Ar-Rehman

Mars' gravity has an effect on Earth's orbit and oceans

We are all too familiar of the Moon's effect on our planet. It's relentless tug causes our tides but even Mars, which is always at least 55 million km's away, can have a subtle effect too. A study has revealed a 2.4 million year cycle in the geological records that show the gentle warming and cooling of our oceans. The records match the interactions between the orbits of Earth and Mars over the longest timescales. These are known as the 'astronomical grand cycles' but to date, not much evidence has been found. Earth and Mars don’t just circle the Sun. They also tug on each other. Because the planets sit tens of millions of miles apart, that pull is comparatively weak. Still, gravity’s impact is ever present, and over eons, the effects build up until they become measurable in surprising ways. Scientists call the tiny tugs between Earth and Mars gravitational perturbations. About every 26 months, the planets reach an opposition, when they move closest to each other. During those moments, Mars gives Earth’s orbit a slight nudge. That nudge doesn’t “steer” Earth in any dramatic way. Over millions of years, though, it can slightly change the shape of Earth’s orbit and the way Earth tilts. Those slow changes can alter how much sunlight reaches Earth over long stretches of time, and that can affect climate patterns.

The rhythmical rising and falling of the oceans has been well documented. Even the Sun at an average distance of 150 million km's exerts enough of a pull to enhance the effect from the Moon, giving us the spring and neap tides. The Moon's influence is easy to understand due to its proximity, the Sun's too due to its enormous mass but Mars is a different story. After all, it's about half the size of Earth and even at its closest is about 55 million km's away. Ocean scientists watch the Atlantic Meridional Overturning Circulation (AMOC) closely. Many people call it an ocean “conveyor belt.” It transports warm water from the tropics toward the Northern Hemisphere and helps move heat into the deep ocean. Some scientists warn that it could weaken sharply in the coming decades. We know there are at least two separate mechanisms that contribute to the vigor of deep-water mixing in the oceans. Even if a big circulation pattern slows, smaller-scale mixing can still keep deep water from going stale. Eddies can move water around, help distribute oxygen, and keep heat from getting locked into one layer for too long. This will potentially keep the ocean from becoming stagnant even if Atlantic meridional overturning circulation slows or stops altogether.

As Earth and Mars orbit around the Sun, their interactions, or rather the gravitational pull from each upon each other are cyclical. These are the astronomical grand cycles and for Earth and Mars they cycle every 2.4 million years. A study used geological records from the deep sea and to their surprise found a connection between the astronomical grand cycles, global warming patterns and deep ocean circulation. They found a 2.4 million year waxing and waning of deep ocean currents and that seemed to link to increased climate. Researchers at the University of Sydney used satellite data to map sediment accumulation on the ocean floor across millions of years. They found gaps in the seafloor record. Those gaps can appear when stronger deep currents disrupt normal sediment deposition. “The gravity fields of the planets in the solar system interfere with each other, and this interaction, called a resonance, changes planetary eccentricity, a measure of how close to circular their orbits are,” explained study co-author Dietmar Müller, a geophysics professor at the University of Sydney.

A definite link emerged but it should be noted that ocean currents are not the only cause of global temperature changes. The current temperature increases have a much stronger link to the human emission of greenhouse gasses. The paper was authored by Dr Adriana Dutkiewicz and Professor Dietmar Muller from the University of Sydney and Associate Professor Slah Boulila from the Sorbonne University. They reached their conclusion following analysis of the deep-sea sediment records acquired from over half a century of drilling data from hundreds of sites worldwide. The 2.4 million year cycle they found can only have been caused by the interactions between Earth and Mars. Resonance between Earth and Mars changes Earth’s orbital eccentricity in a repeating way. At certain points in that cycle, Mars’ gravitational pull draws Earth slightly closer to the Sun. Th position increases solar radiation and warms the climate. Earth then drifts back again. The full pattern repeats about every 2.4 million years. “Our deep-sea data spanning 65 million years suggests that warmer oceans have more vigorous deep circulation,” explained Adriana Dutkiewicz, the study’s lead author and a sedimentologist at the University of Sydney.

The researchers also emphasized one point that matters right now. This slow, million-year cycle does not explain today’s rapid climate warming. Human greenhouse gas emissions heat the planet on a much shorter timeline and through a different physical cause. The interaction of the gravitational field of the two planets means periods of higher incoming solar radiation every 2.4 million years and with it, an increase in global temperatures. Their analysis of the sediments showed breaks in the sedimentary deposits which related to periods of warmer temperatures and more vigorous deep ocean circulation. The deep ocean moves constantly. It carries heat, salt and dissolved gases around the planet. It also shapes the ocean floor. When deep currents run stronger, they can disturb sediment and leave uneven records behind. Scientists call these cycles “astronomical grand cycles.” During stronger phases, the deep ocean can develop powerful eddies which reaches the abyssal depths and erode sediment that had quietly piled up. We tend to think of the deep ocean as something passive. A cold, slow place where stuff settles and sits. This study flips that. The deep ocean has a pulse, and that pulse runs to a beat set tens of millions of miles away. Mars and Earth, locked in their slow gravitational back-and-forth, leave fingerprints on the seafloor every 2.4 million years.

When the cycle peaks, the abyss gets restless. Currents pick up. Eddies churn. Sediment that had been quietly stacking up for ages gets swept aside. It’s a strange thing to imagine, a planet you can barely see in the night sky helping stir the bottom of our ocean. None of this rewrites what’s happening to Earth’s climate now, and the researchers are clear about that. Mars isn’t behind the heat we’re feeling. That’s on us, and on a timeline measured in decades, not millions of years. The result helps us to understand how deep ocean eddies are key to warming ocean temperatures. Understanding these can help us to understand and model future periods of warming. It may even go some way to mitigate a temporary cessation in ocean currents due to a change in the Atlantic meridional overturning circulation. This drives the Gulf Stream which helps to keep Europe and other temperature countries the nice warm climate it has become accustomed to in our world.