Giant Planets that can Potentially Host Habitable Moons

Díaz et al. (2016) present the detection of 4 gas giant planets in long-period orbits around stars that are somewhat more luminous than the Sun. The 4 planets were detected using the radial velocity method, and they are identified as HD191806b, HD214823b, HD221585b and HD16175b. The suffix "b" denotes their planetary nature. All 4 planets have orbits that are largely within the habitable zone of their host stars. Furthermore, because all 4 planets are much more massive than Jupiter, they can host correspondingly more massive moons that might be habitable.

Figure 1: Artist's impression of a gas giant planet with a large habitable moon.

HD191806b is estimated to have at least 8.52 ± 0.63 times the mass of Jupiter. It orbits its host star every 1606.3 ± 7.2 days with an orbital eccentricity estimated to be 0.259 ± 0.017. Its host star has 1.14 ± 0.12 times the mass and 2.23 ± 0.16 times the luminosity of the Sun, and its effective temperature is 6010 ± 30 K. The average amount of insolation HD191806b receives is 0.30 ± 0.03 times of what Earth gets from the Sun. The relatively low average insolation that HD191806b receives places it on the cold side of the habitable zone.

HD214823b is estimated to have at least 19.2 ± 1.4 times the mass of Jupiter. It orbits its host star every 1877 ± 15 days with an orbital eccentricity estimated to be 0.154 ± 0.014. Its host star has 1.22 ± 0.13 times the mass and 4.35 ± 0.58 times the luminosity of the Sun, and its effective temperature is 6215 ± 30 K. The average amount of insolation HD214823b receives is 0.44 ± 0.07 times of what Earth gets from the Sun. The high mass of HD214823b suggests that it is more appropriate to classify it as a brown dwarf instead of a planet.

HD221585b is estimated to have at least 1.61 ± 0.14 times the mass of Jupiter. It orbits its host star every 1173 ± 16 days with an orbital eccentricity estimated to be 0.123 ± 0.069. Its host star has 1.19 ± 0.12 times the mass and 2.64 ± 0.18 times the luminosity of the Sun, and its effective temperature is 5620 ± 27 K. The average amount of insolation HD221585b receives is approximately half of what Earth gets from the Sun.

HD16175b is estimated to have at least 4.77 ± 0.37 times the mass of Jupiter. It orbits its host star every 995.4 ± 2.8 days with an orbital eccentricity estimated to be 0.637 ± 0.020. Its host star has 1.34 ± 0.14 times the mass and 3.22 ± 0.25 times the luminosity of the Sun, and its effective temperature is 6022 ± 34 K. The average amount of insolation HD16175b receives is 0.91 ± 0.10 times of what Earth gets from the Sun. The large eccentricity of the planet's orbit causes the amount of insolation it gets from its host star to vary by a factor of approximately 20. A hypothetical large rocky moon in orbit around HD16175b can still be habitable provided it can maintain a relatively constant temperature throughout the planet's orbit.

Figure 2: Schematic view of the orbits of HD191806b, HD214823b, HD221585b and HD16175b. The filled green areas denote the habitable zone. Díaz et al. (2016)

Reference:
Díaz et al. (2016), "The SOPHIE search for northern extrasolar planets. XI. Three new companions and an orbit update: Giant planets in the habitable zone", arXiv:1604.07610 [astro-ph.EP]