It can be hard to believe that our planet isn’t permanent. That not only did the
wider universe exist for more than nine billion years before the sun, the Earth,
and the rest of the solar system... but that the universe will also continue
long after our home is no more. But how, exactly, is the inevitable death of Earth
going to unfold? Scientists may have just enjoyed a front row seat to the preview.
This is Unveiled, and today we’re answering the extraordinary question;
did scientists just discover how the Earth will end?
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In 2023, a years-long research effort finally concluded, and a team of scientists published
a paper in the journal “Nature” announcing that, for the first time, we’d been able to observe what
happens when a star eats a planet. Previously, while we were aware that this occurs regularly,
we’d never actually been able to witness it firsthand. A major cosmological event, but it
was one that had still been shrouded in mystery. And interestingly, in the 2023 study, scientists
at first weren’t even looking for what they eventually found. The research began as a search
for binary star systems, in particular, where two stars orbit each other harmoniously – for the most
part. So, how did that unveil such a dramatic and violent event as planet-by-star consumption?
Sometimes, the stars in a binary system move too close toward each other, and one will start to
siphon off (and absorb) the stellar material of the other. The two might then collide and merge
completely into one even bigger star. And, when this happens, large amounts of light
are (unsurprisingly) released, meaning that we should, in theory and under the right conditions,
be able to see such an event from Earth. In practice, however, it’s simply been too
difficult to find these events in the first place, seeing as there’s only an estimated one per ten
thousand years, per star cluster in a galaxy. But, then again, there are many more galaxies
out there, and many of them are visible to us – which is why, in fact, in 2017,
such a merger of two neutron stars was actually observed. Although, in that case, it was thanks to
the detection of gravitational waves rather than the burst of blinding light that must have also
accompanied it. All to say, though, that even star collisions are very hard to chance upon.
But, back to the 2023 paper. Once again, the research behind it was centered on searching
for large, telltale instances of light in the cosmos. And, in 2020, one particular light burst
was observed, leading to a rush to try to parse what had happened. But researchers soon realized
that the amount of light was much too small to be representative of another star-to-star collision.
So, what made it if not that? It took a few years, and a lot of sifting through endless data
from multiple sources… but, eventually, scientists concluded that what they’d witnessed in 2020 was
actually the very final moments in the life of a massive planet. A massive planet that had met its
star and disappeared forever, and science (for the first time) had captured that very moment.
The planet in question is (or was) an estimated ten times more massive than Jupiter is,
the biggest planet in our solar system. Making it an extraordinarily large world, which is one
reason why it registered on our Earthly tech at all. But, no matter the size and mass it once was,
it disappeared very quickly. Again, so quickly that it took researchers literally years to
work out what had actually happened in those moments. To the casual onlooker,
the end of this apparently monster planet might well have looked like
nothing more than a brief and flickering glitch within just a tiny speck of space.
The star in question - the one that just killed its one time satellite - is estimated to be
roughly 12,000 lightyears away from us, inside the Milky Way. The entire process of that star
gaining luminosity and drawing the planet in, as a prelude to the planet-devouring
act itself – described as an optical outburst – lasted for around 13 months total. The final,
peak outburst then went on for some ten days. The star, which hasn’t been named
(beyond its classification as ZTF-SLRN-2020) isn’t entirely alien to us, though. In fact,
it’s not so different from our own star; the sun. It’s on its way to becoming a red giant,
although still at an early stage toward that. But, as is now widely known, this is exactly what will
eventually happen to our sun, as well. The fate of that now-dead planet will be the fate of us, too.
A red giant is what you get when a low-mass star begins to die. It indicates that that star has
run out of hydrogen in its core, and can no longer fuse that hydrogen into heavier elements. Hydrogen
on the exterior is fused instead, which makes the star much bigger as it expands. On average,
therefore, a red giant has a radius – that being the distance from the star’s center to its outer
shell – around 200 times bigger than the radius of the sun right now. This expanded shell is then
what’s called an envelope, and it’s the growing envelope that hungrily destroys anything that
gets in its way – like the massive planet in this particular case. That red giant envelope is hot,
huge, and it will burn without mercy whatever it touches. And, again,
this is the fate that awaits Earth someday, when the Sun, too, runs out of hydrogen.
