On Mars, spring explodes into action with violent transformations. Frost avalanches, carbon dioxide gas geysers, and powerful winds reshape its surface, leaving behind stunning patterns like swirling polar troughs and spider-like marks. Scientists use the Mars Reconnaissance Orbiter to study these seasonal phenomena, which vary between hemispheres.
As Earth celebrates New Year’s Eve today, scientists studying Mars are already ahead of schedule. The Red Planet completed its latest orbit around the Sun on November 12, 2024, giving researchers a reason to celebrate.
A Martian year lasts 687 Earth days and ends quite differently from a year on Earth, especially in the northern hemisphere. While winter settles in here, spring begins on Mars, bringing rising temperatures and thinning ice. This triggers dramatic events: frost avalanches tumble down cliffs, carbon dioxide gas bursts from the ground, and fierce winds reshape the planet’s north pole.
“Springtime on Earth has lots of trickling as water ice gradually melts. But on Mars, everything happens with a bang,” said Serina Diniega, who studies planetary surfaces at NASA’s Jet Propulsion Laboratory (JPL) in Southern California.
It’s a new year on Mars, and while New Year’s means winter in Earth’s northern hemisphere, it’s the start of spring in the same region of the Red Planet. And that means ice is thawing, leading to all sorts of interesting things. JPL research scientist Serina Diniega explains. Credit: NASA/JPL-Caltech
Sublimation: Ice and Explosions
Mars’ wispy atmosphere doesn’t allow liquids to pool on the surface, like on Earth. Instead of melting, ice sublimates, turning directly into a gas. The sudden transition in spring means a lot of violent changes as both water ice and carbon dioxide ice — dry ice, which is much more plentiful on Mars than frozen water — weaken and break.
“You get lots of cracks and explosions instead of melting,” Diniega said. “I imagine it gets really noisy.”
Using the cameras and other sensors aboard NASA’s Mars Reconnaissance Orbiter (MRO), which launched in 2005, scientists study all this activity to improve their understanding of the forces shaping the dynamic Martian surface. Here’s some of what they track.
Frost Avalanches: A Dramatic Display
In 2015, MRO’s High-Resolution Imaging Science Experiment (HiRISE) camera captured a 66-foot-wide (20-meter-wide) chunk of carbon dioxide frost in freefall. Chance observations like this are reminders of just how different Mars is from Earth, Diniega said, especially in springtime, when these surface changes are most noticeable.
“We’re lucky we’ve had a spacecraft like MRO observing Mars for as long as it has,” Diniega said. “Watching for almost 20 years has let us catch dramatic moments like these avalanches.”
Gas Geysers: Explosive Springtime Jets
Diniega has relied on HiRISE to study another quirk of Martian springtime: gas geysers that blast out of the surface, throwing out dark fans of sand and dust. These explosive jets form due to energetic sublimation of carbon dioxide ice. As sunlight shines through the ice, its bottom layers turn to gas, building pressure until it bursts into the air, creating those dark fans of material.
But to see the best examples of the newest fans, researchers will have to wait until December 2025, when spring starts in the southern hemisphere. There, the fans are bigger and more clearly defined.
Credit: NASA/JPL-Caltech/University of Arizona
Martian Spiders: Mysteries of the Northern Hemisphere
Another difference between ice-related action in the two hemispheres: Once all the ice around some northern geysers has sublimated in summer, what’s left behind in the dirt are scour marks that, from space, look like giant spider legs. Researchers recently re-created this process in a JPL lab.
Powerful Winds and Polar Swirls
For Isaac Smith of Toronto’s York University, one of the most fascinating subjects in springtime is the Texas-size ice cap at Mars’ north pole. Etched into the icy dome are swirling troughs, revealing traces of the red surface below. The effect is like a swirl of milk in a café latte.
“These things are enormous,” Smith said, noting that some are a long as California. “You can find similar troughs in Antarctica but nothing at this scale.”
Fast, warm wind has carved the spiral shapes over eons, and the troughs act as channels for springtime wind gusts that become more powerful as ice at the north pole starts to thaw. Just like the Santa Ana winds in Southern California or the Chinook winds in the Rocky Mountains, these gusts pick up speed and temperature as they ride down the troughs — what’s called an adiabatic process.
Migrating Dunes: The Dance of Spring
The winds that carve the north pole’s troughs also reshape Mars’ sand dunes, causing sand to pile up on one side while removing sand from the other side. Over time, the process causes dunes to migrate, just as it does with dunes on Earth.
This past September, Smith coauthored a paper detailing how carbon dioxide frost settles on top of polar sand dunes during winter, freezing them in place. When the frost all thaws away in the spring, the dunes begin migrating again.
Each northern spring is a little different, with variations leading to ice sublimating faster or slower, controlling the pace of all these phenomena on the surface. And these strange phenomena are just part of the seasonal changes on Mars: the southern hemisphere has its own unique activity.
More About MRO
The Mars Reconnaissance Orbiter (MRO) is a pivotal spacecraft managed by NASA’s Jet Propulsion Laboratory (JPL), a division of Caltech in Pasadena, California, for NASA’s Science Mission Directorate. Since its launch in 2005, MRO has been studying Mars’ surface, climate, and geology, providing invaluable data for both scientific research and future exploration.
One of its standout instruments is the High-Resolution Imaging Science Experiment (HiRISE) camera, operated by the University of Arizona in Tucson. HiRISE, built by Ball Aerospace & Technologies Corp. in Boulder, Colorado, captures incredibly detailed images of the Martian surface, enabling scientists to study dynamic processes like avalanches, dunes, and seasonal changes. Together with other advanced instruments aboard MRO, HiRISE has significantly advanced our understanding of the Red Planet, making the orbiter one of NASA’s most successful missions to date.
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