Why is the Earth moving further and further away from the Sun?

Each year, the Earth drifts away from the Sun by a few centimeters due to the loss of the Sun's mass and the forces acting on it.

Earth and Sun seen from space. Photo: Bernt Ove Moss/EyeEm

On average, Earth is about 150 million kilometers from the sun, according to NASA. However, the Earth's orbit is not completely circular but somewhat elliptical. This means that the distance between the Earth and the Sun could be between 147.1 - 152.1 million km. However, on average, the distance between the Earth and the Sun is increasing over time. The two main causes are the loss of mass of the Sun and the same forces that cause tides on Earth.

The fusion reactions that power the Sun convert mass into energy. As the Sun continuously produces energy, it also gradually loses mass. It is predicted that during the remaining lifetime of the Sun - an estimated 5 billion years - the star will lose about 0.1% of its total mass, said Brian DiGiorgio, an astronomer at the University of California, Santa Cruz, shared with Live Science on August 7.

0.1% doesn't sound like much, but it's actually very massive, about the same size as Jupiter, according to DiGiorgio. Jupiter has about 318 times the mass of Earth. The gravitational force of an object is proportional to the mass of that object. As the Sun decreases in mass, the gravitational pull on the Earth also weakens, causing the Earth to drift away about 6 cm per year.

Just as the Moon's gravity causes the tides on Earth, the Earth's gravity also affects the Sun. This stretches the part of the Sun facing the Earth, leading to a "tidal bulge," according to Britt Scharringhausen, an associate professor of physics and astronomy at Beloit University.

The Sun rotates on its axis about once every 27 days, faster than it takes for Earth to complete one orbit around the Sun (about 365 days), so the tidal bulge is in front of the Earth. The gravity of this bulge pulls the Earth forward and moves the Earth further away from the Sun. The same phenomenon is causing the Moon to gradually drift away from the Earth. However, these tidal forces have a very weak effect on Earth's orbit. They only move the Earth away from the Sun by about 0.0003 centimeters per year, DiGiorgio estimates.

"As the Earth moves away from the Sun, sunlight will become dimmer. The Earth-Sun distance could increase by 0.2% in the next 5 billion years, corresponding to the amount of solar energy reaching the Sun. Earth's surface decreases by 0.4%. This is relatively small compared to normal fluctuations in the Sun's luminosity caused by Earth's elliptical orbit. So there's nothing to worry about." DiGiorgio said.

Illustration of the Sun and planets in the solar system. Photo: ChrisGorgio

What's more concerning is that over the next 5 billion years, the Sun is predicted to increase in luminosity by about 6% every one billion years, causing the Earth's temperature to gradually increase and boil the oceans. "This will make it impossible for humans to live on Earth, before the prospect of the Sun swallowing the Earth can happen," he said.

Specifically, in about 5 billion years, after exhausting hydrogen fuel, the Sun will begin to swell, becoming a red giant. Scientists currently have some disagreement about how much the Sun expands. It's unlikely that the Sun will bulge large enough to reach Earth, but most estimates suggest that the star could swallow the blue planet.

"However, even if the Earth existed, humans would not be able to live on it. The heat and radiation from the Sun not only boils the oceans and atmosphere, but can also boil the Earth itself. ", DiGiorgio explained.

If people still want to live on Earth when the Sun expands, humans will have to gradually move the blue planet outward, to about the orbit of Saturn, helping the Earth maintain temperate conditions suitable for life. "However, this is quite unrealistic. The simpler solution is to leave Earth and find another planet or star system to live," DiGiorgio said.