| Discovery | |
|---|---|
| Discovered by | First:Setiawanet al. New study:Atacama Large Millimeter Array |
| Discovery site | First: GermanyNew study:  Chile |
| Discovery date | First: December 2007 (disproven) New study: September 2016 |
| Orbital characteristics | |
| 22 AU (3.3×109 km) | |
| Star | TW Hydrae |
| Physical characteristics | |
| ~4.25R🜨 | |
| Mass | 23.72[1]ME |
| Temperature | ≥40 K (−233.2 °C; −387.7 °F) |
TW Hydrae b is a likelyextrasolar planet orbiting the youngT Tauri starTW Hydrae approximately 176light-years (54parsecs, or nearly1.665×1016km) away in theconstellation ofHydra. It is likely a Neptune-like planet orbiting at a distance of nearly 22 AU from its star.[1]
TW Hydrae b is anice giant, an exoplanet with a radius and mass close to that of the ice giantsNeptune andUranus. It may have anequilibrium temperature of around 40 K (−233.2 °C; −387.7 °F). It has an estimated mass of around 22.72ME (or 1.5MNeptune) and a possible radius of 4.25R🜨.
The planet orbits a (K-type)T Tauri star namedTW Hydrae. The star has a mass of 0.8M☉ and a radius of 1.1R☉. It has a temperature of 4000K and is about 9 million years old. In comparison, theSun is 4.6 billion years old[2] and has a temperature of 5778 K.[3] Its luminosity (L☉) is 28% of that of the Sun.[note 1]
The star'sapparent magnitude, or how bright it appears from Earth's perspective, is 11.27. Therefore, it is too dim to be seen with the naked eye.
TW Hydrae b orbits its host star at a distance of 22 AU (somewhat less than the orbital distance ofNeptune from the Sun, which is 30.11AU). The orbital period is not known, although taken its similar orbital distance as Neptune, the orbital period may be around the same value.
In December 2007, a team led by Johny Setiawan of theMax Planck Institute for Astronomy inHeidelberg,Germany announced discovery of a planet orbiting TW Hydrae, dubbed "TW Hydrae b" with a minimum mass around 1.2Jupiter masses, a period of 3.56 days, and an orbital radius of 0.04astronomical units (inside the inner rim of the protoplanetary disk). Assuming it orbited in the same plane as the outer part of the dust disk (inclination 7±1°[4]), it would have a true mass of 9.8±3.3 Jupiter masses.[4][5] However, if the inclination was similar to the inner part of the dust disk (4.3±1.0°[6]), the mass would be 16+5
−3 Jupiter masses, making it abrown dwarf.[6] Since the star itself is so young, it was presumed this was the youngest extrasolar planet yet discovered, and essentially still in formation.[7] (only surpassed byK2-33b andV830 Tau b, both discovered nearly 9 years later).
In 2008 a team of Spanish researchers concluded that the planet did not exist: the radial velocity variations were not consistent when observed at differentwavelengths, which would not occur if the origin of the radial velocity variations was caused by an orbiting planet. Instead, the data was better modelled bystarspots on TW Hydrae's surface passing in and out of view as the star rotates. "Results support the spot scenario rather than the presence of a hot Jupiter around TW Hya".[8] Similar wavelength-dependent radial velocity variations, also caused by starspots, have been detected on other T Tauri stars.[9]
In 2016, astronomers studying the protoplanetary disk of the star began to speculate why there was small dust grains in the gaps, including the one at 22 AU, but not large dust grains. Further investigations began to suggest that there may be a 1.5MNeptune ice giant orbiting within the gap at 22 AU, which would be responsible for the observed gaps.
The study was then published in the online journal archivearXiv on September 1, 2016, gaining wide interest from media outlets.[1]
2016 in space | ||
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Space probe launches |
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| Impact events | ||
| SelectedNEOs | ||
| Exoplanets |
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| Discoveries |
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| Novae | ||
| Comets | ||
| Space exploration | ||
