GJ 504b, a cold Jovian exoplanet in a wide orbit about a Sun-like star.

In the past two decades a large number of planets have been discovered orbiting other stars (exoplanets). The vast majority of these have been large planets orbiting close to their host stars, such planets being easier to detect due to the influence that their gravity has on the star. Planets further from their stars are harder to detect, as their gravity has less effect upon the star, and they have long orbital periods which will tend to mask this anyway. Such planets are more likely to be detected by direct imaging, though this will require separate observations over a long period of time to confirm the relationship with the host star.

In a paper published on the online arXiv database at the Cornell University Library on 12 August 2013 and in The Astrophysical Journal on 1 September 2013, a team of scientists led by Masayuki Kuzuhara of the Department of Earth and Planetary Science at The University of Tokyo and the National Astronomical Observatory of Japan and the Department of Earth and Planetary Sciences at the Tokyo Institute of Technology describe the detection of a superjovian planet orbiting the Sun-like star GJ 504 at a distance of 43.5 AU (i.e. 43.5 times the distance between the Earth and the Sun).

GJ 504 (or Gliese 504 or 59 Virginis) is 57 light years from Earth in the constellation of Virgo. It is a G-type Yelow Dwarf Star estimated to have 1.22 times the mass of the Sun, and to be about 160 million years old.Kuzahara et al. observed this star using the Subaru Telescope operated by the National Astronimical Observatory of Japan on Mauna Kea, Hawaii, between 26 March 2011 and 25 May 2012.

These observations enabled them to detect a smaller object close to the star, and establish that it is in fact gravitationally bound (orbiting) the larger body. The planet is named GJ 504b (Gliese 504b), making the parent body GJ 504A (when naming bodies in stellar systems other than our own, stars are indicated with an upper case letter and planets with a lower case letter.

Image of GJ 504A and GJ 504b produced by the Subaru 8.2 m telescope on Mauna Kea. Kazahara et al. (2013).

GJ 504b is thought to have a mass approximatelly four times that of Jupiter, making it the largest planet discovered by direct imaging (larger planets have previously been discovered by the influence of their gravity on their parent stars, but these have all been to close to their stars for direct imaging), and to orbit the star GJ 504A at a distance of 43.5 AU, making it amoungst the fursthest planets from its parent star yet discovered. The planet is thought to have an effective surface temperature of 510 k (237°C), making it the coolest superjovian lanet yet discovered.

See also Three giant exoplanets in very wide orbits around young stars, Kepler 63b; a giant planet in a polar orbit, A superjovian exoplanet directly imaged orbiting the A-class pre main-sequence star HD 95086, A fourth body in the KOI-13 system, and KOI-13b, a big, hot planet not a Brown Dwarf.

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Three giant exoplanets in very wide orbits around young stars.

In the past two decades a large number of planets have been discovered orbiting other stars (exoplanets). The vast majority of these have been large planets orbiting close to their host stars, such planets being easier to detect due to the influence that their gravity has on the star. Planets further from their stars are harder to detect, as their gravity has less effect upon the star, and they have long orbital periods which will tend to mask this anyway. Such planets are more likely to be detected by direct imaging, though this will require separate observations over a long period of time to confirm the relationship with the host star.

In a paper published on the online arXiv database at Cornell University Library on 29 November 2013 and accepted for publication in The Astrophysics Journal, a team of scientists led by Adam Kraus of the Department of Astronomy at the The University of Texas at Austin and the Harvard-Smithsonian Center for Astrophysics describe three giant planets orbiting young stars at distances in excess of 100 AU (i.e. more than 100 times the distance at which the planet Earth orbits the Sun). All three bodies had previously been noted as potential planets over a decade ago, but can only now be confirmed as objects in orbit about their stars, due to follow-up observations that have tracked their movement. 

Large planets in very wide orbits about young stars presents a considerable challenge for conventional models of planet formation, since it should in theory take far longer for a planet to form this far from a star, potentially never accreting into a large body at all. Our own system contains considerable material beyond the orbit of Neptune (30 AU from the Sun), but this has apparently never accreted into a large planet, despite the 5 billion year age of the Solar System.

