Just in time for Halloween, a team of astronomers has announced the discovery of a planet very similar to Earth, but much hotter. New studies of an Earth-sized planet circling the sun-like star Kepler-78 have shown that it has quantities of iron and rock comparable to those in Earth, and it is the first world of this size for which astrophysicists are able to calculate both its density and diameter. (Kepler-78 is located about 400 light years away in the constellation Cygnus.)

Unfortunately the new planet, known to astronomers as Kepler-78b, is certainly not habitable for humanity. Its orbit is much closer to its parent star, creating very hot surface temperatures and no liquid water. It is so hot and dry, no life as we know it could exit there.

However these results also have implications for the rarity of Earth-like planets. The first Earth sized planet to be studied in detail has a similar chemical composition and density to the Earth, indicating that such small rocky planets are actually far more common than believed before. Furthermore, these calculations were performed independently by two separate research groups adding weight to their validity.

Unfortunately the Kepler probe, which detected this planet last spring and for which the planet is named, has been de-activated due to system failures. Before its break-down It had been observing over 150,000 stars for signs of orbiting planets, and quite successfully it would seem.

The size of the planet was calculated by measuring how much the parent star's (Kepler-78) light dimmed, which is how astronomers know that it is approximately the same size as Earth. The density was calculated using ground-based telescopes to measure the strength of gravitational forces that the planet exerted on its parent star. Using that information, scientists could work out how much rock and how much iron Kepler-78b contains.

The period of the planet's transits also suggested an orbit of just 8.5-hours (ie, they have three years pass in just over one day), indicating that Kepler-78b is almost inside the surface of its parent star. In such a location, temperatures would be approximately 2,000 degrees hotter than the Earth, creating a molten surface and virtually no atmosphere. 

As yet, this is the only Earth-sized rocky world outside of our own solar system. But its mere existence suggests that planets like ours could be very common in the galaxy and the Universe, which brings a new optimism for the future of space travel and life on other planets. This is indeed a very interesting new result.