Advanced civilization on planet with atmosphere only in large sinkholes

I want to have an Earth-sized planet (with similar gravity) with an extremely low-density atmosphere (comparable to Mars) at most of its surface. Complex life, including an information-age civilization, lives in enormous sinkholes many kilometers across, some up to 100 km across. Due to the lower elevation, the air pressure and composition is comparable to Earth"˜s. The sinkholes are flat on the bottom and have vertical-ish walls, so they're shaped like carved-out cylinders. The planet has many such giant sinkholes, and they're connected by underground rivers.

is a duplicate

This question has been asked before and has already been answered. It should be marked as a duplicate.

Please enter the URL of the proposed duplicate in the details field below.

not constructive

This question cannot be answered in a way that is helpful to anyone. It's not possible to learn something from possible answers, except for the solution for the specific problem of the asker.

Communities

Advanced civilization on planet with atmosphere only in large sinkholes

0 comment threads

0 answers