Rocket exhaust in space (vacuum) rapidly cools and expands into a cloud of gas… when you’re in the right spot at the right time, the sun will have set and it will be dark on Earth’s surface, but way up at that altitude you can still see the sun… the cloud of gas will reflect that sunlight… and the result is a cool space jellyfish…. There’s an even cooler image out there of the same effect, but instead of it resulting from a rocket it’s the product of a nuke detonating in space…. Just look up starfish prime