The Sun moves in such a predictable way across the sky that you might never suspect that its relationship to Earth is changing all the time. In fact, the average distance between the Earth and the sun is not static over the years. Do we know if The Earth is it moving closer or further away from the sun? And what forces act on our planet and our star to make this happen?
In short, on sun moves away from Earth with time. On average, Earth is about 93 million miles (150 million kilometers) from the sun, according to NASA (opens in new tab). However, its orbit is not perfectly circular; it has a slightly elliptical or oval shape. This means that Earth’s distance from the sun can vary from about 91.4 million to 94.5 million miles (147.1 million to 152.1 million km), NASA (opens in new tab) says.
However, on average, the space between the Earth and the sun slowly increases over time. This increasing distance has two main reasons. One is that the sun is losing mass. The other involves the same forces cause ebb and flow on the ground.
Connected: When will the sun break out?
The sun is shrinking
The nuclear fusion the reactions that power the sun convert mass into energy, following Einstein’s famous equation E = mc^2. As the sun is constantly producing energy, it is also constantly losing mass. Over the course of the sun’s remaining life – estimated to be about another 5 billion years, according to NASA (opens in new tab) — models of how stars evolve over time predict that the sun will lose about 0.1 percent 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% may not sound like much, “that’s a lot of mass,” DiGiorgio said. “That’s about the same amount of mass as JupiterJupiter, on the other hand, is about 318 times the mass of Earth, according to Exploratorium (opens in new tab) in California.
The strength of an object’s gravitational pull is proportional to how much mass it has. As the sun loses mass, its pull on Earth weakens, causing our planet to move away from our star by about 2.36 inches (6 centimeters) a year, DiGiorgio said. But we should not yet organize the sun for a good journey.
“This is quite insignificant, especially compared to the normal change in Earth’s orbital distance that occurs due to its slightly elliptical orbit – about 3%,” Di Giorgio said.
The effects of tides
Just like on moongravitational pull causes the Earth’s tides to ebb and flow, as does Earth’s gravity Pull the sun. This stretches the side of the sun that faces Earth, leading to a “tidal bulge,” writes Britt Scharringhausen, associate professor of physics and astronomy at Beloit College in Wisconsin, for Cornell University Ask an astronomer (opens in new tab) page.
The sun rotates on its axis approximately once every 27 days, according to NASA (opens in new tab). Because this is faster than the approximately 365 days it takes Earth to complete one orbit around the sun, the tidal bulge that Earth generates on the sun is located in front of Earth. The mass of the bulge has a gravitational pull associated with it, pulling the Earth forward in its orbit and throwing it further away from the sun, Scharinghausen noted. (A similar effect is leading Earth’s moon is slowly moving away from our planet (opens in new tab).)
However, these tidal forces have very little effect on Earth’s orbit: They cause Earth to move about 0.0001 inch (0.0003 cm) away from the sun each year, DiGiorgio calculated.
Any major climate change?
Could Earth’s increasing distance from the sun affect Earth’s climate?
“As the Earth moves away from the sun, the sunlight will become weaker,” Di Giorgio said. Given that Earth’s distance from the sun could increase by 0.2% over the next 5 billion years, “this dimming corresponds to a 0.4% decrease in solar energy hitting the Earth’s surface,” he said. “This is relatively small compared to the normal variations in the sun’s brightness that occur due to Earth’s elliptical orbit, so it’s not much to worry about.”
The bigger 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 from the oceans,” said Di Giorgio. “This will make the Earth uninhabitable for humans long before the sun engulfs it.”
Recent work suggests the orbits of Jupiter and other planets in solar system have changed over time. Could their orbits become unstable enough to one day affect Earth’s orbit, throwing it closer to or farther from the sun? Or could some other 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, meaning they are impossible to predict with any certainty,” Di Giorgio said. “We have no idea exactly where the planets will be on time scales longer than about 100 million years, because small measurement errors and perturbations from unmodeled interactions become too large over 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 new tab) who performed about 2,500 simulations of the solar system found that in about 1% of them, mercurythe orbit of has become unstable, causing it to crash into either the sun or the Venus. “So it’s theoretically possible for Mercury to move past Earth and change its orbit significantly, as it did with Mars in one simulation,” Di Giorgio said. “However, this is highly unlikely, as evidenced by its rarity in their simulations.”
It’s also highly unlikely that a passing star, planet or other body will disrupt Earth’s orbit, DiGiorgio said. “My back-of-the-envelope calculations say that we should expect a star to come closer than Pluto’s orbit once every trillion years,” Di Giorgio said. “All kinds comets there will no longer be enough mass or energy in our solar system to significantly affect our orbit.”
The death of the sun
In about 5 billion years, after the sun has exhausted its hydrogen fuel, it will begin to expand, becoming a red giant star. Assuming the Earth continued on its course, would it have moved far enough from the dying sun to survive the death throes of our star?
There is currently some disagreement about how much the sun will bulge during its red giant phase, Di Giorgio said. There’s a chance it won’t inflate enough to reach Earth, meaning our planet could survive and continue orbiting. However, most estimates suggest that the sun will grow enough to engulf Earth, sending the planet spiraling “inward into oblivion,” Di Giorgio said.
“However, even if the Earth survives, there is no chance that humans will be able to survive with it,” Di Giorgio said. “The heat and radiation from the invading sun will not only boil the oceans and atmosphere, but probably boil the Earth itself. People will have to leave the burning ball of lava long before it’s even consumed.”
If humans are still around 5 billion years from now and want Earth to remain habitable during the Sun’s expansion, we’ll have to slowly move the planet outwards around the orbit of Saturnkeeping it moderate enough for life as we know it as the sun continued to radiate more and more energy.
“However, this is quite impractical,” said Di Giorgio. “The easier solution would be to just abandon Earth and find another planet or solar system to live on.”
Originally published on Live Science.