Gliese 357 d

Gliese 357 d is an exoplanet, considered to be a "Super-Earth" within the circumstellar habitable zone of its parent star.^[3][4][5][6] The planet orbits Gliese 357, 31 light-years from the Solar System,^[4] The system is part of the Hydra constellation.^[4]

GJ 357 d

Discovery
Discovered by	Rafael Luque, Diana Kossakowski
Discovery site	TESS
Discovery date	2019
Detection method	Radial velocity
Orbital characteristics
Semi-major axis	0.204±0.015 AU[1]
Eccentricity	≈0.033 ± 0.057[2]
Orbital period (sidereal)	55.70±0.05 d[1]
Inclination	<40°[2]
Star	Gliese 357
Physical characteristics
Mass	6.1±1.0 M🜨[1] 7.20±1.07 M🜨[2]
Temperature	219.6 ± 5.9 K (−53.55 ± 5.90 °C; −64.39 ± 10.62 °F)[1]

The planet was discovered by the TESS team and announced in July 2019. The data confirming the presence of the planet was uncovered in ground-based observation dating back to 1998 while confirming the TESS detection of Gliese 357 b, a “hot earth” that orbits much closer to the parent star.^[6] Even though Gliese 357 d is 20% closer to Gliese 357 than Earth is to the Sun, Gliese 357 is much smaller than the Sun, receiving only as much energy as Mars. As a result, it is estimated that the average temperature is -64°F (-53°C), but this temperature is survivable for humans; if there is a thick enough atmosphere, the actual temperature could be much higher. If humans traveled there using modern spacecraft, it would take them about 660,000 years to get there.^[a] The planet is 6.1 times more massive than Earth and 2.3 times Earth's size.^[8]

Footnotes

1. Calculated assuming the spacecraft travels at 14 km/s. For comparison, the New Horizons spacecraft is exiting the solar system at a velocity of 13.7 km/s as of June 2024.^[7]