Gale is a crater, and probable dry lake, on Mars near the northwestern part of the Aeolis quadrangle at 5°24′S 137°48′E / 5. 4°S 137. 8°E / -5. 4; 137. 8. It is 154 km (96 mi) in diameter and estimated to be about 3. 5-3. 8 billion years old. The crater was named after Walter Frederick Gale, an amateur astronomer from Sydney, Australia, who observed Mars in the late 19th century. Aeolis Mons is a mountain in the center of Gale and rises 5. 5 km (18,000 ft) high. Aeolis Palus is the plain between the northern wall of Gale and the northern foothills of Aeolis Mons. Peace Vallis, a nearby outflow channel, 'flows' down from the hills to the Aeolis Palus below and seems to have been carved by flowing water. Several lines of evidence suggest that a lake existed inside Gale shortly after the formation of the crater.