 Time-lapsed photo sequence of WISE 0855−0714's movement in the sky using captured images from the JWST | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 08h 55m 10.83168s[1] |
| Declination | −07° 14′ 42.5256″[1] |
| Characteristics | |
| Evolutionary stage | Sub-brown dwarf |
| Spectral type | Y4V[2][3] |
| Apparent magnitude (J) | 25.00±0.53[1] |
| Apparent magnitude (H) | 23.83±0.24[1] |
| Astrometry | |
| Proper motion (μ) | RA: −8,123.7±1.3mas/yr[2] Dec.: 673.2±1.3mas/yr[2] |
| Parallax (π) | 439.0±2.4 mas[2] |
| Distance | 7.43 ± 0.04 ly (2.28 ± 0.01 pc) |
| Details[4] | |
| Mass | ~3–10 MJup |
| Radius | 0.89[a] RJup |
| Radius | 63,500 km |
| Luminosity | 4.9545×10−8[b] L☉ |
| Surface gravity (log g) | ~4 cgs |
| Temperature | 285 K |
| Metallicity[Fe/H] | ~0 dex |
| Age | 1–10 Gyr |
| Other designations | |
| WISEA J085510.74-071442.5,GJ 11286[5] | |
| Database references | |
| SIMBAD | data |
  WISE 0855−0714 Location of WISE 0855−0714 in the constellationHydra | |
WISE 0855−0714 (full designationWISE J085510.83−071442.5,[6] orW0855 for short) is asub-brown dwarf ofspectral class Y4, located 7.4light-years (2.3parsecs) from the Sun in theconstellationHydra. It is the fourth-closest star or (sub-) brown dwarf system to the Sun and was discovered byKevin Luhman in 2013 using data from theWide-field Infrared Survey Explorer (WISE). It is the coldest brown dwarf found yet, having a temperature of about 285 K (12 °C; 53 °F).[4] It has an estimated mass between 3 and 10Jupiter masses, which makes it aplanetary-mass object below the 13 Jupiter mass rough limit fordeuterium fusion.
WISE 0855−0714 was first imaged by the WISE telescope on 4 May 2010 during its primary mission of surveying the entire sky.[6] It was later discovered byKevin Luhman in March 2013, who noticed the object's unusually highproper motion while searching forpotential binary companions of the Sun in WISE images.[7][8] In the interest of confirming the object'sspectral properties and nearby distance to the Sun, Luhman made follow-up observations with theSpitzer Space Telescope and theGemini North telescope in 2013–2014.[8][6] The discovery of the object was announced in a NASA press release in April 2014.[8]
Since WISE 0855−0714 is an isolated object, itsluminosity primarily comes fromthermal radiation.[8] WISE 0855−0714's temperature is low enough that it roughly matchesroom temperature, which means WISE 0855−0714's luminosity is very low and it primarily emitsinfrared light as thermal radiation.[8] Hence, it is best observed withinfrared telescopes such as WISE and theJames Webb Space Telescope (JWST).[4] WISE 0855−0714 has been detected inspectralwavelengths as short as1.15 μm—in thisnear-infrared wavelength, the object appears extremely dim with anapparent magnitude of 26.3.[9][10] WISE 0855−0714's brightness decreases with decreasing wavelength, so the object is practically invisible invisible light.[8]
Based on direct observations, WISE 0855−0714 has a largeparallax of439.0±2.4 mas, which corresponds to a distance of around2.28±0.01 parsecs (7.43±0.04 light-years).[2] This makes WISE 0855−0714 the fourth-closest star or (sub-) brown dwarf system to the Sun. WISE 0855−0714 also has an exceptionally highproper motion of8,151.6±1.8 mas/yr,[2] the third-highest afterBarnard's Star (10,300 mas/yr) andKapteyn's Star (8,600 mas/yr)[6]
Its luminosity in different bands of the thermal infrared in combination with itsabsolute magnitude—because of its known distance—was used to place it in context of different models; the best characterization of its brightness was in theW2 band of4.6 μm at anapparent magnitude of13.89±0.05, though it was brighter into the deeper infrared.[6] Infrared images taken with theMagellan Baade Telescope suggest evidence ofsulfide clouds belowwater ice clouds.[11]
Near- and mid-infrared spectra in the L- and M-band were taken with the GNIRS instrument on theGemini North Telescope. TheM-band (4.5–5.1 μm) spectrum is dominated by water vapour (H2O) absorption. TheL-band (3.4–4.14 μm) spectrum is dominated bymethane absorption. Both the M- and L-band surprisingly have no detection ofphosphine (PH3), which appears in the atmosphere ofJupiter. The M-band spectrum shows evidence for water ice clouds and the near-infrared photometry WISE 0855 is faint compared to models, suggesting an additional absorber, probably clouds made ofammonium dihydrogen phosphate (NH4)(H2PO4), which are below the water ice clouds.[12][13] An approved JWST proposal describes how the team is planning to use a near-infrared time-series to study thehydrological cycle in the atmosphere of WISE 0855 withNIRSpec.[14]
