Mars spiders are not living animals. They look like dark, spider-shaped marks with long, branching “legs” spread across bright or dusty ground near the south pole of Mars.
These are real surface features that only look like spiders from far away.
You are seeing araneiform features, strange patterns that form when carbon dioxide ice and escaping gas interact, not actual creatures on Mars.
What They Look Like From Orbit
From orbit, these features appear as tiny black or dark brown spiders scattered across the Martian south polar region. ESA captured them with Mars Express and the Mars Express High Resolution Stereo Camera as part of araneiform terrain.
Dark Spots
You usually notice the centers first. They appear as small dark spots on pale ground, and ESA reports that these spots can range from about 45 meters to 1 kilometer across.
They stand out because the surface around them is lighter.
Radial Legs and Web-Like Patterns
The “legs” are narrow dark channels that spread outward from the center in all directions. That web-like layout leads people to call them spiders.
The patterns can look messy, branched, and organic, almost as if a living thing moved across the ice.
How Size and Shape Change Across the Terrain
The shapes vary. Some are compact and round, while others stretch across hills, plateaus, and troughs.
Their size depends on local ice thickness, cracks, and how much gas escapes beneath the surface.
Why They Resemble Spiders
Craters usually have raised rims and bowl shapes. Dunes tend to form smooth mounds and ripples.
Mars spiders have a center with many branching arms, which makes them seem like arachnids from above.
Why These Patterns Form In Spring
These patterns appear when Martian seasons change and sunlight reaches frozen ground near the pole. The key ingredients are frozen carbon dioxide and carbon dioxide ice, which behave differently as temperatures rise.
How Frozen Carbon Dioxide Builds Up In Winter
During winter, layers of carbon dioxide ice build up on the surface. ESA explains that this ice can lie over dark ground and form slabs up to a meter thick.
The layer traps dust and sets the stage for spring activity.
Gas Jets, Dust Plumes, and Carbon Dioxide Ice Sublimation
When spring sunlight warms the ice, the lower layer turns from solid directly into gas. That gas builds pressure, breaks through the overlying ice, and escapes in jets or geysers.
As it bursts out, it carries dark dust upward and leaves the spider-like marks behind.
The Difference Between Surface Marks and Channels Under the Ice
The dark spots are the visible evidence on the surface, while the branching channels form below the ice. The surface spots show where gas escaped, and the hidden channels map out the path the gas took under the frozen layer.
Where Scientists See Them Best
Scientists spot these features most clearly near Mars’s south pole, especially in places with layered ice and rough, broken terrain.
Some of the best views come from Angustus Labyrinthus, also called Inca City, where the spider-like marks sit among ridges, mesas, and dusty plains.
Inca City and Angustus Labyrinthus Near the South Pole
Inca City is the informal name for Angustus Labyrinthus, a maze-like region near the south pole. ESA notes that the dark spots there often sit near the edge of the region and spread across plateaus and canyons.
What Mars Express and the High Resolution Stereo Camera Show
Mars Express, especially the High Resolution Stereo Camera, provides a broad view of the dark spots on the surface.
These images reveal how the features cluster across a wide area and how they relate to hills, troughs, and layered deposits.
How ExoMars Trace Gas Orbiter Reveals Finer Spider Details
The ExoMars Trace Gas Orbiter shows the finer, tendril-like channels more clearly. Its images help scientists see the web-like structure beneath the surface, not just the dark dots left after the gas escapes.
How Researchers Interpret and Study the Features
Researchers study Mars spiders as geology, not biology. The features differ from Curiosity’s spiderweb-like boxwork, which comes from another process in a different part of Mars.
Why Mars Spiders Differ From Curiosity’s Spiderweb-Like Boxwork
Curiosity has seen spiderweb-like rock patterns that form through a different process and setting. Those features belong to layered rock and erosion, while Mars spiders are seasonal marks created by carbon dioxide ice and gas.
What NASA and ESA Observations Suggest
NASA and ESA observe a repeating seasonal process near the poles. The features appear when sunlight hits carbon dioxide ice, gas builds up underneath, and dust gets dragged to the surface.
ESA’s orbiters have tracked the spots and channels for years, making the pattern clear.
Lab Tests and Imaging Work from Jet Propulsion Laboratory and Caltech
Scientists at the Jet Propulsion Laboratory and Caltech recreated Mars-like conditions to test how the features form.
Lab work helps researchers match the orbital images with a physical process.
You can see how thin ice, trapped gas, and dust work together to make the spider shape.
