Scientists say that Earth may not be engulfed by the expanding fiery sphere of the dying Sun, which has long been considered our planet’s ultimate fate. Don’t worry: this is not expected to happen for another 5 billion years, long after all life on Earth has disappeared.
The Expansion of the Sun
When the Sun burns through all the hydrogen in its core, it will pass through two enormous expansion phases: first becoming a red giant, and then, after exhausting its helium, transforming into an AGB star.
This violent death will cause some major changes here on Earth. As the Sun grows, increased gravitational forces will pull Earth toward it. For Earth and the Moon, this force creates tidal movements in our oceans. The energy of these tides, which dissipates on the ocean floor, slows Earth’s rotation and gradually pushes the Moon away from us.
A Contest Between Gravity and the Solar Wind
As the Sun expands and its scorching surface moves closer to Earth, powerful tidal waves will arise inside the star. As these waves dissipate, they will draw Earth into its doomed embrace. However, the growing Sun will also lose a great deal of its mass through stellar wind, which will push our planet farther away.
“The fate of Earth depends on a delicate balance between these two effects,” explained Mats Esselders, lead author of the study published in Astronomy & Astrophysics. “If tidal interactions dominate, Earth will be swallowed by the Sun. If solar mass loss dominates, Earth will escape into an orbit larger than the radius of its star,” said the astrophysicist from KU Leuven in Belgium in a statement. Until now, scientists had favored the first hypothesis.
New Simulations and the Future Fate of the Sun and Planets
However, astronomers’ calculations had been based on relatively simple descriptions of tidal dissipation in giant stars. Advances in modeling these tides over the past 15 years allowed the study’s authors to show that “dissipation is weaker than previously expected,” Stéphane Mathis, an astrophysicist at the CEA Paris-Saclay center in France, told AFP.
To estimate how much mass the Sun might lose, the team focused in particular on a nearby star called L2 Puppis, which is something like an “older cousin” of the Sun.
“A better understanding of tidal physics and the most advanced constraints we have on mass loss allow us to say that — based on the current state of knowledge — Earth may move away from the Sun, contrary to what had previously been predicted,” Mathis said.
According to the new modeling, Mars will also avoid being fatally swallowed by the Sun. But the two planets closest to the Sun, Mercury and Venus, will not be so lucky. They will be inexorably consumed by the expanding ball of fire.
After all this, the Sun will eventually become an extremely dense star known as a white dwarf. It will no longer be able to sustain thermonuclear reactions and will gradually dim and cool over time.
According to phys.org
