understanding this process of shaping culture will enable us, as scientists, to plot a better course going forward.

PT: What are you currently reading?

JOHNSON: I’m reading Unjust Deeds by Jeffrey Gonda, which recounts the history of black Americans fighting against housing discrimination in the decades just before the Civil Rights movement. I’m fascinated by the many stories that are largely ignored or erased by popular history. This story in particular is highly relevant given the ongoing struggles of people of color against housing discrimination and the existence of the massive racial wealth gap. Learning about how people in the past solved problems, and studying their victories and failures, allows us to solve the problems of the present—and the same goes for astronomy.

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