The first of the three new planets orbits the binary system FW Tau AB near the center of the Taurus- Auriga complex, 473 light years from Earth. The FW Tau system comprises two red dwarf stars  (FW Tau A and FW Tau B) each though to have a mass 28% of our Sun's orbiting one another at a distance of 11 AU (11 times the distance between the Sun and the Earth). The system is thought to be about 1.8 million years old. The planet, FW Tau b (when naming objects in other stellar systems stars are given upper case letters and planets lower case letters), is calculate to have a mass 10 times that of Jupiter and orbit at a distance of 330 AU (over 10 times the distance at which Neptune orbits the Sun). 

Infrared image of the FW Tau system. The image is not coronagraphic; most of the image is shown with a linear stretch that saturates at 110% of the peak brightness of the wide companion, while a box of size 0.5′′ is instead shown with a linear stretch that saturates at 110% of the peak brightness of the primary star in the close binary. North is up. The scale bar is 1 arc inch; i.e. 1/21 600th of the circumference of an imaginary sphere around the Earth. Kraus et al. (2013).

The second new planet orbits the binary star ROXs 42B, 440 light years from Earth in the constellation of Ophiuchus. The binary system comprises two stars with masses of 89% that of the Sun and 36% that of the Sun, orbiting at a distance of less than 10 AU. The system is thought to be 6.8 million years old. The new planet, ROXs 42B b is calculated to orbit this pair at a distance of 140 AU and have a mass 10 times that of Jupiter. A second, potential body in the system, provisionally dubbed ROXs 42B cc1, is thought to be a background star.

Infrared image of the ROXs 42B system. The image is not coronagraphic; most of the image is shown with a linear stretch that saturates at 110% of the peak brightness of the wide companion, while a box of size 0.5′′ is instead shown with a linear stretch that saturates at 110% of the peak brightness of the primary star in the close binary. North is up. The scale bar is 1 arc inch; i.e. 1/21 600th of the circumference of an imaginary sphere around the Earth. Kraus et al. (2013).

The third new planet orbits ROXs 12, another star in the constellation of Ophiuchus, 391 light years from Earth. ROXs 12 is thought to have a mass 87% of that of the Sun and to be 7.6 million years old. ROXs 12b orbits this star at a distance of 210 AU, and has a mass 16 times that of Jupiter.

Infrared image of the ROXs 12 system. The image is not coronagraphic; most of the image is shown with a linear stretch that saturates at 110% of the peak brightness of the wide companion, while a box of size 0.5′′ is instead shown with a linear stretch that saturates at 110% of the peak brightness of the primary star in the close binary. North is up. The scale bar is 1 arc inch; i.e. 1/21 600th of the circumference of an imaginary sphere around the Earth. Kraus et al. (2013).

See also Kepler 63b; a giant planet in a polar orbit, A superjovian exoplanet directly imaged orbiting the A-class pre main-sequence star HD 95086, A fourth body in the KOI-13 system, Wasp-12b; slowly boiling away... and KOI-13b, a big, hot planet not a Brown Dwarf.

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Kepler 63b; a giant planet in a polar orbit.

KIC 11554435 (or Kepler Input Catalogue 11554435) is a young, sunlike star 652 light years from the Earth. It is thought to be between 200 and 300 million years old with a mass 98% of the Sun's and an effective surface temperature of ~5576 K, as opposed to 5778 K for the Sun. As a young star it rotates considerably faster than the Sun, roughly once every 5.4 days, while the Sun takes slightly under 24.5 days to complete a rotation, and has a high level of starspot activity (the same as sunspot activity but on a different star).

In a paper published on the online arXiv database at Cornell University Library on 26 August 2013, and accepted for publication in The Astrophysical Journal, a team of scientists led by Roberto Sanchis-Ojeda of the Department of Physics and Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology, describe the discovery of a superjovian planet in orbit about KIC 11554435 by the Kepler Space Telescope. The system is renamed Kepler 63, with the star becoming Kepler 63A and the planet Kepler 63b (naming conventions dictate that stars are given upper case letters and planets lower case letters).

