The 5.7 update introduced the new lava feature. The lowest areas on a world melt into lava at a temperature of above 1,500,000 mK. Further hating the world will cause the lava level to rise (because more land is melting). Above 2,000,000 mK, the whole world is molten.
Lava glows, so even when the sun is facing away from the planet, it will still look bright.
Cooling the world reverses the process, but the areas that used to be molten will be a dark gray color, and the elevation ranges are changed to a certain pattern.
You can find lava worlds in the random planet generator, or simply heat up any world to the melting temperatures. Mercury is best for this purpose because it is already hot (Venus is good too, but you risk your buildings getting crushed and because of the atmosphere, you only see the lava in map mode).
You can't build on lava, and anything submerged beneath rising lava oceans will be completely destroyed, as with water flooding.
City Melted[edit | edit source]
[City] has been submerged beneath lava on the melting surface of [World]! [number] people were killed, and the city has been completely destroyed.
[Outpost/Mine] Melted[edit | edit source]
[Outpost name/mine name] has been submerged beneath lava on the melting surface of [World]!
Unlike water flooding, the threatened cities won't evacuate when the lava gets too close.