"The Mars Elephant" -- NASA Mars Reconnassance Orbiter (HiRISE), 2012NASA/JPL-Caltech/Univ. of Ariz.

The "Elephant"

Ever since Italian astronomer Giovanni Schiaparelli described his discovery of canals on Mars in 1877 and American astronomer Percival Lowell started to map them, we humans have been fascinated with the Red Planet. Although the canals were nothing more than a case of mistaken identity and our technology has come a long way since Schiaparelli and Lowell's telescopes, Mars continues to serve up its fair share of illusions, hoaxes and misunderstandings.

For the most part, these illusions are triggered by a psychological quirk of our brains that creates familiar objects from apparently random shapes. This phenomenon is known as "pareidolia" -- the same phenomenon that makes some people see the face of Jesus in burnt toast and bunnies in clouds. In the case of Mars, pareidolia makes us see bigfoot, parrots, flowers and faces in the otherwise barren orange landscape. Most recently, the case of the "Mars rat" captivated the mainstream media, but how does it measure up against other examples?

Pictured here, an ancient lava flow Elysium Planitia was imaged by the High-Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter (MRO). To the HiRISE mission scientists, far from it being a barren landscape, the head of an elephant etched into the surface jumped out at them.

Read more: Is That an Elephant on Mars?

Rolling Stones

Rolling Stones Logo -- NASA Mars Reconnassance Orbiter (HiRISE), 2011NASA/JPL-Caltech/Univ. of Ariz.

In another landscape shot captured by the HiRISE team, an odd-looking crater appears to be sticking its tongue out. In reality, this isn't a crude scribble of the famous Rolling Stones logo, it's actually material flowing out of an old impact crater down a slope.

The "Morchid"

'The Mars Flower' -- NASA Mars Science Laboratory, 2012NASA/JPL-Caltech

During operations at 'Yellowknife Bay' inside Gale Crater, NASA's Mars Science Laboratory (MSL) Curiosity spotted something quite peculiar embedded in a rock. The robot's arm-mounted Mars Hand Lens Imager (MAHLI) zoomed in to show what looked like the petals of a flower. Alas, those spoilsport scientists explained the object away, saying that it was most likely a concentration of light-colored minerals, and not a Mars orchid (or "Morchid"). Bummer.

Read more: Curiosity Spots Mystery Mars 'Flower'

Happy Crater

"The Smiling Crater" -- NASA Mars Global Surveyor, 1999NASA

Galle Crater was first imaged by the Viking 1 Orbiter in the 1970s and then, in 1999, NASA's Mars Global Surveyor took this shot. Although the two 'eyes' and 'mouth' are known to be raised features and mountains, it's hard to shake the image of a 230 kilometer-wide smiley face.

Dead Parrot

"The Mars Parrot" -- NASA Mars Global Surveyor, 2002NASA/JPL-Caltech

"... that's what I call a dead parrot." -- Dead Parrot Sketch, Monty Python.

Is this proof of intelligent life on Mars? So intelligent that, in order to send a message into space, Martians built a huge mound that resembles a belly-up parrot? According to some conspiracy theorists, this makes perfect logical sense. To the rest of the world, that parrot theory is well and truly dead.

Read more: Is This a Parrot on Mars?

Mars Pharaoh

Alien artifacts? -- NASA Mars Exploration Rover Opportunity, 2008NASA/JPL-Caltech

The Mars rovers have taken thousands of photos of the Mars surface, each one presenting a veritable feast of science and discovery. But, there's also evidence of alien technology and, possibly, artiness.

This photo snapped by rover Opportunity in 2008 of a rocky outcrop at Victoria Crater appears to have a Martian sculpture of some kind of pharaoh (exhibit A) and a spaceship component half buried in the sand (exhibit B). Sadly, both are just angular rock shapes.

The Infamous Yeti

"Mars Bigfoot" (a.k.a. "Mars Yeti") -- NASA Mars Exploration Rover Spirit, 2008NASA/JPL-Caltech

If there really are alien artifacts on Mars, who the heck is making them? According to some, this photo by NASA's Spirit rover is an eerie example of one of those humanoids. Either that, or it's Bigfoot seeing out his retirement on Mars. But there's a problem. This "Mars Bigfoot" isn't very big at all -- it's about 6 centimeters tall. And guess what? It's made of rock.

Trees on Mars?

Trees on Mars? -- NASA Mars Reconnassance Orbiter (HiRISE), 2011NASA/JPL-Caltech/Univ. of Ariz.

When the HiRISE team first released this image to the world, we were all entranced by the beautiful tree-lined landscape-- wait. Trees on Mars? Actually, this is a lovely optical illusion. The "trees" are in fact flow channels of dark material slipping off the tops of sand dunes a couple of hundred miles south of the planet's north pole. The slides were caused by the melting and sublimation of carbon dioxide frost as the northern hemisphere entered summer.

Mars Gopher!

"The Mars Rat" -- NASA Mars Science Laboratory, 2012NASA/JPL-Caltech

Once you see it, you can't un-see it. Yep, that looks like a rat alright. Or a gopher. Still, it looks like a small rodent hiding in the rocks near Mars rover Curiosity. And who can blame the poor little guy? I'd be hiding from that car-sized, nuclear-powered, laser-toting, rock-drilling alien robot too! Sadly, the little furball isn't a Martian rodent, it's a rock with an uncanny resemblance of one.

Read more: Rat on Mars?

The Face of Mars

'The Face of Mars' -- NASA Viking 1 Orbiter, 1976NASA/JPL-Caltech

Although the Face of Mars has been debunked more times than I've had hot dinners, it's hard not to be impressed by this classic trick of the light. This observation was taken by the Viking 1 Orbiter in 1976. As follow-up observations have since shown us, the "face" is in fact a Mars mesa (a hill) in the Cydonia region. But this original low-resolution, lucky photo launched countless theories of intelligent life on Mars, inspiring numerous sci-fi books and movies.

This is, without doubt, the most enduring case of Martian pariedolia, and although it is just an illusion, it's a reminder of the beautiful mystery the Red Planet still holds over us.