Is the Sun Getting Closer to the Earth?

Earth is not moving closer to the Sun. The opposite is happening: our planet’s orbit is slowly expanding, pushing us a tiny bit farther from the Sun each year. The primary reason is that the Sun is constantly losing mass, and a lighter Sun exerts a slightly weaker gravitational pull. The drift is so small you would never notice it in a human lifetime, or even across all of recorded history, but it is real and measurable. The more interesting question, and the one that actually matters for life on Earth, is what the Sun is doing with its brightness.

Why Earth Is Drifting Away

The Sun powers itself by fusing hydrogen into helium deep in its core, and that process converts a small fraction of matter into energy. That energy radiates outward as sunlight. The Sun also sheds material directly through the solar wind, a stream of charged particles flowing outward in all directions. Together, these two processes mean the Sun is getting lighter over time. The rate of mass loss works out to roughly 9.13 × 10⁻¹⁴ solar masses per year, a number so small it barely registers on a cosmic scale, but it has real orbital consequences.¹

Gravity depends on mass. When the Sun loses mass, its gravitational grip on the planets weakens slightly, and every planet responds by spiraling outward just a touch. Earth’s orbit expands at the same fractional rate as the Sun’s mass loss, and Earth’s orbital period lengthens at twice that rate. In practical terms, the Earth-Sun distance grows by roughly 1.5 centimeters per year. Over a million years, that adds up to about 15 kilometers, which sounds like a lot until you remember the current average distance is about 150 million kilometers. The change is vanishingly small relative to the orbit itself.

Could Gravity Itself Be Changing?

Some readers encounter the claim that the gravitational constant, the fundamental number that sets the strength of gravity everywhere in the universe, might be slowly changing over time. If gravity were weakening, that would also push planets outward. Physicists have tested this idea for decades, and the constraints have gotten tighter and tighter. Early estimates from before the 1980s suggested a possible drift on the order of 10⁻¹¹ to 10⁻¹⁰ per year, but modern measurements have pushed the upper limit down dramatically. Recent work using lunar laser ranging and planetary ephemeris data puts any possible variation at the level of 10⁻¹⁴ to 10⁻¹³ per year, which is essentially zero for practical purposes.²

An independent approach uses transiting exoplanets observed by the Kepler spacecraft as precision clocks. If gravity’s strength were drifting, the orbital periods of planets around other stars would shift in a detectable way. Analysis of ten transiting systems observed between 2009 and 2013 found no measurable change, constraining any variation to less than about one part in a million per year.³ The bottom line is that gravity appears to be holding steady. The outward drift of Earth’s orbit is driven by the Sun’s mass loss, not by any weakening of gravity itself.

What About Seasonal Changes in Distance?

Earth’s orbit is not a perfect circle; it is slightly elliptical. That means the Earth-Sun distance varies over the course of each year by about 5 million kilometers. Earth reaches its closest point to the Sun (perihelion) around January 3 and its farthest point (aphelion) around July 4. If you live in the Northern Hemisphere, this can feel counterintuitive: you are closest to the Sun in the dead of winter.

This annual wobble has nothing to do with the long-term drift we have been discussing. The elliptical shape of the orbit is a feature of how Earth moves under gravity, and the seasonal difference in distance is thousands of times larger than the centimeter-per-year outward drift caused by solar mass loss. The two effects operate on completely different timescales. The seasonal distance change affects how much solar energy Earth receives at different times of year by about 7%, though Earth’s axial tilt is what actually drives the seasons, not the distance variation.

Over much longer timescales, the shape of Earth’s orbit does change. Gravitational tugging from Jupiter and Saturn stretches and squashes Earth’s orbital ellipse on cycles of roughly 100,000 and 400,000 years. These eccentricity cycles play a role in ice ages by modulating how much the perihelion-to-aphelion distance swing matters for climate. But even these oscillations do not change the average Earth-Sun distance in a permanent way. They change the shape of the orbit, not its average size.

The Sun Is Getting Brighter, Not Closer

Here is the part that actually matters for Earth’s future. While the Sun is losing mass and Earth is drifting slightly outward, the Sun is simultaneously getting more luminous. As it fuses hydrogen in its core, the core gradually contracts and heats up, which makes nuclear reactions run faster. The result is that the Sun’s energy output increases by roughly 10% for every billion years that passes.⁴

This brightening effect overwhelms the outward orbital drift by a huge margin. Moving 15 kilometers farther from the Sun over a million years barely changes the solar energy hitting Earth. But a 1% increase in the Sun’s luminosity over 100 million years means measurably more energy arriving at Earth’s surface, regardless of the slight increase in distance. Over billions of years, this is a serious issue. About a billion years from now, the Sun will be bright enough to start boiling away Earth’s oceans, making the planet uninhabitable even though Earth will technically be a bit farther from the Sun than it is today.

