 Pan-STARRS image of PSO J318.5-22 | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Capricornus |
| Right ascension | 21h 14m 08.0256s[1] |
| Declination | −22° 51′ 35.838″[1] |
| Characteristics | |
| Evolutionary stage | Free-floating planetary-mass object |
| Spectral type | L7.5[1] |
| Variable type | rotational variable[2] |
| Astrometry | |
| Radial velocity (Rv) | 6.0+0.8 −1.1[3] km/s |
| Proper motion (μ) | RA: 136.3 ±1mas/yr[4] Dec.: -144.3 ±1.3mas/yr[4] |
| Parallax (π) | 45.1±1.7 mas[4] |
| Distance | 72 ± 3 ly (22.2 ± 0.8 pc) |
| Details | |
| Mass | 8.3 ±0.5[3] MJup |
| Radius | 1.464 ±0.010[3] RJup |
| Luminosity (bolometric) | 10-4.52 ±0.04[3] L☉ |
| Surface gravity (log g) | 4.01 ±0.03[3] cgs |
| Temperature | 1127+24 −26[3] K |
| Rotation | 8.45 ± 0.05 hours[5] |
| Rotational velocity (v sin i) | 17.5+2.3 −2.8[3] km/s |
| Age | 23 ±3[3] Myr |
| Other designations | |
| 2MASS J21140802-2251358, CNS5 5236,TIC 24266526,WISE J211408.13-225137.3 | |
| Database references | |
| SIMBAD | data |
PSO J318.5−22 is anextrasolar object ofplanetary mass that does not orbit a parent star, it is an analog todirectly imaged younggas giants.[6] There is no consensus yet among astronomers whether the object should be referred to as arogue planet,[7][8] as a youngbrown dwarf,[9][10] or as asub-brown dwarf.[11][12] It is approximately 80 light-years away and belongs to theBeta Pictoris moving group.[13] The object was discovered in 2013 in images taken by thePan-STARRS PS1 wide-field telescope.[14] PSO J318.5-22's age is inferred to be 23 million years, the same age as the Beta Pictoris moving group. Based on its calculated temperature and age, it is classified under thebrown dwarf spectral typeL7.[6]
PSO J318.5-22 was discovered in data ofPan-STARRS and2MASS in 2013. Follow-up observations were carried out withURKIRT (photometry),NASA IRTF andGemini North (bothspectroscopy).[6] The team leader,Michael Liu of theInstitute for Astronomy at theUniversity of Hawaii, stated, "We have never before seen an object free-floating in space that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone."[15]
The spectrum of PSO J318.5-22 is in its redness in between low-gravity brown dwarfs and the planetary-mass companion2M1207b, which is redder than PSO J318.5-22. The Gemini spectrum also shows several absorption features, such as weakiron hydride,sodium andpotassium. Their weakness and a triangularH-band spectrum indicate a lowgravity. Molecular absorption fromwater vapor andcarbon monoxide are also detected.[6] Low abundance ofmethane was detected in theL-bandKeck/NIRSPEC spectrum of PSO J318.5-22. The team found that strong vertical mixing and photospheric clouds can explain the spectrum of PSO J318.5-22.[16]
PSO J318.5-22 was initially suspected to be a member of the Beta Pictoris Moving group, butradial velocity was not available at this time.[6] Later radial velocity measurement with the help of high-resolution spectroscopy from Gemini North confirmed it as a Beta Pictoris member. This group also revised the physical properties due to Beta Pictoris being older than previously thought. It has a mass of 8.3 ±0.5MJ.[3]
Variability was first detected with theNew Technology Telescope, showing a rotation period larger than 5 hours and an amplitude of 7% to 10% in theJs band. The team found that the variability is likely driven by an inhomogeneous cloud cover.[2] Later the rotational velocity helped to constrain the inclination to >29° and the rotation period to 5-10.2 hours.[3] Later PSO J318.5-22 was observed simultaneously withHubble WFC3 andSpitzer IRAC. This helped to narrow down the rotation period to 8.6 ± 0.1 hours and the inclination to 56.2 ± 8.1°. The amplitude is 3.4 ± 0.1% for Spitzer channel 2 (4.5 μm) and 4.4-5.8% for WFC3 (1.07-1.67 μm). The near-infrared and mid-infrared light curves have a phase offset between 200° and 210°, likely due to a depth-dependent longitudinal atmospheric structure. The clouds are suspected to be a patchy haze layer over thickiron clouds. This patchy haze layer could be made ofsodium sulfide,chromium ormanganese sulfide.[17] Another group did observe PSO J318.5-22 with the NTT Js and Ks-band and found a rotation period of 8.45 ± 0.05 hours and an amplitude of 2.4 ± 0.2 % in Js and 0.48 ± 0.08 % in Ks.[5] Estimated temperatures inside its clouds exceed 1,100 K (800 °C). The clouds, made of hot dust and molten iron, show how widespread clouds are in planets and planet-like objects.[18] However, by 2020, modeling showed that the brightness variability could not be unambiguously attributed to clouds.[12]
Current theories about such objects include the possibility thatgravitational perturbations may have kicked them out of their planetary systems soon after they formed throughplanetaryaccretion, or they may have been formed by some other means.[19]
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