Tiny Mars has a Big Impact on Our Climate

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Mr.Millions of years ago, an ice age began that forever changed the course of life on Earth. The evolution of ocean currents has made the climate of the Horn of Africa drier. There, the dense forests became rarer and isolated in the middle of the savannahs. The arboreal primates that lived there were then forced to cross the tall grass, thus exposing them to the risk of predation.

For one primate species, this changing landscape represented a crisis and an opportunity. Over millions of years of evolution, they adapted to their new habitat by developing the ability to walk upright, freeing their hands to care for newborns, and eventually using tools. They were our ancestors. Without this ice age, we might not exist. And without Mars, this ice age might not exist, according to a new study published in Publications of the Astronomical Society of the Pacific.

Ice ages are caused by periodic changes in Earth’s orbit, the tilt of its axis, and its wobble as it rotates. Called Milankovitch cycles, these changes are governed by the gravitational pull of other planets and affect the amount of solar energy that reaches Earth.

Stephen Kane, a planetary scientist at the University of California, Riverside, was initially skeptical about Mars’ important role in the Milankovitch cycles. “I knew Mars had some effect on Earth, but I thought it was tiny,” Kane said in a statement. “I thought its gravitational influence would be too weak to be easily observed in Earth’s geological history. I sort of decided to check my own hypotheses.”

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To better understand Mars’ role, Kane turned to computer simulations, modeling Earth’s orbit over tens of millions of years. When Mars was removed from the simulation, the longest Milankovitch cycle was not changed. But somewhat surprisingly, two other cycles completely disappeared. In other words, Mars, which is one-tenth the mass of Earth, played an outsized role in Earth’s climate.

“The closer it is to the sun, the more a planet is dominated by solar gravity,” Kane said. “As Mars is further from the Sun, it has a greater gravitational effect on Earth than if it were closer. It punches above its weight.”

Kane’s research also has important implications outside our solar system. Planets with periodically eccentric orbits might be more conducive to the evolution of life, in part because of differential temperature gradients in the oceans favoring the exchange of organic matter as a “biological pump.”

“When I look at other planetary systems and I find an Earth-sized planet in the habitable zone, planets farther away in the system could have an effect on the climate of that Earth-like planet,” Kane explained.

Yet Kane can’t help but look at a planet like Mars – which could be humanity’s future – and imagine its impact on humanity’s past.

“Without Mars, Earth’s orbit would not experience major climate cycles,” Kane added. “What would humans and other animals look like if Mars wasn’t here?”

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Main image: NASA, ESA and STScI

• Jake Currie

  Published on January 20, 2026

  Jake Currie is a writer based in Brooklyn, New York.