Exoplanet Excursions: September 2014

Jon takes another leap into the future to witness the eventual fate of a star like ours.

With great trepidation I must visit the system of Kepler 56. This star, some 2,800 lightyears away and around four times the size of our Sun, has become what’s known as a ‘G0V’. It has crossed that critical, irreversible borderline on its transition to the status of a red giant.

Credit: Illustration by Mark Garlick

There’s a sense of volatile instability, even anger as Kepler 56 burns through the helium at its core and undergoes a savage, unstoppable, ballooning expansion. Viewing Kepler 56 in this state conjures a sound in the imagination of every timpani drum in the world being played simultaneously with increasing, raging intensity. 

The planets orbiting Kepler 56 seem utterly powerless other than to accept a fate of cataclysmic destruction as their star expands to consume them, and it brings a disconcerting chill to realise this fate awaits the planets around our own star. Planets Kepler 56b, 56c and 56d could easily be Mercury, Venus and Earth trapped on an orbital death row of impending incineration.

I steer the Cruiser Globe near to the second planet out, Saturn-sized Kepler 56c, which takes about 21 days to complete its orbit. With another deft leap forwards in time, aimed for 24 million years in the future, I reach a point in time when the immolation of this world will be most fearsomely and soberingly visible.

The Cruiser Globe’s heat, gravity and force-field controls need ratcheting to maximum to stabilise my position, 950,000km away from one of 56c’s rocky moons. From here, the full destructive drama plays out in a most terrifying way. The outer layers of gas giant Kepler 56c are boiling away, making the planet look like a supermassive comet.

What appears like a giant cometary tail is laced with blindingly luminous colours as all the chemical elements in the planet burn in their appropriate shades. Four moons are visible in the heat blast and they glow dazzling silver, just like the pellet-sized pieces of magnesium my physics teacher used to hold with tongs over a Bunsen burner.

That this could happen to Earth – the thought of seeing cities, forests, oceans and all of those familiar Earthy features mercilessly vaporised by the advancing expansion of a red giant star – brings a nauseating pang: our Sun, once so benevolent and life-giving, now turning on us like a hyena eating its young.

Kepler 56c continues to be obliterated and shall do steadily for a few million years yet. Altered gravity makes it buckle out, so it takes on the guise of a superheated egg against the backdrop of the red giant filling the sky.

It seems a sad and horrifyingly ruthless process. But let’s think forward a moment: once the red giant phase of Kepler 56 is done, a protoplanetary nebula and a white dwarf will remain. These in turn will slowly dissipate into space and live on to become part of other, brand new star-forming and planet-forming regions. The ebbing, flowing, renewing and recycling process plays out perfectly in the rivers of time.

Jon Culshaw is a comedian, impressionist and guest on The Sky at Night

This column appeared in the September 2014 issue of BBC Sky at Night Magazine

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