Gamma Cephei Ab, also known as Tadmor, is an extrasolar planet 45 light years away from the Earth in the Cepheus constellation. The planet was confirmed to be in orbit around Gamma Cephei A in 2002, but it was first discovered in 1988, making it arguably the first exoplanet discovered, before PSR B1257+12 B and C in 1992.
The planet was named "Tadmor" in December 2015 by the IAU, whom had a competition for naming certain exoplanets. It was submitted by the Syrian Astronomical Association and is the ancient Semitic name, and modern Arabic name, for the city of Palmyra.
Hubble astrometric observations has determined the mass is 9.4 Jupiter masses, making this a giant planet.
Detection and discovery[]
1988[]
In July 1988, the planet was identified by a Canadian team of astronomers who were led by Bruce Campbell, Gordon Walker, and Stephenson Yang, and its existence was also announced by Anthony Lawton and P. Wright in 1989. While it wasn't confirmed, this would've been the first real discovery of an extrasolaor planet. The claim, however, was rejected in 1992 due to the quality of data not being sufficient towards making a discovery.
2002[]
The planet was confirmed on September 24, 2002, announced by a team of astronomers (William D. Cochran, Artie P. Hatzes) at the Planetary Systems and their Formation Workshop. They estimated the planet had a minimum mass of 1.59 times that of Jupiter. The parameters were later recalculated when direct detection of the secondary star Gamma Cephei B allowed astronomers to better constrain the properties of the system. Gamma Cephei Ab moves in an elliptical orbit with a semimajor axis of 2.044 AU which takes almost two-and-a-half years to complete. The eccentricity is 0.115, which means it moves between 1.81 and 2.28 AU in orbital distance around Gamma Cephei A, which would place it from slightly beyond the orbit of Mars, to the inner asteroid belt in the Solar System.
2018[]
In 2018, an astrometric observation from the Hubble Space Telescope revealed the mass of the planet to be 9.4 Jupiter masses.