K2-32

K2-32 is a G9-type main sequence star slightly smaller and less massive than the sun.^[4] Four confirmed transiting exoplanets are known to orbit this star.^[9] A study of atmospheric escape from the planet K2-32b caused by high-energy stellar irradiation indicates that the star has always been a very slow rotator.^[10]

K2-32

Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus[1]
Right ascension	16h 49m 42.2602s[2]
Declination	−19° 32′ 34.151″[2]
Apparent magnitude (V)	12.31±0.02[3]
Characteristics
Spectral type	G9V[4]
Apparent magnitude (J)	10.404±0.024[5]
Apparent magnitude (H)	9.993±0.025[5]
Apparent magnitude (K)	9.821±0.019[5]
Variable type	Planetary transit variable[6]
Astrometry
Radial velocity (Rv)	−1.82±0.14[7] km/s
Proper motion (μ)	RA: −16.662(18)[2] mas/yr Dec.: −53.564(13)[2] mas/yr
Parallax (π)	6.3939±0.0153 mas[2]
Distance	510 ± 1 ly (156.4 ± 0.4 pc)
Details[3]
Mass	0.856±0.028 M☉
Radius	0.845+0.044 −0.035 R☉
Surface gravity (log g)	4.49±0.05 cgs
Temperature	5275±60 K
Metallicity [Fe/H]	−0.02±0.04 dex
Rotational velocity (v sin i)	0.7 km/s
Age	7.9±4.5 Gyr
Other designations
Gaia DR2 4130539180358512768, EPIC 205071984, 2MASS J16494226-1932340[8]
Database references
SIMBAD	data

Planetary system

Discovery

The star K2-32 was initially found to have three transiting planet candidates by Andrew Vanderburg and collaborators in 2016.^[7] The innermost planet candidate, at that time, K2-32b was confirmed using radial velocity measurements made with the Keck telescope.^[4] Confirmation of planets c and d was made by Sinukoff et al. using adaptive optics imaging and computer analysis to eliminate possible false positives.^[6]

The Earth-sized planet K2-32e was discovered and validated by René Heller and team in 2019.^[9][11]

Transit light curves of all four planets orbiting the star K2-32.^[9]

Characteristics

With periods of 4.34, 8.99, 20.66 and 31.71 days the four planets orbits are very close to a 1:2:5:7 orbital resonance chain. The densities of planets b, c, and d are between those of Saturn and Neptune, which suggests large and massive atmospheres. The planet K2-32e with a radius almost identical to that of the Earth is almost certainly a terrestrial planet.^[9] All four planets are well inside even the optimistic inner boundary of the habitable zone located at 0.58 astronomical units.^[12]

Planetary system of the star K2-32 showing planetary radii and orbital resonances.^[9]

The K2-32 planetary system^[9][3][13]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
e	2.1+1.3 −1.1 M🜨	0.04899+0.00041 −0.00038	4.34934±0.00039	0.043+0.048 −0.030	89.0±0.7°	1.212+0.052 −0.046 R🜨
b	15.0+1.8 −1.7 M🜨	0.07950+0.00066 −0.00062	8.992±0.00008	0.03+0.032 −0.02	89.0+0.5 −0.3°	5.299±0.191 R🜨
c	8.1±2.4 M🜨	0.13843+0.00115 −0.00108	20.66093+0.00080 −0.00079	0.049+0.046 −0.035	89.4+0.3 −0.2°	2.134+0.123 −0.102 R🜨
d	6.7±2.5 M🜨	0.18422+0.00152 −0.00144	31.71701+0.00101 −0.00096	0.05+0.053 −0.035	89.4±0.1°	3.484+0.112 −0.129 R🜨