So the common worry has the physics backwards. The threat is not that the Sun is creeping closer. The threat, on a geological timescale, is that the Sun is turning up its brightness dial while Earth inches away too slowly for the extra distance to help.

The Faint Young Sun Paradox

If the Sun has been getting brighter over time, then billions of years ago it was significantly dimmer than it is today. About 4 billion years ago, the Sun was roughly 30% fainter than now. That should have left the early Earth frozen solid, a snowball with no liquid water. And yet geological evidence clearly shows that liquid water existed on Earth’s surface very early in its history, and life was already thriving by at least 3.5 billion years ago. This contradiction is called the faint young Sun paradox, and it has puzzled scientists since Carl Sagan and George Mullen first pointed it out in the early 1970s.

The leading explanation is that Earth’s early atmosphere contained much higher concentrations of greenhouse gases, particularly carbon dioxide. Modeling work has shown that a CO₂-rich greenhouse could have efficiently counterbalanced the weaker sunlight before about 3 billion years ago, keeping temperatures warm enough for liquid water.⁵ Methane may have contributed as well, especially before the rise of atmospheric oxygen. The paradox is not fully resolved to everyone’s satisfaction, and some researchers argue additional factors like different cloud properties or a slightly more massive young Sun may have played a role, but the high-CO₂ explanation is the most widely supported.

The faint young Sun paradox underscores an important point: the relationship between the Sun’s output and Earth’s surface temperature is not simple. Atmospheric composition, cloud cover, ice reflectivity, and ocean circulation all act as intermediaries. A small change in solar distance or brightness can be amplified or dampened depending on what the atmosphere and surface are doing. This is why the centimeter-per-year orbital drift is genuinely unimportant for climate, while changes in atmospheric greenhouse gases are enormously important.

Other Forces Nudging Earth’s Orbit

Solar mass loss is the main reason Earth’s orbit is expanding, but it is not the only force acting on the orbit. Solar radiation pressure, the physical push that sunlight exerts on anything it hits, is a real force. Photons carry momentum, and when sunlight strikes Earth, it imparts a tiny outward push. This pressure depends on the Sun’s luminosity, the distance from the Sun, and the ratio of an object’s surface area to its mass.⁶

For a planet as massive as Earth, radiation pressure is negligible. It matters much more for small, low-mass objects like dust grains, spacecraft, and the particles that make up planetary rings. Radiation pressure from the Sun can destabilize rings around distant bodies by exciting the eccentricity of ring particle orbits, which is relevant for understanding rings around objects in the outer solar system.⁷ For Earth, though, the effect is so tiny compared to gravity that it can be safely ignored when thinking about our orbit’s evolution.

Gravitational perturbations from the other planets are a more meaningful influence. Jupiter’s gravity, in particular, continuously tugs on Earth’s orbit, altering its eccentricity and the orientation of its orbital plane over tens of thousands of years. These perturbations are the main driver of the Milankovitch cycles that pace ice ages. But again, they change the shape and orientation of the orbit, not its average radius. The overall trend of slow outward expansion is driven by the Sun’s mass loss.

How Scientists Measure Such Tiny Changes

You might wonder how anyone can detect a drift of 1.5 centimeters per year across a distance of 150 million kilometers. The answer comes from multiple converging methods. Planetary radar ranging, where radio signals are bounced off planets and the travel time measured with extraordinary precision, has been used since the 1960s. Spacecraft tracking is even more precise: when a probe orbits another planet, the Doppler shift of its radio signal reveals the distance between Earth and that planet to an accuracy of meters or better. These measurements over decades allow astronomers to build detailed models of the solar system’s geometry, called planetary ephemerides, that track how the orbits are evolving.

