Earth’s Swansong

Earth’s Swansong


The Sun will go black
Earth sink in the sea,
Heaven be stripped of its
bright stars;
Smoke rage and fire, leaping
the flame
Lick heaven itself.

-The Deluding of Gylf

Strange times are upon us, we seem beset by continuing problems with our inability to respect and harness our planet’s limited resources. Climate change, carbon emissions, destruction of rain forests, wildlife habitats, depletion of fish stocks, oceans full of plastic, wet markets, finning of sharks (100 million a year killed just to make soup), and only the other day a picture of a couple kissing in front of a dead lion they’d shot (bred for slaughter).

The most useless bunch of politicos worldwide that I can remember in my lifetime; venal, shallow, liars and narcissists, the lot of them (excepting a couple of female leaders), with only one short term driving instinct, to remain in power.

Is that it, well no, not really, much of the above is connected to our increasing vulnerability to viruses that can jump species (coronaviruses), this country in particular didn’t learn much from previous outbreaks of Sars and Mers and now has one of the worst death rates in the world.
Welcome to planet Earth, intergalactic visitor and on the menu today we have a selection of exotic dishes! Bears paw soup, Shark fin soup, fancy a Pangolin, be my guest, or better still suck on fried Bat fæces. What do these ridiculous meals signify: status, hierarchy, greed, not culinary delights.
Backache, arthritis, virility problems? try the pharmacy sir, we have a number of unproven exotic medicinal cures, Rhino horn for your hangover, Pangolin scales for your arthritis, may I suggest ground Tiger penis to sort out the limp gland!

So, what’s the good news, well it’s still an astronomy page and our Sun has a finite life, so we all know the ending: everyone gets to die. We tend to think of a main sequence star like the Sun as a constant, but its far from it. It maintains what astronomers call hydrostatic equilibrium- the outward pressure exerted by the core’s hot gas balances the inward crush of gravity. If the Sun’s central temperature were to drop slightly, for example, the gas pressure would also fall. Gravity then would force our star to contract and heat up, restoring its equilibrium. The outer parts of the Sun still maintain that balance, but in the core, where nuclear fusion rules, helium levels continuously rise.

In the far future at this distant point, the Sun and the Earth have taken nearly opposite paths. Even one or two billion years from now, the Sun will look basically the same as it does today, a little bigger and brighter, but recognizable. However the Sun’s internal structure will have changed markedly. Its centre will be largely helium, although lots of hydrogen will still exist in the core. For Earth, on the other hand, the surface would be hardly recognizable. Our “pale blue marble” will be more of a muted brown, and blistering temperatures will make it uninhabitable.

As time marches on, changes in the Sun and the rest of the solar system will become more pronounced. The real changes start roughly 5 billion years from now, when the Sun exhausts the hydrogen fuel in its core and prepares to leave the main sequence. As the Sun takes its first tentative steps into old age, it will shine some 70% brighter than it does now.

It will take some 1 to 1.5 billion years for the Sun to evolve from the close of its main sequence life to a fully-fledged red giant. As a red giant, it will appear 100 times bigger than today and will have swallowed the innermost planet Mercury.

The Moon of course has given up on us by this point, having kept us on a stable axis for most of our existence, it has been moving away from us at the rate of 3.78 centimetres, now it’s moved too far to have this stabilizing effect and the Earth will be free to tilt from pole to equator and back, creating a very unstable climatic environment for any existing plants or animals to evolve further.

Meanwhile back to the Sun, carbon ash will build up in the centre, surrounded by a helium-burning shell which, in turn, will be surrounded by a hydrogen-burning shell, the star will expand again, bigger and more luminous, until it is an “asymptotic giant-branch star”. At this stage it will be 500 times its current diameter and swell beyond the orbit of Mars. Its outer layers will claim their second victim Venus, our “toxic twin”.
However, the mass loss of the Sun will cause the orbits of the planets to migrate outwards, Earth and Mars might survive intact, but the Sun’s internal instability during this asymptotic-giant-branch stage will cause our star to pulsate with a period measured in hundreds of days, so not really conducive to any remaining life.

In just a few tens of thousands of years, the Sun will puff off its outer layers. The Sun’s core, made of carbon and oxygen, will be left behind as a white-dwarf star. The star will then contain half the Sun’s mass compressed into a sphere the size of the Earth. High-energy radiation will energize the expanding shell, causing it to glow, until the it finally dissipates into the interstellar medium. Eventually the white dwarf itself will steadily cool off, extinguishing the light that nurtured billions of years of life in our solar system.

Yep, we all get to die in the end, along with our solar system, but the good news; we all get recycled into the interstellar medium again, hopefully to do a better job next time round.

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