NASA/JPL-Caltech
An artist’s drawing shows TOI-715b, a ‘super-Earth’ exoplanet orbiting a red dwarf star within the habitable zone.
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Astronomers have detected a “super-Earth,” a planet larger than ours, circling a star about 137 light-years away. It’s also possible that a second planet, similar in size to Earth, may be orbiting the same star.
The super-Earth, named TOI-715b, orbits a cooler and smaller red dwarf star than our sun. The planet was discovered using NASA’s TESS (Transiting Exoplanet Survey Satellite) mission. The discovery was detailed in a study published in January in the Monthly Notices of the Royal Astronomical Society.
Scientists have calculated that the planet, roughly one and a half times wider than Earth, takes a little over 19 Earth days to complete one orbit around its star. It exists within the habitable zone of its star, where the temperature may be suitable for liquid water to exist on its surface.
The habitable zone is usually determined based on factors such as the star’s size, temperature, and mass, as well as the planet’s surface reflectivity. However, there can be significant margins of error associated with these factors, raising doubts about whether a planet truly resides in the habitable zone, as explained by lead study author Dr. Georgina Dransfield, a postdoctoral researcher at the University of Birmingham’s School of Physics and Astronomy in the UK.
Astronomers believe that TOI-715b is located in a more optimal region around the star called the conservative habitable zone, which is less likely to be affected by the margins of error.
“This discovery is exciting as it’s the first super-Earth from TESS found within the conservative habitable zone,” Dransfield stated. “Additionally, as it’s relatively close by, the system is suitable for further atmospheric investigations.”
Since its launch in 2018, TESS has assisted astronomers in locating planets around nearby stars that are suitable for follow-up observations using ground- and space-based observatories.
“This is allowing us to gain a much clearer understanding of the variety of exoplanetary systems orbiting a wide range of stellar types,” Dransfield added.
Telescopes can detect dips in starlight indicating that a planet is passing in front of its star, known as transits. TOI-715b, being close to its star and having a quick orbit, transits frequently. Consequently, it is an ideal candidate for future observations using the James Webb Space Telescope. The Webb telescope operates in infrared light, which is not visible to the human eye, and can analyze the atmospheres of planets.
As the planet transits the star, starlight passes through it, allowing Webb to search for indications of an atmosphere and even determine the planet’s atmospheric composition. Knowing if planets have atmospheres can provide insight into their potential habitability for life.
“We really want to know the planet’s mass with high precision to understand if it’s a true super-Earth or a member of the novel category of ocean worlds,” Dransfield noted. This information will guide further investigations and enhance our understanding of exoplanet demographics.
To confirm the existence of the potential Earth-size second planet, researchers require more successful observations of the planet’s transits in different light wavelengths, Dransfield stated.
If the Earth-size planet is confirmed, it will be the smallest planet discovered in a habitable zone by TESS.
Red dwarf stars are the most common in our galaxy, and several have been found to host small, rocky worlds, such as the recently discovered TRAPPIST system with its seven planets, located 40 light-years away. Planets that orbit closer to these smaller, cooler stars could receive enough heat to be potentially habitable.
However, a crucial question is whether these planets are also close enough to be affected by stellar flares and radiation, which could erode their atmospheres, evaporate water, and limit their potential habitability.
TOI-715b’s star has only shown a couple of flares within the past two years and is considered inactive, making it an old star, according to Dransfield.
In the future, astronomers aspire to search for planets around stars more similar to our sun, which will require the ability to block intense starlight to find faint Earth-size planets.
Upcoming missions like the European Space Agency’s PLATO (PLAnetary Transits and Oscillations of stars) will utilize 26 cameras to study Earth-like planets in habitable zone orbits around sun-like stars, set to launch in 2026.
“So far, no telescope has been capable of this, but it should be possible within the next decade,” Dransfield noted, referring to PLATO. “This will be one of the most anticipated discoveries, as it will begin to show us how common planets truly similar to Earth really are.”
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