But how the heck do we get to actually find out about these amazing discoveries Spirit and Opportunity make? Well, it's not exactly your great-uncle's ham radio setup. While there's also a low-power and low-speed UHF radio with a meager data rate, it's primarily used as a backup, and at landing stage.
In general, the orbiters are only communicating about three hours of information directly to Earth. The rest is actually intercepted and sent to the orbiting Mars Odyssey and Mars Global Surveyor, which transmit to Earth -- and vice versa. The orbiter moves from horizon to horizon in about 16 minutes; 10 of those minutes can be used for communicating with the rovers [source: NASA]. If we were to guess, about 10 megabytes of daily data can be sent to Earth. This is especially helpful because orbiters are in closer contact with both the rovers, and have a much longer window to communicate with Earth than either rover.
The rovers each use two antennas for communication: a high-gain antenna that can steer itself to beam information toward an antenna on Earth, and a low-gain antenna that can receive and send information from every direction at a lower rate than the high-gain antenna. All these communications occur on the Deep Space Network (DSN), an international network of antennas with communication facilities in the Mojave Desert of California, Madrid, Spain, and Canberra, Australia.
Steer yourself onto the next page to learn about what a rover does on a typical day.