What Would Happen If the Sun Disappeared?

This question has been answered all over the internet, and the short version that is often given is "everyone dies." This is true. This is also just the tip of the iceberg. Lots of things happen and most don't involve humans. For the things that happen to humans, here are a few good articles:

Pros:
XKCD, Sunless Earth

Cons:
PopSci,  If the Sun Went Out, How Long Would Life On Earth Survive?

After the sun went out, a few things would happen quite quickly. Due to the speed of light, at the moment when the sun went out, we would still see its light for 8 minutes and 20 seconds, or long enough to listen to "It's the End of the World as we Know It" by R.E.M. about twice. Because gravity travels at the speed of light, we would stay in our orbit for the same 8:20 until we started moving in a straight line tangent to that orbit into space.

Image: NASA/SDO (AIA)

Fig.1

<sidenote>
If you were in the U.S. on the night side of Earth when this happened, you wouldn't feel much of a change in the motion of the Earth, or a drop in temperature, so there is roughly a 40% chance that you would first hear about the sun going out on either Facebook or Twitter. </sidenote>

Shortly after the sun's disappearance, the human world descends into existential chaos, and for excellent reason; we're not long for this universe. If you had previously come to terms with your demise, and the recent change in timescale didn't bother you too much, you could get out a pair of binoculars or a  telescope and point it at Jupiter or Saturn for a once-in-a-lifetime view. The sun has gone out, but light from the newly non-existent sun is still illuminating these planets, and if you watched them carefully, you could watch them blink out, reflecting the last of the sun's light, and be the last human to ever see them (Fig. 2).

Image: NASA

Fig. 2

When I initially thought about this, I suspected that you would get lovely vistas in cities with the Milky Way sprawled out over the sky, but this is only partially true, and only for the day-lit side of the earth. Light pollution wouldn't just go away; many lights in the cities are on all day, and many more are activated by a light sensor and would turn on immediately, and others would soon be manually activated. So much for that silver lining...

Image: savmonks

Fig. 3

How would the humans fare? Humans are plucky and rather fond of surviving (Fig. 3), so there are a few schemes that could prolong our existence for a while (before problems develop), but in a few hundred years (wild guess) we'd probably all be gone. Without plants undergoing photosynthesis, the food chain collapses and there is no longer any energy input to the ecosystem. Without life replenishing oxygen, the Earth loses oxygen on the timescale of thousands of years. The Earth eventually becomes cold enough that the nitrogen in the atmosphere condenses onto the surface and eventually freezes into solid nitrogen. That seems like the end of the story, but there's more.

On the Earth's surface, the main source of energy is the Sun, but within the planet itself is where the real heat lies. When the Earth formed, it gravitationally collected material, differentiated, and to this day, there is still radioactive material heating the interior of the Earth. This internal source of energy is available to a select few creatures that live near the sea floor, near hydrothermal vents.

These entire ecosystems would lose two sources of nutrients: marine snow, and whale falls (just what it sounds like), but retain the third, chemosynthesis. These ecosystems would probably be able to limp along, form a new equilibrium, and stick around for millions, maybe billions of years as the Earth went aimlessly drifting through space, carrying its living cargo.

Right then was where I was going to stop, but I then thought about where the Earth may drift off to. Depending on when the sun disappeared, and where the Earth was in its orbit, the Earth could potentially end up anywhere along the plane of its orbit. I downloaded a copy of the free-to-use Stellarium and learned how to use it to answer this question of where the Earth may end up after drifting through space.

To find objects that the Earth may run into, in Stellarium, I placed myself on the equator, on the equinox, and looked directly East or West. This particular East-West line puts the me tangent to the Earth's orbit, so anything appearing along this line is a potential target.

Let's start with a few of the closest objects Earth could potentially encounter.*

Among the closest was a star in the constellation Aquarius (below). This struck me because if Earth is captured in a tight, stable orbit around this pair of stars, we could become an arid planet with 2 suns, just like Tatooine, from Star Wars. This star system is about 100 light years away, and would take about a million years to get to.

Image: Stellarium

If we want some company, there are a few exoplanets that are relatively nearby that we could go visit. This one is a "Hot Jupiter," or a large planet very close to its star. it's about 100 light years away, and we could reach it in just over a million years. We honestly would probably want to leave this one alone. (Sidenote: It was one of the first extrasolar planets discovered)

Image: Stellarium

A more homey planetary system we could visit is is HD 164509b. I've heard it's lovely there; it's a Sun(ish) star being orbited by a Venus(ish) planet. We'd fit right in. It would take us about 1.7 million years to get to this planet 169 light years away.

Image: Stellarium

Here's where things get interesting. In 9 million years, we could potentially reach a Reflection Nebula known as Messier 78 (900 light years away). This nebula is quite lovely and would make a great backdrop for our floating tomb:

Image: ESO/APEX (MPIfR/ESO/OSO)/T. Stanke et al./Igor Chekalin/Digitized Sky Survey 2

My personal favorite part of the sun disappearing is that there is a tiny chance we will be heading straight for this:

Image: ESO

Two beautiful spiral galaxies about to collide with each other. These galaxies are going to spend the next few billion years passing through one another and eventually forming an elliptical galaxy. The downside, however, is pretty insurmountable. Due to their extraordinary distance, and our meandering pace, we couldn't possibly get to them in time to observe this interaction. In fact, it would take us over 3 trillion years, or 220 times the age of the universe to get there. By then these galaxies may not even exist, let alone be in the same spot.

Here's the upshot: if we left our galaxy right now, and started to travel, we would be able to see Andromeda colliding with the Milky Way from pretty close by, (about 20 galactic radii). That view might just make the whole thing worth it...

...if we could possibly survive. The only things that could survive would be in the ocean under miles of ice, but in a few billion years, maybe some intelligent life will evolve and make a foray out beyond the ice to see this great collision unfold.

Super-intelligent Trout

Cheers,

    - Scott


*Due to the fact that the objects I chose were within a half a degree of tangent means that there is a vanishingly small chance that the Earth would even get within a light year of the nearest one, but it's fun to think about nonetheless.






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