������ý

The gravitational tug of Mars may be strong enough to stir up Earth’s ocean, shifting its sediments as part of a 2.4-million-year climate cycle, researchers claim.

It has long been accepted that wobbles in Earth’s orbit around the sun influence the planet’s climate, with these Milankovitch cycles operating on periods measured in thousands of years. Now, at the University of Sydney and her colleagues say they have found a 2.4-million-year “Grand Cycle”, which they believe is driven by Mars and has had dramatic impacts on currents in Earth’s oceans for at least 40 million years.

The evidence for this cycle comes from almost 300 deep-sea drill cores that reveal unexpected variation in the deposition of ocean sediment. During periods of stable ocean currents, oceanographers expect sediment to settle in steady layers, but unusual currents and eddies can see it accumulate elsewhere.

According to the team, absences or hiatuses in the sediment deposition record line up with times when Mars’s gravity exerts maximum force on Earth, subtly impacting our planet’s orbital stability. This changes solar radiation levels and climate, manifesting as stronger currents and eddies in the oceans.

Team member , also at the University of Sydney, acknowledges that the distance between Earth and Mars is so vast that it is hard to conceive of any significant gravitational force being exerted. “But there are so many feedbacks that can amplify even subtle changes,” he says. “Mars’s impact on Earth’s climate is akin to a butterfly effect.”

Free newsletter

Sign up to Launchpad

Bring the galaxy to your inbox every month, with the latest space news, launches and astronomical occurrences from New ������ý’s Leah Crane.

Sign up to newsletter

at the University of Leeds, UK, says the drill cores provide more evidence for the existence of “megacycles” in global environmental change.

“Many of us have seen these multi-million-year cycles in various different geological, geochemical and biological records – including during the famous explosion of animal life in the Cambrian Period,” he says. “This paper helps cement these ideas as key parts of environmental change.”

But at the University of New South Wales in Sydney says that while he welcomes the work and thinks it adds to an understanding of climate cycles at a geological scale, he isn’t convinced by the paper’s conclusions.

“I’m sceptical of the link to Mars, given its gravitational pull on Earth is so weak – at only about one one-millionth of that of the sun,” he says. “Even Jupiter has a stronger gravitational field for Earth.”

England also points out that even if Mars is having an influence, it is nothing compared with human-driven climate change. “Greenhouse gas forcing is like a sledgehammer in comparison, so this has no bearing on present-day climate, where we are seeing melting ice sheets reduce the ocean overturning circulation.”