NASA's planet-hunting satellite found another potentially habitable Earth-sized planet

Jonathan Shieber

NASA's Transiting Exoplanet Survey Satellite (TESS) has discovered another Earth-sized, potentially habitable planet orbiting around a star in the range of distances where conditions could allow for the presence of liquid water on the planet's surface.

Using NASA's Spitzer Space Telescope, scientists confirmed the find, called TOI 700 d, according to a statement from NASA's  Jet Propulsion Laboratory in Pasadena.

The new planet joins other Earth-sized planets discovered by NASA, including several in the TRAPPIST-1 system, and other worlds discovered by NASA's Kepler Space Telescope, JPL said.

"TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington, in a statement. "Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet's size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."

The TESS satellite monitors sectors of the sky for 27 days at a time, allowing the satellite to track changes in the brightness of a star caused by an orbiting planet crossing in front of it.

Scientists determined that TOI 700 d is a small, cool M dwarf star (also known as a red dwarf) located more than 100 light-years away in the southern constellation Dorado, according to JPL.

The star that TESS examined has about 40% of the mass of the Sun and has a lower surface temperature -- roughly half of the Sun's 9940.73 degrees Fahrenheit. Three planets orbit the star, which initially appeared larger and hotter than they now are considered, thanks to a misclassification in the TESS database, which originally labeled its star as more similar to the Sun (the error was spotted by a team of researchers, including high school student Alton Spencer).

"When we corrected the star's parameters, the sizes of its planets dropped, and we realized the outermost one was about the size of Earth and in the habitable zone," said Emily Gilbert, a graduate student at the University of Chicago. "Additionally, in 11 months of data we saw no flares from the star, which improves the chances TOI 700 d is habitable and makes it easier to model its atmospheric and surface conditions."

The nearest planet to the star is almost exactly the same size of the Earth, according to JPL, and completes its orbit every 10 days. The star's middle planet is 2.6 times larger than Earth -- between the sizes of Earth and Neptune -- and has a 16-day orbit.

It's the outermost planet -- one about 20% larger than Earth -- that exists in the habitable zone. That planet orbits every 37 days and receives about 86% of the energy from its star that Earth receives from the Sun.

All of the planets are thought to be tidally locked to their star, which means that they rotate once per orbit. And because TOI 700 d is tidally locked to its star, the planet's cloud formations and wind patterns may be strikingly different from Earth's.

Right now, scientists will rely on computer modeling based on the planet's size and the type of star it's orbiting to make predictions about its composition and potential geography.

In one simulation, scientists envisioned an ocean-covered world with a dense, carbon-dioxide rich atmosphere akin to their assumptions about what Mars was like when it was first forming. That model of the atmosphere has a deep layer of clouds on the star-facing side. Meanwhile, another potential vision of the planet predicts a cloudless, entirely land-covered version of Earth, where winds whip from the night side of the planet and converge on a point directly facing the planet's star.

Researchers use signals called spectral lines, which are detected from the passage of starlight through the planet's atmosphere, to project what the planet's surface might look like.

When starlight passes through a planet's atmosphere, it interacts with molecules like carbon dioxide and nitrogen to produce distinct signals, called spectral lines.

"Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model," said Gabrielle Engelmann-Suissa, a Universities Space Research Association visiting research assistant at Goddard, and the leader of the modeling team. "It's exciting because no matter what we find out about the planet, it's going to look completely different from what we have here on Earth."

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Mass., and managed by NASA's Goddard Space Flight Center. Additional partners include Northrop Grumman,  based in Falls Church, Va.; NASA's Ames Research Center in California's Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; MIT's Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore, according to a statement.