Gliese 436 b

Gliese 436 b /ˈɡliːzə/ (sometimes called GJ 436 b) is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436. It was the first hot Neptune discovered with certainty (in 2007) and was among the smallest known transiting planets in mass and radius, until the much smaller Kepler exoplanet discoveries started coming in by 2010.

In December 2013, NASA reported that clouds may have been detected in the atmosphere of GJ 436 b.

Discovery

Gliese 436 b was discovered in August 2004 by R. Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and University of California, Berkeley, respectively, using the radial velocity method. Together with 55 Cancri e, it was then the first of a new class of planets with a minimum mass (M sini) similar to Neptune.

The planet was recorded to transit its star by an automatic process at NMSU on January 11, 2005, but this event went unheeded at the time. In 2007, Gillon led a team which observed the transit, grazing the stellar disc relative to Earth. Transit observations led to the determination of Gliese 436 b's exact mass and radius, both of which are very similar to Neptune. Gliese 436 b then became the smallest known transiting extrasolar planet. The planet is about 4000 km larger in diameter than Uranus and 5000 km larger than Neptune and a bit more massive. Gliese 436b (also known as GJ 436b) orbits its star at a distance of 4,000,000 km or 15 times closer than Mercury's average distance from the Sun.

Gliese 436

Gliese 436 is a red dwarf approximately 33.1 light-years (10.1 parsecs) away in the zodiac constellation of Leo. It has an apparent visual magnitude of 10.67, which is much too faint to be seen with the naked eye. However, it can be viewed with even a modest telescope of 2.4 in (6 cm) aperture. In 2004, the existence of a transiting extrasolar planet, Gliese 436b, was verified as orbiting the star. In 2012, the existence of a second planet, UCF-1.01, was also verified.

Properties

Gliese 436 is a M2.5V star, which means it is a red dwarf. Stellar models give an estimated size of about 42% of the Sun's radius. The same model predicts that the outer atmosphere has an effective temperature of 3,318 K, giving it the orange-red hue of an M-type star. Small stars such as this generate energy at a low rate, giving it only 2.5% of the Sun's luminosity.

Gliese 436 is older than the Sun by several billion years and it has an abundance of heavy elements (with masses greater than helium-4) equal to 48% that of the Sun. The projected rotation velocity is 1.0 km/s, and the chromosphere has a low level of magnetic activity. Gliese 436 is a member of the "old-disk population" with velocity components in the galactic coordinate system of U=+44, V=−20 and W=+20 km/s.