| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius[1] |
| Right ascension | 16h 10m 17.6977s[2] |
| Declination | −24° 59′ 25.261″[2] |
| Apparent magnitude (V) | 11.068±0.110[3] |
| Characteristics | |
| Spectral type | G3V[4] |
| Apparent magnitude (J) | 9.635±0.024[5] |
| Apparent magnitude (H) | 9.294±0.022[5] |
| Apparent magnitude (K) | 9.180±0.021[5] |
| Variable type | Planetary transit[4] |
| Astrometry | |
| Radial velocity (Rv) | 1.18(32)[2] km/s |
| Proper motion (μ) | RA: −59.891(21)[2]mas/yr Dec.: −58.702(14)[2]mas/yr |
| Parallax (π) | 5.8273±0.0169 mas[2] |
| Distance | 560 ± 2 ly (171.6 ± 0.5 pc) |
| Details[6] | |
| Mass | 1.041+0.017 −0.016 M☉ |
| Radius | 1.185±0.011 R☉ |
| Surface gravity (log g) | 4.48±0.03 cgs |
| Temperature | 5726±65 K |
| Metallicity [Fe/H] | 0.41±0.05 dex |
| Age | 4.9±1.7 Gyr |
| Other designations | |
| Gaia DR2 6049750234317822208,EPIC 203771098,TYC 6784-837-1,2MASS J16101770-2459251[7] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
K2-24 (also known asEPIC 203771098) is ametal-richG3-typemain sequence star larger and more massive than the Sun, located 560light-years (172parsecs) away in theconstellationScorpius. Two confirmedtransitingexoplanets are known to orbit this star.[4] An attempt to detect stellar companions usingadaptive optics imaging at theKeck telescope was negative[4] however later observations usinglucky imaging at the Danish 1.54 m telescope atLa Silla Observatory detected a possible companion at 3.8arcseconds distance from K2-24. This candidate companion being over 8magnitudes fainter than K2-24 and with acolor temperature of5400 Kelvin, is inconsistent with a bound main sequence companion.[8]
Erik A. Petigura and team analyzed data obtained from theKepler space telescope during its observation of theK2 Campaign 2 field. They reported the discovery and confirmation of both planets b and c.[4] The Planetary signals were independently detected by Andrew Vanderburg and collaborators.[9]
The two known planets in this system have radii equal to 5.4 and 7.5 times that of the Earth. This places both planets radii between that ofUranus andSaturn, a range not present within theSolar System. Withorbital periods of 20.9 days and 42.4 days, the planets are within 1% of the2:1 mean-motion resonance. The low observed eccentricities and near orbital resonance provide evidence regarding the formation and evolution of the system, suggesting that they could possibly have resulted from gravitational interactions with aprotoplanetary disk. K2-24c at 15.4 earth masses is significantly lighter than K2-24b's 19 Earth masses despite being a larger planet. It is estimated that K2-24b's atmosphere makes up 26% of its mass while K2-24c's atmosphere makes up 52%. The current model of core-nucleated accretion predicts that runaway accretion should occur when a planet reaches approximately 50% atmosphere by mass, this makes K2-24c a potential challenge to the model.[10]
There is also a candidate planet, K2-24d, with a mass of 53 ME and an orbital period of 470 days. While theradial velocity signal of planet was confirmed, no validation tests were run to confirm its existence, rendering it as unconfirmed.[6]
A transit observation of K2-24b with theHubble Space Telescope'sWide Field Camera 3 suggested the presence of ammonia, in a high abundance, but did not find evidence for water.[11]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 19.0+2.2 −2.1 M🜨 | 0.1673+0.0034 −0.0056 | 20.88977+0.00034 −0.00035[10] | 0.06±0.01[10] | 89.63±0.25° | 5.638+0.065 −0.061 R🜨 |
| c | 16.4+1.3 −0.2 M🜨 | 0.262+0.014 −0.011 | 42.3391±0.0012[10] | <0.05[12] | 89.44+0.15 −0.11° | 7.93+0.12 −0.13 R🜨 |
| d(unconfirmed) | 54+9 −4M🜨 | — | 469+10 −15 | 0.00 | — | — |
