A small cold Brown Dwarf, 7.175 light years from Earth.

Brown Dwarfs are curious objects, intermediate between stars and planets. They lack the mass to fuse hydrogen in their cores like true stars, but are massive enough to fuse deuterium (a heavy isotope hydrogen, containing one proton and one neutron in its atomic nucleus), unlike planets. Brown Dwarfs therefore emit light in the infrared part of the spectrum, rather than simply reflecting light like a planet; though Brown Dwarfs within systems with true stars may reflect more light than they emit.

In a paper published in The Astrophysical Journal Letters on 21 April 2014, and on the arXiv database at Cornell University Library on 25 April 2014. Kevin Luhman of the Department of Astronomy and Astrophysics and Center for Exoplanets and Habitable Worlds at The Pennsylvania State University, describes the discovery of an exceptionally small and cool Brown Dwarf 7.175 light years from Earth.

The Brown Dwarf was initially discovered during the Wide-field Infrared Survey Explorer (WISE space telescope) survey, which repeatedly scanned the entire sky at infrared wavelengths between 7 January 2010 and 1 February 2011, showing up as a dim but discernible object moving between frames (a sign of an object close enough that its apparent position is changed by the Earth's motion around the Sun. This prompted follow-up surveys by the Spitzer Space Telescope's Infrared Array Camera on 21 June 2013 and 20 January 2014, which confirmed the existence of the object, which was named WISE 0855–0714 (from the WISE space telescope, plus a set of coordinates). 

Images of WISE 0855−0714 from VISTA, WISE, Gemini, and Spitzer. In the WISE images, WISE 0855−0714 is a blend of a moving object that dominates at W2 and two stationary sources that likely dominate at W1. The circles indicate the positions of the moving component in the WISE and Spitzer images; it is not detected by VISTA or Gemini. The size of each image is 1′ × 1′. Luhman (2014).

WISE 0855-0714 is calculated to be 7.175 light years from Earth, based upon its parallax (the extent to which it apparently moves in six months due to actual the motion of the Earth). This makes it the fourth closest known object or system to our Solar System, after the Alpha Centauri/Proxima Centauri system (4.364 and 4.277 light years from Earth), Barnard's Star (5.982 light years from Earth) and WISE J104915.57−531906.1 AB (a binary system comprising two Brown Dwarfs also discovered by the WISE space telescope, 6.588 light years from Earth).

It has an estimated surface temperature of just 225–260 K (between -48°C and -13°C) and a mass 3-10 times that of Jupiter (making it possible that it is a giant planet rather than a small Brown Dwarf, though Luhman concludes this is unlikely due to its heat emissions) and is probably between one and ten billion years old. Luhman suggests that the surface of WISE 0855-0714 might have clouds of sulphides, alkali salts and water ice covering half its surface.

Our Solar System's closest Neighbours. Wikipedia/NASA/Pennsylvania State University.

See also...

 A fourth body in the KOI-13 system.

 Direct imaging of a Brown Dwarf orbiting the Red Dwarf star 1RXS J235133.3+312720.

 Third body in the AV Canis Minoris system.

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The atmosphere of Wasp 12b.

Wasp-12b is a super-Jovian Hot Jupiter type planet (a planet larger than Jupiter orbiting very close to its parent star) 871 light years from Earth in the constellation of Auriga. It orbits Wasp-12A, a G-type yellow dwarf star slightly bigger and hotter than our sun (1.35 × the Sun's mass, with a surface temperature of 6300 K, as opposed to 5770 K for our sun), every 26 hours at a distance of 0.229 AU (2.29 % of the distance at which the Earth orbit's the Sun more than ten times as close to its star as Mercury). Wasp-12b is 1.39 as massive as Jupiter but has 28.3 times its volume, being inflated by the heat of the star, with an average surface temperature of 2525 K. Wasp-12b is probably elliptical in shape, and tidally locked, with one face (end) pointing permanently to the star. This face of the planet would reach temperatures in excess of 3000 K, hot enough for the atmosphere to slowly boil away into space. The material lost in this way probably forms an accretionary disk about the star, which will slowly be drawing mass from the planet.

An artist's impression of Wasp 12b. NASA/JPL/Caltech.

In a paper published on the arXiv database at Cornell University Library on 7 May 2013, a team of scientists led by Kevin Stevenson of the Department of Astronomy and Astrophysics at the University of Chicago describe the results of a spectrographic study Wasp 12b by the Spitzer Space Telescope.

