The red planet Mars - as captured by the Hope orbiter - has an unexpected impact on our seasons (Credit : Kevin Gill)
Have you ever wondered what really drives Earth's ice ages? What if I told you that Mars—a planet 140 million miles away—plays a starring role in whether our planet freezes or thaws?
Welcome to FreeAstroScience, where we break down complex scientific discoveries into ideas you can grasp over your morning coffee. I'm Gerd Dani, and today we're exploring one of the most surprising findings in planetary science this year.
Here's what stopped me in my tracks: a planet barely 10% of Earth's mass somehow helps decide when glaciers advance and retreat on our world. That's not science fiction. That's our solar system at work.
Grab a seat. This one's going to change how you see Mars—and our own planet's climate story. Stick with me to the end, because the implications stretch far beyond Earth.
What Are Milankovitch Cycles, Anyway?
Let's start with the basics. Earth doesn't orbit the Sun in a perfect, unchanging path. Our orbit slowly stretches and squishes. Our planet wobbles on its axis. The direction our poles point gradually shifts over thousands of years.
These changes happen because Earth doesn't exist alone. Every planet in our solar system tugs on every other planet. Jupiter pulls. Venus pulls. Even tiny Mars pulls. These gravitational nudges add up over millennia .
Scientists call these slow orbital variations Milankovitch cycles, named after Serbian mathematician Milutin Milankovitch. He proposed in the 1920s that these orbital changes control ice ages. He was right.
Three main components drive these cycles:
- Eccentricity: How stretched or circular Earth's orbit becomes
- Obliquity: The tilt of Earth's axis (currently about 23.4°)
- Precession: The wobble in Earth's spin axis direction
Each component operates on different timescales. And here's where Mars enters the story .
The Discovery: Mars Punches Above Its Weight
For decades, astronomers focused on Jupiter and Venus when studying Milankovitch cycles. Makes sense—Jupiter is massive. Venus is our closest planetary neighbor. Mars? It seemed too small to matter much.
A new study led by Stephen Kane at the University of California, Riverside, just upended that assumption .
Kane's team ran computer simulations—lots of them. They varied Mars's mass from zero to ten times its current value. Then they tracked how these changes affected Earth's orbital variations over 100 million years .
The results? Mars matters. A lot.
"Despite its small mass, a Mars-type planet exerts a non-negligible amount of influence on the climate of other terrestrial planets," the researchers concluded.
That's the aha moment right there. Size isn't everything in orbital dynamics. Position and gravitational coupling matter just as much.
The 405,000-Year Metronome: Steady as She Goes
Not everything in Earth's climate rhythm depends on Mars. Some patterns are rock-solid, no matter what you do to the Red Planet.
The most stable feature Kane's team found was the 405,000-year eccentricity cycle. Think of it as Earth's master clock—a metronome ticking away in the background of our climate system.
This cycle comes from the gravitational dance between Venus and Jupiter. Scientists call it the g₂ - g₅ beat (the subscripts refer to each planet's specific orbital frequency). The 405-kyr cycle persisted in every simulation, whether Mars was absent or ten times heavier .
Geologists love this cycle. They've found its signature in rock layers spanning hundreds of millions of years. It's so reliable that researchers use it to date ancient sediments.
| Cycle Period | Type | Primary Driver | Mars Dependence |
|---|---|---|---|
| ~405,000 years | Long Eccentricity | Venus–Jupiter (g₂ - g₅) | Low |
| ~100,000 years | Short Eccentricity | Inner planet coupling | High |
| ~41,000 years | Obliquity | Earth–Mars (s₃, s₄) | High |
| ~2.4 million years | Grand Cycle | Earth–Mars (g₄ - g₃) | Complete |
The ~100,000-Year Ice Age Rhythm: Mars Takes the Wheel
Here's where things get interesting. The shorter eccentricity cycles—the ones near 100,000 years—respond directly to Mars's presence .
These cycles pace ice age transitions. When Earth's orbit becomes more stretched (higher eccentricity), seasonal temperature differences intensify. Ice sheets grow and shrink in response.
In Kane's simulations, something striking happened as Mars grew more massive: the ~100,000-year cycles lengthened and gained power . The coupling between inner planets' orbital motions strengthened.
When Mars was removed entirely (0% mass), these cycles shifted from about 95,000 years to roughly 101,000–102,000 years. The total power in these bands dropped .
