The sun moves so predictably across the sky that you may never suspect its relationship to Earth is changing all the time. In fact, the average distance between the Earth and the sun is not static from year to year. So do we know if Earth move closer or further from the sun? And what forces act on our planet and our star to make this happen?
In short, the Sun moves away from Earth over time. On average, the Earth is about 93 million miles (150 million kilometers) from the sun, according to NASA (opens in a new tab). However, its orbit is not perfectly circular; it is slightly elliptical or oval. This means that the distance between the Earth and the sun can vary from approximately 91.4 million to 94.5 million miles (147.1 million to 152.1 million km), Nasa (opens in a new tab) said.
Yet, on average, the expanse between the Earth and the sun increases slowly over time. This growing estrangement has two main causes. The first is that the sun loses mass. The other involves the same forces that cause tides on earth.
Related: When will the sun explode?
The sun is shrinking
The nuclear fusion the reactions that power the sun convert mass into energy, according to Einstein’s famous equation E = mc^2. Because the sun is constantly producing energy, it is also steadily losing mass. Over the remaining lifetime of the sun – estimated to be around 5 billion more years, according to NASA (opens in a new tab) – models of star evolution over time predict that the sun will lose about 0.1% of its total mass before it begins to die, Brian DiGiorgio, an astronomer at the University of California, Santa Cruz, told Live Science in an email.
While 0.1% might not seem like a lot, “that’s a lot of mass,” DiGiorgio said. “It’s about the same amount of mass as Jupiter.” Jupiter, in turn, is about 318 times the mass of Earth, according to the Exploratory (opens in a new tab) in California.
The force of gravitational attraction of an object is proportional to its mass. Because the sun loses mass, its pull on Earth weakens, causing our planet to move away from our star about 2.36 inches (6 centimeters) per year, DiGiorgio said. But we shouldn’t be having a bon voyage in the sun party just yet.
“That’s pretty negligible, especially compared to the normal variation in Earth’s orbital distance that occurs due to its slightly elliptical orbit — about 3%,” DiGiorgio said.
The effects of the tides
Just like the moonEarth’s gravitational pull drives tides on Earth, just like Earth’s gravity shoot the sun. This stretches the side of the sun that faces Earth, resulting in a “tidal bulge”, wrote Britt Scharringhausen, associate professor of physics and astronomy at Beloit College in Wisconsin, for Cornell University. Ask an astronomer (opens in a new tab) page.
The sun rotates on its axis approximately once every 27 days, according to NASA (opens in a new tab). Because this is faster than the roughly 365 days it takes Earth to complete one orbit around the sun, the tidal bulge that Earth generates on the sun is in front of Earth. The bulge’s mass is associated with gravitational pull, pulling Earth forward in its orbit and away from the sun, Scharringhausen noted. (A similar effect leads Earth’s moon will slowly move away from our planet (opens in a new tab).)
However, these tidal forces have a very small effect on Earth’s orbit: they cause the Earth to move about 0.0001 inch (0.0003 cm) away from the sun each year, DiGiorgio calculated.
Major climate change?
Could the increasing distance between the Earth and the sun influence the Earth’s climate?
“As the Earth moves away from the sun, the sunlight will become weaker,” DiGiorgio said. Given that the distance between the Earth and the sun could increase by 0.2% over the next 5 billion years, “this attenuation corresponds to a 0.4% reduction in the solar energy striking the surface of the Earth,” he said. “That’s relatively small compared to normal variations in the sun’s brightness that occur due to Earth’s elliptical orbit, so there’s no need to worry.”
The biggest thing to worry about” is that as the sun evolves over the next 5 billion years, stellar evolution models predict that its brightness will increase by about 6% every 1 billion. years, slowly increasing the brightness of the Earth. temperatures and boiling oceans,” DiGiorgio said. “It will make Earth uninhabitable for humans long before the sun potentially swallows it.”
Recent work suggests the orbits of Jupiter and other planets in the solar system have changed over time. So, could their orbits become unstable enough to one day influence the Earth’s orbit, throwing it closer or farther from the sun? Or could another rogue body pass close enough to the solar system to have a similar effect?
“The problem with trying to predict the gravitational interactions of many-body systems like the solar system or nearby stars is that they are chaotic, which means they are impossible to predict with certainty,” DiGiorgio said. “We have no idea where, specifically, the planets will be on timescales beyond about 100 million years, because the tiny measurement errors and perturbations from unmodeled interactions become too large. with time.”
Still, “we can use this chaos to our advantage by running many simulations of the same chaotic system to see how likely an event is to occur,” DiGiorgio said. This is similar to how predictive weather models work, he noted.
A 2009 study in the journal Nature (opens in a new tab) who performed about 2,500 simulations of the solar system found that in about 1% of them, MercuryThe orbit of became unstable, causing it to crash into either the sun or Venus. “So it’s theoretically possible for Mercury to move close to Earth and change its orbit significantly, like it did to Mars in a simulation,” DiGiorgio said. “It’s highly unlikely, however, as evidenced by its rarity in their simulations.”
It’s also highly unlikely that a passing star, planet or other body could disrupt Earth’s orbit, DiGiorgio said. “My bottom-of-the-envelope calculations say that we should only expect a star to approach Pluto’s orbit about once every trillion years,” DiGiorgio said. “Any comets nor will it already in our solar system have enough mass or energy to substantially affect our orbit.”
The death of the sun
In about 5 billion years, after the sun runs out of hydrogen, it will begin to swell, becoming a red giant star. Assuming the Earth continues its course uninterrupted, will it have moved far enough from the dying sun to survive the agony of our star?
There’s currently some disagreement about how much the sun swells during its red giant phase, DiGiorgio said. There’s a chance it won’t blow enough to reach Earth, which means our planet can survive and keep orbiting. However, most estimates suggest the sun will grow big enough to swallow Earth, leading the planet to spiral “inward into oblivion,” DiGiorgio said.
“However, even if Earth survives, there’s no way humans could survive on it,” DiGiorgio said. “The heat and radiation invading sunlight would not only boil the oceans and atmosphere, but it would likely boil the Earth itself. Humans should leave the flaming lava ball long before it is swallowed.”
If humans are still 5 billion years away and want Earth to remain habitable while the sun expands, we should slowly move the planet outward around the orbit of Saturnkeeping it temperate enough for life as we know it as the sun continued to produce more and more energy.
“It’s not practical, though,” DiGiorgio said. “The easiest solution would be to simply abandon Earth and find another planet or solar system to live in.”
Originally posted on Live Science.