Here are some more unused ideas from our still-in-hiatus Star Trek Adventures campaign. These are three unusual planets and possible adventure seeds for each one.
Biswell IV
A planet resembling Earth during the Hadean period of four billion years ago. The Biswell system is late in the process of planetary formation. Large numbers of asteroids and other debris are moving throughout the system. The risk of collision can be mitigated with close attention to sensor readings, careful navigation, and - if it comes to it - a strong deflector system. Biswell IV is under constant bombardment from impactors of all sizes. Conditions on the planet's surface are unwelcoming. Molten rocks cover a barren, geologically active landscape. The surface temperature is over 200 degrees C (over 400 degrees F). The atmospheric pressure is over twenty atmospheres and composition is mostly carbon dioxide - utterly unbreathable. Ship's sensors can predict magma displacements and imminent meteor impacts, but only with enough advance notice to transmit emergency warnings to Away Teams on the surface.
Why would anyone come to this literal hellhole? A bright spark hit on the idea of putting an independent mining colony on the planet. The colony is located underground and is composed of a large processing facility and attached habitats. Mining teams venture out to the fresh deposits of minerals that arrive with every eruption and impact. A position in the colony is highly profitable, but the risks and hard work discourage most from volunteering. Automation is used as much as possible to minimize the workforce required to keep the colony operating and to simplify any possible evacuation.
Adventure Seed: Our Starfleet crew has need of minerals available on Biswell IV to either make repairs or fabricate equipment needed for their current mission. The colony's administrators are happy to make a sale or trade. The Complication: The Biswell IV mining colony broadcasts a distress call just before the player characters arrive in system. The garbled transmission mentions something about the automated systems going haywire and all personnel evacuating to emergency shelters on the surface. Our Starfleet crew must rescue the colonists, figure out what happened to the colony, and get the minerals they need.
Ardan V
A paradise planet in a conflict zone. This lush world is mostly ocean except for a couple of small continents and extensive island chains. The average climate is mild and the equatorial region is a tropical paradise marred intermittently by summer storms. It is an ideal colonization candidate, but every attempt on record was quickly abandoned. Ardan V is far from any major galactic power. The small interstellar governments in the area around Ardan V are in constant conflict. Pirates and other criminals take advantage of the political instability to operate freely. A fledgling colony on Ardan V would be a tempting target. The beginnings of several colonization efforts lie in ruins at various locations across the planet. However, only a few of them were abandoned due to direct attack. Everyone attempting to set up shop on the planet - even scavengers looking for salvage - find themselves packing up and leaving after a month or two. Every interstellar government in the area has given up on claiming it for a variety of reasons. Those aware of its existence consider Ardan V to be "cursed" and "unlucky" or even a "haunted" place.
Adventure Seed #1: Ardan V is an ideal hidey hole for those willing to ignore its reputation. Any group that's been a thorn in the player character's sides - the leadership of a renegade Klingon House, an "off the books" Tal Shiar or Obsidian Order operation, or a ruthlessly pragmatic mercenary company - might see Ardan V as a good place to lay low for awhile. Ardan V could be the end of a thrilling chase or a methodical investigation and the outcome could be a search for a base hidden somewhere on the planet or a siege against a fortress built in the ruins of an abandoned colony site. The Complication: Whatever caused everyone before them to flee the planet - predatory life forms with a talent for traveling around access tunnels, a strange energy field that causes paranoia, innocuous life forms that have a gremlin-like effect on technology - starts acting against the group that the player characters are after. They send out a call for help, preferring capture by Starfleet to whatever is on the planet. How does our Starfleet crew respond?
Advenure Seed #2: The Federation Council is entertaining a proposal to sponsor a colony on Ardan V. The planet is unclaimed, an ideal candidate, and those wishing to establish the colony are quick to dismiss its reputation as superstition. The player characters are to transport a small team of would-be colonists to Ardan V and assist them in surveying potential sites for the initial settlement. This involves a fair bit of work for the Science and Medical departments - they must identify and find ways of dealing with any potential dangers on the planet. The Complication: Naturally, a member of the civilian survey team disappears. Is it one of the nearby governments interfering to prevent the Federation from expanding into the area or does it have something to do with the mystery of Ardan V?
Adventure Seed #3: The indigenous people of Ardan V are powerful telepaths that find the presense of other minds to be painful. They wish no harm to those who come to their world, but broadcast telepathic suggestions to deter efforts to explore or colonize the planet. However, the surrounding governments are expanding into the system to exploit the resources of its asteroid belt and outer planets. They are carefully avoiding Ardan V due to its reputation, but they are still close enough to unsettle the planet's population. Even worse, the competing mining operations are each sponsored by different governments and they are coming into conflict. The miners are calling for military intervention while their governments request Federation mediation. Our Starfleet crew meets with representatives of the mining companies. Accusations of sabotage soon ring loud across the table. There have been constant reports of black outs, lost time, and accidents among the miners. The inhabitants of Ardan V are seeking to drive away the mining operations through more direct telepathic influence. The player characters must keep the situation with the miner from escalating while figuring out what is going on. The Complication: Any overt violence in the system will trigger direct intervention from Ardan V. Can our Starfleet crew make contact with the telepaths of Ardan V and establish a peaceful compromise between the miners or is evacuating the system the only practical response?
Kumarax III
A temperate world hosting an independent colony that recently celebrated its three year anniversary. The colony was established over the objections of experts who recommended a more detailed long term survey. The indigenous life forms all display adaptation for surviving a low pH environment not in evidence on the surface of the planet. This suggested a hidden danger to any colony placed there. The private group who proposed colonization pressed ahead, but were rebuffed by both the Federation Council and Starfleet. The colonists purchased the necessary supplies and leased several ships to transport everything and everyone to their new home. The colony then declared itself independent of the Federation. Kumarax III is far from major trade routes and the colony sees few visitors.
Adventure Seed: It turns out that there is a reason why all indigenous life is able to survive low pH levels. Torrential acid rains begin to scour the colony. The initial surveys missed the danger since the acid monsoons only occur once every several years. Forecasts indicate that the storms will last for several weeks. The colony structures start dissolving after a few hours of exposure. The colonists reluctantly send out a distress call. Starfleet dispatches the player characters to evacuate the colonists. Communications are intermittent due to acid damage to the colony's subspace antenna - it will fail before much longer. The colonists begin to retreat to better protected parts of the colony infrastructure while they await rescue. The Complication: Some of the colonists are refusing to leave their home behind, believing that they can somehow hold out.