What does this mean for Earth? Our ~100,000-year glacial cycles exist partly because Mars exists. Remove Mars from the solar system, and ice ages would march to a different drummer.
The Missing Grand Cycle: When Mars Disappears
Perhaps the most dramatic finding involves the 2.4-million-year "grand cycle."
This long-period rhythm shows up in geological records going back hundreds of millions of years. It modulates how much sunlight Earth receives over deep time. The cycle relates to the slow rotation of both Earth's and Mars's orbits around the Sun .
Mathematically, it arises from the difference between Earth's and Mars's perihelion precession rates—what scientists call g₄ - g₃ .
Here's the kicker: when Mars's mass approaches zero in the simulations, this grand cycle vanishes entirely .
No Mars, no 2.4-million-year beat.
The cycle literally depends on Mars being there. It's a gravitational fingerprint of our planetary neighbor written into Earth's climate record.
| Mars Mass (% of Current) | g₄ - g₃ Period (Myr) | Relative Power |
|---|---|---|
| 0% | Absent | None |
| 100% (Current) | ~2.4 | Moderate |
| 200% | ~1.4 | Strong |
| 1000% | Complex | Dominant |
As Mars's mass increases, the grand cycle period shortens and its power grows . The gravitational coupling between planets intensifies.
Earth's Wobble: A Dance with Mars
Earth doesn't just orbit—it wobbles. Our planet's axial tilt (obliquity) oscillates between about 22.1° and 24.5° over roughly 41,000 years. This wobble affects how sunlight spreads across latitudes and seasons .
You might think the Moon controls this wobble. You'd be mostly right. Our large Moon stabilizes Earth's spin axis against wild swings .
But Mars plays a supporting role here too.
Kane's simulations revealed that the 41,000-year obliquity cycle lengthens as Mars becomes more massive . With a Mars ten times heavier than reality, the dominant obliquity period shifts to 45,000–55,000 years .
That's a big deal. The timing of obliquity cycles affects ice sheet growth and retreat. Change the rhythm, and you change which regions freeze and when.
The mathematical relationship involves what scientists call s-modes—nodal precession frequencies. Earth's s₃ mode and Mars's s₄ mode interact through gravitational coupling . Strengthening that coupling (by adding mass to Mars) retunes the entire system.
What Does This Mean for Exoplanets?
Here's where the research leaps beyond our solar system.
We've now discovered thousands of planets orbiting other stars. Some sit in the "habitable zone" where liquid water could exist. But orbit location isn't everything.
A planet's climate depends on its Milankovitch cycles too. And those cycles depend on its planetary neighbors .
Kane's work gives us a new tool for assessing exoplanet habitability. We can now ask: What kinds of planetary companions help or hurt a world's chances for stable climate?
A terrestrial planet with a massive neighbor in the right orbital position might experience climate variations that prevent runaway freezing. The variations could make seasons more favorable to life .
Conversely, the wrong configuration might produce chaotic obliquity swings or extreme eccentricity variations—bad news for life trying to gain a foothold.
"The Milankovitch spectrum of an Earth-like planet is a sensitive, interpretable probe of its planetary neighborhood," the researchers wrote .
We can read a planet's climate destiny in its orbital companions.
Why Mars Is Small: A Brief History
You might wonder: why isn't Mars bigger? If it were more massive, our climate cycles would be quite different.
Scientists have several theories :
Stranded embryo: Mars formed quickly (within 5–10 million years) and then got cut off from additional material.
Jupiter's influence: Jupiter's early migration may have sculpted the inner solar system, leaving Mars's region depleted.
Early instability: An outer-planet instability may have scattered material away from Mars's orbit.
Giant impact: Mars might have suffered a massive collision that stripped away much of its mass.
Whatever the cause, we ended up with a Mars just the right size to create our particular pattern of ice ages. A different-sized Mars would mean a different climate history for Earth.
The Mathematical Heart of Climate Cycles
For those who want to peek under the hood, here's how the orbital frequencies work.
In classical mechanics, planetary orbits behave like coupled oscillators. Each planet has characteristic frequencies for how its orbit stretches (g-modes) and how it tilts (s-modes) .
