1. They’re covered in molten lava
A lava world is a rocky planet that is entirely covered in molten lava. Some are very close to their host star, while others are young planets in the process of formation.
2. A year on a lava world can last a few hours
Some lava worlds are planets that orbit very closely to their host star. For example, Kepler-78b completes an orbit of its star, Kepler-78 in just 8.5 hours because of its close proximity to its star.
3. They can be torn apart by their stars
Similar to the way the moon Io in our Solar System is stretched and squashed by Jupiter, some lava worlds get their molten surfaces from tidal heating caused by their tight but eccentric orbits.
4. On some lava worlds it rains rock
The exoplanet COROT-7b orbits so close to its star – 23 times closer than Mercury does our Sun – that its atmosphere consists mostly of vaporised rock, which periodically rains down on the planet.
5. Earth was once in a similar state
It is thought that between two and three billion years ago Earth’s surface was covered in molten lava to a depth of 10 to 15 kilometres (six to nine miles) due to an impact with a Mars-sized object.
Image Credit: David A Aguilar (CfA)