About this world
HD 40307 d is a gas giant orbiting HD 40307, an orange dwarf (type K2.5V) 42.2 light-years from Earth. It is about 1.1 times the size of Jupiter (its size estimated from its mass) and holds 5.6 Jupiter masses. It completes an orbit every 20.4 days at 0.13 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 541 K (268 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2009 by radial velocity with La Silla Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 40307 has 5 known planets; the others are HD 40307 b, HD 40307 c, HD 40307 f and HD 40307 g.