Exoplanet Excursions: September 2015

Jon travels to a red dwarf star in Leo to view an ice giant that is slowly spiralling into its stellar host.

Image Credit: 
Mark Garlick
Credit: Illustration by Mark Garlick

Everyone was so heartened to hear Philae had reawakened upon its comet, albeit at the funny angle at which it came to rest. The prospect of viewing a comet as it goes into full fizz around our Sun, from the surface of that very comet, is one of wonderful anticipation.
It brings to mind the days when my Dad used to service an industrial package boiler at a mushroom farm. Every so often he needed to ‘crank a steam valve’ to clear the system. At this moment a monumental column of piping hot vapour emerged from a dented chimney pipe with such force it resembled a giant cumulus cloud being instantly spaghettified. This is how I imagine it would look standing on a comet’s surface and looking back along the tail.
To observe similar phenomena on an immensely larger scale I’m journeying to the constellation of Leo, 33 lightyears from Earth, and the red dwarf star Gliese 436. It seems a frail little star, billions of years older than our Sun, much fainter and just 42 per cent the radius. It defiantly shines with a magnitude of +10.6. 
Orbiting the star is a planet of a similar scale to Uranus named Gliese 436 b. This world has been the focus of a fair amount of attention recently. Perhaps this ice giant is undergoing a sort of planetary migration, with an orbital path skewed so that it is inexorably spiralling towards its parent star. This certainly appears to be what’s happening. 
Gliese 436 b is very close to its star, completing an orbit in only 2.6 Earth days. This proximity reveals a bite point on the planetary migration path. The outcome is this ice giant’s atmosphere is being ruthlessly evaporated by the staggering volumes of radiation and heat. It leaves a colossal wake of boiled-away material stretching far enough to show portions of the planet’s orbital track. The atmospheric trail, a brew that is likely to contain hydrogen and carbon monoxide, has shades of petrol blue and slate grey with parts gently reddened by the star’s glow.
I’ve always loved observing comets. Hale-Bopp was a perky little stub of a comet, charming and fascinating. It reminded me of a chunky tadpole. Comet C/2006 P1 McNaught on the other hand was majestic – it’s not also known as the Great Comet of 2007 for nothing. 
Seeing comet-like activity on a scale 22 times the size of Earth is one of the most compelling things we could witness in any star system. It’s as though the entire island of Madagascar had morphed into a giant sphere and begun steaming across the Indian Ocean, leaving a wake of unimaginable ferocity. The comets we view from Earth are like clockwork yachts in a bathtub compared to this.
Similar beautiful devastations will befall our Earth when the Sun transforms into a red giant. But let’s not dwell on that now.

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

This column originally appeared in the September 2015 issue of BBC Sky at Night Magazine.

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