A team of U.S. astronomers has made a surprising discovery using data collected by NASA’s Kepler/K2 mission: a star called WASP-47, a previously known hot Jupiter exoplanet host, also hosts two additional exoplanets – a Neptune-sized outer planet and a super-Earth inner companion.
WASP-47 (center). Image credit: DSS2 / Centre de Données astronomiques de Strasbourg / SIMBAD.
WASP-47, also known as 2MASS J22044873-1201079, is a G-type main sequence star, slightly smaller and cooler than our Sun at a distance of 652 light-years.
In 2012, astronomers detected evidence that a hot Jupiter, WASP-47b, was circling the star.
Now, a University of Michigan led team has discovered that two other close-in planets are also orbiting WASP-47.
One of the newfound exoplanets, WASP-47d, is about the size of Neptune and orbits the star in about 9 days.
The second newly-discovered planet, WASP-47e, is a so-called super-Earth that whips around the star in a mere 19 hours.
The hot Jupiter WASP-47b orbits its parent star every 4.16 days.
“This is really exciting. People have looked for these hot Jupiter planets and have looked in data that exists for hot Jupiters for years and nothing has come up,” said Juliette Becker of the University of Michigan, lead author of a paper detailing the discovery in the Astrophysical Journal Letters (arXiv.org preprint).
“So people took it to mean that it was not possible to have these close-in planet companions.”
The discovery is helpful to astronomers who are trying to understand how planets form and move in solar systems.
“The whole theory of planet formation and migration is not totally understood,” Becker said. “Even today there is a lot of active work being done to figure out how Jupiter got where it was.”
“So anything we can discover on how hot Jupiters migrate is useful in understanding planet formation and migration as a whole.”
_____
Juliette C. Becker et al. WASP-47: A Hot Jupiter System with Two Additional Planets Discovered by K2. ApJ 812, L18; doi: 10.1088/2041-8205/812/2/L18
