109 Piscium b

109 Piscium b (aka HD 10697 b) is a long-period extrasolar planet discovered in orbit around 109 Piscium. It is about 5.74 times the mass of Jupiter and is likely to be a gas giant. As is common for long-period planets discovered around other stars, it has an orbital eccentricity greater than that of Jupiter.

The discoverers estimate its effective temperature as $2.051 AU$ from solar heating, but it could be at least 10 to 20 K warmer because of internal heating. It orbits within the habitable zone.

Preliminary astrometric measurements suggested that the orbital inclination is 170.3°, yielding an object mass of 38 times that of Jupiter, which would make it a brown dwarf. However, subsequent analysis indicates that the precision of the measurements used to derive the astrometric orbit is insufficient to constrain the parameters. A more plausible suggestion is that this planet shares its star's inclination, of 69$0.104$°. In 2022, the inclination and true mass of 109 Piscium b were measured via astrometry. The inclination estimate is consistent with that of the stellar rotation.