Kepler 63b orbits Kepler 63A every 9.43 days at an estimated distance from the star of 0.08 AU (8% of the distance at which the Earth orbits the Sun), making it a 'Hot Jupiter' type planet, transiting the star (passing in front of it from out point of view) as it does so. It has a highly oblique orbit, at 104° to the plane of the star's rotation. Kepler 63b has a radius 6.1 times that of Jupiter, and while it was not possible to determine its mass, this was given an upper limit of 120 times that of Jupiter.

Sanchis-Ojeda et al. were also able to detect a particularly large and apparently permanent starspot (or cluster of starspots) close the the pole of rotation of Kepler 63A that is turned towards us. This moves around the pole with the star's rotation, so that it is sometimes in line with the orbit of the planet and sometimes not.

Locations of the spot, transit chord, and planet at midtransit, according to the best-fitting model. Sanchis-Ojeda et al. (2013).

See also A superjovian exoplanet directly imaged orbiting the A-class pre main-sequence star HD 95086, The debris disk of 49 Ceti, The planets of NN Serpentis, Water and Hydroxides in the Circumstellar Disk around HD 163296 and The formation of a Keplerian Disk in the L1551 NE Protostellar System.

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A superjovian exoplanet directly imaged orbiting the A-class pre main-sequence star HD 95086.

HD 95086 is an A-class pre main-sequence star (young star which has not yet begun to fuse hydrogen, but which is emitting energy due to gravitational contraction) in the constellation of Carina, 295 light years from the Earth. It is believed to be between 10 and 17 million years old, has a mass 1.6 times that of the Sun, and has previously been shown to be surrounded by a debris disk (ring of asteroidal or cometary material).

In a paper published on the online arXiv database at Cornell University Library on 30 August 2013, a team of scientists led by Julien Rameau of the Institut de Planétologie et d’Astrophysique de Grenoble at Université Joseph Fourier describe the discovery of a planet orbiting HD 95086 by direct imaging with  the Nasmyth Adaptive Optics System Near-Infrared Imager and Spectrograph on the Very Large Telescope on Cerro Paranal in the Atacama Desert of northern Chile.

The planet is assigned the name HD 95086b, making the star HD 95086A; when naming objects in other stellar systems astronomers give upper case letters to stars and lower case letters to planets. It is thought to have a mass 4-5 times that of Jupiter, making it the smallest exoplanet yet discovered by direct imaging, and to orbit HD 90586A at a distance of 56 AU, i.e. it is 56 times as far from its parent star as the Earth, or nearly twice as far as Neptune.

Infra-red image of HD 95086b made using the Nasmyth Adaptive Optics System Near-Infrared Imager and Spectrograph on the Very Large Telescope in the Atacama Desert of northern Chile. Rameau et al. (2013).

The HD 95086 system was observed at infra-red wavelengths in January 2012 and February and March 2013, in order to confirm that the movement of the two bodies relative to one-another.

Chart of the Carina Constellation showing the position of the HD 95086 system (center of red circle). European Southern Observatory.

See also The planets of NN Serpentis, The formation of a Keplerian Disk in the L1551 NE Protostellar System, Fomalhaut b; not a planet after all? Giant planet in the RR Caeli System and A new study of the HAT-P-13 planetary system.

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A fourth body in the KOI-13 system.

The KOI-13 system (Kepler Object of Interest system) comprises a pair of A-type White Dwarf stars 1630 light years from Earth, orbiting each to closely to be well differentiated. The larger of these, KOI-13α, has a mass 2.05 times that of the Sun, the smaller, KOI-13β, has a mass 1.95 times that of the Sun. In 2011 the Kepler Space Telescope discovered an object (KOI-13.01) orbiting one of these stars every 1.76 days. This object was discovered by the dimming it caused as it passed in front of the star, which meant it was possible to calculate its radius (2.2 times that of Jupiter), but not its mass, leaving scientists unsure whether the object was a very large planet or a Brown Dwarf. In February 2012, a team from the University of Cambridge published a model of the KOI-13 system which suggested that KOI-13.01 was likely to be a super-heated (and therefore super-inflated) Hot Jupiter type planet, with a mass 8.3 times that of Jupiter.

