The sun moves across the sky in such a predictable way that you might never guess that its relationship with the earth is constantly changing. In fact, the average distance between the Earth and the Sun is not static year after year. So we know if Earth are you getting closer or farther away from the sun? And what forces are at work on our planet and our star to make this possible?
In short, the Sun moves farther and farther 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 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 range 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 distance between the Earth and the Sun slowly increases over time. This growing distance has two main causes. One of them is that the sun is losing mass. The other involves the same forces that cause tides on earth.
Related: When does the sun explode?
The sun is shrinking
That nuclear fusion Reactions that power the sun convert mass to energy according to Einstein’s famous equation E = mc^2. Since the sun is constantly producing energy, it is also constantly losing mass. Over the remaining life of the Sun – estimated at another 5 billion years or so – according to NASA (opens in new tab) – Models of how stars evolve over time predict 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% may not sound like a lot, “that’s a lot of mass,” DiGiorgio said. “It’s about the same mass as Jupiter.” Jupiter, on the other hand, has about 318 times the mass of Earth, according to the study exploratory (opens in new tab) in California.
The strength of an object’s gravitational pull is proportional to its mass. As the Sun loses mass, its gravitational pull on Earth weakens, causing our planet to drift away from our star at about 6 centimeters per year, DiGiorgio said. But let’s not throw the sun a bon voyage party just yet.
“That’s pretty negligible, especially compared to the normal variation in Earth’s orbit that occurs because of its slightly elliptical orbit — about 3%,” DiGiorgio said.
The Effects of the Tides
Just like them moonThe gravitational pull of leads to tides on Earth, as does Earth’s heaviness draw in the sun. This stretches the Earth-facing side of the Sun, 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 new tab) Side.
The sun rotates on its axis about once every 27 days, according to NASA (opens in new tab). Because this is faster than the approximately 365 days it takes for Earth to orbit the Sun, the tidal bulge that Earth creates on the Sun is in front of Earth. The mass of the bulge has an associated gravitational force that pulls the Earth forward in its orbit, throwing it farther away from the Sun, Scharringhausen noted. (A similar effect is leading Earth’s moon is slowly drifting away from our planet (opens in new tab).)
However, these tidal forces have very little effect on Earth’s orbit: they cause the Earth to move about 0.0001 inches (0.0003 cm) away from the Sun each year, DiGiorgio calculated.
Any major climate changes?
Could Earth’s growing distance from the Sun affect Earth’s climate?
“As the Earth moves away from the Sun, the light from the Sun gets weaker,” DiGiorgio 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% reduction in the amount of solar energy hitting the Earth’s surface,” he said. “That’s relatively small compared to the normal fluctuations in the Sun’s brightness that occur due to Earth’s elliptical orbit, so it’s not a cause for concern.”
Related: What is the maximum number of planets that could orbit the sun?
The bigger thing to worry about “is that the Sun’s evolution over the next 5 billion years is predicted by stellar evolution models to increase in brightness by about 6% every 1 billion years, making Earth’s slowly increasing temperatures and the boiling off of the oceans,” DiGiorgio said. “This will render the Earth uninhabitable for humans long before the sun possibly 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 affect Earth’s orbit, knocking it closer or farther from the Sun? Or could another rogue body pass close enough to the solar system to produce 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’re chaotic, which means they’re impossible to predict with certainty,” DiGiorgio said. “We have no idea where the planets will be on timescales beyond about 100 million years because the tiny 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 what the probability is that an event will occur,” DiGiorgio said. This is similar to how forecast weather models work, he noted.
A 2009 study in the journal Nature (opens in new tab) who have done about 2,500 simulations of the solar system found that about 1% of them mercuryThe orbit of became unstable, causing it to crash into either the Sun or into the Sun Venus. “So it’s theoretically possible for Mercury to pass Earth and change its orbit significantly, as Mars did in a simulation,” DiGiorgio said. “However, this is very unlikely, as indicated by the rarity in their simulations.”
It’s also very unlikely that a passing star, planet, or other body could disrupt Earth’s orbit, DiGiorgio said. “My calculations on the back of the cover say that we should only expect a star to come closer than orbiting Pluto every trillion years or so,” DiGiorgio said. “Any comets already in our solar system will also not have enough mass or energy to significantly affect our orbit.”
The death of the sun
In about 5 billion years, after the sun runs out of hydrogen fuel, it will expand and become a red giant star. Assuming the Earth continues on its course uninterrupted, will it have moved far enough from the dying Sun to survive our star’s death throes?
There’s 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 can survive and continue orbiting. However, most estimates suggest that the sun will grow enough to swallow the Earth, causing the planet to spiral “inward toward oblivion,” DiGiorgio said.
“But even if Earth survives, there’s no chance humans can survive on it,” DiGiorgio said. “The heat and radiation the invading sun would not only boil the oceans and atmosphere, but likely the Earth itself as well. Humans would have to leave the flaming ball of lava long before it was even swallowed.”
If humans were still alive about 5 billion years from now and wanted the Earth to remain habitable while the Sun was expanding, we would have to slowly move the planet outward to about the orbit of Saturnto keep it tempered for life as we know it as the sun released more and more energy.
“It’s pretty impractical, though,” DiGiorgio said. “The simpler solution would be to just leave Earth and find another planet or solar system to live on.”
Originally published on Live Science.
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