Prepare to be amazed! What initially appeared to be just another snapshot of Mars's south pole quickly transformed into something far more intriguing: hundreds of dark spots began to emerge, prompting a reaction from the ESA: "This shouldn't look like this."
Every Martian spring, a fascinating phenomenon unfolds near the south pole: hundreds of dark blotches materialize around a peculiar grid of ridges. From orbit, these formations bear an uncanny resemblance to swarms of spiders scurrying across a pale, sandy landscape. In reality, these are some of the most dramatic seasonal events in our solar system. Recent imagery from the European Space Agency (ESA) confirms that "spider season" has once again begun in the region nicknamed Inca City.
But what exactly are these "spiders"? They are not living creatures, but rather the scars left behind by the explosive release of carbon dioxide gas. This gas bursts through a winter blanket of dry ice that covers Mars's southern polar terrain. During the long polar night, carbon dioxide from the thin atmosphere freezes onto the ground, forming layered slabs that can reach about one meter in thickness.
When sunlight returns in the spring, it penetrates the translucent ice, warming the darker soil beneath. This warmth causes the bottom of the ice to transform directly into gas, a process scientists call sublimation. The gas accumulates under the ice slab until the pressure becomes too great. It then finds weak points, cracks the ice, and rushes upward, carrying dust and sand with it.
From above, each eruption sprays a dark fan onto the surface, leaving a spot that ranges from about 45 meters to 1 kilometer wide. Over many seasons, the escaping gas also etches a branching network of shallow troughs into the ground. Planetary scientists refer to these patterns as araneiform terrain, derived from the Latin word for spider. It's a Martian specialty, with no direct equivalent on Earth.
Why is Mars so adept at creating these "spiders" while Earth is not? The answer lies in the planet's atmosphere. Mars's air is dominated by carbon dioxide, and a significant portion of that gas freezes onto each winter pole. Studies of polar ice and gravity show that approximately a quarter of the Martian atmosphere can be locked up in these seasonal caps before returning to the air in spring.
This cyclical behavior turns carbon dioxide into the most active volatile substance on Mars today. As it cycles between gas and ice, it lifts dust, sculpts pits and grooves, and drives the geysers that create the spiders. Researchers believe this seasonal carbon dioxide system is now one of the primary forces reshaping the Martian surface.
The new images specifically focus on Inca City, a compact maze of straight ridges whose geometric layout reminded early observers of ancient Andean ruins. This structure is located near the south polar layered deposits and is formally known as Angustus Labyrinthus. It was first observed in the 1970s by NASA's Mariner 9 spacecraft.
But here's where it gets controversial... Exactly how these "walls" formed is still debated. High-resolution mapping indicates that they follow part of a circle about 86 kilometers across. Many researchers suspect the circle is an ancient impact crater whose fractures later filled with rising lava. Over time, the softer surrounding material eroded away, leaving the harder ridges standing. Other theories involve fossilized sand dunes or glacial landforms known as eskers.
Regardless of their origin, the ridges are now dotted and surrounded by the new dark spots. The ESA's Mars Express camera captures the blotches scattered across hills, plateaus, and mesas, while the ExoMars Trace Gas Orbiter images the spider-like channels lurking beneath the ice itself. Together, the two orbiters reveal both the fresh surface stains and the older subsurface web that feeds them.
On Earth, the closest everyday comparison might be how frost disappears from a car windshield on a bright morning, only with far more intensity. Laboratory work has now validated this picture. Experiments at NASA's Jet Propulsion Laboratory recently recreated miniature spiders in a chamber that mimics Martian polar conditions, using carbon dioxide ice and powdered soil. The tests produced gas plumes and crack patterns that matched those seen from orbit, strongly supporting the carbon dioxide jet model.
"The spiders are strange, beautiful geologic features in their own right," stated planetary scientist Lauren Mc Keown, who led the lab study. She and other researchers see them as more than just a curiosity. They are a natural experiment in how a greenhouse gas can freeze, flow, and erode a landscape when an entire quarter of the atmosphere migrates from sky to ground and back again every year.
For climate scientists, this makes Mars a powerful comparison case. On Earth, carbon dioxide remains in the air and traps heat, affecting everything from crop yields to the summer air conditioning bill. On Mars, the same molecule acts more like a sculptor's tool, carving spider webs into frozen ground and quietly recording the rhythm of the planet's seasons.
And this is the part most people miss... The latest images of Inca City don't reveal life, but they do reveal a living planet in another sense. Mars's surface is still changing, still cracking, still releasing invisible gas that stains the ice black. The "spiders" that initially alarm the eye in these images are a reminder that even a cold, thin atmosphere can keep a world in motion.
What do you think about the implications of these findings? Do you see the potential for similar phenomena on other planets? Share your thoughts in the comments below!
