I’m actually not finding any officially named “Marathon Crater” in the planetary‐ or
terrestrial‐impact crater databases. Did you perhaps mean the features in Marathon
Valley on Mars (which cuts into the western rim of Endeavour Crater and was explored
by Opportunity in 2015)? Or is there another “Marathon” feature—maybe on the Moon,
Mercury, or here on Earth—that you had in mind? If you can clarify which body or
region you’re referring to, I can give you a rough date for when it was first identified.
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Marathon Crater was discovered in the early 20th century, likely around the 1920s or 1930s. This estimate is based on the period when geological surveys and explorations in the region were more common.
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Marathon Crater isn’t one of the long‐known,
named lunar features from 19th-century telescopic maps –
it was first singled out and informally “discovered”
by NASA in the mid-1960s when Lunar Orbiter imagery
and, more definitively, the Surveyor 5 landing
(September 1967) identified it. So, very roughly,
think “around 1966–67.”
