Although Mars is small compared to Earth, it has had a major impact on our planet’s climate.
Credit: NASA
Stephen Kane, professor of planetary astrophysics at UC Riverside, became skeptical when he read recent studies that showed the gravitational pull from Mars was linked to Earth’s long-term climate patterns. These studies have shown that sediment layers at the bottom of our oceans have recorded climate cycles influenced by the Red Planet, despite their distance from Earth and small size. Mars measures only half the diameter of Earth and has 10 percent of its mass.
“I knew Mars had some influence on Earth, but I thought it was small,” Kane said. “I thought its gravitational effect would be too small to be easily observed in Earth’s geologic history. I set out to test my assumptions.”
For his study, Kane ran computer simulations of long-term changes in our planet’s tilt, which controls what angle sunlight reaches the surface over a period of thousands to millions of years.
cycling through time
These so-called Milankovitch cycles – named after Milutin Milankovitch, the Serbian geophysicist who discovered them – are central to understanding how and when ice ages begin and end. An ice age is a long period when there are permanent ice sheets at the planet’s poles. The Earth has gone through at least five major ice ages in its 4.5 billion year history. The most recent began 2.6 million years ago and continues to this day.
A famous Milankovitch cycle is caused by the gravitational pull of Venus and Jupiter and lasts for 430,000 years. During that time, Earth’s orbital path gradually shifts from nearly circular to more elongated and backward. This change determines how much energy from the Sun reaches our planet. Over long periods of time, this could cause ice sheets to grow or shrink.
That 430,000-year cycle was present in Kane’s simulations, whether Mars was there or not. But when they removed Mars, two other major cycles, one of 100,000 years and the other of 2.3 million years, disappeared.
“When you remove Mars, those cycles disappear,” Kane said. “And if you increase the mass of Mars, they get smaller and smaller as Mars’ influence gets larger.”
These cycles affect the eccentricity of Earth’s orbit, the time of Earth’s closest approach to the Sun, and how much our planet’s axis tilts. These three parameters, in turn, determine how much sunlight different parts of the Earth receive. And this affects glacial cycles and long-term climate patterns.
“The closer it gets to the Sun, the more a planet dominates the Sun’s gravity. Because Mars is farther from the Sun, its gravitational influence on Earth is greater than it would have been if it had been closer to Earth. It holds up more than its own weight,” Kane said.
Even more
One unexpected thing Ken discovered was how Mars’ mass affects the rate of change in Earth’s tilt. Our planet is currently tilted about 23.44°, an angle that changes slowly over time.
“As the mass of Mars increased in our simulations, the rate of change in Earth’s tilt decreased,” Kane said. “So increasing the mass of Mars has a kind of stabilizing effect on our tilt.”
The paper was published in Publications of the Astronomical Society of the Pacific. A far-reaching implication is that Kane’s simulations suggest that small exoplanets in other solar systems may also shape the climate of worlds where life might exist.
“When I look at other planetary systems and find an Earth-sized planet in the habitable zone, planets further in the system can have an impact on the climate of that Earth-like planet,” Kane said.
Finally, how might Earth have evolved differently without the Red Planet where it is?
“Without Mars, major climate cycles in Earth’s orbit would be missing,” Kane said. “What would humans and other animals look like if Mars did not exist?”
