Penumbra

Summary
Penumbra planets have absolutely no sunlight, and this is their defining characteristic. The surface is often covered in a bit of a humid mist, with a strong plethora of plant and animal life. Trees comprised of energy wood can also be found on the surface and will yield Penumbrite when put into an Extractor. The main means of obtaining Penumbrite however is to dig underground, the same depth as most vanilla ores, and look for glowing blue ore. '''Warning! These worlds contain weather and/or biodiversity that may cause psionic collapse. Proceed with caution on these ancient planets.'''

Appearance
These worlds are very dark, but often lit up with bioluminescent plant life. However, bringing a flashlight or torches is recommended. The surface is often comprised of void dirt, a dark and easily-mined substance that proves useful when extracted from. It's also common to find black tar here, both on the surface and underground. These planets are almost oppressively dark, and can often be identified on the star map just by looking for planets using black and other dark colors.

They have been seen to commonly orbit dark stars but they can spawn anywhere, orbiting any star.

Codex description
Sunlight rarely penetrates penumbral atmospheres. Rich sources of Penumbrite Ore detected.

Penumbra planets have a unique makeup that blocks light but not UV. They are the sole source of Penumbrite Ore.

Dark, but with plenty of bioluminescent fauna, penumbra worlds are the only known viable source of Penumbrite.

Dangers
There are relatively few dangers on Penumbra worlds, despite how intimidating they may appear. The atmosphere is warm, but not dangerously hot. You will not need any suit protections to explore one, but mid-tier weapons and armor are recommended. Penumbra worlds are similar in threat levels to Proto Worlds in terms of the hostile wildlife, but there is a lack of deadly weather here. The surface is usually relatively safe, provided you can fend off the less hospitable residents. In terms of hazards, the most noteworthy are the Black Slime blocks (which will poison you when stepped upon) and radioactive stone, which will give you radiation poisoning. Using poison protection can prevent this, and dumping healing water on them can turn them into blue slime that heals you instead. The lack of light is the most dangerous thing you'll encounter here, so be absolutely sure to bring some lights if you plan to dig, lest you fall to your death.

Notable Features
The occasional underground deposit of Telebrium, Prisilite and Penumbrite makes visiting a penumbra world even more profitable. Additionally, as of an unspecified update, these worlds can now contain small pools of liquid Aether, which can further your profits if extracted. Sometimes you can start hearing creepy whisper-like sounds that inflict the Insanity debuff; if you hear these, it's advised to hide or use anything that gives Insanity protection.

Possible Weather
Mist, Fog, Gravity Rain, Light Gravity Rain, Misty Rain, Acid Rain, Light Acid Rain, and Insanity Pulses.