The mysterious Caloris Basin on the planet Mercury has long been a source of mystery. The 1550 Km wide impact crater has been of interest to scientists since its was first observed in 1974 by the Mariner 10 probe.
It is ringed by mountains up to 2 km high. Inside the crater walls, the floor of the crater is filled by lava plains similar to the maria of the Moon. These plains are superposed by explosive vents associated with pyroclastic material. Outside the walls, material ejected in the impact which created the basin extends for 1,000 km, and concentric rings surround the crater.

The most interesting feature of this basin is what has been dubbed “The Spider” The feature is named Pantheon Fossae. What caused the almost 200 distinct lines is quite unknown. Nothing else like it has been seen anywhere else in the Solar System.

Some have suggested that this is the result of living creatures. Others have proposed it is the work of some unknown geological event.

For now the Caloris Basin remains one of the mysteries of our Solar System.

Source Material
Photo from Messenger Orbitor