Astronomers have discovered a "super-Earth" exoplanet worthy of further study, orbiting a small, reddish star that is fairly close to us by astronomical standards - only 137 light-years away. The system may also contain a second planet, about the same size as Earth.
The larger planet, named TOI-715b, is about 1.5 times as wide as Earth and orbits within the "conservative" habitable zone around its parent star. This is the distance from its star that provides the right temperature for liquid water to form on the planet's surface.
Of course, the existence of surface water also requires the cooperation of other factors, especially a suitable atmosphere. But the conservative habitable zone - a narrower and potentially more robust definition than the broad "optimistic" habitable zone - puts it at the top of the list, at least by current rough measurements.
The smaller planet may be only slightly larger than Earth and may lie just inside the conservative habitable zone.
Progress in exoplanet research
Astronomers are beginning to write a new chapter in our understanding of exoplanets - planets outside our solar system. The latest spaceborne instruments, including those aboard NASA's James Webb Space Telescope, are not just designed to detect these distant worlds, but to reveal some of their characteristics. This includes their atmospheric composition, which may provide clues to the presence of life.
The recently discovered super-Earth -- TOI-715b -- may appear at just the right time. Its parent star is a red dwarf, smaller and cooler than our sun; many such stars are known to harbor small rocky worlds. Currently, they are the best option for finding habitable planets.
These planets orbit much closer than those around stars like the sun, but because red dwarfs are smaller and cooler, the planets can be squeezed closer together and still stay safely within the star's habitable zone. Tighter orbits also mean that planets that cross the surface of a star - that is, when observed by our space telescopes - do so much more frequently.
As far as TOI-175b is concerned, it orbits once every 19 days, which is "a year" in this strange world. As a result, these interstellar ("transiting") planets are easier to detect and observed more frequently.
That's the case with TESS (Transiting Exoplanet Survey Satellite), which discovered the new planet and has been adding to astronomers' stockpile of habitable zone exoplanets since its launch in 2018. Observing such a transit of an Earth-sized planet around a sun-like star (and waiting one Earth year, or 365 days, to catch another transit) is beyond the capabilities of existing space telescopes.
Potential for further discoveries
Planet TOI-175b joins the list of habitable zone planets, and the Webb telescope may take a closer look at it and may even find signs of an atmosphere. Much depends on the planet's other properties, including how massive it is and whether it can be classified as a "water world" -- making its atmosphere (if it exists) more prominent and less detectable than the atmospheres of more massive, denser, drier worlds, which may be closer to the surface.
If a possible second Earth-sized planet in the system is also confirmed, it would become the smallest habitable zone planet discovered by TESS to date. The discovery also exceeded TESS's early expectations, as it discovered an Earth-sized world in the habitable zone.
An international team of scientists led by Georgina Dransfield of the University of Birmingham in the United Kingdom published a paper in the Monthly Notices of the Royal Astronomical Society in January 2024, introducing their findings: "A planet orbiting M4 near the south pole of the ecliptic The international array of facilities used to identify the 1.55R⊕ Habitable Zone Planet hosted by the star TOI-715 includes the Gemini-South Telescope, the Las Cumbres Observatory Telescope, the ExTrA Telescope, the SPECULOOS Network, and the TRAPPIST-South Telescope.
Compiled source: ScitechDaily