WISE J0855-0714

PSU, CalTech, JPL, NASA










Composite infrared images.










The brown dwarf exhibits
the high proper motion
expected for those objects
located relatively close
to Sol (more).

After noticing the fast proper motion of WISE J0855-0714 across infrared images in March of 2013 (the third highest observed outside the Solar System, behind Bernard's and Kapteyn's stars), Luhman analyzed additional images taken with Spitzer infrared space telescope and the Gemini South telescope. Spitzer's infrared observations helped to determine its chilly temperature of between minus 54 and 9 degrees Fahrenheit (minus 48 to minus 13 degrees Celsius). As a result, the object is the coldest brown dwarf discovered as of April 25, 2014, as the previous coldest dwarfs were no colder than room temperature. Also the reddest as well as coldest brown dwarf known, it should probably be classified as a "Y" dwarf (Kevin L. Luhman, 2014).

PSU, NASA



Larger and jumbo illustrations.



The brown dwarf could be the
fourth closest celestial system
to Sol, after Alpha Centauri 3,
Barnard's Star, and Luhman
16 ab (more).

If WISE J0855-0714 is between one and 10 billion years old like most nearby stars, then it may have around 3 to 10 times Jupiter's mass. At that mass range, it is one of the least massive brown dwarfs known as of April 25, 2014. While it could be a gas giant that was ejected by gravitational perturbations from its star system, it probably developed as a solitary brown dwarf rather than a planet around a star.

Robert Hurt, IPAC, NASA

Larger illustration: Sol; M,L,T dwarfs;
and Jupiter.

At one billion years in age, large brown
dwarfs are reddish like the smallest
M-type stars, but cooler, dimmer T-dwarfs
are more magenta in hue (more; and Kevin L. Luhman, 2013).

Although brown dwarfs lack sufficient mass (at least 75-80 Jupiters) to ignite core hydrogen fusion, the smallest true stars (red dwarfs) can have such cool atmospheric temperatures (below 4,000° K) that it is difficult to distinguish them from young brown dwarfs. While Jupiter-class planets may be much less massive than brown dwarfs, they are about the same diameter and may contain many of the same atmospheric molecules.

© American Scientist



Artwork by Linda Huff
(for Martin et al, 1997)
used with permission.

Brown Dwarfs or Planets?

When brown dwarfs were just a theoretical concern, astronomers differentiated those hypothetical objects from planets by how they were formed. If a substellar object was formed the way a star does, from a collapsing cloud of interstellar gas and dust, then it would be called a brown dwarf. If it was formed by gradually accumulating gas and dust inside a star's circumstellar disk, however, it was called a planet. Once the first brown dwarf candidates were actually found, however, astronomers realized that it was actually quite difficult to definitely rule on the validity of competing hypotheses about how a substellar object was actually formed without having been there. This problem is particularly difficult to resolve in the case of stellar companions, objects that orbit a star -- or two.

Astronomer Ben R. Oppenheimer, who helped to discover the other nearby brown dwarf, Gliese 229 b, is part of a growing group that would like to define a brown dwarf as an substellar object with the mass of 13 to 80 (or so) Jupiters. While these objects cannot fuse "ordinary" hydrogen (a single proton nucleus) like stars, they have enough mass to briefly fuse deuterium (hydrogen with a proton-neutron nucleus). Therefore, stellar companions with less than 13 Jupiter masses would be defined as planets.

© Anglo-Australian Telescope Board
(Image by Chris Tinney)



Wide field image with satellite trail.



"True-color" image of the brown
dwarf binary DENIS 1228-1547
(more information).

Other prominent astronomers, such as astronomer Geoffrey W. Marcy who also has helped to discover many extrasolar planets, note that there may in fact be many different physical processes that lead to the formation of planets. Similarly, there may also be many different processes that lead to the creation of brown dwarfs, and some of these may also lead to planets. Hence, more observational data may be needed before astronomers can determine how to make justifiable distinctions in the classification of such substellar objects.