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Discovery alert! A weird alien Mercury as big as Earth

Illustration of a grey planet with a star.

Planet: K2-229 b

Discovered by: A. Santerne et al. using NASA's Kepler telescope

Date: March 26, 2018

Key Facts: Mercury, the planet closest to the Sun, isn't alone...there are more Mercury-like worlds out there. This new discovery resembles our solar system's innermost planet, but much bigger. K2-229 b is like Mercury on steroids; about the size of Earth, it's four times bigger and five times hotter. It orbits a star like our Sun, but the day side of the planet can get up to temperatures hot enough to vaporize rock– around 3,700 degrees Fahrenheit (2,000 Celsius). Like Mercury, K2-229 b is made mostly of heavy elements, like iron and nickle. These heavy elements can survive being close to the heat of a star. And unlike the Earth which is only 35 percent iron, K2-229 b, like Mercury, is 70 percent iron.

Fun fact: Mercury's name comes from the Roman god Mercury, the herald and messenger in Roman mythology. K2-229 b's name comes from the mission that found it, the Kepler telescope's K2 mission.

What's new: Humanity is just now on the brink of learning more about exoplanets, or the planets beyond our solar system. Everything up until now has been focused on the discovery of these worlds, but now we're beginning to characterize them. This latest find from the Kepler telescope looks like a planet in our solar system...but it's also not like anything we find in our solar system. That means there may be another Earth out there, with a personality all its own.

See details and check the official NASA planet count at the NASA Exoplanet Archive