Mars is only about half the size of Earth and has just one-tenth of our planet’s mass.
Compared with giants like Jupiter, it seems far too small to matter. But new research shows that Mars has been quietly playing an important role in shaping Earth’s long-term climate, including the cycles that bring ice ages.
The study, published in Publications of the Astronomical Society of the Pacific, was led by Stephen Kane, a professor of planetary astrophysics at the University of California, Riverside.
Kane originally doubted earlier research suggesting that Mars could influence Earth’s ancient climate.
Some scientists had linked layers of sediment on the ocean floor to long-term climate cycles driven partly by Mars’ gravity.
“I knew Mars had some effect on Earth, but I assumed it was tiny,” Kane said. “I thought its influence would be too small to clearly see in Earth’s geologic record.”
To test this idea, Kane ran detailed computer simulations of the solar system. He looked at how Earth’s orbit and tilt change over tens of thousands to millions of years.
These slow, repeating changes are known as Milankovitch cycles, and they control how sunlight is distributed across the planet. Over time, these cycles help trigger the advance and retreat of ice sheets, shaping ice ages.
Earth has experienced at least five major ice ages in its 4.5-billion-year history. The most recent one began about 2.6 million years ago and continues today, even though we are currently in a warmer phase.
One well-known Milankovitch cycle lasts about 430,000 years and is mainly driven by the gravity of Venus and Jupiter. Kane found that this cycle remained unchanged even when Mars was removed from his simulations. But the surprise came with two other important cycles. A 100,000-year cycle and a much longer 2.3-million-year cycle completely disappeared when Mars was taken out.
“When you remove Mars, those cycles vanish,” Kane said. “And when you increase the mass of Mars, the cycles speed up, showing that Mars is directly responsible for them.”
These cycles affect how stretched or circular Earth’s orbit becomes, the timing of when Earth is closest to the Sun, and how much Earth’s axis tilts. All of these factors influence how much sunlight different regions receive, which strongly affects climate and ice ages.
One unexpected result was that a heavier Mars actually stabilized Earth’s tilt. Earth’s current tilt of about 23.5 degrees slowly changes over time, but increasing Mars’ mass in the simulations reduced how fast that tilt shifted.
Mars’ influence is stronger than expected because it lies farther from the Sun. At greater distances, a planet’s gravity is less overwhelmed by the Sun’s pull, allowing Mars to “punch above its weight,” as Kane put it.
The findings also matter beyond our solar system. Small outer planets around distant stars could quietly shape the climates of Earth-like worlds, possibly influencing whether life can thrive.
The research even raises a fascinating question: without Mars, Earth would be missing major climate cycles that helped drive evolution. If those cycles never existed, humans and many other species might have turned out very differently.
