Astronomers have found that another world is quite similar to our own: It has a radius just 1.17 times and a mass only 1.9 times that of Earth. Though its size is familiar, it has the troubling problem of orbiting about 100 times closer to its star than our own planet.

That means surface temperatures on the planet, called Kepler-78b, range from 2,240 to nearly 5,000 degrees Fahrenheit. Kepler-78b is basically a planet of lava. The scorched world zips around its parent star, completing a year every eight and a half hours.

The exoplanet was found around a star called Kepler 78 that sits about 700 light-years away from Earth. Astronomers discovered the world by watching the star dim just a tiny bit as the exoplanet passed in front of its face, blocking its light. Because it orbits so close, a separate set of measurements were able to determine how much the exoplanet tugs gravitationally on its parent star. Together, these data allow scientists to calculate the planet's mass and therefore its density, which is 5.57 g/cm3 or basically the same as our own world. This makes Kepler-78b a rocky planet, one of the few confirmed to have a composition similar to Earth.

Because it orbits so close to its parent star, Kepler-78b is something of a mystery for astronomers. According to our current theories of planet formation, no world should be able to form at such a close distance. But as scientists are finding out from the hundreds of newly-discovered exoplanets and other star systems, their theories on planet formation are probably wrong.

The planet was spotted using NASA's Kepler space telescope, one of the main machines searching for exoplanets, which has discovered more than 130 other worlds. Kepler recently suffered a mechanical failure that put it out of commission. Though its planet-hunting days are probably over, scientists are trying to figure out if the mission can be salvaged in any way and used for other purposes.

Images: David A. Aguilar (CfA)