Although Mars' atmosphere is comprised of vastly different elements than Earth's and is approximately 100 times less dense than our own, the planet does have clouds. But one strange, curious cloud near a massive volcano is puzzling onlookers and even inciting conspiracy theories about what may be hiding below.

The cloud, described as "curious" by the European Space Agency, was first spotted over the Arsia Mons volcano on the planet on Sept. 13 by the Mars Express spacecraft. The ESA does not believe it is a volcanic cloud since no volcano has been active on the planet in about 50 years, but rather they believe it is a water ice cloud.

"In spite of its location, this atmospheric feature is not linked to volcanic activity but is rather a water ice cloud driven by the influence of the volcano’s leeward slope on the air flow – something that scientists call an orographic or lee cloud – and a regular phenomenon in this region," the ESA said in a statement on its website.

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The space agency noted that the cloud has grown and changed shape throughout the day. It grows "in length during local morning downwind of the volcano, almost parallel to the equator, and reaching such an impressive size that could make it visible even to telescopes on Earth," the ESA added.

Mars' winter solstice on its northern hemisphere occurred on Oct. 16 and the ESA noted that a "seasonally recurrent water ice cloud," like the aforementioned cloud, has formed along the southwestern flank of the volcano in the past. The Mars Express craft and others have actually observed the cloud in 2009, 2012 and 2015, the ESA said.

Despite the proclamation from the ESA, that has not stopped conspiracy theorists on the internet proclaiming it could be from the volcano or something else.

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"I don't understand the conspiracy theory contingent that's going off re: the clouds over Arsia Mons," wrote Dr. Tanya Harrison, the Director of Research for Arizona State University's Space Technology and Science Initiative.

"What possible reason would we have to hide volcanic eruptions on Mars? Heck, NASA has shared plenty of pics of volcanoes erupting on Io (shown here) & geysers on Enceladus!"

Others sarcastically joked that it was not "a puff of white smoke that indicates that the Martian council has selected a new leader."

The ESA has set up a Flickr page for those interested in seeing the changes to the cloud over the volcano.

Follow Chris Ciaccia on Twitter @Chris_Ciaccia