These planets would seem to be the result of a bit of "mad science". They can be quite volatile with their frequent storms, some even dropping deadly Bio-Ooze instead of rain. This powerful poison can also be found in pools above and underground on these worlds.
However, despite the apparent dangers, Proto Worlds prove to be valuable to any spacefaring scientist. Proto Worlds are just about the only place one can find Protocite, as you would imagine. It can also be found in its liquid form here as well, both of which can be used to craft a multitude of tools, weapons, and so forth.
Proto Worlds are typically covered in tall trees and a large variety of plants. The soil and even the rock that forms the planet's surface have a uniquely colorful appearance unlike anything found on other planets. Almost everything you see on a Proto World is 100% Frackin Universe original.
Proto worlds are permeated with a strange sort of toxin that seeps in through exposed skin and slowly drains the individual. As such, you should come equipped with something to counter Proto-Poison.
There are powerful and dangerous storms to watch out for as well as Bio-Ooze to avoid, even underground. Threat levels vary, but typically Proto Worlds don't teeter much on the extreme end, with most being Moderate or Dangerous at worst. The lack of atmospheric dangers means that a careful adventurer can seek out Protocite fairly easily by digging underground and watching one's footing, drawing little attention from the local wildlife.
As mentioned, storms don't always drop Bio-Ooze but they will still cause damage both to the player and to plants growing on the surface. This will make collection of plants and fibres much simpler, but at the risk of taking damage from the storms.
Codex description Edit
These bizarre planets are not inhospitable, but the natural biological slime there can melt your flesh. Plus the slime storms, ew. And really, really weird plant life. But they are the only place to get the extremely valuable Protocyte. You'll need it.
Proto Worlds can be found orbiting Dying Stars