TW Hydrae b
A candidate ice giant exoplanet in the Hydra constellation.
TW Hydrae b is a likely Neptune-like extrasolar planet orbiting the young T Tauri star TW Hydrae, approximately 176 light-years away in the constellation of Hydra. It is notable for its orbital distance of nearly 22 AU and its potential status as an ice giant within a protoplanetary disk gap.
Quick Facts
- Discoverer
- First: Setiawan et al.; New study: Atacama Large Millimeter Array
- Discovery site
- First: Germany; New study: Chile
- Discovered
- First: December 2007 (disproven); New study: September 2016
- Apsis
- astron
- Star
- TW Hydrae
- Single temperature
- ≥40 K
Facts from the source article.
Characteristics
TW Hydrae b is an ice giant, with a radius and mass close to those of Neptune and Uranus. Its estimated mass is about 22.72 Earth masses, or 1.5 Neptune masses, and its possible radius is 4.25 Earth radii. The planet may have an equilibrium temperature of around 40 K. It orbits the K-type T Tauri star TW Hydrae, which has a mass of 0.8 solar masses, a radius of 1.1 solar radii, a temperature of 4000 K, and an age of about 9 million years. The star's apparent magnitude is 11.27, making it too dim to be seen with the naked eye. The orbital period of TW Hydrae b is not known, though its orbital distance of 22 AU is somewhat less than Neptune's 30.11 AU.
Discovery
In December 2007, a team led by Johny Setiawan of the Max Planck Institute for Astronomy in Heidelberg, Germany announced the discovery of a planet orbiting TW Hydrae, designated TW Hydrae b, with a minimum mass around 1.2 Jupiter masses, a period of 3.56 days, and an orbital radius of 0.04 AU. Assuming it orbited in the same plane as the outer part of the dust disk, its true mass would be 9.8±3.3 Jupiter masses; if the inclination matched the inner part of the dust disk, the mass would be 16 Jupiter masses, making it a brown dwarf. This was presumed the youngest extrasolar planet yet discovered, later surpassed by K2-33b and V830 Tau b. In 2008, a Spanish research team concluded the planet did not exist, finding that radial velocity variations were not consistent across different wavelengths and were better modelled by starspots on TW Hydrae's surface. In 2016, astronomers studying the protoplanetary disk noted small dust grains in gaps, including one at 22 AU, but not large dust grains, suggesting a 1.5 Neptune-mass ice giant orbiting within that gap. The study was added to the online preprint archive arXiv on September 1, 2016, gaining wide media interest.
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