Astronomers have found a second Earth-sized planet in an intriguing alien solar system

NASA’s lead planet-finding spacecraft has discovered its second planet, which is about the size of Earth and possibly capable of holding liquid water – and both worlds orbit the same star.

NASA’s Transiting Exoplanet Exploration Satellite (TESS) launched in April 2018; since then, the mission has found 285 confirmed exoplanets and more than 6,000 candidates. One of the most intriguing confirmed planets is an Earth-sized world dubbed TOI 700 d located in its star’s habitable zone. Scientists have now determined that the planet has a similarly tantalizing neighbor, thanks to an October 2021 warning that a ground-based orbiting telescope saw something interesting.

“We first started looking at this and we were like, ‘Is this real?’,” Emily Gilbert, an astronomer at NASA’s Jet Propulsion Laboratory in California, told Gilbert and her colleagues are presenting the study at the 241st meeting of the American Astronomical Society, which will be held this week in Seattle and virtually.

“I was very excited,” Gilbert said. (Timing helped too: “It was the day before my birthday.”)

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Artist’s rendering of exoplanet TOI 700 e, an Earth-sized world in its star’s habitable zone. (Image credit: NASA/JPL-Caltech/Robert Hurt)

TESS finds planets by looking at the stars for a month, looking for small dips in brightness that could indicate a planet passing between the star and the telescope. From these dips, astronomers can estimate the size of the planet and measure its orbit.

In 2020, Gilbert and her colleagues reported the discovery of three planets around a small star called TOI 700 (TOI stands for TESS Object of Interest), which is about 100 light-years from Earth. This star is a red dwarf, but unlike many of its siblings, TOI 700 is relatively quiet, with no sudden bursts of activity that could fry any life on a neighboring world.

“In the full two-year TESS dataset, we see no evidence of optical flares,” Gilbert said.

Two of the three planets that TESS originally discovered in the TOI 700 system orbit too close to the star to be Earth-like, but the third world, known as TOI 700 d, is particularly attractive. Scientists have found that this world is about 20% larger than Earth and orbits a star every 37 Earth days, placing it in what scientists call the habitable zone, where temperatures should allow liquid water to exist on the surface.

With just these three planets, scientists have already compared the system to TRAPPIST-1, a system 39.5 light-years away that is known for its seven Earth-sized planets. “It’s definitely a very interesting comparison,” Gilbert said. But further study of the TOI 700 system will be easier, she noted, given that TRAPPIST-1 is a more active and dimmer star. “The TRAPPIST system is super-super-compact, all these planets are very densely packed.”

Now Gilbert and her colleagues say the TOI 700 d has a third sibling, and a very intriguing one at that. This planet, dubbed TOI 700 e, is not exactly in what astronomers usually call the habitable zone, but that definition is constantly changing. In particular, as astronomers realized that Venus and Mars likely once contained water on their surfaces, some have proposed an “optimistic” habitable zone that TOI 700 e lies in.

Gilbert and her colleagues calculated that TOI 700 e is about 95% the size of the Earth, so it is likely rocky and orbits about once every 28 Earth days, which is between TOI 700 c and d. The newly discovered world is also likely tidally locked and always faces its star on the same side.

“This is most of what we know at the moment only from the TESS data, but we currently have several other campaigns to better characterize it,” Gilbert said. “There are no results yet, but exciting things are coming.”

TESS will return its views on the TOI 700 in just over a week, Gilbert said, with data coming in another nine months or so over the course of next year. And the researchers also brought reinforcements. Gilbert is currently monitoring the system with the Very Large Telescope in Chile, using his Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), which is designed to characterize Earth-like exoplanets. The researchers hope that the ESPRESSO observations will allow them to determine the masses of all four planets in the system, and their colleagues are using the Hubble Space Telescope to estimate the star’s ultraviolet output, information that could be used in climate models for these planets.

While the James Webb Space Telescope has already proven its ability to detect the components of an exoplanetary atmosphere, this skill will not be used on either TOI 700 d or e, both of which are so small that analysis of the atmosphere would take too long. be practical given the star’s small size, Gilbert said. However, he may be able to study the largest planet, TOI 700 b, she added.

Gilbert said the new find shows the value of TESS’s expanded mission. The spacecraft was originally intended to operate for two years; it began its second mission expansion in September 2022, which will last until October 2024. TOI 700 is located in a patch of space that TESS constantly sees when it surveys the southern sky. All in all, Gilbert and her colleagues needed to combine the observations of 14 different TOI 700 transits and confirm that the signal was real.

“If the star were a little closer or the planet a little bigger, we might have detected TOI 700 e in the first year of TESS data collection,” says Ben Hord, a doctoral student at the University of Maryland at College Park. a graduate student at NASA’s Goddard Space Flight Center in Maryland, the statement said. “But the signal was so weak that it took us an extra year of transit observations to identify it.”

Email Meghan Bartels at mbartels@ or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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