It is white on the inside and becomes narrower with increasing depth. The cause of the Mohole is a terrain glitch in the heightmap and until 0.90 it wasn't sure if this would be fixed. With 0.90 the Mohole became a dedicated biome and is thus not so easy to remove without changing the biome maps and science results. There are anomalous forces surrounding the Mohole, known to cause sudden acceleration toward the Mohole. Once at the bottom, a Kerbonaut on EVA will experience multiple changes in the direction of gravity, which are normally harmless.
Until 0.90 there was no official name for this feature and the name Mohole was devised by the community. So it's complicated to get the real origin for that name but it may be named after one or more of the following things:
- It is most likely a pun for Moho and Hole
- It may be a reference to Project Mohole, an attempt to drill a borehole all the way down to the Earth's Mohorovichic discontinuity.
- It may be named after a deep well called the "Mohole" in Red Faction: Guerrilla
- It may be a reference to Kim Stanley Robinson's novel Red Mars, in which "moholes" are kilometers-deep holes used as geothermal wells for the terraforming of Mars.