New research indicates Earth could escape engulfment by the Sun
A recent study using updated tidal models and stellar-mass-loss data suggests Earth may drift outward and avoid being swallowed when the Sun expands into a red giant and later an asymptotic giant branch star.
A study published in Astronomy & Astrophysics challenges the long-standing view that Earth will be engulfed by the Sun as it expands in about five billion years. The research, led by astrophysicist Mats Esseldeurs of the University of Leuven, finds that a balance between tidal forces pulling the planet inward and the Sun’s loss of mass could allow Earth’s orbit to move outward beyond the star’s expanded radius.
The Sun is expected to exhaust hydrogen in its core and first swell into a red giant, then later become an even larger asymptotic giant branch (AGB) star. During this evolution, two opposing effects influence Earth’s trajectory. Tidal interactions, driven by dynamical tides within the Sun, can dissipate energy and draw the planet closer. Conversely, the Sun will shed material through stellar winds, reducing its gravitational pull and permitting the Earth’s orbit to expand.
"Earth’s fate depends on a delicate balance between these two effects," Esseldeurs said. "If tidal interactions predominate, Earth is engulfed by the Sun. If the Sun’s mass loss predominates, Earth escapes into an orbit larger than the radius of its star."
Previous models favored engulfment, but they relied on simplified descriptions of tidal dissipation in giant stars. Over the past decade, more sophisticated tidal models have shown that energy loss inside such stars is lower than earlier estimates. Astrophysicist Stéphane Mathis of CEA Paris-Saclay explained that this revised understanding, combined with observations of the nearby star L2 Puppis—a star considered a close analog of the Sun’s future—supports the possibility of orbital expansion.
"The dissipation is lower than previously expected," Mathis told AFP. "A better understanding of tidal physics and the most advanced constraints we have on mass loss allow us to say that, in the current state of knowledge, Earth could move away from the Sun, contrary to what was predicted before."
The study also suggests that Mars may experience a similar outward drift, while Mercury and Venus are still likely to be consumed by the Sun’s expansion. Ultimately, the Sun will shed its outer layers and settle as a white dwarf, cooling over billions of years. The authors note that any changes to Earth’s orbit would occur long after the Sun’s increasing brightness makes the planet uninhabitable.
