Short answers, pulled from the story.
A canyon is a deep cleft between escarpments or cliffs created by weathering and the erosive activity of a river over geologic time scales. Rivers cut downward toward a baseline elevation, wearing away softer rock layers while harder strata such as sandstone and granite remain standing as walls. Frost wedging, tectonic uplift, and limestone cave collapse are additional formation processes.
The Yarlung Tsangpo Grand Canyon in Tibet, China, is regarded by some as the deepest canyon on Earth at 5,500 meters. Others consider the Kali Gandaki Gorge in Nepal deeper, with a 6,400-meter difference between the river level and the surrounding peaks.
Greenland's Grand Canyon, discovered through analysis of Operation IceBridge data and reported in August 2013, is believed to be the longest canyon in the world at 750 kilometers. It lies beneath the Greenland ice sheet.
The Capertee Valley in New South Wales, Australia, is the widest canyon in the world, measuring one kilometer wider than the Grand Canyon of Arizona.
Canyon is predominantly used in North America, derived from the Spanish cañón, while gorge and ravine are French in origin and common in Europe and Oceania. In Canada, a gorge is generally narrow while a ravine is more open and often wooded. South Africa uses the local term kloof alongside both canyon and gorge.
Yes. Valles Marineris on Mars is the largest-known canyon in the Solar System. Venus has a trough and canyon system stretching more than 6,400 kilometers. Titan, Saturn's largest moon, hosts Vid Flumina, the only known liquid-floored canyon in the Solar System besides those on Earth.