Astronomers have recently discovered a new object near our Solar System, named WISE 0855-0714. This brown dwarf, which is a type of celestial object that is too large to be a planet and not massive enough to sustain hydrogen-1 fusion reactions in its core, is one of the closest neighbors to our Sun, located just 7.13 light years away. The combination of astrometry from the Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope has measured a proper motion of approximately 18,000 miles per year (29,000 km/yr) for WISE 0855-0714.
This brown dwarf stands out as one of the coldest known brown dwarfs, with an estimated effective temperature of 225-260 Kelvin (-48 to -13°C, -54 to 8°F). Based on its absolute magnitude at 4.5 micrometers and its color, astronomers have estimated its mass to be between 3-10 Jupiter masses. WISE 0855-0714 also boasts the third highest proper motion and fourth largest parallax of any known star or brown dwarf. Proper motion is the angular change in position of a celestial object relative to the observer over time. Parallax is the apparent shift in an object’s position as seen from two different locations. The third highest proper motion and fourth largest parallax of WISE 0855-0714 means that it moves faster and appears to change position more than many other known stars or brown dwarfs, making it an interesting object to study.
WISE 0855-0714 presents a unique opportunity for astronomers to study a planet-like atmosphere in an unexplored temperature regime. Time-series photometric monitoring of WISE 0855-0714 has shown variability in its light curves, leading scientists to consider the presence of patchy clouds or inhomogeneities in its atmosphere. Some models have even predicted the appearance of water ice clouds at temperatures below 375 Kelvin (102°C, 215°F).
Despite the lack of robust evidence of water ice clouds, the similarity in mid-infrared variability amplitudes between WISE 0855-0714 and somewhat warmer T and Y dwarfs has prompted some scientists to suggest a common origin for their variability. However, more research is needed to determine the cause of the variability.
In recent discussions, some amateur astronomers have suggested naming WISE 0855-0714 “Niflheim.” This Norse mythology reference is fitting for the cold, distant brown dwarf. But the question remains: should Niflheim be classified as an exoplanet? Further study is necessary to answer this question and to shed more light on the unique properties of this fascinating celestial object.