I should preface it by saying that for scenario purposes Ceres has a partially liquid interior (somewhat like theory predicts for the real Ceres), with ammonia dissolved in the water acting as anti-freeze.
The expedition’s base camp consists of three domes, set up by the previous expedition, a few hundred yards from the crevasse where the ice tunnel was found. A landing pad has been cleared and levelled, and landing poles and lights have been installed to guide ships to a safe touchdown – it’s actually a little too close to the domes for safety, but so far there haven’t been problems. The domes contain basic accommodation, a workshop, and a laboratory, and can accommodate up to twelve persons without overloading the life support system.
The base has three vehicles, small caterpillar-tracked “trucks” holding up to four persons plus several tons of cargo. One is fitted with an extending crane, another has a bulldozer blade. In Ceres’ low gravity they are a little too powerful, it’s easy to drive over a rise and find that a truck flies ten or twenty yards before landing.
At this point the outer crust of Ceres is unusually thin, just a few hundred feet, and a ravine has opened revealing the underlying ice, with a deep vertical crevasse in the floor of the widest part of the ravine. The ravine appears to be several hundred thousand years old, and there have been land-slips on the South side. The crevasse appears to be very recent in geological terms, and probably hasn’t been open more than 300-400 years. The ice tunnel runs within a few feet of the crevasse floor; the ice isn’t completely clear, but at the closest point the tunnel is visible as a slightly darker blue-grey shadow below the surface.
The floor of the crevasse is level. Mention this but don’t explain it unless the players ask; on a Difficulty 4 Science roll it’s apparent that at some time in the past the bottom of the crevasse filled with water, which then froze. One possible explanation is that the crevasse was originally deeper and filled from the tunnel. If analysed, the ice is almost pure water, with very little dissolved ammonia. The most likely explanation is that the ammonia evaporated in vacuum, leaving the water to freeze.
Sound OK? Too dry and technical? All comments welcomed.