Lunar laser ranging, where laser pulses are bounced off reflectors left on the Moon by Apollo astronauts, provides another independent check. While this primarily measures the Earth-Moon distance (which is increasing at about 3.8 centimeters per year as tidal forces transfer energy from Earth’s rotation to the Moon’s orbit), the same data can constrain changes in the gravitational constant and in Earth’s orbital parameters. The precision of these measurements is what allowed researchers to push the limits on gravitational constant variation down to the 10⁻¹⁴ per year level mentioned earlier.²

Ancient geological records provide a completely different window into orbital history. Tidal rhythmites, layered sedimentary deposits that record the daily and monthly tidal cycles, preserve information about Earth’s rotation rate and the Moon’s distance at the time of deposition. Analysis of 1.4-billion-year-old rhythmites has indicated that the Earth-Moon distance was around 340,900 kilometers at that time, compared to today’s average of about 384,400 kilometers, and that a day was only about 18.68 hours long.⁸ While this tells us about the Earth-Moon system rather than the Earth-Sun distance directly, it demonstrates that orbital dynamics leave physical fingerprints in the rock record that can be read billions of years later.

Why the Misconception Persists

The idea that the Sun might be getting closer to Earth pops up regularly online, often tied to anxieties about climate change. The logic seems intuitive: if the planet is warming, maybe the Sun is moving closer or getting stronger. But the warming Earth is experiencing today is happening on a timescale of decades, not billions of years. The Sun’s luminosity increase is about 10% per billion years, which works out to a rate so slow it is irrelevant on any human timescale. And the slight outward drift of Earth’s orbit is similarly inconsequential.

Modern climate change is driven by the rapid increase in atmospheric greenhouse gases from burning fossil fuels, not by any change in Earth’s distance from the Sun or the Sun’s brightness. Solar output does vary slightly over the roughly 11-year sunspot cycle, but the amplitude of that variation is about 0.1%, far too small to explain the warming trend observed since the mid-20th century. The faint young Sun paradox actually makes this point elegantly: Earth’s temperature has always depended more on what is in the atmosphere than on how bright the Sun is.

Another source of confusion is the occasional viral headline claiming that Earth’s orbit is “decaying” or that we will spiral into the Sun. In reality, orbital decay through gravitational wave emission, the process that causes extremely close binary star systems to spiral together, is laughably weak for Earth. The gravitational wave energy radiated by the Earth-Sun system is about 200 watts, roughly enough to power two light bulbs. At that rate, it would take far longer than the age of the universe for the orbit to shrink appreciably, and the Sun’s mass loss pushes us outward far faster than gravitational radiation pulls us in.

What Happens on Really Long Timescales

If you zoom out far enough, Earth’s relationship with the Sun does change dramatically, but not because we are falling inward. In about 5 billion years, the Sun will exhaust the hydrogen in its core and begin expanding into a red giant. Its outer layers will swell enormously, potentially reaching the current orbit of Mars. Whether Earth is consumed or not depends on how much the Sun’s mass loss accelerates during this phase and how far outward that pushes our orbit. Some models suggest Earth will barely escape engulfment; others suggest it will not.

Before that happens, the brightening Sun will have long since made Earth uninhabitable. As the Sun’s luminosity increases, the inner edge of the habitable zone, the range of distances where liquid water can exist on a planet’s surface, moves outward. In roughly a billion years, Earth will fall inside that edge, and the runaway greenhouse effect will turn our planet into something resembling Venus. Researchers have even calculated the rate at which Earth’s orbit would need to expand to keep pace with the brightening Sun and maintain current temperatures, a thought experiment sometimes called the “Earth rocket” scenario.⁴ The required expansion rate is vastly larger than the natural drift caused by solar mass loss, which is another way of saying nature will not solve this problem for us.

The irony is worth sitting with. Earth is moving away from the Sun, just not fast enough. The slow outward drift caused by the Sun’s mass loss is a real physical effect, confirmed by precise measurements, but it is dwarfed by the Sun’s increasing brightness. On every timescale that matters for life, the problem is not distance. It is energy.

1
arXiv. Solar Mass Loss, the Astronomical Unit, and the Scale of the Solar System
2
Monthly Notices of the Royal Astronomical Society. Influence of the time variation of the gravitational constant on the orbital elements of planets
3
Publications of the Astronomical Society of Japan. Transiting planets as a precision clock to constrain the time variation of the gravitational constant
4
arXiv. The ‘Earth Rocket’: a Method for Keeping the Earth in the Habitable Zone
5
PubMed Central. A CO2 greenhouse efficiently warmed the early Earth and decreased seawater 18O/16O before the onset of plate tectonics
6
Monthly Notices of the Royal Astronomical Society. On orbital disturbing effects of the solar radiation
7
Astronomy & Astrophysics. Celestial sunflowers
8
PubMed Central. Proterozoic Milankovitch cycles and the history of the solar system