An artists impression of the KOI-13 system. Inset is a telescope image of the stars, scale bar is 1 arc-second. Konkoly Observatory.

In a paper published on the online arXiv database at Cornell University Library on 10 August 2012, and in the journal Astronomy & Astrophysics on 13 August 2012, a team of scientists led by Alexandre  Santerne of the Laboratoire d’Astrophysique de Marseille and Observatoire de Haute-Provence at the Université d’Aix-Marseille & CNRS, detailing the results of a new study of the KOI-13 system using the SOPHIE Spectrograph at the Observatoire de Haute-Provence.  This study used the radial velocity method, which measures the wobble of stars caused by the gravity of objects orbiting around them, to try to determine the mass of KOI-13.01. 

Santerne et al. concluded that KOI-13.01 has a maximum mass of 14.8 times that of Jupiter if it orbits KOI-13α and 9.4 times that of Jupiter if it orbits KOI-13β, supporting the theory that this is a large Hot Jupiter type planet rather than a Brown Dwarf. 

They also found evidence for an extra stellar-mass object within the system, which they name KOI-13γ. This appears to have a mass between 0.4 and 1.0 that of our Sun, and to orbit one of the stars every 65.8 days in an eccentric orbit that does not cross the plane of the star when seen from Earth. KOI-13γ could be potentially the same star as KOI-13.01 if it is towards the smaller end of this mass range, but the most likely scenario that could be modeled was that KOI-13.01 orbits KOI-13α, while KOI-13γ orbits KOI-13β.

See also KOI-13b, a big, hot planet not a Brown Dwarf and Exoplanets on Sciency Thoughts YouTube.

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Wasp-12b; slowly boiling away...

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. It was discovered in 2008 by the SuperWASP planetary survey, and its discovery announced in a paper in The Astrophysical Journal in 2009, by a team of scientists led by Leslie Hebb of the School of Physics and Astronomy at the University of St. Andrews.

In a paper published on 26 January 2012 in the online arXiv database at Cornell University Library a team of scientists led by Nicolas Cowan of the Center for Interdisciplinary Exploration and Research in Astrophysics and the Department of Physics & Astronomy at Northwestern University describe a new study of Wasp-12b, based upon data from the Spitzer Space Telescope.

Cowan et al. came to the conclusion that 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, by Greg Bacon of The Space Telescope Science Institute.

See also The impossible planets of HU Aquarii, A fresh look at Wasp-43b, A planet disintegrating in the heat of its own sun, Wasp-19b: a Highly Irradiated Hot Jupiter and Exoplanets on Sciency Thoughts YouTube.

KOI-13b, a big, hot planet not a Brown Dwarf.

The KOI-13 (Kepler Object of Interest-13, otherwise BD+46 2629) system is composed of a pair of A-type White Dwarf stars roughly 1630 light years from the Earth. The larger of these stars, KOI-13 A, has a mass 2.05 times that of our sun, is 30.5 times as luminous, and has 2.55 times the sun's radius. The smaller star, KOI-13 B, has a mass 1.95 times that of the sun, is 23 times as luminous and has a radius 2.38 times that of the sun.

Image of the KOI-13 system from the 1m RCC telescope at Konkoly Observatory in Hungary. Image from Szabó et al. (2011). See below.

In 2011 the Kepler Space Telescope detected an object orbiting KOI-12 A. This was described in a paper published on the arXiv database at Cornell University Library by a team lead by Gyula Szabó of the Konkoly Observatory of the Hungarian Academy of Sciences and the Department of Experimental Physics at the University of Szeged, as being a Brown Dwarf, or possibly a very small Red Dwarf Star. Brown Dwarfs are objects to large to be considered planets, but to small to be considered stars; they are thought to be able to fuse deuterium in their cores, but not hydrogen. Red Dwarfs are the smallest type of stars, they burn dimly, but can be very long lived. KOI-13b (or KOI-13.01) was envisaged as an object borderline between these two types of objects, with a mass 20% of that of the sun and a radius 2.2 times that of Jupiter. Such an object orbiting so close to a very hot A-type star would probably receive more heat than it emitted.

