GJ 523b: A Strange Mega-Earth

Astronomers have discovered an unusual “mega-Earth” called GJ 523b. It has about 23.5 times Earth’s mass, but only 2.5 times Earth’s radius.

A planet this massive should have collected a thick layer of hydrogen and helium while forming and looked more like Neptune. Instead, GJ 523b is unusually dense and seems to contain little gas.

Its orbit is even stranger: it is strongly tilted compared with its star’s equator and is probably almost polar. Scientists often explain orbits like this as the effect of other massive planets, but no object that could cause it has yet been found in this system. Scientists still do not know how GJ 523b formed or reached its current orbit.