Mars appears small when compared with Earth, and in popular imagination it is often treated as a quiet and distant neighbour. The red planet carries only about one tenth of Earth’s mass and today shows little of the geological activity that defines our own world. Yet new orbital simulations reveal that Mars plays a far more significant role in Earth’s long term climate rhythm than most people realize. The gravitational influence of this relatively small planet helps shape the slow orbital cycles that control how sunlight reaches Earth over tens of thousands and millions of years.
Earth’s climate history contains a clear pattern that has been recognized for more than a century. Geological layers, ocean sediments, and ice cores preserve repeating cycles that track changes in Earth’s orbit and orientation in space. These cycles, known as Milankovitch cycles, arise because Earth’s orbit gradually changes shape, the direction of the orbit slowly rotates, and the planet’s axis tilts back and forth. Each of these motions alters how solar energy is distributed across the surface of the planet. Over long time scales those shifts influence glacial periods, warming intervals, and the overall rhythm of Earth’s climate system.
Three main components define the Milankovitch system. Orbital eccentricity describes how stretched or circular Earth’s orbit becomes. Axial tilt controls how strongly the seasons change from summer to winter. Orbital precession refers to the slow rotation of Earth’s orbital ellipse through space. Together these motions create cycles lasting roughly twenty three thousand years, forty one thousand years, one hundred thousand years, and even longer. These periods appear repeatedly in geological records spanning millions of years.
What is often overlooked is that Earth does not control these cycles by itself. The orbit of every planet in the solar system is shaped by the gravitational influence of the others. Each planet pulls slightly on the others as they move around the Sun. Those tiny gravitational forces accumulate over enormous spans of time, gradually altering orbital shapes and orientations. The Milankovitch cycles are therefore not simply properties of Earth. They are the result of the entire architecture of the solar system.
Mars occupies a position where its orbit interacts directly with Earth’s orbital motion. Although the planet is small compared with Earth, it sits close enough that its gravitational influence contributes to the frequencies that appear in Earth’s orbital variations. To understand how strong that influence might be, researchers performed a series of long term computer simulations of the solar system. The models reproduced the orbital motions of all eight planets and then altered the mass of Mars to see how Earth’s orbital behaviour would change.
Several versions of the solar system were tested. In one simulation Mars was removed entirely. In another it remained at its present mass. Additional runs increased the mass of Mars to twice its current value, and the most extreme scenario increased Mars to roughly the mass of Earth. Each simulated system was then allowed to evolve for one hundred million years of modeled time. This duration allows the slow orbital cycles that define Milankovitch behaviour to emerge clearly.
One of the first results appeared in Earth’s orbital eccentricity. This parameter measures how elliptical the orbit becomes as it evolves through time. When the orbit becomes more elongated the distance between Earth and the Sun varies more strongly over the course of a year. These changes influence how solar energy is distributed between seasons and across latitudes.
In the present solar system eccentricity variations contain a well known cluster of cycles around one hundred thousand years. These cycles have long been linked to the timing of major ice ages and interglacial periods visible in the geological record. The simulations revealed that Mars plays an important role in shaping this pattern. When Mars was removed from the model the familiar one hundred thousand year structure changed noticeably. The dominant frequencies shifted toward longer periods and the strength of the signal weakened. The eccentricity spectrum became simpler and less structured.
When Mars was included with its real mass the structure returned to the form recognized in geological data. The gravitational interaction between Earth and Mars produces several nearby frequencies within the eccentricity spectrum. These frequencies interact with each other, creating the complex cluster that appears around the one hundred thousand year band. Increasing the mass of Mars strengthened this effect. When Mars was doubled in mass the short eccentricity cycles became slightly shorter and gained power, showing that stronger gravitational coupling between the two planets intensifies the orbital modulation.
The simulations also revealed the importance of a much longer orbital cycle. Earth’s eccentricity contains a slow modulation lasting roughly 2.4 million years. This long period oscillation acts as an envelope that strengthens or weakens the shorter cycles across geological time. The models showed that this multi million year cycle is directly connected to the interaction between Earth and Mars. It arises from the difference between the orbital precession rates of the two planets. Their gravitational interaction creates a slow beat pattern that unfolds across millions of years.
When Mars was removed from the simulation this cycle disappeared completely. Without Mars the frequencies required to generate the beat pattern no longer exist, and Earth’s eccentricity loses the long modulation. When Mars was restored the cycle immediately returned. Increasing the mass of Mars shortened the period of the cycle and amplified its strength, demonstrating how strongly Earth’s orbital rhythm depends on the presence of its neighbouring planet.
Mars also influences the direction that Earth’s orbital ellipse points in space. This motion is described by a parameter called the longitude of perihelion, which identifies the orientation of the point where Earth comes closest to the Sun. The simulations showed that the dominant frequencies in this motion cluster around seventy thousand year periods. When Mars was absent from the solar system one of the major components within this frequency band vanished. When Mars was present an additional signal appeared that corresponded directly to the orbital motion of Mars. Increasing the mass of Mars strengthened this signal and shifted its period slightly.
The researchers also examined how Mars affects the orientation of Earth’s orbital plane. This property, called the longitude of the ascending node, describes how the orbit tilts relative to the main plane of the solar system. In the present solar system this motion occurs on timescales close to seventy thousand years. Removing Mars simplified the nodal motion and reduced the complexity of the frequency spectrum. When Mars was included a second strong component appeared. Increasing the mass of Mars shortened the nodal periods and introduced additional complexity into the system.
The final element examined in the simulations involved Earth’s axial tilt. Earth’s obliquity oscillates around a dominant cycle lasting about forty one thousand years. This tilt cycle strongly influences the distribution of sunlight across the planet and therefore affects seasonal contrasts and long term climate behaviour. The Moon is the primary stabilizing influence that keeps Earth’s tilt from wandering chaotically, yet the simulations show that Mars still contributes to shaping the structure of the tilt cycle.
When Mars was removed from the model the dominant tilt cycle shifted slightly toward forty two thousand years and the surrounding side frequencies weakened. When Mars remained present the familiar forty one thousand year pattern appeared along with additional modulation on longer time scales. Increasing the mass of Mars gradually broadened the range of tilt cycles. When Mars approached Earth’s mass the dominant oscillation shifted toward roughly fifty thousand years and the spectrum expanded across a wider range of frequencies.
These results show that Mars exerts a measurable influence on several key elements of Earth’s orbital behaviour. The red planet contributes to the structure of the one hundred thousand year eccentricity cycles, produces the long 2.4 million year modulation of Earth’s orbit, and affects the precise frequencies that control orbital orientation and axial tilt. Even though Mars contains only a fraction of Earth’s mass, its gravitational presence forms part of the mechanism that shapes Earth’s long term climate rhythm.
Planetary systems are extremely sensitive to their architecture. Small differences in planetary mass or orbital distance can alter the gravitational interactions that generate long term orbital cycles. The modern solar system happens to produce a relatively stable configuration in which Earth’s Milankovitch cycles remain well defined and persistent across millions of years.
The simulations demonstrate that if Mars had formed slightly larger, or if it had never formed at all, Earth’s orbital behaviour would be different. The rhythms that paced ice ages and climate transitions across geological history would follow different patterns. The small red planet orbiting beyond Earth therefore acts as one of the hidden components in the gravitational system that governs the long term evolution of Earth’s climate.
Source:
Kane, S. R., Vervoort, P., & Horner, J. (2025). The Dependence of Earth Milankovitch Cycles on Martian Mass. Publications of the Astronomical Society of the Pacific.
https://doi.org/10.1088/1538-3873/ae2800
