Illustration of the exoplanet Kepler-78b orbiting its star Kepler 78. The planet, which has a diameter 20 per cent larger than Earth's, orbits extremely close to its star. The orbit is 40 times closer than Mercury's is to our Sun and is completed in 8.5 hours. Due to this the planet's surface temperature is estimated at between 2,300 and 3,100 Kelvin. Kepler-78 is located in the constellation Cygnus.