HD 156295 b may be a massive planet in a habitable zone

HD 156295 b is a candidate planet with an estimated mass of 6.3 times Jupiter’s. Its orbit may place it in the star’s habitable zone, where temperatures could allow liquid water under suitable conditions. The candidate emerged from timing changes in the star’s pulsations, alongside eight candidate brown dwarfs. More observations are needed to confirm the planet.

Star system: HD 156295 | Distance from the Sun: 143 light years

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HD 156295 b may be a massive planet in a habitable zone

Star system: HD 156295 | Distance from the Sun: 143 light years

HD 156295 b is a candidate planet with an estimated mass of 6.3 ± 1.1 times Jupiter’s. Its orbit may place it in the star’s habitable zone, the region where temperatures could allow liquid water on a planet’s surface under suitable conditions. The candidate is not yet confirmed. If it is real, HD 156295 would be the hottest known star to host a habitable-zone planet.

The candidate emerged from changes in the timing of the star’s pulsations. The analysis used observations from NASA’s Transiting Exoplanet Survey Satellite, or TESS, which recorded brightness changes in 16,440 δ Scuti stars. These stars regularly expand and contract, creating repeating variations in their light. An orbiting companion can shift when those variations reach us because the star moves slightly toward or away from Earth. Measuring these timing shifts, called pulsation timing, can reveal clues about a companion’s orbit.

The planet’s estimated mass agrees with a separate constraint from Hipparcos and Gaia measurements: those data set a two-sigma upper limit of 10.5 Jupiter masses. The analysis also identified eight candidate brown dwarfs, objects more massive than planets but not massive enough to sustain normal hydrogen fusion like stars. If HD 156295 b is not a planet and the signal is a false positive, the estimated occurrence rates for similar planets have one-sigma and two-sigma upper limits of 19% and 39%. Follow-up measurements of the star’s motion could test the planet candidate. At least two of the brown dwarf candidates are suitable targets for direct imaging, which attempts to capture light from an orbiting object.

Key findings
HD 156295 b is a candidate planet with an estimated mass of 6.3 ± 1.1 Jupiter masses.
If confirmed, it would orbit the hottest star known to host a habitable-zone planet.
The planet’s estimated mass is consistent with a 10.5-Jupiter-mass, two-sigma upper limit from Hipparcos and Gaia astrometry.
The analysis found eight candidate brown dwarfs among 16,440 δ Scuti pulsators observed by TESS.
If the planet candidate is a false positive, the one-sigma and two-sigma upper limits on the occurrence rate of similar planets are 19% and 39%.
Astrometric follow-up could test the planet candidate, and at least two brown dwarf candidates may be observed directly.

Scientific study

A Search for Substellar Companions around A-type Stars: Pulsation Timing Detection of Eight Brown Dwarf Candidates and a Possible Habitable-zone Planet (external link)