Observations withNIRSpec detected methane (CH4),water vapor (H2O),ammonia (NH3) andcarbon monoxide (CO) in the atmosphere, but was not able to confirm anyphosphine (PH3) orcarbon dioxide (CO2) in the atmosphere. Water ice clouds are also not confirmed and the spectrum is well matched with a cloudless model.[4] Observations withMIRI showed a water vapor depletion and a water abundance that is variable withpressure. This is consistent with watercondensing out in the upper atmosphere. The observations did however not detect any water ice clouds, which were predicted in previous studies. This discrepancy is explained with the rainout of the water: Water condenses into particles in the upper atmosphere, which quickly sink into the lower atmosphere. Clouds only form if upward mixing is present. A similar process is present foralkali metals inL- andT-dwarfs. A direct rainout would suggest weak mixing, but disequilibrium chemistry suggest rigours mixing. Future variable studies might resolve if upward mixing or settling is the dominant process. Cloud models however potentially detected deep ammonium dihydrogen phosphate (NH4)(H2PO4) clouds. The observations also detected15NH3 for the first time in WISE 0855. The atmosphere has a mass fraction of14NH3/15NH3 =332+63
−43, meaning it has about 99.7%14N and about 0.3%15N. Compared to solar values and the ratio ofWISE 1828, the atmosphere of WISE 0855 is enriched in15N. The nitrogen isotope ratio is closer to today's15N-enrichedinterstellar medium. This could mean that WISE 0855 formed from a younger cloud, but more measurements of15N in other brown dwarfs are needed to establish evolutionary trends.[15] In November 2024 a team used archived and new NIRSpec data to detect deuterated methane (CH3D) and about onepart per billion PH3 in WISE 0855. This detection ofdeuterium showed that WISE 0855 has a mass below the deuterium-burning-limit. The low amount of PH3 is on the other hand in disagreement with predictions, showing incomplete knowledge ofphosphorus chemistry.[16]
Variability of WISE 0855 in the infrared was measured withSpitzer IRAC. A relative smallamplitude of 4–5% was measured. Water ice cloud models predicted a large amplitude. This small amplitude might suggest that thehemispheres of WISE 0855 have very small deviation in cloud coverage. The light curve is too irregular to produce a good fit and rotation periods between 9.7 and 14 hours were measured.[17]
The mass and age of WISE 0855−0714 are neither known with certainty, but can be constrained with its known present-day temperature. The age of WISE 0855−0714 depends on its mass; a lower mass would lead to a faster rate of cooling and thus a younger age for WISE 0855−0714, whereas a higher mass would lead to a slower rate of cooling and thus an older age for WISE 0855−0714.[6] Assuming an age range of 1–10 billion years, evolutionary models for brown dwarfs predict that WISE 0855−0714 should have a mass between3 and 10 MJup.[8][6] This mass is in the range of asub-brown dwarf orplanetary-mass object.
As of 2003, theInternational Astronomical Union considers an object with a mass above13 MJup, capable of fusingdeuterium, to be a brown dwarf. A lighter object and one orbiting another object is considered a planet.[18] However, if the distinction is based on how the object formed then it might be considered a failed star, a theory advanced for the objectCha 110913-773444. In this case it could be termed a sub-brown dwarf.[19]
Combining its luminosity, distance, and mass it is estimated to be the coldest-known brown dwarf, with a modeled effective temperature of 225 to 260 K (−48 to −13 °C; −55 to 8 °F), depending on the model.[8] Models matching the NIRSpec spectrum are well fitted with a temperature of 285 K (12 °C; 53 °F).[4]
A team of researchers used 11 hours of JWST observations to search fortransits caused byexomoons around WISE 0855. The researchers do not find any transits. By injecting transits into the light curve the researchers find that they could have detected ≥0.5% deep transits with a detection rate of 96%. This transit depth is consistent with an object about twice as large as the moonTitan.[20]
![Time-lapsed photo sequence of WISE 0855−0714's movement in the sky using captured images from the WISE and the Spitzer telescopes.[8]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWISE_J085510.83%25E2%2580%2593071442.5_movement_(PIA18002).gif)
.png)