For the recently lost planet (and for us in the future) this period of ruthless expansion will
last for millions of years, until eventually, the envelope will have dissipated completely.
What then remains is a white dwarf, the dead core of the star that once was, which isn’t fusing any
elements but is still extremely hot. White dwarfs will, in theory, eventually cool down and fade
so much that they become black dwarfs. But this process is thought to take SUCH a long time, that
no black dwarf stars exist yet in the universe - and black dwarfs are therefore still theoretical.
Unfortunately, since the process for a plain old red giant to become a white dwarf takes
so long on its own, we’re almost certainly not going to be able to see it play out to the end,
even with this distant, planet-eating star that we have at least registered. Unless, of course,
humanity does end up finding a way to live for millions of years from now, and so can keep an
eye on it. But, nevertheless, it’s still a star much further along in its lifespan than our sun
is… so it will still be useful to observe. And, indeed, the researchers tracking it are excited,
because this distant star does provide at least a glimpse of what our sun will be like when it
begins to die. We now know, for example, that when the envelope does eventually reach Earth,
it perhaps won’t be an instantaneous end for our planet, but will instead be a days-long,
hellish event. Luckily, what we are confident about (and have been for a while) is that it
isn’t going to happen to us for about five billion years, or so. With the first truly
intolerable living conditions not arriving on Earth until around one billion years from now.
But, the solar system isn’t only ours. There are other planets, and some that
are closer to the sun. So, exactly how much of the solar system might be consumed? Given,
again, that average radius of a red giant shell... it’s predicted that the sun’s envelope will likely
stretch for about 86 million miles in every direction. But of course, the average isn’t
the only number that matters here, since it will only get bigger and bigger. And,
at its biggest, the red giant sun is probably going to be nearer to 185 million - perhaps 200
million - miles across. Considering that Earth is, on average, 93 million miles away from the Sun,
this is obviously pretty bad news for us. We sit right in the middle of that maximum
distance. And it’s definitely bad news for Mercury and Venus. Jupiter, on the other hand,
is 480 million miles away, and so it would hopefully survive, as will all the other
outer planets. Jupiter would then settle down to become the new Mercury, to some degree;
the now-closest planet to our star. Unless Mars escapes, too, by the skin of its teeth.
But, what about us, humankind? If humans are still alive by this point - which is a pretty big
if - then we’ll hopefully have already mastered the technology needed to survive this cataclysm,
too. Perhaps the most obvious route to species safety would be by setting up human colonies on
the moons of the outer planets. And we might want to make it all the way out to Saturn,
or even further, just to be on the safe side. And, on the face of it, there are a few options
for us. Europa in the Jovian system; Titan orbiting Saturn; or even Triton, Neptune’s
largest moon and potentially a former dwarf planet that was once captured by the ice giant.
But, while we might be able to run, we wouldn’t be able to hide from the existential problems
forever. They will only return, but in different forms. Significantly, when the red giant envelope
does dissipate, the white dwarf that’s left behind won’t then be as hot or as
luminous as a living star. It won’t ever again provide the equivalent energy that our vibrant,
present-day sun ever did. So, what then? What would your solution be? Perhaps we could build
ourselves out of trouble by constructing new and artificial planets to orbit close enough
to the white dwarf for safety? Or maybe we would need to have fled the solar system long before,
to stand any chance of continued longevity? Let us know your plan of action in the comments.
For now, science has known for a long time that the sun is going to someday devour the Earth,
but only now have we finally been able to witness what this might
actually look like… when it does happen a few billion years from
now. And that’s why scientists did just discover how the Earth will end.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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