If the Sun vanished, Earth’s surface would freeze within days to weeks, oceans would seal under thick ice within years to centuries, and the atmosphere would begin to collapse as gases liquefied and froze. The deep ocean and crust would stay warm much longer from internal heat, with liquid water persisting near hydrothermal vents for millions of years. Earth would never reach absolute zero; instead it would asymptotically cool toward a temperature set by its small internal heat flow, then continue cooling over billions of years as that heat dwindles.
What happens immediately if the Sun disappears?
We would see and feel no change for about 8 minutes, the time sunlight needs to reach Earth. After that, daylight and direct solar heating stop everywhere at once.
Sunlight takes about 8 minutes 20 seconds to reach Earth (Cornell Ask an Astronomer).
If the Sun’s gravity also disappeared, Earth would coast along a straight-line path through space, but this would not meaningfully change how fast the planet loses heat. Space already presents an effectively 3 kelvin background, so Earth cools by radiation much as it does on its night side.
How fast would Earth’s surface and atmosphere cool?
Cooling begins immediately once solar input stops. Land areas with dry, clear skies lose heat fastest; humid or cloudy regions cool more slowly. Global-average cooling is buffered by the oceans’ enormous heat capacity, so the planet does not plunge to cryogenic temperatures in days, but habitability degrades quickly.
- Hours to days: Widespread subfreezing temperatures; most mid-latitude and polar regions drop well below 0 °C.
- Weeks: Many regions reach tens of degrees below zero; precipitation and the rain cycle largely cease as evaporation collapses.
- Months to a year: The oceans acquire a continuous ice lid from polar regions into lower latitudes; sea ice thickens to many meters. Surface air temperatures in the interior of continents can average below −40 °C or colder.
As the surface cools further, atmospheric constituents begin to condense. Carbon dioxide would freeze out first once local temperatures fall near its sublimation point, reducing greenhouse warming and accelerating cooling. At sufficiently low temperatures, oxygen and nitrogen would liquefy and then freeze, thinning the atmosphere dramatically.
At 1 atmosphere, oxygen liquefies near 90 K and nitrogen near 77 K (NIST Chemistry WebBook).
When would the oceans freeze, and how deep would the ice get?
The ocean surface freezes relatively quickly because the atmosphere above can radiate heat to space much faster than liquid water can retain it. Early on, tens of watts per square meter of net heat loss can drive rapid formation of sea ice; latent heat released by freezing then slows further cooling.
Over longer times, ice thickness grows until the upward conduction of heat through the ice matches the small upward geothermal heat flux from Earth’s interior. Using typical thermal conductivity for ice and a global-average geothermal flux of about 0.09 W/m², the steady-state ice lid could reach kilometers in thickness, potentially freezing most of the ocean solid except in regions with strong local heating.
Earth’s internal heat flow is about 47 terawatts globally, or roughly 0.09 W/m² on average (Davies & Davies, Solid Earth, 2010).
Hydrothermal systems and seafloor volcanism would keep pockets of the deep ocean liquid beneath the ice for geologic timescales. Ecosystems near hydrothermal vents do not depend on sunlight and would likely persist the longest.
For context, studies of “Snowball Earth” suggest very thick sea ice when external heating is weak; in a no-Sun case, equilibrium thicknesses could be vastly greater because geothermal heat alone must be conducted through the ice (Warren & Brandt, JGR Oceans, 2006).
How much does Earth’s internal heat matter?
Even without the Sun, Earth still produces heat from the decay of radioactive elements and residual heat from its formation. This internal power is tiny compared with absorbed solar energy in the present climate (roughly 0.09 W/m² versus about 240 W/m²), but it becomes dominant once sunlight is gone.
Without sunlight, a planet radiating only its internal heat would equilibrate near 30–40 K, computed from the Stefan–Boltzmann law using 0.09 W/m² (NASA Earth Observatory: Earth’s Energy Budget).
Importantly, that 30–40 K is not a near-term surface air temperature forecast; it is the effective radiating temperature the planet tends toward once thick ice, a collapsed atmosphere, and very low infrared emission all come into play. Reaching such cryogenic conditions globally would take far longer than the initial surface freeze-up because heat must be extracted from the vast thermal reservoirs of the oceans and crust.
Would Earth ever “completely” cool down?
Not in any finite time, and certainly not on human timescales. Physically, Earth cools asymptotically. Practical milestones are:
- Days to weeks: Surface habitability ends across most of the planet.
- Years to centuries: Ocean surfaces are sealed by thick ice; the atmosphere becomes thin as gases condense and freeze.
- Millions of years: Liquid water persists around hydrothermal vents beneath the ice; crust and upper mantle remain warm.
- Billions of years: Earth’s interior gradually loses its radiogenic and primordial heat. The total heat content of the planet is so enormous that, at today’s global heat-loss rate, shedding enough heat to cool the bulk interior by even 1000 K would take on the order of billions of years, and the rate itself slows as the planet cools (Davies & Davies, 2010).
In short, the surface becomes uninhabitably cold quickly, the hydrosphere and atmosphere collapse over years to geologic timescales, and the solid Earth remains warm for many billions of years. The Sun’s disappearance determines how fast the surface freezes, but it hardly affects the ultimate longevity of Earth’s internal heat.