1. What was discovered on Mars?

Flat-plate collectors

Flat plates are the simplest collectors: at their most basic, they're little more than water pipes running through shallow metal boxes coated with thick black glass. The glass collects and traps the heat (like a greenhouse), which the water running through the pipes picks up and transfers to your hot water tank.

Evacuated tubes

These are a bit more sophisticated. They look like a row of side-by-side fluorescent strip lights, except that they absorb light rather than giving it out. Each tube in the row is actually made of two glass tubes, an inner one and an outer one, separated by an insulating vacuum space (like vacuum flasks). The inner tube is coated with a light-absorbing chemical and filled with a copper conductor and a volatile fluid that heats up, evaporates, carries its heat up the inner tube to a collecting device (called a manifold) at the top, where it condenses and returns to the bottom of the tube pick up more heat. The manifold collects the heat from the whole row of tubes and ferries it to your hot water tank. Unlike flat-plate collectors, evacuated tubes don't let as much heat escape back out again, so they're more efficient. However, since they're a bit more hi-tech and sophisticated, they are usually much more expensive.