This study concludes that the atmosphere of Wasp 12b is probably dark and opaque. Stevenson et al. suggest that the atmosphere of Wasp 12b is either rich in Oxygen with Titanium Oxide, Vanadium Oxide and water forming major components, or rich in Carbon, containing substantial concentrations of Titanium Hydride, Methane and Hydrogen Cyanide.

See also The HATNet project announces the discovery of three new Hot Jupiter type planets, Two Hot Jupiters found in the Beehive Cluster, Two new views of τ Boötis b, HATSouth network discovers its first planet and Planets discovered orbiting the ancient, second generation star HIP 11952.

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Thermal imaging 55 Cancri e.

55 Cancri (or Rho¹ Cancri) is a binary star system in the constellation of Cancer, 40 light years from Earth; it is naked eye visible. It comprises two stars, 55 Cancri A, a Sun-like G-type star with 95% of the Sun's mass, 1.15 times its radius (6.4 times its volume) and an effective temperature of 5373 K (compared to 5778 K for our Sun), which is orbited by 55 Cancri B, a smaller, cooler Red Dwarf star, at a distance of 1000 AU (i.e 1000 times the distance at which the Earth orbits the Sun, or 33.3 times the distance at which Neptune orbits). The system also has at least 5 planets.

Finding 55 Cancri within the constellation Cancer. University of Illinois.

The first of these, 55 Cancri b (or 55 Cancri Ab to distinguish it from 55 Cancri B) was detected in April 1996, by scientists at the Lick Observatory in California, who were able to detect the wobble of 55 Cancri A caused by the gravity of the planet as it orbits the star. 55 Cancri b orbits 55 Cancri A at a distance of 0.115 AU (11.6% of the distance at which the Earth orbits the Sun, less than half the orbital distance of Mercury) every 14.6 days. It is thought to have a mass slightly over that of Jupiter.

Two further planets were discovered in June 2002, by the same team, using a refinement of the technique that enabled subtler influences on the star's movement to be detected. 55 Cancri c has a mass 0.169 times that of Jupiter (54 times that of Earth), and orbits 55 Cancri A every 44.3 days at a distance of 0.24 AU (two thirds of Mercury's orbit). 55 Cancri d has a mass 3.8 times that of Jupiter and orbits 55 Cancri A at a distance of 5.77 AU (comparable to 5.2 AU for Jupiter) every 5218 days (14.3 Earth years).

In August 2004 a fourth planet was discovered, using the Hobby-Eberly Telescope in Texas, again by its gravitational influence on the star. 55 Cancri e has a mass 7.81 times that of Earth and orbits 55 Cancri A at a distance of 0.0156 AU, every 18 hours.

In April 2005 a fifth planet, 55 Cancri f, was discovered using further refinements on the gravitational wobble of 55 Cancri A, and data from the Lick and Keck Observatories. This planet orbits at 0.78 AU every 260 days, placing it firmly within 55 Cancri's habitable zone (the zone in which a reasonably Earthlike planet might host liquid water, and therefore potentially life), though with a mass of at least 0.144 that of Jupiter (at least half that of Saturn) 55 Cancri f is unlikely to do so.

Diagram showing the relative orbits of the known planets of 55 Cancri. Orbits of the planets of our Solar system (grey) shown for comparison. The Visual Exoplanet Catalogue.

Uniquely among these planets, 55 Cancri e transits (passes in front of) its star, when seen from Earth, giving it greater potential for further study. In a paper published on the arXiv database at Cornell University Library on 8 May 2012, and accepted for publication in The Astrophysical Journal Letters, a team of scientists led by Brice-Oliver Demory of the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology preset the result of a study of 55 Cancri e's infrared emissions during a series of transits of 55 Cancri A, made using the Spitzer Space Telescope.

They obtained an estimated temperature of 2360 K for 55 Cancri e, which is hot, but cooler than expected for a planet this close to a star. This suggests it has a low Bond albedo; i.e. it reflects less of the infrared radiation that falls onto it back into space than would be expected. This could be caused by a temperature inversion in the atmosphere, i.e. a warmer layer of gasses trapped below a cooler one, but this would need to be very large (over 500 K) which is improbable. Alternatively it could imply that the planet is rocky with little atmosphere (Mercury and the Moon both have low Bond albedos), which would be surprising for a planet of this mass, but could be explained by its proximity to 55 Cancri A, which could have evaporated its atmosphere away (the 55 Cancri system is 7.4-8.7 billion years old).

An artist's impression of 55 Cancri e. NASA/JPL.

See also Looking for HD 97658b, Planets discovered orbiting the ancient, second generation star HIP 11952, The atmosphere of WASP-24b, Cooking the planets if CoRoT-7 and Exoplanets on Sciency Thoughts YouTube.

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