Astronomers are setting their sights on launching ambitious telescopes to seek out biosignatures on distant worlds. A recently unveiled planetary body, initially announced at the Rocky Worlds conference and subsequently detailed in a paper published in The Astrophysical Journal Letters, could serve as an excellent candidate for this forthcoming research.
The planet, designated HD 137010 b, closely matches Earth’s dimensions. Its year, lasting 355 days, is also nearly identical to ours. Furthermore, its host star is luminous and resides just 146 light-years away—near enough for detailed scrutiny with forthcoming telescopic technology.
Although astronomers managed to observe the planet only once back in 2017 using NASA’s Kepler Space Telescope, they took steps to rule out potential confounding factors. “They really did all the requisite groundwork,” states Steven Kane, a planetary astrophysicist at the University of California, Riverside, who was not involved in the study. “I’m very eager to see what more we uncover about it going forward.”
HD 137010 b’s star is a K-type dwarf, relatively bright but cooler than the Sun by roughly 1000°C. Consequently, despite the planet orbiting at a distance comparable to Earth’s, it receives less energy from its star than Mars does. This places it right on the chilly boundary of the star’s habitable zone—the orbital region where a world might retain liquid water on its surface. However, there is a possibility the planet could be warmer. The team calculated a roughly 40% chance that it orbits closer to its star, firmly within the habitable zone.
The initial hints of HD 137010 b’s existence were spotted by citizen scientists participating in the Planet Hunters project, an initiative that enlists volunteers to scan Kepler and other planet-hunting telescope data for orbiting bodies. Alexander Wibner from the Max Planck Institute for Astronomy, who presented the findings, mentioned he joined Planet Hunters nearly a decade ago as a high school student. Upon starting his doctoral research, he revisited Planet Hunters to scope out intriguing planets for deeper analysis and stumbled upon HD 137010 b.
The Kepler mission, which concluded in 2018, monitored over 500,000 stars, awaiting planetary transits across their faces. Transiting planets obscure a fraction of the starlight, causing a dimming event used to confirm the planet and determine its size. Professional astronomers overlooked HD 137010 b because their established algorithms required multiple transit events for confirmation, whereas this world only showed one. “It was totally missed,” Wibner remarked. “The best way to find it was just to look.”
Wibner and his collaborators successfully dismissed alternative explanations, such as the presence of an unseen binary companion star that might have caused the Kepler dimming signal. They found that an Earth-sized planet provided the best fit for the data and utilized the transit timing to ascertain its likely orbit.
In total, astronomers have identified over 6,000 exoplanets. Yet, the vast majority are large, hot, or both, as such worlds are easiest to detect. Among the few dozen known, potentially habitable, Earth-sized exoplanets, most orbit tight orbits around M-dwarf stars. These dimmer but volatile stars emit high-energy radiation that appears to strip away planetary atmospheres.
The Kepler telescope did locate a handful of rocky planets in the habitable zones of quieter, Sun-like stars; the first terrestrial-sized world, Kepler-186f, was discovered in 2014. However, all these worlds circle stars that are too distant and faint for follow-up observations capable of detecting atmospheres—and one day, perhaps, signs of life within them.
For HD 137010 b, this proximity isn’t an issue, owing to its relatively close and bright host star. While researchers are unsure of the precise moment the planet will next cross its star, Wibner suggests HD 137010 b is an ideal target for upcoming endeavors like the Terra Hunting Experiment, slated to begin this year on the Isaac Newton Telescope in Spain’s La Palma, or the European Space Agency’s PLATO orbiting observatory, Kepler’s successor, scheduled for launch in about a year.
“A lot of these instruments are fundamentally designed to stare at specific, bright, Sun-like stars for many years,” Wibner explains hopefully, anticipating the chance detection of a potentially inhabited world. “The advantage here is that we already know a planet with Earth-like attributes exists around this star.”
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