The elongated "water ice cloud" seen lingering over Arsia Mons on Sept. 13, 2018.

(European Space Agency)

At a Glance

There's a long, curious cloud lingering over Mars' massive Arsia Mons volcano.Despite its location, the European Space Agency says it's not linked to volcanic activity. Volcanic activity at Arsia Mons has been extinct for about 50 million years now.

There's a long, curious cloud lingering over Mars' Arsia Mons volcano that the European Space Agency (ESA) has been observing for well over a month now. , the agency said.

Since Sept. 13, the ESA has had their eyes fixed on the elongated cloud that appears to be spawning from the 12-mile-high volcano. However, in a recent release, the agency said it's a regular phenomenon for the area.

The 930-mile-long mass is a "water ice cloud" createdby air in the Martian atmosphere interacting with the southwest slope of the defunct volcano. Scientists refer to such phenomena as a lee cloud, since the influence on the air flow occurs on the leeward slope of the volcano.

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For size comparison, 930 miles is roughly the distance between Jacksonville, Florida, and New York City.

Despite looking like an eruption, activity from Arsia Mons has been long extinct. NASA research released last March revealed that — about the same time the dinosaurs, along with a large number of plant and animals species, went extinct on Earth.

The same elongated cloud is seen on Sept. 21, 2018

(European Space Agency)

Arsia Mons is about 30 times the size of the largest volcanoes that are scattered across Earth, and similar clouds like the one spotted in September have been observed in 2009, 2012 and 2015.

Each of these past clouds made themselves known right before the Martian winter. This one was no different, showing up just a few weeks before the planet's winter solstice on Oct. 16.

The ESA added that the massive dust storm that enveloped the planet was likely a factor in the cloud's size and visibility.