The key beat frequencies driving Earth's climate come from differences between planets:
405-kyr cycle: g₂ - g₅ (Venus minus Jupiter)
~100-kyr cycles: Combinations involving g₃, g₄, g₅ (Earth, Mars, Jupiter)
2.4-Myr cycle: g₄ - g₃ (Mars minus Earth)
~41-kyr obliquity: α - s₃ (precession constant minus Earth's nodal frequency)
When you change Mars's mass, you shift g₄ and s₄. All the beat frequencies involving Mars shift too. The entire climate-forcing spectrum reorganizes .
A Geological Orrery
Scientists have a beautiful phrase for what Milankovitch cycles provide: a "geological orrery" .
An orrery is a mechanical model of the solar system—those beautiful brass contraptions with little planets on arms that rotate. Earth's sedimentary record works the same way. Rock layers preserve the beat of orbital cycles going back hundreds of millions of years.
Geologists can read these rhythms in sediment cores, limestone beds, and ancient ocean deposits. The 405,000-year metronome shows up everywhere. So do the shorter cycles .
This deep-time record confirms that Mars has been influencing Earth's climate for as long as both planets have existed.
What If Mars Were Different?
Let me paint a picture of alternate Earths.
No Mars at all: The 2.4-million-year grand cycle vanishes. The ~100,000-year ice age rhythm weakens and lengthens. Earth's climate would still cycle, but to a simpler beat. Ice ages might be less pronounced.
Double Mars (200% mass): The grand cycle shortens to about 1.4 million years. Short eccentricity cycles gain power. Climate variations intensify. Ice ages come faster and hit harder.
Earth-mass Mars (1000%): Everything fragments. The clean periodicity breaks down into complex interference patterns. Predicting ice ages becomes nearly impossible. Climate chaos reigns.
We live, it turns out, in a sweet spot. Our Mars is just massive enough to create recognizable climate rhythms without overwhelming the system.
Feeling Small Yet?
Here's what I find moving about this research.
We spend so much time thinking about climate as something local. Carbon dioxide, ocean currents, forests, ice caps. All important. All real.
But beneath those processes lies a deeper rhythm—one set by the gravitational symphony of worlds we'll never touch.
Mars pulls on Earth. Jupiter pulls on Venus. Venus pulls on everyone. And somewhere in that cosmic tug-of-war, ice ages are born and die.
You're not alone in this. Your ancestors felt these cycles without knowing their cause. The climate your grandchildren inherit will still respond to Mars's gravity.
We're connected to the solar system in ways we're only beginning to understand.
The Bigger Picture
Kane's research reminds us of something profound: Earth doesn't exist in isolation.
Our planet is part of an interconnected system where distant neighbors shape our weather, our seasons, and the rhythm of ice ages that have driven evolution for millions of years.
The sleep of reason breeds monsters, as Goya warned. When we stop questioning, stop wondering, we lose touch with these deep connections.
FreeAstroScience exists to keep those questions alive. Complex ideas deserve simple explanations. Everyone deserves to understand the cosmos they're part of.
Wrapping Up: What We've Learned
Let's pull together the threads:
- Milankovitch cycles drive Earth's ice ages through orbital variations
- Mars, despite its small size, strongly influences several key cycles
- The 405,000-year metronome (Venus–Jupiter) remains stable regardless of Mars
- The ~100,000-year ice age rhythm depends directly on Mars's presence and mass
- The 2.4-million-year grand cycle disappears entirely without Mars
- Earth's obliquity cycles lengthen as Mars becomes more massive
- Exoplanet habitability depends on similar planetary interactions
Mars isn't just a rusty world we're trying to explore. It's a gravitational partner in Earth's climate story—a partner we've had for billions of years.
Keep Your Mind Active
At FreeAstroScience.com, we believe science belongs to everyone. Not just researchers. Not just students. Everyone.
These ideas aren't locked away in academic journals. They're part of your world. The ice ages that shaped human evolution? Mars helped pace them. The climate your great-great-grandchildren will inherit? Mars will still be there, pulling.
Come back to FreeAstroScience whenever curiosity strikes. We'll keep breaking down the universe, one discovery at a time.
Because the sleep of reason breeds monsters—but an active mind? That breeds wonder.
Sources
Kane, S. R., Vervoort, P., & Horner, J. (2025). "The Dependence of Earth Milankovitch Cycles on Martian Mass." arXiv:2512.02108v2.
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