How To Eat The Earth

“An appeaser is one who feeds a crocodile, hoping it will eat him last.”
-Winston Churchill

Ever wonder what will happen to the Earth once the Sun dies? Although it’s happening very slowly, the Sun is burning through the nuclear fuel that powers it, giving off a tremendous amount of energy all the time as it happens.

(Image credit: NASA’s STEREO A spacecraft.)

Like all stars, the Sun burns progressively hotter as it ages. A few billion years ago, solar output was 10% less than it is today, and a few billion years from now, it will burn so hot that our oceans will boil, something that only currently happens when lava spews out into the seas!

(Image credit: National Geographic and Steven Alvarez.)

Of course, this won’t physically destroy the Earth itself, just most of the life on it. Despite the fact that today’s oceans and land will become cracked and dry, and largely (if not completely) inhospitable to life, the charred, baked Earth will still be here.

(Image credit: crowt59 at FlickR.)

And the Sun — when it finally runs out of fuel after another five-to-seven billion years — will go through its death cycle. It will become a red giant, burn the heavier elements like helium into carbon, nitrogen and oxygen, and will expand, engulfing Mercury and Venus, but perhaps not the Earth.

(Image credit: Brian Smallwood.)

And after that, once the Sun has exhausted its fuel from those heavier elements, all it can do is blow off its outer layers in a planetary nebula, and contract down to a white dwarf at the center.

(Image credit: NOAO.)

The planetary nebula is short lived, lasting only maybe 100,000 years, but the white dwarf will remain for a very long time! With an estimated lifetime soaring into the trillions of years, whatever planetary bodies are left — and that probably includes Earth and definitely includes Mars — should just orbit this tiny stellar corpse at the center of our Solar System.

(Image credit: Richard Pogge at Ohio State.)

What is this white dwarf that gets left behind like? Well, it still has most (maybe 50-70%) of the original mass of the Sun, but in terms of size it’s only about the size of the Earth! The vast majority of this white dwarf will be Carbon, Nitrogen and Oxygen, with a small envelope of hydrogen/helium on the outside.

And — with the planetary leftovers orbiting it — you may think that takes care of everything for trillions of years. That if nothing’s eaten the Earth by now, it’ll simply stick around, orbiting, for the rest of its days.

(Image credit: HST / NASA / H. Bond / STScI.)

Only, the Sun won’t be the first to this state! Already, just within our own galaxy, there are around a hundred billion white dwarf stars, including many found in globular cluster M4, above.

But just as asteroids and comets get hurled around the Solar System by planets like Jupiter and Neptune, the same thing ought to happen around these white dwarf stars with the remaining solid bodies that orbit it.

And every once in a rare while, one of these rocky bodies — maybe an asteroid, maybe even a small planet — should get hurled directly towards its parent star!

What would the aftermath of a beautiful catastrophe like this be? The remains of the planet should get kicked up in a dusty storm around the white dwarf, and we should be able to detect the presence of its heavy elements!

How’s that? The white dwarf is still very hot, with a surface temperature of many thousands of degrees, so it emits blackbody radiation just like the Sun does. But these heavy atomic elements will block light at very specific frequencies, telling us what this dust is made out of, and hence how much of each type of elements this recently devoured planet or asteroid once contained. In theory, even a dwarf planet or an Earth-sized object could eventually be eaten by a white dwarf.

Guess what we just found?

At least four known white dwarf stars have eaten something very similar in composition to Earth in their own solar systems!

Magnesium, Chromium, Iron, Nickel, Calcium, Tin and Silicon, among many others, have been found encircling the helium envelope of these white dwarfs, in greater or equal abundance than what the planet Earth has!

(Image credit: Walter Myers.)

The devoured planets have left a signature behind showing that they’re likely somewhere in between the masses of Ceres and the Moon, shown above for comparison with Earth. But there is also something else — of perhaps far greater importance — than the fact that the Earth may someday be eaten by our Sun’s white dwarf future. As Ben Zuckerman, one of the leaders of the study says,

This means that planetlike rocky material is forming at Earthlike distances or temperatures from these stars.

In other words, this is the first hard evidence that we have that there are not only extrasolar planets, but planets made of the same stuff that Earth is made of orbiting other stars, and they were doing it before our Solar System even formed!

Take a look at the whole paper here. Although there are a couple of good writeups of this, the best I can leave you with is the last sentence of the paper’s conclusions:

It is clear that extrasolar planetary systems produce rocky bodies that are compositionally similar to terrestrial planets in our own solar system; Earth-like planet(esimal)s apparently do form elsewhere in the galaxy.

So while the Sun may eventually eat us in the far distant future, the fact that long-dead Suns are eating some of their planetary remnants has allowed us to find out, yet again, that Earth and our Solar System may not be so special after all.

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