Based on direct observations, WISE 0855−0714 has a large parallax, which specifically relates to its distance from the Solar System. This phenomenon results in a distance of around 7.43±0.04 light-years,[2] with a small margin of error due to the strength of the parallax effect and the clarity of observations. WISE 0855−0714 also has an exceptionally high proper motion.[2]
Spectrometry
Its luminosity in different bands of the thermal infrared in combination with its absolute magnitude—because of its known distance—was used to place it in context of different models; the best characterization of its brightness was in the W2 band of 4.6 μm at an apparent magnitude of 13.89±0.05, though it was brighter into the deeper infrared.[6] Infrared images taken with the Magellan Baade Telescope suggest evidence of sulfide clouds below water ice clouds.[8]
Near- and mid-infrared spectra in the L- and M-band were taken with the GNIRS instrument on the Gemini North Telescope. The M-band (4.5–5.1 μm) spectrum is dominated by water vapour (H2O) absorption. The L-band (3.4–4.14 μm) spectrum is dominated by methane absorption. Both the M- and L-band surprisingly have no detection of phosphine (PH3), which appears in the atmosphere of Jupiter. 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 of ammonium dihydrogen phosphate (NH4)(H2PO4), which are below the water ice clouds.[9][10] An approved JWST proposal describes how the team is planning to use a near-infrared time-series to study the hydrological cycle in the atmosphere of WISE 0855 with NIRSpec.[11]
Observations with NIRSpec detected methane (CH4), water vapor (H2O), ammonia (NH3) and carbon monoxide (CO) in the atmosphere, but was not able to confirm any phosphine (PH3) or carbon dioxide (CO2) in the atmosphere. Water ice clouds are also not confirmed and the spectrum is well matched with a cloudless model. Future modelling and inclusion of observations at longer wavelengths with MIRI might help to reveal clouds in WISE 0855.[4]
Variability
Variability of WISE 0855 in the infrared was measured with Spitzer IRAC. A relative small amplitude of 4–5% was measured. Water ice cloud models predicted a large amplitude. This small amplitude might suggest that the hemispheres 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.[12]
Physical parameters
Based on models of brown dwarfs WISE 0855−0714's is estimated to have a mass of 3 to 10MJup.[7] This mass is in the range of a sub-brown dwarf or other planetary-mass object.
As of 2003, the International Astronomical Union considers an object with a mass above 13MJup, capable of fusing deuterium, to be a brown dwarf. A lighter object and one orbiting another object is considered a planet.[13] However, if the distinction is based on how the object formed then it might be considered a failed star, a theory advanced for the object Cha 110913-773444.[14]
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.[7] Models matching the NIRSpec spectrum are well fitted with a temperature of 285 K (12°C; 53 °F).[4]
Gallery
Time-lapsed photo sequence of WISE 0855−0714's movement in the sky using captured images from the WISE and the Spitzer telescopes.[7]
JWST NIRCam observation of W0855 (orange "star" at the center) showing the movement over about half a year.
The position of WISE 0855−0714 on a radar map among all stellar objects or stellar systems within 9 light years (ly) from the map's center, the Sun (Sol). The diamond-shapes are their positions entered according to right ascension in hours angle (indicated at the edge of the map's reference disc), and according to their declination. The second mark shows each's distance from Sol, with the concentric circles indicating the distance in steps of one ly.
Artist's impression of a water cloud planet. It was suggested that WISE 0855 has water ice clouds.
See also
CFBDSIR 2149-0403, the first free-floating object with a confirmed mass below 13MJup.
. Using the solar radius value of 695,700 km, the calculated radius of WISE 0855-0714 converts to approximately 64,000 km, or 0.89 RJ when dividing by the nominal Jupiter radius value of 71,492 km.