Does the following text have an inappropriate shift in verb tense? If so, fix any verbs that
don't match the tense of the verb in bold. If not, submit the text without making any
changes.
The 280-mile-long Grand Canyon is certainly large, but the Valles Marineris
canyon system on Mars is enormous. The Mariner 9 space probe discovered
the more than 2,500-mile-long Martian canyon system in 1971.