This is a thought experiment, and scientists have no reason to expect the Sun to disappear suddenly. As of November 2026, the Sun has been shining for billions of years and will keep shining for about 5 billion more. The Sun gives Earth its light and its warmth, so imagining its absence is a way to ask what each part of our planet depends on. Earth's average surface temperature is about 15 degrees Celsius (59 degrees Fahrenheit), as of November 2026. Plants, oceans and heat itself make good places to start.

Start with plants. Plants use the energy in sunlight to make their food, and this process is called photosynthesis. Photosynthesis is how they turn light energy into food. Plants kept in the dark could not make food this way, according to a report on the science news site Live Science. Some might stay dormant for weeks to months, as they do in winter. Dormant means resting, with growth paused until conditions change.

The ocean shows how quickly light fades with depth. Below about 200 meters there is so little light that photosynthesis is no longer possible. Sunlight reaches only the top of the ocean, and below about 1,000 meters the ocean is completely dark. Earth is the only planet in our solar system with liquid water on its surface.

Next, the heat. The Sun's energy heats Earth's surface and air, powers ocean currents, drives photosynthesis and evaporation, and melts snow and ice. It heats the equator more than the poles, and the atmosphere and oceans work non-stop to even out that heating. The report on Live Science says that at first Earth would cool by an average of roughly 20 degrees Celsius (36 degrees Fahrenheit) every 24 hours, and that the daily drop would shrink as it got colder.

According to that same report, almost the whole world would pass below the temperature at which water turns to ice within two to three days. Small ponds might turn to ice within a week, and lakes might take weeks or months. These are estimates for an imagined case, and they come from a single report, so they show the scale of the change rather than a precise schedule. The oceans come next.

The oceans could stay liquid for many years, maybe decades, the report says. In the deepest parts of the oceans, where there are volcanoes, water might stay liquid for as long as the volcanoes last, perhaps billions of years. Earth has four layers: a solid inner core, a liquid outer core, a mantle and a crust, and the inner core is about 5,400 degrees Celsius (9,800 degrees Fahrenheit). Geothermal energy is heat energy from the earth: geo means earth and thermal means heat.

Deep in the dark ocean, hot springs called hydrothermal vents have living things that do not depend on sunlight. The vents are produced by underwater volcanoes or tectonic activity, and they were discovered near the Galapagos Rift in 1977. Some microbes, including bacteria and archaea, use chemosynthesis, getting energy from chemical bonds in rocks and minerals instead of from sunlight. Giant tube worms at vents have symbiotic bacteria that make food through chemosynthesis, and some vent worms grow to almost five feet long in less than two years.

For comparison, Pluto is about 40 times as far from the Sun as Earth is, and it is extremely cold: about 230 degrees Celsius below zero. Earth, with its inner heat and its deep oceans, is a very different place. The real future of the Sun is also different from our pretend one. The Sun is roughly midway through the longest phase of a star's life, when it steadily fuses hydrogen into helium. Over a billion years from now, its gradual brightening is expected to vaporize Earth's oceans.

Words to know

• photosynthesis: plants making food
• dormant: resting, not growing
• hydrothermal: hot water
• chemosynthesis: food from chemicals
• geothermal: earth heat