The sun moves across the sky in such a predictable way that you might never suspect that its relationship to the earth is constantly changing. In fact, the average distance between the Earth and the Sun is not static from year to year. Then we’ll know Earth coming closer or further from the sun? And what forces act on our planet and our star to make this happen?
In short sun becomes further away from Earth over time. On average, 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 in shape. This means that Earth’s distance from 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) says.
Nevertheless, on average, the distance between the Earth and the Sun increases slowly over time. This increasing distance has two main reasons. One is that the sun is losing mass. The second involves the same forces as cause tides On earth.
Related: When will the sun explode?
The sun shrinks
The nuclear fusion reactions that drive 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. During the Sun’s remaining lifetime – estimated to be another 5 billion years or so, according to NASA (opens in a new tab) “Models of how stars evolve 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. -mail.
While 0.1% might not sound like a lot, “this is a lot of mass,” DiGiorgio said. “It’s about as much mass as Jupiter.” Jupiter, on the other hand, is about 318 times the mass of Earth, according to Exploratorium (opens in a 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 drift away from our star by about 2.36 inches (6 centimeters) per year, DiGiorgio said. But we shouldn’t give the sun a bon voyage party just yet.
“This is 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 tides
Just like moonthe force of gravity results in tides on Earth, as does Earth’s gravity ride on 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’s 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 365 or so days it takes Earth to complete one orbit around the Sun, the tidal bulge Earth generates on the Sun is ahead of Earth. The bulge’s mass has a gravitational force associated with it, which pulls the Earth forward in its orbit and throws it farther from the Sun, Scharringhausen noted. (A similar effect is conductive Earth’s moon too slowly drifting away from our planet (opens in a new tab).)
However, these tidal forces have a very weak 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 changes in the climate?
Can the Earth’s increasing distance from the Sun affect the Earth’s climate?
“As the Earth moves away from the Sun, the Sun’s light will dim,” DiGiorgio said. Given that Earth’s distance from the Sun could grow by 0.2% over the next 5 billion years, “this dimming corresponds to a 0.4% reduction 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 the Earth’s elliptical orbit, so it’s not much to worry about.”
Related: What is the maximum number of planets that can orbit the sun?
The biggest thing to worry about” is that as the Sun evolves over the next 5 billion years, stellar evolution models predict that it will increase in brightness by about 6% every 1 billion years, slowly increasing Earth’s temperatures and boils the oceans,” DiGiorgio said. “This will make Earth uninhabitable for humans long before the sun ever potentially engulfs it.”
Recent work suggests the orbits of Jupiter and other planets i the solar system has changed over time. So could their orbits grow unstable enough to one day affect Earth’s orbit, throwing it closer or further 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, meaning they are impossible to predict with any certainty,” DiGiorgio said. “We have no idea where, specifically, the planets will be on time scales longer than about 100 million years because the small errors in measurement 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 what the probability is for an event to occur,” DiGiorgio said. This is similar to how predictive weather models work, he noted.
A study from 2009 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, Mercuryits orbit became unstable, causing it to crash into either the Sun or Venus. “So it’s theoretically possible for Mercury to move along Earth and change its orbit significantly, as it did to Mars in a simulation,” DiGiorgio said. “However, this is highly unlikely, given 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 back-of-the-envelope calculations say that we should only expect a star to come closer than Pluto’s orbit about once every trillion years,” DiGiorgio said. “Some comets already in our solar system will not have enough mass or energy to significantly affect our orbit either.”
The death of the sun
In about 5 billion years, after the Sun has used up its hydrogen fuel, it will begin to swell and become a red giant star. Assuming the Earth continues unabated on its course, will it have grown far enough away from the dying Sun to survive the star’s death throes?
There is currently some disagreement about how much the Sun will swell during its red giant phase, DiGiorgio said. There’s a chance it won’t blow out enough to reach Earth, meaning our planet could survive and continue orbiting. However, most estimates suggest the Sun will grow enough to swallow Earth, causing the planet to spiral “inward toward oblivion,” DiGiorgio said.
“But even if Earth survives, there’s no chance humans would be able to survive with it,” DiGiorgio said. “The heat and radiation from the encroaching sun would not only boil the oceans and atmosphere, but it would probably boil the earth itself. Humans had to leave the flaming ball of lava long before it was swallowed.”
If humans are still around 5 billion years from now and wanted Earth to remain habitable during the Sun’s expansion, we would have to slowly move the planet outward to around the orbit of Saturnkeeping it temperate enough for life as we know it, as the sun continued to produce more and more energy.
“However, this is quite impractical,” DiGiorgio said. “The easier solution would be to just leave Earth and find another planet or solar system to live in.”
Originally published on Live Science.