Astronomers may have found an exoplanet orbiting in the habitable zone of the hottest star yet known to host such a world. The candidate, dubbed HD 156295 b, sits about 140 light-years from Earth. The team detailed the find in a paper published in The Astrophysical Journal.
The host star, HD 156295, is an A-type star with a surface temperature of roughly 7,500°C (13,500°F) — about 2,000 degrees Celsius hotter than the Sun. Roughly twice the Sun's size and nine times as luminous, it shines bluish-white and is bright enough to be seen with the naked eye. If confirmed, HD 156295 would be the hottest star known to host a planet in its habitable zone, and this would be the first known exoplanet in the habitable zone of a massive A-type star.
The candidate is a gas giant an estimated six times the mass of Jupiter, orbiting about 3.9 astronomical units from its star — roughly four times the Earth–Sun distance — placing it at the outer edge of the star's habitable zone, the region where liquid water could theoretically exist. One orbit takes about 2,200 days, close to six Earth years.
The detection relied on pulsation timing. HD 156295 is a Delta Scuti star, whose brightness rises and falls on a regular cycle like a metronome. Working with data from NASA's Transiting Exoplanet Survey Satellite (TESS), the researchers screened some 16,500 such pulsating stars, effectively using each star as a highly precise cosmic clock: a planet's gravity tugs the star back and forth, making its pulses arrive a tiny bit early or late. That narrowed the search to nine systems — eight consistent with brown dwarfs, and one, HD 156295, pointing to a planet. The study was led by Logan Wilson, a Harvard undergraduate who did the work during a research internship at the University of Hawaiʻi's Institute for Astronomy, together with astronomers Benjamin Shappee, Daniel Hey and Daniel Huber.
The researchers stress this is an indirect observation: they estimate the chance the planet actually exists at only slightly above 50 percent — a cosmic coin flip at the edge of what TESS can measure. The American Astronomical Society's research digest, AAS Nova, reported the find with the same "if confirmed" caveat. Follow-up observations with larger telescopes will be needed to settle it.
Even if real, HD 156295 b is no second Earth. A gas giant six times Jupiter's mass cannot host life as we know it; the "habitable zone" here is a theoretical concept about where liquid water could exist, and a gas giant has no solid surface. The scientific interest is not in finding aliens but in understanding how planets form around hot, massive stars.
The result hints that massive planets on intermediate orbits may be more common around A-type stars than around Sun-like stars — hot, massive stars could form such companions more efficiently. The eight brown-dwarf candidates found in the same survey support that trend. For now, astronomers will keep their biggest telescopes trained on HD 156295 to learn whether the hottest habitable-zone planet candidate is real.