Level 1 - Absolute Beginner
Mars has long, narrow channels called gullies. They look like water made them, just like gullies on Earth.
But Mars is very cold. Its air is very thin. Liquid water cannot stay on the surface of Mars today.
A scientist named Apolline Leclef led a new study. She works in France. The study looked at a place on Mars called Sisyphi Cavi.
The team found that frozen carbon dioxide, not water, changes the gullies. This helps us understand Mars better.
- gully
- a long, narrow channel cut into the ground, often by water or other forces
- study
- careful scientific work done to learn about something
- surface
- the outside or top part of something, like the ground on Mars
- liquid
- a wet substance, like water, that flows and is not solid or gas
- carbon dioxide
- a gas; when it freezes, it becomes a type of ice called dry ice
- sublimation
- when a solid changes straight into a gas, without becoming a liquid first
- debris flow
- a fast-moving mix of rocks, dust, and ice sliding down a slope
- orbiter
- a spacecraft that flies around a planet to study it from above
Level 2 - Elementary
For years, scientists have wondered about strange channels on Mars called gullies. They look like something similar on Earth, where flowing water cuts paths into hillsides.
However, Mars today is extremely cold, and its atmosphere is far too thin for liquid water to survive on the surface. So what is shaping these gullies?
A new study led by Apolline Leclef, from the Institut d'Astrophysique Spatiale at the Universite Paris-Saclay in France, looked closely at a region called Sisyphi Cavi. The team used data from two instruments: CRISM, on NASA's Mars Reconnaissance Orbiter, and OMEGA, on the European Space Agency's Mars Express orbiter.
They discovered that the gullies are reshaped in the late stages of carbon dioxide ice sublimation, when frozen CO2 turns directly into gas. This process seems to trigger debris flows or avalanches that carve and reshape the gullies, not liquid water.
- atmosphere
- the layer of gases surrounding a planet
- reshape
- to change the shape or form of something
- instrument
- a scientific tool used to measure or observe something
- spectrometer
- an instrument that analyzes light to learn what something is made of
- frost
- a thin layer of ice that forms on a surface
- avalanche
- a sudden, fast movement of material, like snow, ice, or debris, down a slope
- preprint
- a scientific paper shared publicly before it is formally reviewed and published
- present-day
- happening now, in current times, rather than in the past
Level 3 - Intermediate
One of the more persistent puzzles in planetary science concerns the gullies that cut across many Martian slopes. These landforms bear a striking resemblance to water-carved gullies on Earth, yet Mars's present-day climate makes liquid water on its surface essentially impossible: the planet is too cold, and its atmosphere is far too thin to sustain it.
A new study, led by Apolline Leclef of the Institut d'Astrophysique Spatiale at the Universite Paris-Saclay in France and published as a preprint in September 2026, offers a compelling explanation. The research focused on a region known as Sisyphi Cavi, drawing on data from two complementary instruments: the CRISM spectrometer aboard NASA's Mars Reconnaissance Orbiter and the OMEGA spectrometer aboard the European Space Agency's Mars Express orbiter.
Combining observations from both instruments, the team found that the gullies in Sisyphi Cavi are actively modified during the late stages of carbon dioxide ice sublimation, the process by which frozen CO2 transitions directly into gas without passing through a liquid phase. This sublimation appears to destabilize surface material, triggering debris flows or avalanches that actively carve and reshape the gullies.
The findings lend strong support to the idea that carbon dioxide frost, rather than liquid water, is the agent currently reshaping Mars's gullies. It is a significant step toward understanding how these landforms remain dynamic in a world where liquid water simply cannot exist on the surface.
- persistent
- continuing to exist or occur over a long period of time
- landform
- a natural feature of a planet's surface, such as a mountain, valley, or gully
- resemblance
- a similarity in appearance between two things
- complementary
- combining well with something else, each adding something the other lacks
- destabilize
- to make something less stable or secure, causing it to shift or collapse
- dynamic
- constantly changing or active, rather than staying fixed
- agent
- a cause or force that produces a particular effect
- transition
- a change or shift from one state or form to another
Level 4 - Advanced
Among the enduring enigmas of Martian geomorphology are the gullies etched into countless crater walls and slopes across the planet, landforms whose morphology so closely mirrors water-carved channels on Earth that early interpretations leaned heavily on fluvial explanations. Yet such readings sit uneasily against present-day Martian conditions: frigid temperatures and an atmosphere too tenuous by orders of magnitude to permit liquid water to persist at the surface.
A newly circulated preprint, led by Apolline Leclef of the Institut d'Astrophysique Spatiale at the Universite Paris-Saclay in France and released in September 2026, advances a resolution grounded not in speculation but in multi-instrument spectral evidence. Focusing on the Sisyphi Cavi region, the investigation draws on two complementary orbital datasets: the CRISM spectrometer aboard NASA's Mars Reconnaissance Orbiter and the OMEGA spectrometer aboard the European Space Agency's Mars Express orbiter, instruments capable of detecting the compositional signatures of surface ice.
Synthesizing these observations, the researchers demonstrate that the gullies undergo active modification during the terminal stages of carbon dioxide ice sublimation, the direct solid-to-gas transition of frozen CO2. This process, they argue, destabilizes accumulated debris on the slopes, precipitating flows or avalanches that progressively carve and reconfigure the gully morphology, a mechanism entirely independent of liquid water.
The implications extend well beyond a single region: the work substantiates a broader reconceptualization in which seasonal carbon dioxide frost, rather than any vestige of liquid water, functions as the principal agent of ongoing geomorphological change on Mars. In doing so, it sharpens our understanding of how a planet bereft of surface liquid water can nonetheless sustain landforms that remain, against initial appearances, strikingly active today.
- geomorphology
- the scientific study of the physical features of a planet's or landscape's surface and how they form
- morphology
- the form, shape, or structure of something, such as a landform
- fluvial
- relating to or produced by the action of flowing water, such as a river
- tenuous
- extremely thin, weak, or lacking substance
- spectral
- relating to a range of light or energy wavelengths, used to analyze composition
- synthesize
- to combine separate pieces of information or evidence into a single coherent understanding
- precipitate
- to cause an event or process to happen suddenly or sooner
- reconceptualization
- a fundamental rethinking or reframing of an idea or explanation
Talk about this article with KatePractice this story's vocabulary in a real spoken conversation with your AI tutor