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Exoplanet astronomer searches for a brighter future

Professor John Asher Johnson.
Jim Harrison

By Pat Brennan,
NASA's Exoplanet Exploration Program

Johnson is a professor of astronomy at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts

The detection and characterization of planets orbiting other stars is one of today’s most active fields of astronomy, and John Asher Johnson, 40, is among that field’s brightest lights. Using some of the world’s most powerful telescopes, Johnson and his research group detect and observe extrasolar planets, gather data, and design and build instruments used in the hunt for worlds beyond our solar system.

His ultimate goal: a predictive model of planet formation, from swirling dust and gas to planetesimals to fully formed planets.

Johnson also is deeply involved in efforts to increase the representation of African Americans, and other under-represented groups, in the astronomical sciences. To that end, he created the Banneker Institute at Harvard. With its partner, the Aztlán Institute, Banneker conducts 10-week summer programs to prepare talented undergraduates for top graduate programs in astronomy.

Any surprises in your recent research, or with exoplanets in general?

I think the reason to be truly surprised is when you have hard data, that nature should work in some way, and you discover it doesn’t always do that. In the early days of planet detection, we didn’t have any hard data, other than our solar system. People erroneously assumed (other) planetary systems would look like our own. The very first detection, 51 Pegasi, completely threw that notion out.

Every class of planets could be considered a surprise if you’re expecting something to look like our solar system. Nothing does. In that sense, we’re still in a state of constantly being surprised.

How would a “predictive model” of planet formation help in the search for life among the stars?

If we had a completely predictive model for planet formation, we could look at the side effects of the formation process. We could look at water delivery to rocky planets, or the frequency of planets with rocky surfaces and thin atmospheres in the habitable zones of other stars. If we had that model, I think understanding the formation of life, and the precursors of life, would be a really nice secondary effect.

What are some of your biggest discoveries?

Some of the discoveries I’m most proud of– we’ve found a number of really compact systems, small, rocky planets around M-dwarf stars. We had the record-holder for a little while, Kepler-42, KOI 961. That was a Mars-size planet, along with some Earth-size planets. All the planets had an orbital period of less than two days. My group is responsible for what is known about the “Kepler dichotomy.” It reveals that planetary systems either come in nice, neat, circular, co-planar orbits (orbiting in the same plane)– like our solar system, but scaled down– or are in systems with the planets misaligned with respect to one another, misaligned with respect to their stars, in highly eccentric orbits. Some formed in neat, orderly ways, some formed in catastrophic, disorderly ways, or were thrown into disarray at some point in their lives.

Most recently, I was part of a team that found a disintegrating asteroid-size body around a white dwarf star.

How is the astrophysics community doing in terms of inclusion of African-American scientists, and other minorities?

Frankly, we’re doing a really horrible job. You can believe that all people are created equal, or you can believe in a meritocracy, but you can’t look at the under-representation of people of color and have both be true. Fewer than 1 percent of astronomers are black. We have an order of magnitude to go.