Using data from NASA’s Kepler spacecraft, astronomers have discovered the first rocky, Earth-sized planet orbiting a distant star. The planet, Kepler-78b, may be ‘Earth-sized’ but it is not ‘Earth-like.’ It whizzes closely around its host star in just 8.5 hours, and is so hot that it is uninhabitable for life as we know it.

Kepler-78b was first identified by the Kepler space telescope, which has spent four years searching for planets around more than 150,000 stars. Two teams used ground-based observations to confirm the planet’s existence and to study its properties

A small number of planets have been found that have a similar size or mass to the Earth. Kepler-78b is the first planet where measurements for both size and mass are known. Scientists were able to use this information to calculate its density and determine what the planet is made of.

Papers from each team were published in the journal Nature, the first under lead author Andrew Howard and the second under lead author Francesco Pepe.