Scientists are examining a mysterious giant scar stretching across Mars — and do not know how it got there.

The incredible feature, longer than the 446km (227-mile) Grand Canyon at roughly 600km (373 miles), has been captured by the ESA spacecraft Mars Express.

The scar, known as Aganippe Fossa, cuts across the lower flank of one of the Red Planet’s largest volcanoes, Arsia Mons.

The ravine was first spotted in 1930, but this is the first time scientists have been able to see it up close.

ESA describes it as “a dark, uneven scar slicing through marbled ground at the foot of a giant volcano” and “a ditch-like groove with steep walls on either side.”

The space agency say Mars Express regularly observes Arsia Mons and its nearby companions in the region of Tharsis, where several of Mars’ behemoth volcanoes are found.

This includes Olympus Mons, the tallest volcano in the solar system.

Arsia Mons itself measures 435km (270 miles) in diameter and rises more than 9km (5.5 miles) above the surrounding plains.

For context, the highest dormant volcano on Earth, Ojos del Salado on the Argentina-Chile border, is almost 7km (4.3 miles) high.

ESA says, “We’re still unsure of how and when Aganippe Fossa came to be, but it seems likely that it was formed as magma rising underneath the colossal mass of the Tharsis volcanoes caused Mars’ crust to stretch and crack.”

Mars Express has been orbiting the Red Planet since 2003.

It is imaging Mars’ surface, mapping its minerals, identifying the composition and circulation of its tenuous atmosphere, probing beneath its crust, and exploring how various phenomena interact in the Martian environment.