Airgead Marbh resides within a system of another similiar sized planet, along with a similiar sized sun. This causes the unpredictable gravity pattern known as the "three body problem" in which all three bodies constantly pull and rip at each other, drawing them closer and slingshotting the others to the boundy of gravitational pull.
While Ethao, the other planet, is considered a lifeless hust of a planet, Airgead Marbh still holds the surface remains of a once great empire. The few brave enough to explore the planet have told of endless labyriths of wealth and technology just below the surface, but getting anything good and getting out before the sun swings too close, or Airgead Marbh gets launched into deep space is a fools gambit for most.
Whoever once resided within the walls of the remaining empire no longer walks the surface. Any history or culture once engraved on the walls or monuments built under the sky have long been scorched away when the system's sun gets pulled to close, turning the surface temparature up to inhospitable degrees, even with the most powerful of magic.
When the sun strays too close at high speeds, the land will rupture and burst, spewing debries and boulders across the surface in a massive storm of boiling hot temperatures.
While Airgead Marbh is launched far away from the sun, darkness consumers the land and harsh cold winds shear across the rocky remains.
If Ethao strays too closely in a cycle, gravity becomes a bargain at best. Massive sections of earth will slip away into the sky just a bit, as though debating jumping between the planets. In rare cases, explorers have said that they spotted strange artifacts leave Ethao's orbit and plummet into Airgead Marbh.
Across the planet though are various massive stone structures. The different styles imply once a diversity in the previous inhabitants, but explorers haven't found a consistent way to enter any of the buildings. Each one is a new gamble.
Once a way into a structure is discovered, delving just a bit reveals that almost all of them climb deep into the core of the planet. Cursory explorations have revealed traps, hidden doors, unknown technology, and the possibility of things living within the hallways of the structures, but also a massive amount of potential treasure.
Risking going into Airgead Marbh means finding a good time frame to approach, get in, and hopefully get out. It's possible to hide in the structures if deep enough until a new window of hospitable weather comes around again, but with the unpredictiblity of the orientations means you'll never know when the next time will swing around.
Nothing can survive on the surface, including spelljammers. Ships have to drop off any explorers or stay and risk potentially losing the ship to extreme weather.
Predicting upcoming planetary rotations is possible in a small enough time frame, providing some needed general guidelines of when it's safe to land.
Once a spelljammer is within the Crystal Sphere of Airgead Marbh, the Navigator of the spelljammer can spend an hour in researching the current trajectory of the celestial bodies in order to try to predict how much time they will have on the surface.
In order to get an accurate prediction, the Navigator will need to roll an Investigation (INT) check of a DC 20. For a result that is between 10-14, the DM will roll 1d6 and add that many days to the prediction for a broader timeframe. For a result that is between 5-9, the DM will roll 2d6 instead, and for a result that is between 4 or less, the DM will roll 3d6 instead.
A Navigator will also be able to spend another hour to roll another Investigation (INT) check of a DC 25 to attempt to predicte how long the next inhospitale timeframe will last, helping the crew to judge that if they get stuck on the surface, how long they'll have to be planet-side before another safe window opens up for possible escape.