Eulogy for a Dead Planet

The fate of the ZTF SLRN-2020 system awaits us all

In a new article in Nature, published May 3, a group of astronomers announce that they have observed a planet being destroyed by a dying sun.

Like all extrasolar planets, this planet could not be seen directly, not even through a powerful telescope. But its fate was discernible through analysis of changes in the light emitted from the star. That analysis indicated that the star, an ancient red giant bearing the poetic and deeply evocative name ZTF SLRN-2020, engulfed and consumed a gas giant in close orbit around it over the course of ten days.

A hapless astronomer at the Palomar Observatory in California (whom I hope will receive counseling) stumbled upon the grisly demise of the planet. Though horrific, it was a remarkable discovery. When you consider the fact that the planet had likely been around for billions of years, the sheer luck of catching it at the very moment of its death is incredible. On a cosmological scale, ten days is a flash, the twinkling of an eye.

Watching Our Future Unfold

If you enjoy the intersection of astronomy and eschatology, you have probably read that this may be the eventual fate of Earth. Sun-sized stars typically swell as they age into enormous red giants many times their original size. This causes them to engulf the inner planets of their systems, destroying them.

Our own sun is expected to engulf Mercury, Venus, and possibly Earth. Earth is far enough from the sun that its fate is not certain. We may be engulfed, or we may merely be toasted - which will still cause all life on Earth to perish. Then, whether the earth has been toasted and eaten or merely toasted, the sun will collapse from a massive red giant into a dull white dwarf, which will burn on faintly for some billions of years until it finally goes out.

In the past, this theory was supported by the discovery of apparent remnants of burnt-up planets circling white dwarfs, as well as changes in the chemical make-up of some stars consistent with the idea that they had already absorbed planets. But the destructive event itself had not been observed - until now.

Not only is this the first time we have witnessed the destruction of a planet by means of planetary engulfment, it is the first time – as far as I know – that humanity has directly witnessed the end of any planet by any means at all. Up until now, we have observed the shards and smoke of lost worlds, but never witnessed their destruction as it happened. This is a historic moment – the last historic moment for the poor gas giant, but for us, a historic first.

Sometimes, these historic firsts don’t receive the fanfare they deserve, because the existence of the phenomenon has been accepted by science for so long that we forget we haven’t actually witnessed it before. So I think it’s worth taking a moment to feel the gravity of what we have just seen.

Our jaded modern outlook may make that difficult, of course, so I’ll turn to a fictional depiction of the end of a world to help us out.

Witnesses of the End

C.S. Lewis describes a remarkably similar apocalypse in The Last Battle. The characters gather at the Stable Door, on the threshold of Aslan’s Country, and watch the destruction of Narnia unfold:

A streak of dreary and disastrous dawn spread along the horizon, and widened and grew brighter, till in the end they hardly noticed the light of the stars who stood behind them. At last the sun came up. When it did, the Lord Digory and the Lady Polly looked at one another and gave a little nod: those two, in a different world, had once seen a dying sun, and so they knew at once that this sun also was dying. It was three times - twenty times - as big as it ought to be, and very dark red. As its rays fell upon the great Time-giant, he turned red too: and in the reflection of that sun the whole waste of shoreless waters looked like blood.

Then the Moon came up, quite in her wrong position, very close to the sun, and she also looked red. And at the sight of her the sun began shooting out great flames, like whiskers or snakes of crimson fire, towards her. It is as if he were an octopus trying to draw her to himself in his tentacles. And perhaps he did draw her. At any rate she came to him, slowly at first, but then more and more quickly, till at last his long flames licked round her and the two ran together and became one huge ball like a burning coal. Great lumps of fire came dropping out of it into the sea and clouds of steam rose up.

Then Aslan said, "Now make an end."

The giant threw his horn into the sea. Then he stretched out one arm - very black it looked, and thousands of miles long - across the sky till his hand reached the Sun. He took the Sun and squeezed it in his hand as you would squeeze an orange. And instantly there was total darkness.

Everyone except Aslan jumped back from the ice-cold air which now blew through the Doorway. Its edges were already covered with icicles.

"Peter, High King of Narnia," said Aslan. "Shut the Door."

Peter, shivering with cold, leaned out into the darkness and pulled the Door to. It scraped over ice as he pulled it. Then, rather clumsily (for even in that moment his hands had gone numb and blue) he took out a golden key and locked it.

Lewis’s depiction is very much consistent with what contemporary astronomy predicts will be the fate of all worlds in our universe (minus a few personifying details like the Time-giant). If God doesn’t intervene sooner, what has just happened to the gas giant and ZTF SLRN-2020, or some variation thereof, will happen to all the stars and planets – until every last planet is burned up or left lifeless, sunless and orphaned, and every last star has flared up and burned out. Then the universe will be all darkness and stillness and cold, forever.

That won’t be the end of the universe, though. It will merely be the end of everything interesting in it. In our universe as it is now, nothing is really destroyed – it merely changes form. Only if our world is cast out from the presence of God, will it truly cease to be, for “in him we live and move and have our being.”

So the real End will come when the door to Aslan’s Country is pulled shut:

Then I saw a great white throne and him who was seated on it. The earth and the heavens fled from his presence, and there was no place for them (Revelation 20:11).

Next thing we know, we will be standing on a new earth, beneath a new sky, which we have never seen before – though our hearts perhaps have glimpsed them. The newness there will never turn to old, for the old order of things will have passed away, and there will be no longer any curse.

Let Us Say Farewell

That may still be a long way off. But the beginning of the end, which will come to our own solar system one day, has already come to ZTF SLRN-2020. And like the Pevensie children, and Eustace and Jill, and Digory and Polly, we have the sobering honor and privilege of standing at a safe distance and watching a realm meet its end.

Of course, from our vantage point, we don’t get quite as theatrical a show. Staring at pages of data about non-visible-spectrum light wavelengths isn’t quite as moving as staring through the door of a magic stable. And because light is very slow (or the cosmos very wide) the event we just witnessed actually happened about 12,000 years ago. Nonetheless, it is well that we are here to witness the end of the world. We may well be the only witnesses; if that solar system ever had any inhabitants, they are likely all long gone by now. So it falls to us to bear witness, and to mourn – if we can find anything within ourselves that considers a world worth mourning.

While we watch, we should take this memento mori to heart. As St. John said, the world is passing away, along with its desires. The tragic tale of ZTF SLRN-2020 is our tale, in the end.

Farewell, Unknown World of the Red Sun ZTF SLRN-2020. All worlds must end, yet we should be cold-hearted not to mourn you.

May we visit you one day in Aslan’s Country.