This 'Habitable Planets Catalog' Will Help NASA Probe's Hunt for Alien Worlds

NASA's Transiting Exoplanet Survey Satellite will fly in a unique highly-elliptical orbit to search for exoplanets around the nearest and brightest stars.
Artist's illustration of NASA's Transiting Exoplanet Survey Satellite (TESS), which is hunting for exoplanets around stars close to the sun. (Image credit: NASA)

NASA's newest planet-hunting mission just got a list of high-priority targets.

Astronomers have put together a "habitable planets catalog" for the Transiting Exoplanet Survey Satellite (TESS), in an attempt to help the spacecraft's hunt for potentially Earth-like worlds.

"Life could exist on all sorts of worlds, but the kind we know can support life is our own, so it makes sense to first look for Earth-like planets," TESS science team member Lisa Kaltenegger, a professor of astronomy at Cornell University in New York and director of the school's Carl Sagan Institute, said in a statement. 

Related: NASA's TESS Exoplanet-Hunting Mission in Pictures

"This catalog is important for TESS, because anyone working with the data wants to know around which stars we can find the closest Earth analogs," added Kaltenegger, who led a new study announcing the catalog.

TESS launched to Earth orbit atop a SpaceX Falcon 9 rocket in April 2018. The spacecraft is searching for exoplanets around nearby stars by looking for tiny brightness dips caused when these worlds cross the faces of their host stars from TESS's perspective. 

NASA's recently deceased Kepler space telescope used this same "transit method" to great effect: Kepler has found about 70 percent of the roughly 4,000 known exoplanets to date. (And more discoveries are in the offing; nearly 3,000 Kepler "candidates" await confirmation by follow-up observations or analysis.)

TESS, whose haul may ultimately exceed Kepler's, is expected to observe about 400,000 stars during its two-year prime mission. Not all of those stars were created equal from the mission's perspective, and that's where the new catalog comes in. 

Kaltenegger and her colleagues identified 1,822 stars around which TESS could spot, in just a single transit, planets down to twice the size of Earth that receive about the same amount of stellar radiation as our planet does. (These worlds may, therefore, have Earth-like surface temperatures.) 

The team further highlighted 408 stars where TESS could find such a presumably temperate planet that's about Earth's size — again, in one transit.

"I have 408 new favorite stars," Kaltenegger said. "It is amazing that I don't have to pick just one; I now get to search hundreds of stars."

The catalog includes 137 stars that NASA's $8.9 billion James Webb Space Telescope will be able to view continuously, the researchers said. James Webb, which is scheduled to launch in 2021, will be able to characterize the atmospheres of some nearby exoplanets — work that will include searching for possible "biosignature" gases such as oxygen and methane.

"We don't know how many planets TESS will find around the hundreds of stars in our catalog or whether they will be habitable, but the odds are in our favor," Kaltenegger said. "Some studies indicate that there are many rocky planets in the habitable zone of cool stars, like the ones in our catalog. We're excited to see what worlds we'll find."

The study was published late last month in The Astrophysical Journal Letters.

Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.