I was playing on Slowest and had 177 turns left.

All of a sudden it said there was 1 turn left.

I guess I had researched everything, but I had not built the satellite or mars shuttle. I was hoping to get some more stuff built.

Then it's over. What happened?

Great post

Researching all tech is one of the end game conditions. When you start a new game, you can see the end games listed.

There are other ones aside from turn 300, such as pollution. That actually happened to me once, on a tiny map at fast speed and Humankind difficulty; an AI smoked everyone out and the game ended.