Humans have been seeing strange things on the surface of Mars for centuries. Perhaps it's because, other than Earth, Mars is the closest thing in the solar system to a habitable planet, or perhaps it's simply because it's close enough to get a pretty good look at.
Either way, Earthlings have been fooled time and again by the rocky Martian surface and their own psychology. People have at various times reported finding everything from canals to spooky humanoid faces to alien Martian bases on the surface of the Red Planet — though each sighting has been thoroughly debunked.
In this vast universe, are Earthlings just desperate for next-door neighbors to play with? Looking back over the long history of Martian illusions (and human delusions), it certainly seems so.
Land and sea
In 1784, Sir William Herschel, a famous British astronomer, wrote that dark areas on Mars were oceans and lighter areas were land. He speculated that Mars was inhabited by intelligent beings who "probably enjoy a situation similar to our own," according to NASA. Herschel's theory prevailed for a century, with other astronomers claiming that vegetation could even be observed in the lighter-colored regions that were taken to be land. Fortunately for Herschel, his other contributions to astronomy — which have earned him the honor of being the namesake of two powerful observatories — were great enough to keep his theories on Martians near the bottom of his biography.
Canali vs. canals
During Mars' close approach to Earth in 1877, the Italian astronomer Giovanni Schiaparelli peered through his telescope and observed grooves on the Red Planet's surface. The Italian word he used for them, "canali," meaning channels, was translated to "canals" in English, leading many in the English-speaking world to conclude that Mars had intelligent life that had built a system of waterways.
That misconception was popularized by an astronomer named Percival Lowell, who in 1895 presented drawings of the canals in a book, titled "Mars," and argued his full theory in a second book, "Mars as the Abode of Life," in 1908. The inaccuracy was further fueled, according to NASA, by excitement over the construction of the Suez Canal, an engineering marvel of the era completed in 1869.
The theory was debunked in the early 20th century, when it was demonstrated that the "canals" were merely optical illusions: When viewed through poor-quality telescopes, pointlike features, such as Mars' mountains and craters, appear to be joined together by straight lines. Later, spectroscopic analysis of the light coming from Mars showed that there was no water on its surface.
It all started back in 1976, when NASA released an image of an interesting mountain on Mars, taken by the Viking 1 spacecraft, complete with a caption that described the formation as appearing to have eyes and nostrils. More than 30 years later, the "Face on Mars" still inspires myths and conspiracy theories, with many people believing it to be an artificial structure built by an ancient Martian civilization.
From a bird's-eye view, shadows on the mountain really do make it look like a face. From other angles, however, seen in photos taken by the Mars Express Orbiter and other spacecraft, the mountain is clearly just that, and doesn't look much like a face at all.
Pareidolia is the scientific term for seeing faces (or other significant objects) where they aren't. Face pareidolia happens, scientists say, as a byproduct of our heightened sensitivity to the details of human faces. Takeo Watanabe of the Boston University Visual Sciences Laboratory put it this way: "We've over-learned human faces so we see them where they aren't."
2001: A Mars tree
In 2001, seven years before he died, the famous science fiction writer Arthur C. Clarke, co-creator of "2001: A Space Odyssey", announced that he had spotted patches of vegetation, including trees, in new photos of Mars taken by the then-orbiting Mars Global Surveyor. "I'm quite serious when I say, have a really good look at these new Mars images," Clarke said at the time, speaking via phone during the Wernher von Braun Memorial Lecture series at the Smithsonian's National Air and Space Museum. "Something is actually moving and changing with the seasons that suggests, at least, vegetation."
He continued, "Where there's vegetation, you can bet there'll be something nibbling on it. I'm still hoping we'll find some Martians up there, holding up a sign that says 'Yankee go home.'"
The branches that Clarke thought he saw on the Martian surface are what Mars geologists call "spiders": They do look like branches, and they do vary seasonally, but they're due to the seasonal melting of the carbon dioxide ice caps that exist at Mars' poles. When the CO2 ice sublimate turns into a gas it flows out along paths that look like branches, Live Science previously reported.
In 2007, the Mars rover Spirit captured quite a sight in its Red Planet home: what appeared to be a human being wearing a robe and kneeling in prayer. Spirit captured a panoramic view of the plateau called Home Plate, located in the inner basin of the Columbia Hills range inside Gusev Crater. Of course, the "human" in the image is merely a rock, which morphs into human form in our brains because of pareidolia.
The face of Ghandi
The 1976 Mars face was just the start. With the launch of Google Mars in 2009, a map program created from compiled satellite images of the planet, users could careen around the surface of the Red Planet, finding all sorts of interesting lumps and bumps. One such bump, discovered by an Italian man named Matteo Ianneo, looked eerily like Indian independence activist Mahatma Gandhi, who was assassinated in 1948.
