This Martian Lava Tube Skylight is 50 Meters Across. The Biggest Lava Tube on Earth is Only 15 Meters Across

NASA’s Mariner 9 was the first spacecraft to orbit another planet when it reached Mars in late 1971. It got there only a few weeks before the Soviet Union’s Mars 2 and Mars 3 spacecraft, despite being launched 11 days later than those missions. Unfortunately, there was a major dust storm when Mariner 9 arrived, and NASA had to wait until January before the spacecraft could get good images.

When it did get those images, they revealed a surprise: volcanoes and lava flows cover large portions of the Martian surface.

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