The planet WASP-38b is 1.08 times the radius of Jupiter, the largest planet in our Solar System. It is thus about ten times the radius of our Earth.

WASP-38b is roughly 2 and a half the mass of Jupiter so is about twice as dense as Jupiter. Maybe it has a dense rocky core surrounded by an envelope of hydrogen gas.

The star WASP-38 is 1.37 times the radius of the Sun. Its spectral type is F8 which makes it hotter than our Sun. It has a brightness of visual magnitude 9.4.

WASP-38b orbits at a distance of 11.3 million km, taking 6.9 days to go round its orbit.

WASP-38 lies in the constellation of Hercules. Its coordinates are right ascension 16:15:50.0 and declination +10:01:57. The system is at a distance of 135 parsecs away from us.

The brightest stars in the plot have magnitude 0 and the faintest have magnitude 6, so, with a visual magnitude 9.4, WASP-38 is fainter than these stars. But you could see it in a good pair of binoculars if you knew exactly where to look.

The above plot shows radial velocity measurements of the star WASP-38 over the orbit of WASP-38b. These tell us how the star is moving, and thus how it is being tugged around by the gravity of the planet. The interesting finding is that the orbit of WASP-38b is slightly eccentric. That means that it is in an elliptical orbit, not a circular one. Despite that, the planet is in an aligned orbit. That means that the track of the orbit runs along the equator of the star. This is interesting because we expect that hot-Jupiter orbits become circular faster than they become aligned.


Transits of WASP-38b were spotted in data from the SuperWASP-North camera array on La Palma. The discovery was announced in a paper led by Susana Cristina Cabral de Barros.

For more information visit http://exoplanet.eu/catalog/wasp-38_b/.