It is a common question whether Earth’s orbit, which appears stable, is changing over time. The distance between our planet and the Sun is fundamental to life, but the forces governing the solar system are not entirely static. While orbital changes are incredibly subtle on a human timescale, the physics of a changing star means our planet is not fixed in its current path.
The Direct Answer: Yes, But Why?
The answer to whether Earth is drifting away from the Sun is yes, primarily because of the Sun itself. The Sun continuously loses mass, and the strength of its gravitational pull depends directly on that mass. As the Sun’s mass decreases, its gravitational influence on Earth weakens, causing the planet’s orbit to expand slowly over time.
This mass loss occurs mainly through two processes inherent to the Sun’s life cycle. The first is nuclear fusion, where hydrogen atoms convert into helium in the core, transforming mass into the immense energy that radiates as sunlight. The second process is the solar wind, a constant stream of charged particles ejected into space from the Sun’s surface.
The mass lost as pure energy from fusion is greater than the mass lost as physical particles in the solar wind. Combined, the Sun sheds about 5.5 million tons of material every second. This continuous reduction in the Sun’s total mass mandates a gradual outward spiral for all orbiting planets, including Earth, to conserve angular momentum.
Measuring the Orbital Change
The current rate of Earth’s outward drift is small, requiring precise measurements to detect. Calculations based on the Sun’s current mass loss rate indicate that Earth moves away by approximately 1.5 centimeters (six inches) every year. This change is so minute that it is negligible in any practical sense for human life.
To put this into perspective, the annual change is less than the length a human fingernail grows in a year. While the effect is unambiguous and calculable, it is undetectable without specialized astronomical methods. Even over a billion years, the change in distance due to solar mass loss is only a few times Earth’s own diameter.
Other Forces Influencing Earth’s Orbit
Solar mass loss is the dominant factor driving the current outward drift, but other physical forces also subtly influence the Earth-Sun distance. One factor is tidal acceleration, which involves the gravitational interaction between two orbiting bodies that raises a tidal bulge. Earth’s mass creates a tiny tidal bulge on the Sun, and the gravitational tug of this bulge causes a slight acceleration that marginally contributes to the outward drift.
The effect of solar tides on Earth’s orbit is small, causing an outward change of less than one-thousandth of a centimeter per year. This mechanism is more pronounced in the Earth-Moon system, where the Moon is moving away from Earth at a faster rate of about 3.8 centimeters annually.
General Relativity, Einstein’s theory of gravity, also plays a minor role in orbital dynamics. The theory describes gravity as the curvature of spacetime caused by mass and energy. While Newtonian physics is sufficient for most solar system calculations, General Relativity introduces subtle corrections that cause a planet’s elliptical orbit to slowly rotate, or precess. The overall impact of this effect on Earth’s current average distance from the Sun is insignificant compared to the mass loss effect.
The Ultimate Fate of Earth’s Orbit
The gentle drift Earth currently experiences will become a dramatic exodus billions of years in the future, dictated by the Sun’s stellar evolution. Approximately five billion years from now, the Sun will exhaust the hydrogen fuel in its core and begin its transition into a Red Giant star. This event will trigger an accelerated phase of mass loss, causing Earth’s orbit to expand more rapidly.
During the Red Giant phase, the Sun’s outer layers will swell dramatically, potentially reaching Earth’s current orbit (one astronomical unit, or 1 AU). As the Sun expands and sheds mass, Earth’s orbit will simultaneously widen. Current models suggest it is a close race whether Earth will be engulfed by the Sun’s enlarged atmosphere or if its outward-spiraling orbit will be enough to escape.
Even if Earth is not consumed by the Red Giant, the intense heat and radiation will have boiled away the oceans and stripped the planet of its atmosphere, making it uninhabitable. After this phase, the Sun will shed its outer layers entirely, leaving behind a dense, cooling core known as a white dwarf. If Earth survives, it would orbit this stellar remnant at a significantly greater distance than its current path.