A new study reveals that Mars plays a surprisingly crucial role in Earth's climate cycles, with new simulations showing that the mass of our planetary neighbours directly controls the timing and intensity of Milankovitch cycles that drive ice ages. By varying Mars's mass from zero to ten times its current value in computer models, researchers discovered that a more massive Mars strengthens the ~100,000 year climate cycles and creates the 2.4 million year "grand cycle" that influences Earth's long term climate. This finding demonstrates that Earth's climate rhythms are connected to the gravitational structure of the inner Solar System, not just the Sun and Moon.