The path of KOI-13b across the face of KOI-13 A, as detected by Kepler. From Szabó et al. (2011)

This month, in a paper published on the arXiv database and in the Monthly Notes of the Royal Astronomical Society, Dimitris Mislis and Simon Hodgkin of the Institute of Astronomy at the University of Cambridge, describe a new study of the KOI-13 system, which reveals KOI-13b as a large planet rather than a Brown Dwarf or small star.

Mislis and Hodgkin conclude KOI-13b is a super-Jovian planet with a mass of 8.3 times that of Jupiter and 1.4 times Jupiter's radius. This is big and dense for a planet, but well short of the mass needed to fuse deuterium, so it is not a Brown Dwarf. KOI-13b orbits KOI-13 A every 25.4 hours at a distance of 0.0367 AU (3.67% of the distance between the Earth and the sun. Since KOI-13 A is very hot, with a surface temperature of 8511K (compared to 5778K for our sun), and KOI-13b is very close to it, KOI-13b is thought likely to have a very high surface temperature itself, modeled by Mislis and Hodgkin as 2864K, warmer than the coolest Red Dwarf stars.

See also A new study of XO-2b, a planet in a wide binary star system, Giant planet in the RR Caeli System, Could there be a habitable planet in the Kepler-16 system? and Exoplanets on Sciency Thoughts YouTube.

Giant planet in the RR Caeli System.

RR Caeli is an eclipsing binary star system in the constellation of Caelum, 36 light years from Earth. The name implies the tenth variable star in the constellation of Caelum, but the variability is in fact the two stars passing in front of one-another in our line of sight (eclipsing), rather than any variation in their output. The system is referred to as a pre-cataclysmic binary, as the two stars are thought to be in a decaying orbit, that will eventually cause them to collide, but this will not happen for 9-20 billion years, so we are unlikely to be around to see it (our own sun will probably swell into a Red Giant and swallow the Earth in about 5.4 billion years, so the 'pre-cataclysmic' RR Caeli system should be safe for longer than our own solar system).

The position of RR Caeli (RR Cae). The position of East (bottom right)is reversed as this is a map of the sky. The scale bar is 5 arc-minutes; the sky is divided into 360 degrees (assuming the Earth is invisible and you can see underneath you) and each degree into 60 arc-minutes. From Bruch and Diaz (1998).

The two stars of the RR Caeli system are a cool White Dwarf star 44% of the mass of the Sun and a smaller M4-type Red Dwarf with 18.2% of the Sun's mass. These two orbit about one-another every 7.3 hours.

On 2 January 2012 a team lead by S.B. Qian of the Yunnan Observatory and the Chinese Academy of Sciences published a paper on arXiv online database at Cornell University Library, detailing the discovery a planet in the RR Caeli system, using data collected by the Jorge Sahade Telescope at the Complejo Astronómico El Leoncito in San Juan, Argentina.

Qian et al. were able to detect minute variations in the period of RR Caili, from which they were able to infer the presence of a planet with a mass of 4.2 times that of Jupiter, orbiting RR Caeli at a distance of 5.3 AU (5.3 times the distance between the Earth and the Sun, or 2% more than the distance at which Jupiter orbits the Sun) every 11.9 years, with an apparent eccentricity of zero (i.e. in a completely circular path, rather than an elliptical one like most planets). The orbital period of 11.9 years is so close to the orbital period of Jupiter (11.86 years) that the team were concerned that the gravitation influence of Jupiter might be somehow influencing their findings, however they were eventually able to rule this out.

See also Could there be a habitable planet in the Kepler-16 system? The strange debris disk of 99 Herculis, Third body in the AV Canis Minoris system and Exoplanets on Sciency Thoughts YouTube.