HIP 57274 d is anexoplanet orbiting theK-type main sequence starHIP 57274 about 84.5light-years (26parsecs, or nearly8.022×10¹⁶km) fromEarth in theconstellationCetus. It orbits within the outer part of its star'shabitable zone, at a distance of 1.01AU. The exoplanet was found by using theradial velocity method, fromradial-velocity measurements via observation ofDoppler shifts in thespectrum of theplanet's parent star.

HIP 57274 d is agas giant, a planet that has a radius and mass close to that of the gas giantsJupiter andSaturn. It has a temperature of 167 K (−106 °C; −159 °F). It has an estimated mass of around 0.527M_J (167M_🜨), and a potential radius of around 9R_🜨 based on its mass, since it is slightly more massive than Saturn.

The planet orbits a (K-type) star namedHIP 57274, orbited by a total of three planets. The star has a mass of 0.73M_☉ and a radius of 0.68R_☉. It has a surface temperature of 4640K and is 7 billion years old. In comparison, the Sun is about 4.6 billion years old^[3] and has a surface temperature of 5778 K.^[4]

The star'sapparent magnitude, or how bright it appears from Earth's perspective, is 8.96. Therefore, HIP 57274 is too dim to be seen with the naked eye, but can be seen with good binoculars.

HIP 57274 d orbits its star every 432 days at a distance of 1.01AU. This is very similar to that ofEarth's orbital period and distance.

HIP 57274 d resides in the outer part of circumstellarhabitable zone of the parent star. The exoplanet, with a mass of 0.527M_J, is too massive to be rocky, and because of this the planet itself may not be habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life.

For a stable orbit the ratio between the moon'sorbital periodP_s around its primary and that of the primary around its starP_p must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.^[5][6] Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet orbrown dwarf that orbits 1AU from a Sun-like star.^[7] In the case of HIP 57274 d, the moon's orbit would have to be roughly 40 days to support a stable orbit.

Tidal effects could also allow the moon to sustainplate tectonics, which would cause volcanic activity to regulate the moon's temperature^[8][9] and create ageodynamo effect which would give the satellite a strongmagnetic field.^[10]

To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07M_🜨.^[11] One way to decrease loss fromsputtering is for the moon to have a strongmagnetic field that can deflectstellar wind and radiation belts. NASA'sGalileo's measurements hints large moons can have magnetic fields; it found thatJupiter's moonGanymede has its own magnetosphere, even though its mass is only 0.025M_🜨.^[7]

• Kepler-90h
• HD 69830 d
• Kepler-47c

• Exoplanets discovered in 2011
• Exoplanets detected by radial velocity
• Giant planets in the habitable zone
• Ursa Major

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