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Valles Marineris

American  
[val-uhs-mar-uh-nair-is] / ˈvæl əsˌmær əˈnɛər ɪs /

noun

Astronomy.

  1. a canyon on Mars, 3,100 miles (5,000 km) in length, named after the Mariner spacecraft.

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Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.