WASP-47

WASP-47 is a star similar in size and brightness to the Sun about 870 light-years away in the constellation Aquarius. It lies within the Kepler K2 campaign field 3. It was first noticed to have a hot Jupiter exoplanet orbiting every 4 days in 2012 by the Wide Angle Search for Planets (WASP) team.^[3] While it was thought to be a typical hot Jupiter system, three more planets were found in 2015:^[4][5] an outer gas giant within the habitable zone, a hot Neptune exterior to the hot Jupiter's orbit and a super-Earth interior to the hot Jupiter's orbit. WASP-47 is the only planetary system known to have both planets near the hot Jupiter and another planet much further out.^[6]

Nomenclature and history[]

Prior to the discovery of its planets, WASP-47 was given the 2MASS designation of 2MASS J22044873-1201079. It was also observed by the Wide-field Infrared Survey Explorer and given the designation WISE J220448.74-120108.4. When observed by NASA's K2 mission, it was given the Ecliptic Plane Input Catalog designation of EPIC 206103150, and later named K2-23 after the discovery of planets d and e.

In 2012, a team from the SuperWASP group, led by Coel Hellier, announced the discovery of a Hot Jupiter exoplanet, with the designation WASP-47b, orbiting every 4.17 days.^[3] Three years later in 2015, Neveu-Van Malle et al. found a second planet, WASP-47c, orbiting within the habitable zone of the system using the HARPS spectrograph at the La Silla Observatory in Chile.^[5] Using data from NASA's K2 mission a Planet Hunters volunteer discovered multiple planets around WASP-47^[7] and after analysing the data the researchers (Becker et al. 2015) published the two additional transiting planets, the Hot Neptune WASP-47d and the Mega-Earth WASP-47e, orbiting near WASP-47b.^[4]

Stellar characteristics[]

WASP-47 is a G-type main-sequence star of spectral type G9V, making it quite similar to the Sun. It is 1.11 M_☉ and 1.16 R_☉, with a temperature of 5576 K and an age of about 6.5 billion years. In comparison, the Sun has a slightly higher temperature of 5778 K but is significantly younger, at 4.5 billion years old.^[6]

The star is very metal-rich, with a metallicity ([Fe/H]) of about +0.36, or about twice the amount of iron and other elements heavier than Hydrogen and Helium than the Sun.^[6] This would explain how two massive gas giants, as well as a Mega-Earth, were able to form around the same star. WASP-47 is estimated to have a luminosity of 1.16 L_☉.^[8]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is around 12. Therefore, it is far too faint to be seen with the unaided eye.

Planetary system[]