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Astronomers have discovered a “Super-Earth,” or world larger than our planet, orbiting a star about 137 light-years away. A second planet, estimated to be the size of Earth, may also be orbiting the same star.
The super-Earth exoplanet, known as TOI-715b, orbits a red dwarf star that is cooler and smaller than our sun. Astronomers spotted the planet using NASA’s TESS mission, or Transiting Exoplanet Survey Satellite. A study detailing the discovery was published in January in the Monthly Notices of the Royal Astronomical Society.
Researchers have determined that the planet, which is estimated to be one and a half times as wide as our planet, takes just over 19 Earth days to complete one orbit around its star. The planet is close enough to its star to exist within the habitable zone, or the distance from a star that provides the right temperature for a planet to have liquid water on its surface.
The habitable zone is usually calculated based on factors such as the size, temperature and mass of a star as well as the reflectivity of the planet’s surface. But these factors can have large margins of error, calling into question whether planets in the habitable zone really are inhabited, said lead study author Dr Georgina Dransfield, a postdoctoral researcher at the School of Physics and Birmingham University Astronomy in the area. United Kingdom.
Astronomers believe that TOI-715b exists in a narrower and more optimal region around the star known as the conservative habitable zone, which is less likely to be affected by margins of error.
“This discovery is exciting because it is the first Super-Earth from TESS to be found within the conservative habitable zone,” said Dransfield. “Furthermore, because it is relatively close, the system is suitable for further atmospheric investigations.”
TESS, the planet hunter
Since its launch in 2018, TESS has helped astronomers find planets around nearby stars suitable for follow-up observations with ground-based and space-based observatories.
“This allows us to get a much clearer picture of the variety of exoplanetary systems orbiting a wide variety of galaxy types,” Dransfield said.
Telescopes can pick up dips in starlight that indicate the planet is passing in front of its star, and these dips in starlight are called transits. TOI-715b is close to its star and has a fast orbit, meaning that the planet often passes in front of its star, or transits it. As a result, the exoplanet is the best candidate for future observations with the James Webb Space Telescope. The Webb telescope sees the universe in infrared light, which is invisible to the human eye, and can peer inside the planets’ atmospheres.
As the planet passes the star, the starlight filters through, allowing Webb to look for evidence of an atmosphere and even determine the planet’s atmospheric composition. And understanding whether planets have atmospheres can reveal more about their ability to be habitable to life.
“We want to know the mass of the planet with high precision to understand whether it is a true super-Earth or a member of the novel category of ocean life,” said Dransfield, referring to moons with oceans. worlds such as Jupiter’s Europa or Saturn’s Enceladus. “This will allow us to really shape our follow-up investigations and learn more about exoplanet demographics as a whole.”
To confirm that a second Earth-sized planet is likely, researchers need more successful observations of the planet’s transits in different wavelengths of light, Dransfield said.
If an Earth-sized planet is confirmed, it will be the smallest planet yet found by TESS in a habitable zone.
The search for Earth-like planets
Red dwarf stars are the most common stars in our galaxy, and some have been found to host small rocky worlds, such as the recently discovered TRAPPIST system and its seven planets, located 40 light years away. Planets in closer orbits to these smaller, cooler stars could gain enough heat to be habitable.
But a key question is whether these planets are also close enough to be hit by large flares and radiation, which could erode their atmospheres, evaporate water and limit their ability to be habitable for life .
The star TOI-715b has shown only a few flares in the past two years and is not considered active, making it an old star, Dransfield said.
In the future, astronomers hope to have the ability to search for planets around stars more similar to our sun, which will require the ability to block intense starlight to find Earth-sized planets.
Future missions such as the European Space Agency’s PLATO, or Planetary Transits and Escalations of stars, will have 26 cameras to study Earth-like planets in habitable zone orbits around sun-like stars. The mission is expected to launch in 2026.
“Until now, no telescope has been able to do this, but it should be possible within the next decade,” Dransfield said, referring to PLATO. “This will be one of the most anticipated discoveries, as it will begin to show us how similar common planets really are to Earth.”
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