By Lee Billings
Can NASA’s next big space telescope take a picture of an alien Earth-like planet orbiting another star? Astronomers have long dreamed of such pictures, which would allow them to study worlds beyond our solar system for signs of habitability and life. But for as long as astronomers have dreamed, the technology to make those dreams a reality has seemed decades away. Now, however, a growing number of experts believe NASA’s Wide-Field Infrared Survey Telescope (WFIRST) could take snapshots of “other Earths”—and soon. The agency formally started work on WFIRST in February of this year and plans to launch the observatory in 2025.
WFIRST was conceived in 2010 as the top-ranked priority of the National Academy of Sciences’ Decadal Survey, a report from U.S. astronomers that proposes a wish list of future missions for NASA and other federal science agencies. The telescope’s heart is a 2.4-meter mirror that, although the same size and quality as the Hubble Space Telescope’s, promises panoramic views of the heavens a hundred times larger than anything Hubble could manage. Using a camera called the Wide Field Instrument, WFIRST’s primary objective will be to study dark energy, the mysterious force driving the universe’s accelerating expansion. But another hot topic—the existential quest to know whether we are alone in the universe—is already influencing the mission.
Researchers have discovered more than a thousand exoplanets—planets around other stars—since the Decadal Survey’s crucial recommendation of WFIRST as NASA’s top-priority next-generation astrophysics mission. They expect to find tens of thousands more within the next 10 years. Many will be discovered by WFIRST itself when it surveys the Milky Way’s galactic bulge for stars that briefly brighten as planets cross in front of them, acting as gravitational lenses to magnify their light. That survey could yield at least as many worlds as NASA’s wildly successful planet-hunting Kepler space telescope, which used different techniques to net about 5,000 probable planets before hardware failures ended its primary mission in 2013.
Already, rough statistics from the entirety of known planets suggest that every star in the sky is accompanied by at least one, and that perhaps one in five sunlike stars bears a rocky orb in a not-too-hot, not-too-cold “habitable zone” where liquid water can exist. The best way to learn whether any of these worlds are Earth-like is to see them—but taking a planet’s picture from light-years away is far from easy. A habitable world would be a faint dot lost in the overpowering glare of its larger, 10-billion-times-brighter star. Glimpsing it would be like seeing a firefly fluttering next to a searchlight or a wisp of bioluminescent algae on a wave crashing against a lighthouse.
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