Mercury's long-lost cousin found in distant planetary system

AN EXOPLANET remarkably similar to Mercury has been found, and it might shed light on why our diminutive neighbour has such a big heart.

Mercury has an immense iron core that makes up roughly 70 per cent of its volume. That’s massive compared with Earth’s, which is just 30 per cent of its volume. But without another planet like Mercury in the solar system, astronomers have had a difficult time describing how such a wacky world formed.

Now, Alexandre Santerne at Aix-Marseille University in France and his colleagues have discovered an exoplanet that seems like a bigger version of Mercury.…