Higher-resolution imagery showed the shape to be not a mountain or hill, but a pit, which does indeed look a bit like a human head in profile, though what appears to be an eye and brow in the Google Mars image is less pronounced in the high resolution picture. Gandhi might be a stretch — the ear is too large, and Gandhi never sported a double chin — but it's easy to see how pareidolia works when comparing the high- and low-resolution images of the same feature.
Bio Station Alpha
In 2011, yet another smidgen of evidence arose that initially seemed to support the notion that there's life on Mars. In a viral Youtube video, a self-described "armchair astronaut" claimed to have identified a human (or alien) base on Mars, which he dubbed Bio Station Alpha. He found a somewhat mysterious linear structure that appears to be on the Red Planet's surface as seen in Google Mars.
Astronomers immediately identified the structure as just a white, pixelated streak — an artifact deposited by a cosmic ray in the image sensor of the camera that snapped the photo. "With space images that are taken outside our magnetosphere, such as those taken by orbiting telescopes, it's very common to see these cosmic ray hits," said Alfred McEwen, a planetary geologist at the Lunar and Planetary Lab at the University of Arizona and the director of the Planetary Imaging Research Laboratory.
Cosmic rays are energetic particles emitted by the sun. They deposit electric charge in camera pixels as they penetrate them, momentarily saturating them and creating a white streak in any photo snapped at the time.
When the raw image file was converted to a JPEG for use in Google Mars, McEwen said compression probably caused the cosmic ray artifact to become more rectangular and "Bio Station"-like. This was subsequently proven to be the case, when the original source photo that Google used was identified. It contained an obvious cosmic ray artifact, which, when processed, turned into the structure that the "armchair astronaut" mistook for a Mars base.
A hairy blue spider
Images taken by a European Space Agency (ESA) orbiter in 2019 seem to show an enormous hairy spider sprawling out its legs across a Martian mountain.
The reality is almost cooler. These spindly "legs" are actually the paths of hundreds of tiny tornadoes, or dust devils, that have traversed the ridge. It's not clear why the mountain is such a tornado hotspot, but ESA scientists said that the way air masses move around the region might be conducive to the formation of the dust devils.
Or maybe a beetle?
Seeing creepy-crawlies seems to be a theme on Mars. Also in 2019, William Romoser, a professor emeritus who studies viruses in insects and other arthropods made a surprising claim: He said he could see beetles and other insects, and even reptiles, on the surface of Mars.
Romoser came to this conclusion after examining photographs taken by the NASA Mars rovers, which show plenty of vaguely oval, blobby shapes on the Martian surface. But pareidolia strikes again: What else looks like a vaguely oval blob? Most rocks.
"I do not think there are insects on Mars. The photographs that are in that press release you sent are entirely unconvincing, as they fall within the range expected in zillions of non-insect objects photographed in lowish resolution on a Marscape," David Maddison, a professor in the integrative biology department at Oregon State University, told Live Science at the time. "It is vastly more parsimonious to presume the blobs are simply rocks. As has been said, 'extraordinary claims require extraordinary evidence'; those pictures are far, far less than extraordinary."
A big splat
Finally, something that looks like what it really is. Sometime between July and September 2019, a space object — a meteor perhaps, or a fragment of comet — hit the southern ice cap of Mars and punctured a thin layer of ice, shooting a shower of red dust up and out of the hole. The result is a dark red splat that looks like something a cartoon character might make while running headfirst into a wall. A large camera called HiRISE (High Resolution Imaging Science Experiment) aboard NASA's Mars Reconnaissance Orbiter captured the splat, which is about 0.62 miles (1 kilometer) across.
Weird green rock
Mars, as we all know, is the Red Planet. So what's with this weird green rock discovered by the Perseverance rover?
Everyone would like to know. "Is it something weathered out of the local bedrock?," a tweet posted March 31 by the rover's PR team wondered. "Is it a piece of Mars plopped into the area from a far-flung impact event? Is it a meteorite? Or something else?"
The rock is about 6 inches (15 centimeters) long and sits in Mars' Jezero Crater, close to the rover's landing site. The rover has already zapped the rock with a laser to vaporize part of it. The vapor cloud will be analyzed by the rover's cameras and spectrometers to reveal its chemical composition. Perhaps we'll have an answer to this mystery sooner rather than later.
Originally published on Live Science.
Editor's note: This article was updated on Aug. 3, 2021, to include more recent Martian illusions.