When astronomers discovered the first worlds orbiting other stars thirty years ago, they also began taking what might be called the galactic planetary census, tallying up the numbers and types of exoplanets in the Milky Way. Although it’s infeasible to thoroughly survey all of our galaxy’s hundreds of billions of stars, a representative sample of them could offer important information. By studying the planetary populations of such a sample, researchers hope to learn which sorts of worlds are most common or rare—and how our own Earth and solar system measure up against them.
But there are several different ways to find planets, and each tends to work best for different types of worlds, leading to potentially skewed results. The dominant techniques to date infer a planet’s presence by looking for its subtle influence on its star, and they are most sensitive to giant planets very close to their stars. Such worlds have orbital “years” as small as a few days or weeks—and none exist in the solar system. In contrast, viewing planets directly—called direct imaging—requires distinguishing them from a star’s overwhelming glare, which is easiest to do for giant planets at a system’s outskirts. If such orbits were around our own sun, they would place most of these planets far beyond Pluto.
Fortunately, new methods and more expansive data sets are now letting scientists bridge the gap between these extremes, combining results from multiple planet-hunting techniques to gain better, clearer views of the Milky Way’s true planetary population. A new study published in Science is one of the first successes in this synergistic approach, netting not only a newfound “middle of the road” planet but also a broader strategy for finding and investigating many others. The biggest and brightest of those to-be-discovered planets could also be good candidates for future direct imaging efforts, potentially allowing astronomers to discern their atmospheres and climates.
“When we combine [motion and imagery] together, we get all three key properties of the planet—its orbit, its mass and its atmosphere—so we learn a lot more,” says Thayne Currie, a planet-hunter at NASA’s Ames Research Center and lead author of the study.
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