Forget the dramatic dust storms you’ve seen in movies about Mars. While those are certainly eye-catching, new research suggests the real force shaping Mars’s climate is far more subtle: microscopic atmospheric “gravity waves.” These aren’t the ripples in space-time from colliding black holes, but rather everyday disturbances in the air, similar to what happens when you throw a pebble into a pond. A recent study, involving scientists from the University of Tokyo, reveals these tiny ripples wield an outsized influence on Martian air currents, far more than their counterparts do on Earth. This unexpected finding challenges our long-held ideas about Martian weather and could dramatically change how we plan for future human missions to the Red Planet.
Unraveling Martian Air Currents: A Digital Twin Approach
To truly understand how Mars’s atmosphere operates, scientists need to track its unseen air currents, a vast “conveyor belt” that moves heat and air around the planet. This new study zeroed in on what’s called the “residual mean circulation”—essentially the average, long-term movement of air. To do this, researchers used a sophisticated tool known as the Ensemble Mars Atmosphere Reanalysis System, or EMARS. Think of EMARS as a highly detailed digital model of the Martian atmosphere. It combines actual observations from Mars-orbiting spacecraft, like the Mars Global Surveyor and the Mars Reconnaissance Orbiter, with advanced computer models. This process, called data assimilation, builds a complete, three-dimensional picture of the Martian atmosphere, including temperature and winds, even in areas where direct observations are scarce.
The study focused on four “Mars Years” (a Mars year is roughly two Earth years) that were free of major global dust storms. This allowed the scientists to examine the typical patterns of atmospheric circulation, rather than the extreme conditions caused by planet-wide dust events. The data covered altitudes from the surface up to about 100 kilometers (roughly 62 miles) high.
A key challenge in this research was that many important atmospheric ripples, especially smaller ones like gravity waves, are “unresolved.” This means they’re too tiny to be directly captured by the large grid patterns used in the EMARS data. To get around this, the researchers used a clever “indirect method.” They calculated all the other known forces acting on the atmosphere and then attributed any leftover push or pull to these invisible, unresolved waves, including gravity waves. This innovative approach allowed them to estimate the hidden but significant influence of these smaller waves on the overall circulation.
The Surprising Power of Small Ripples
The analysis produced clear and quite surprising results for atmospheric scientists. On Earth, the middle atmosphere’s circulation is primarily driven by large-scale atmospheric waves called Rossby waves. These are vast, slow-moving eddies created by our planet’s rotation and temperature differences, guiding our weather patterns.
However, Mars tells a different story. The study found that these “unresolved waves,” mainly gravity waves, are the dominant force driving the middle atmosphere’s circulation, particularly at higher altitudes (above approximately 50 kilometers, or about 30 miles). This means that these smaller ripples, often generated by Mars’s topography (like mountains) or rising air (convection), are the primary movers of its atmospheric conveyor belt at these heights.
A pivotal finding is that the contribution of these unresolved waves to the Martian atmosphere is more impactful than what’s seen on Earth. While gravity waves exist and play a role in our atmosphere, their influence is generally secondary to Rossby waves in our stratosphere. On Mars, their importance is significantly elevated. Even at lower altitudes, where larger waves also contribute, the overall shape of the circulation is still largely influenced by gravity waves. It’s clear: gravity waves are the quiet but powerful conductors of Mars’s atmospheric symphony.
Further distinctions from Earth emerged: a component of atmospheric circulation known as the “Stokes correction” is relatively large on Earth, contributing significantly to Rossby wave-driven circulation. Yet, on Mars, this correction is generally small. This observation indicates that Mars’s north-south air movement isn’t primarily driven by upward-moving Rossby waves, marking a stark contrast to Earth. The Martian circulation was also found to be “notably stronger than that in the Earth’s middle atmosphere.”
Why Mars is Different: A Thin, Responsive Atmosphere
Why do these smaller gravity waves exert such a profound influence on Mars compared to Earth? Several factors likely play a role. Mars has a much thinner atmosphere than Earth, with a lower capacity to hold heat. This makes it more responsive to localized heating and cooling, which can readily generate gravity waves. Also, Mars lacks vast oceans, meaning its surface warms and cools quickly. This leads to much larger seasonal atmospheric changes than on Earth, further contributing to the generation and spread of gravity waves.
This study builds upon earlier modeling efforts that hinted at the importance of gravity waves on Mars. However, it’s the first to provide a comprehensive, observation-based analysis that quantifies their widespread impact across the planet. This is crucial because while models offer predictions, real-world data, combined through data assimilation, provides a more accurate reflection of the actual Martian atmosphere.
What This Means for Future Martian Exploration
This research fundamentally reshapes our understanding of how Mars’s atmosphere works. It underscores that while our own planet provides valuable lessons, Mars operates under its own unique atmospheric rules. The dominant role of gravity waves means that future atmospheric models for Mars will need to accurately represent these smaller ripples to improve weather forecasting and climate predictions for the Red Planet.
As humanity looks forward to sending astronauts to Mars, a precise grasp of its atmospheric behavior becomes paramount. Knowing that subtle ripples, rather than just large-scale storms, are key players in the Martian environment means we need to fine-tune our instruments and models to truly comprehend what awaits. This study provides a vital piece of that complex puzzle, bringing us closer to safely and successfully exploring our intriguing planetary neighbor.
Paper Summary
Methodology
This study analyzed the long-term average (climatology) of the Martian atmosphere’s “residual mean circulation” and the forces driving it, particularly atmospheric waves. It used data from the Ensemble Mars Atmosphere Reanalysis System (EMARS) for four Mars Years (MY 29-32) that were free of major global dust storms. The Transformed Eulerian Mean (TEM) equation system was applied. A key technique involved an indirect method to estimate the influence of “unresolved waves” (like small-scale gravity waves) that are too small to be directly measured in the data.
Results
The study found that “unresolved waves,” primarily gravity waves, are the dominant force driving the Martian middle atmosphere’s circulation, especially at higher altitudes (above approximately 50 kilometers). This impact is notably greater than the influence of gravity waves on Earth. While larger-scale “resolved waves” also contribute, gravity waves largely shape the overall circulation. The Martian circulation was also found to be “notably stronger than that in the Earth’s middle atmosphere,” and the “Stokes correction” (a component of circulation) was generally small on Mars, unlike on Earth.
Limitations
The analysis was limited to Mars Years (MY 29-32) without global dust storms, meaning the findings may not fully represent circulation during such extreme events. The indirect method for estimating unresolved wave forcing relies on assumptions about the accuracy of other atmospheric terms.
Funding and Disclosures
This research was supported by the Japan Society for the Promotion of Science (Grant 22H00169). The authors include Anzu Asumi, Kaoru Sato, Masashi Kohma, and Yoshi-Yuki Hayashi. The data (EMARS Version 1.0) is preserved at Greybush et al. (2018) and openly developed at Penn State Data Commons.
Paper Publication Information
Asumi, A., Sato, K., Kohma, M., & Hayashi, Y.-Y. (2025). Climatology of the residual mean circulation of the martian atmosphere and contributions of resolved and unresolved waves based on a reanalysis data set. Journal of Geophysical Research: Planets, 130, e2023JE008137. DOI: 10.1029/2023JE008137 Received: October 12, 2023 Accepted: February 4, 2025
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