What If the Sun Disappeared?
The short answer
For about 8 minutes and 20 seconds, nothing would change. The Sun's last light would still be on its way, and Earth would keep circling the empty spot, because changes in gravity also travel at the speed of light. Then the sky would go dark and Earth would carry on in a straight line at about 107,000 km/h (67,000 mph).
The Sun can't really vanish. It has about 5 billion years of fuel left.
How we know gravity is that fast
On 17 August 2017, two neutron stars collided about 130 million light years away. Their ripple in gravity reached Earth, and a flash of gamma rays arrived 1.7 seconds later. After a trip of 130 million years, that gap is tiny. It shows that gravity and light travel at the same speed, to about 15 decimal places.
The gap doesn't mean gravity is faster. Most of it was the explosion taking a moment to launch its flash.
Our theory of gravity can't describe mass simply vanishing, because mass and energy can't just disappear. So physicists picture the Sun's mass flying outward at light speed instead. Earth feels no change until that shell passes it, about 8 minutes 20 seconds later.
What goes dark, and what doesn't
The Moon only reflects sunlight, so it goes dark 1 to 3 seconds after the Sun. Counting from the moment the Sun vanishes, Venus goes out after about 12 minutes, Jupiter after about an hour and a quarter, and Saturn after about two and a half hours. The stars stay on, because they make their own light.
Earth doesn't shoot away. It keeps its speed and drifts. After a week it's only 0.7% farther from the empty spot. After about 10 months it's as far out as Jupiter's orbit. The Moon comes along, still circling.
Ice on top, life underneath
Within days to a week, the surface would drop below the freezing point of salt water, about minus 2 °C (28 °F), and the oceans would start to ice over. In a year or so it would be about minus 73 °C (minus 100 °F).
The ice works like a lid. Heat from Earth's interior, about 47 terawatts, keeps the water under it liquid. Caltech's David Stevenson put the deepest water freezing after about 1,000 years. It does freeze in the end: a 2011 study found that a planet with no star needs about 3.5 times Earth's mass to keep an ocean under its ice.
At the hot vents, food chains run on chemicals from hot rock. But tube worms and most vent microbes breathe oxygen, and that oxygen was made by sunlit plankton and plants. The life that truly needs no Sun is microbes that need no oxygen either, such as methane making archaea.
Key numbers
| What | Number | Source |
|---|---|---|
| Time for sunlight to reach Earth | about 8 minutes 20 seconds | NASA, Voyager 1: What Is a Light Day? |
| Range of that time over a year | 8 min 11 s (January) to 8 min 27 s (July) | Our arithmetic from NASA, Earth Fact Sheet |
| Distance to the 2017 neutron star collision | about 130 million light years | NASA, first light from a gravitational wave event, 2017 |
| Gap between the gravity ripple and the gamma ray flash | 1.74 s, give or take 0.05 s | LIGO, Virgo, Fermi and INTEGRAL, 2017 |
| Earth's average orbital speed | 29.78 km/s, about 107,000 km/h (67,000 mph) | NASA, Earth Fact Sheet |
| Moon goes dark after the Sun | 1 to 3 seconds | Our arithmetic from NASA, Moon Fact Sheet |
| Jupiter goes dark, seen at night | about 1 h 15 min to 1 h 25 min after the Sun vanishes | Our arithmetic from NASA, Planetary Fact Sheets |
| Surface drops below the freezing point of salt water | within days to a week | David Stevenson, Caltech, 1999 |
| Surface temperature after a year or so | about minus 73 °C (minus 100 °F), 200 K | David Stevenson, Caltech, 1999 |
| Deepest ocean water freezes | after about 1,000 years | David Stevenson, Caltech, 1999 |
| Heat flowing out of Earth's interior | 47 TW, give or take 2 TW | Davies and Davies, 2010 |
| Time the Sun has left | about 5 billion years | NASA, Sun Facts |
What the film simplifies
- The film says "eight minutes twenty". The average is 8 minutes 19 seconds, and it runs from about 8 minutes 11 seconds to 8 minutes 27 seconds over the year.
- The 2017 race is drawn as a photo finish. In fact the gamma rays arrived 1.7 seconds after the gravity ripple, mostly because the explosion took a moment to launch its flash.
- "A hundred degrees below zero" is Fahrenheit, as the sticker in the film says. That's about minus 73 °C.
- The planets click dark one after another within a few seconds. Really it would take from minutes to hours: about 12 minutes for Venus, about two and a half hours for Saturn.
- "Some microbes don't need the Sun at all" is true only of microbes that need no oxygen. Tube worms and most vent life breathe oxygen made by sunlit life.
