The Family Portrait of the Solar System taken by Voyager 1. Image credit: NASA
Every star goes through a life cycle: birth, nuclear fusion and, eventually, when there is nothing left to burn, death. Our own Sun will be no exception.
Whenever we mention to our Inflatable Planetarium visitors that one day the Sun will run out of fuel and die, the immediate question always follows: what will happen to us?
Well, you and I don’t need to worry about the ultimate fate of the Earth because the Sun still has about 4.5 billion years worth of fuel in its stores. But, let’s just say: the distant future looks gloomy. Not just for our planet, but for the whole Solar System!
According to the new paper* published in the November issue of The Astrophysical Journal, within 100 billion years the Solar System will – literally- fall apart. Shall we dig into some gloomy details?
Inner planets
When the Sun runs out of hydrogen in the core to burn, the dramatic changes will begin. First, our star will grow in size and become a red giant. As the Sun expands, it will devour, one by one, its three nearest planetary neighbours. It’s hard to imagine these beautiful worlds vaporizing, but that’s nature’s way. On the bright side: Mars will most likely survive the Sun’s red giant phase.
Next, the outer layers of the Sun – about 46% of the star’s mass – will be blown away, revealing the compact remnant smaller than the Earth in size. Our Sun will become a white dwarf.
Outer planets
To see what happens next, once the Sun’s three closest planets are gone and the Sun itself turns into a white dwarf, the authors of the paper* ran numerical simulations
(the simulations did not include Mars. The Red Planet is so small that it doesn’t affect the dynamics of the what’s left of the Solar System)
Turns out the outer planets will continue their journeys around the center of the Solar System. But things will be a bit different. Between now and a white dwarf phase, the Sun will lose almost half of its mass. As a result, the orbits of the remaining Solar System planets will expand so that their semi-major axes will become 1.85 times of today’s value.
According to the simulations, Jupiter and Saturn will become captured into 5:2 resonance. That means, for every 2 Saturn’s orbit, Jupiter will complete 5 orbits around the Sun.
This could have been the end of the transformation of the Solar System, if not for the other stars in our Galaxy.
Interaction with other stars
As our Solar System travels through the Galaxy, it sometimes passes by other stars on its way. At the moment, these flybys do not disturb our tightly packed planetary system. But once the planets are further out, the stellar encounters, however rare, will affect the orbits of the remaining planets. The simulations show that within 30 billion years the orbital order will turn into chaos and three out of four outer planets will be kicked out of the Solar System. It’s too early to say in what order the planets will be ejected, but it might be Uranus – Neptune – Saturn – Jupiter.
One planet left
“The last planet standing” – whichever one it would be – will continue its lonely journey around the Sun. But within 100 billion years it too will be ejected out of the Solar System, either by a single close encounter with a passing star or by a number of more distant encounters that will gradually stretch the planet’s orbit. The Solar System will be gone.
In a nutshell
In the distant future our orderly Solar System will fall apart. Mercury, Venus and Earth will be vaporized, and the other planets will be ejected and become free-floating (aka rogue) planets.
More information
Here are some other Blog posts about the Sun you might enjoy
How old is the sunlight you see?
What would happen to the Earth if the Sun turned into a black hole?
Why white dwarfs crystallize (and how the Sun will turn into a giant diamond)