At a high point on the landscape of the "Columbia Hills," atop NASA's Mars Exploration Rover Spirit, sit antennas that send information to Earth. Two antennas can be seen in this image taken by Spirit on martian day, or sol, 210 (Aug. 4, 2004). The disk-shaped, high-gain antenna on the right sends and receives X-band microwave signals, similar to frequencies used in alarm-system motion detectors and police radar guns. Mission planners at NASA's Jet Propulsion Laboratory send commands directly to the rover via the high-gain antenna. The tall antenna on the left, sometimes called a low-gain antenna, serves as a backup to the high-gain antenna and also sends, once a day, an X-band microwave signal to Earth. In the foreground, not visible in this view, is a smaller antenna that sends ultra-high-frequency signals, similar to frequencies used in some television broadcasts, to orbiting spacecraft. Orbiters such as the Mars Odyssey spacecraft relay the signals to Earth.
In front of the rover, at the top of the ridge on the "West Spur" region of the Columbia Hills, is a rock outcrop dubbed "Longhorn." On the horizon is the rim of the 165-mile-wide (103-mile-wide) Gusev Crater, inside of which Spirit landed Jan. 4, 2004. This image was taken with Spirit's navigation camera.