- Gravity as a character holding Earth in his hand, the Sun pulling its own lamp chain, and Rocket's brags are cartoon. The Sun can't actually vanish.
At a glance
Runtime 1 minute 2 seconds · Topics: Speed of gravity, Gravitational waves, Earth's orbit, Life without sunlight · Captions on YouTube · Full script below
Test yourself
If the Sun vanished, why would Earth keep orbiting the empty spot for about 8 minutes?
Answer
Changes in gravity travel at the speed of light, like the Sun's last light. Earth only feels the change when that news arrives, about 8 minutes 20 seconds later.
Why would the Moon and planets go dark but the stars stay on?
Answer
The Moon and planets only reflect sunlight. Stars make their own light.
Why would the deep ocean stay liquid under the ice for a time, and would it last forever?
Answer
The ice acts like a lid and heat from Earth's interior warms the water from below. It wouldn't last: Stevenson estimates the deepest water freezes after about 1,000 years.
The script
Host: The Sun just vanished. And for eight minutes, nobody will notice.
Rocket: I noticed! Bye bye, show off!
Host: Its last light is still on the way.
Host: And gravity travels just as fast, so Earth keeps circling nothing.
Host: In 2017, two dead stars crashed.
Host: Their gravity ripple and their flash raced for 130 million years and arrived less than two seconds apart.
Rocket: Photo finish!
Host: At eight minutes twenty, lights out. And Earth heads off in a straight line at 67,000 miles an hour.
Rocket: Now I'm the brightest thing in the solar system!
Host: But the stars stay on.
Rocket: Brightest thing nearby.
Host: Within a week, it's below freezing. In a year, a hundred degrees below zero.
Rocket: I meant to do that.
Host: But ice is a blanket. Under it, the deep sea stays liquid for at least a thousand years.
Host: And at the hot vents on the sea floor, some microbes don't need the Sun at all.
Host: Good thing the Sun can't really vanish.
Rocket: Show off.
Sources
- Sunlight takes about 8 minutes 20 seconds to reach Earth.NASA, Voyager 1: What Is a Light Day?
- Sunlight takes about 8 minutes 20 seconds to reach Earth.Smithsonian, How Things Fly
- Changes in gravity travel at the speed of light; the sky goes dark and Earth leaves its orbit at the same moment; the Sun can't really suddenly disappear.Christopher Baird, WTAMU, 2013
- The Sun vanishing itself breaks the rules of physics, because the Sun's mass and energy are conserved.University of Illinois, Ask the Van (16045)
- GW170817: gamma rays arrived 1.74 ± 0.05 s after the gravitational waves; gravity and light travel at the same speed to within a few parts in 10^15.LIGO, Virgo, Fermi and INTEGRAL, 2017
- The 2017 collision was in galaxy NGC 4993, about 130 million light years away, on 17 August 2017.NASA, first light from a gravitational wave event, 2017
- The gravitational waves and the flash arrived less than 2 seconds apart.LIGO, GW170817 science summary, 2017
- Earth's mean orbital speed is 29.78 km/s; perihelion 147.1 and aphelion 152.1 million km.NASA, Earth Fact Sheet
- The Moon orbits Earth at 1.022 km/s at 384,400 km, so it stays with Earth.NASA, Moon Fact Sheet
- The Moon orbits Earth almost the same way it would if the two were alone.University of Illinois, Ask the Van (18501)
- Planet orbit distances used to work out when each planet goes dark as seen from Earth.NASA, Planetary Fact Sheets
- The Moon does not make its own light.NASA, Moon Phases
- If the string breaks, a swung mass travels off in a straight line along the tangent.HyperPhysics, Centripetal Force
- Below the freezing point of salt water within days to a week; about minus 100 °F in a year or so; the deepest ocean water freezes after 1,000 years.David Stevenson, Caltech, 1999
- A magazine retelling of Stevenson's answer, like a ball swung on a string and let go.Popular Science (Otterbein), 2008
- Heat flow out of Earth's interior is 47 ± 2 TW.Davies and Davies, 2010
- A planet with no star must be about 3.5 times more massive than Earth to keep an ocean under its ice.Abbot and Switzer, 2011
- Vent food chains run on rock chemicals mixing with cold, oxygenated deep sea water; methanogenic archaea.Sievert and Vetriani, 2012
- Most vent life relies directly or indirectly on photosynthesis; only a small portion of anaerobic chemosynthetic microbes can do without it.Biogeosciences Discussions, 2012
- Young sunflowers track the Sun; as they mature they stop moving and face east.UC Davis, 2016
- Young sunflowers track the Sun on an internal clock.Atamian et al., 2016
- The Sun will last about another 5 billion years.NASA, Sun Facts