You all begin descending, the sludge is slippery, but taking care, you are able to descend the ladder safely. It goes down...down...down...until you get to a place so dark that you can barely see the light from whence you came.
You find a solid floor, and after feeling around along the walls, you make your way out of the sludge, after traveling about 100 yards along a long, squarish tunnel.
Krinn remarks,
"I have no knowledge of this specific place. Interesting. Documenting and mapping now."
After some traveling in the dim light of Gunnar's darkvision, you make your way to a very large cavern (probably 500 square feet), and Krinn says,
"Wow! I recognize this now! This is the planar observatory!
"Gunnar, place me over there!"
Gunnar sees a spherical imprint in the wall that Krinn would fit into, and he places the docent into it. Once placed there, the entire cavern lights up, and just like you saw in that room that you met Krinn, you see a much larger-scale version of the moons of Eberron orbiting the planet. Eberron itself is about 15 feet in diameter, and the moons are of varying sizes, but seem to be between 6 feet and 10 feet in diameter each. Each moon has a elliptical line that passes through the center of the moon, which shows the path of orbit for each moon.
There is a 13th sphere, which seems like an empty void, but it still orbits like the other moons.
And then there is a strange object in the far distance, in the far corner of this cavern, with a trajectory line that does not follow the path of an orbit around Eberron. It seems to head in the direction of the farthest moon, Vult (associated with the plane of Shavarath).
Krinn says,
"That strange object is headed in the direction of Vult. It is set on a collision-course with Vult, and should impact it in about 10 days.
"What is that thing?"OOC:
This is where you all can send me what sort of knowledge you may have studied that might have been connected to identifying what this thing is.
Mechanically-speaking, you tell me how your knowledge in a skill or in a set of tools applies to knowledge that might help you know what that is, and if your story is meaningful, I will give you advantage in an Intelligence version of that applied skill or tool proficiency.
As an example, if you have spent time in Arcanix's planetarium or anything like that, you could use a Intelligence (Cartographer's Supplies) tool check or an Intelligence (Perception) skill check with advantage.