A new study shows that this seemingly "small" red planet may play a far greater role in the earth's long-term climate evolution than expected. Stephen Kane, a professor of planetary astrophysics at the University of California, Riverside, found through numerical simulations that Mars’ gravitational influence on changes in Earth’s orbital parameters and spin axis inclination directly affects many key climate rhythms, including the time scale for the emergence and end of ice ages.
Mars is only about half the diameter of the Earth and about one-tenth the mass of the Earth. It has always been regarded as a "lightweight" planet. Previous studies have suggested that certain climate rhythms recorded in the Earth's seafloor sediments are related to gravitational disturbances on Mars. This view was once questioned. Kane admitted that he initially thought that the impact of Mars was "very weak" and even difficult to clearly identify in the geological record. This study was, to some extent, to verify his original suspicion.
To this end, the research team constructed a long-term dynamic model of the solar system to simulate the evolution of the Earth's orbital shape and spin axis inclination over time. These slow but continuous changes determine the spatial and temporal distribution of sunlight on the surface and are the physical basis of the famous "Milankovitch Cycle". Milankovitch cycles are closely related to glacial periods and govern the alternation of warm and cold climate on a scale of tens of thousands to millions of years. Over the past approximately 4.5 billion years, the Earth has experienced at least five major ice ages, the most recent of which began approximately 2.6 million years ago and is still ongoing today.
The research shows that one of the climate cycles of about 430,000 years, driven primarily by the gravitational pull of Jupiter and Saturn, was preserved in the simulations regardless of the presence of Mars. But when Mars was "removed" from the model, two other important rhythms - one with a cycle of about 100,000 years and one with a cycle of about 2.3 million years - disappeared completely. If the mass of Mars is increased in the simulation, these two periods will be shortened, indicating that the greater the mass of Mars, the stronger the impact on the Earth's orbit and climate.
These long-term cycles affect key parameters such as the eccentricity of the Earth's orbit, the timing of Earth's perihelion, and changes in the tilt of its spin axis. They determine the intensity of solar radiation received at different latitudes in different seasons, thereby affecting the expansion and retreat of ice sheets and broader long-term climate patterns. Kane's results show that Mars plays a quantifiable role in many of the above links and is not "insignificant." He pointed out that because Mars orbits farther and is relatively weakly dominated by the sun's gravity, its gravitational disturbance on the earth is more "conspicuous" and can be said to be an "influence beyond its size."
Even more surprising is that changes in Mars' mass also change the rate of change in the tilt of the Earth's spin axis. The current tilt of the Earth's spin axis relative to its orbital plane is about 23.5 degrees, an angle that slowly swings over long timescales. Simulations show that when the mass of Mars is increased, the rate of change in the Earth's tilt decreases, similar to "adding a stabilizer" to the Earth's axis. The research team believes that this means that Mars not only exerts a disturbance on the orbital shape, but also provides an additional stabilizing factor for the Earth's rotation attitude to a certain extent.
This research paper has been published in the "Publications of the Astronomical Society of the Pacific" (Publications of the Astronomical Society of the Pacific), titled "The Dependence of Earth Milankovitch Cycles on Martian Mass." The paper not only quantifies the specific contribution of Mars to the evolution of the Earth's orbit, but also hints at the broader significance of exoplanetology: in other star systems, those "exoplanets" with low mass located outside the habitable zone may also quietly shape the climate stability of an Earth-like planet.
Kane said that when astronomers discover an Earth-like planet in the habitable zone around other stars, they can't just focus on the planet itself. Whether there are Mars-like asteroids in its outer orbit will directly affect the orbital rhythm and rotation stability of this Earth-like planet, thereby affecting whether its climate environment is suitable for the long-term existence of life.
Research can’t help but lead to “alternative hypotheses” about the Earth’s own history. Ice ages have rewritten ecological patterns many times in geological history, shrinking forests and expanding grasslands, and driving a series of key evolutionary changes including upright walking, tool use, and social collaboration. Without Mars, the Earth's orbit would be missing several important climate cycles. Whether the evolutionary paths of humans and other species would be completely different, and even "whether we would still exist as we are now" have become open questions worth asking.