Researchers have found evidence that a massive lake once existed on Mars. Images from NASA's Mars Reconnaissance Orbiter indicate that a 30-mi (50-km) long canyon on the Red Planet was likely carved by water. Scientists believe the lake probably formed about 3.4 billion years ago, covered as much as 80 sq mi (207 sq km), and was up to 1,500 ft (500 m) deep. Of particular interest to scientists is the fact that the lake appears to have existed 300 million years after the planet’s warm, wet period was thought to have ended.