Exoplanet Discovery Arrives in Time for New Telescope Technology

Astronomers call LHS 1140b one of the “best targets” for hunting liquid water with NASA’s James Webb Space Telescope

An illustration of LHS 1140b orbiting its faint red star (M. Weiss / CfA)
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Harvard-Smithsonian researchers have just announced the discovery of a large, close exoplanet revolving around a tiny star—one they say may be one of the best candidates for looking for potential life outside of our solar system.

Unlike the discovery earlier this year of a nearby solar system comprising seven exoplanets around another small star, this discovery comes with more data about the newly found world, known for now only as LHS 1140b. Specifically, its dimensions: "What really sets this planet apart from other ones that have been discovered is that we know the mass and the radius of the planet," says Harvard-Smithsonian Center for Astrophysics exoplanet researcher Jason Dittmann.

The planet's larger mass and size means that it likely has enough gravity to hold an atmosphere, Dittmann says. And while LHS 1140b orbits much closer to its star than Earth does, with a year lasting only about 25 days, the coolness of its star keeps the planet within the habitable zone—that is, the zone in which a planet could potentially have liquid water on its surface.

On the flip side, the star isn’t too cool. Although LHS 1140b receives less than half the light that Earth does from the Sun, much of that light comes in the form of warming infrared rays that could theoretically keep the surface of the planet from freezing. Moreover, the planet has a nearly perfectly circular orbit, meaning it likely experienced fewer violent collisions from other planets and asteroids. "It appears that this planet has formed and evolved in a relatively calm manner, which would help its habitability," Dittmann says.

The richer data researchers have about this planet, coupled with its proximity to Earth, makes LHS 1140b a prime candidate for future study with more powerful telescopes like the James Webb Space Telescope launching next year. Dittmann’s team has already secured telescope time to observe their exoplanet discovery, he says, and he believes that these observations will allow them to closely search for an atmosphere and what molecules it might hold.

"The big one we're all going to be looking for is water," Dittmann says.

"This planet is probably one of the best targets we have going into Cycle 1 [...] for studying atmospheres [in the habitable zone with the James Webb Space Telescope]," says Nikole Lewis, an astronomer at the Space Telescope Science Institute who is leading the effort to prepare for exoplanet observations with the telescope. Lewis, who was not involved in this exoplanet discovery, predicts that in less than 100 hours of observation astronomers will make "good headway" in determining the composition of LHS 1140b's atmosphere with the JWST.

The exoplanet's star, LHS 1140, bears little resemblance to our Sun; it is less than one-fifth of our star's mass and much cooler and dimmer, according to a study announcing the planet’s discovery today in the journal Nature. However, this disparity actually made it an ideal candidate to study for orbiting exoplanets. It's much easier to see the details on planets backlit by a dimmer star—just imagine the difference between looking up at the Sun versus staring at a light bulb.

Dittmann and many other astronomers have recently began focusing their efforts and equipment on the cooler, smaller stars close to Earth, rather than the more Sun-like stars that attracted astronomers of yore. "We're being driven toward these smaller stars because the planets are easier to find and they're easier to characterize," he explains.

This shift in focus, as well as improved tools and techniques, have led to a flood of exoplanet discoveries in recent years. Many have been found using the transit method, a technique that involves looking for changes in a star's spectrum as an exoplanet passes in front of it during its orbit.

Given the recent deluge of planetary discoveries, many could use a reminder of how special this time is for astronomy. In fact, it was only a quarter-century ago that researchers pinpointed the first planet outside of our solar system. Meanwhile, in the four years that NASA's Kepler Mission spent scouring the Milky Way for planets until 2013, it discovered 2,331 confirmed exoplanets—contributing to what Discover magazine recently dubbed "exoplanet fatigue" among the public.

"I think to some extent the astronomical community already has some fatigue," Lewis says, pointing to the many so-called "Earth-like" exoplanet discoveries made with the help of NASA's Kepler Space Telescope. "But I think the astronomical community recognizes when they see something that's amazing—and that's what they're seeing with these recent announcements."

What’s so amazing about the recent discoveries, exactly? For years, Lewis says, many astronomers worried that there wouldn't be good exoplanets located in the habitable zone for the James Webb Space Telescope to study soon after it launched. This newest discovery, along with the TRAPPIST-1 exoplanets discovered earlier this year, have dispelled those fears. "The reality is that we've basically hit the ground running with JWST," Lewis says.

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