Aldebaran b is a candidate exoplanet orbiting the orange giant star

Aldebaran Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Alde ...

, 65 light-years away. It was initially detected in 1993, but was considered doubtful until 2015, when researchers came to a conclusion that there is likely an exoplanet orbiting Aldebaran, consistent with the original calculations, but also compatible with stellar activity. However, in 2019, new data placed doubts on its existence again.

Physical properties

Mass and orbit

Aldebaran b is a

giant In folklore, giants (from Ancient Greek: ''gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...

exoplanet with at least 5.8 times the mass of Jupiter. It orbits at a distance about 45% farther than Earth does from the Sun. The equilibrium temperature of this planet is likely to be around , as it is strongly irradiated by its giant host star. Nevertheless, when Aldebaran was a main sequence star, it is likely that the planet had an equilibrium temperature comparable to that of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

Host star

The host star,

, is an

orange giant A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

star, meaning it has moved off from the main sequence and exhausted the supply of hydrogen in the core. It has a spectral class of K5 III. Aldebaran is a K-type star that is 1.16 ± 0.07 times the mass and 44 times the radius of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. It has a surface temperature of 3,910 K. In comparison, the Sun has a surface temperature of 5778 K. The star's average

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

, or how bright it usually appears from Earth, is 0.86, easily visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

Discovery

1993 proposal

The exoplanet was first proposed in 1993, radial velocity measurements of Aldebaran,

Arcturus , - bgcolor="#FFFAFA" , Note (category: variability): , , H and K emission vary. Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05, it is the third-brightest of the ...

and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a ''substellar companion''. The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

in a 643-day orbit at a separation of in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion.

2015 confirmed status

In 2015, a study showed stable long-term evidence for both a planetary companion and stellar activity.

2019 doubts on existence

In 2019, an analysis of additional data provided by Lick Observatory has placed the existence of Aldebaran b in serious doubt, because of apparent phase jitter of radial-velocity signal; a better data fit is obtained by either two planets or no planets at all around Aldebaran.

References

External links

Aldebaran b at the Extrasolar Planet Encyclopedia
{{Sky, 04, 35, 55.2, , 16, 30, 33, 65 Aldebaran Hot Jupiters Exoplanets discovered in 2015 Taurus (constellation)