JON CULSHAW’S EXOPLANET EXCURSIONS

Jon pilots the Perihelion to a hot, wet gas giant with coffee-coloured bands

S even hundred lightyears away, in the constellation of Virgo, lies a faint star with the name Wasp-39. It shines faintly in our skies with a magnitude of +12.1 – within the grasp of a large telescope set up under dark skies. Wasp-39 is a G8-class, yellow dwarf star very similar to our own Sun, being 93 per cent of its mass and about 90 per cent of its radius. It’s far enough away that the light from it reaching us now began its journey around the time of the Battle of Bannockburn in the early 1300s!

I’m on the way to Wasp-39 in my ship the Perihelion, to take a closer look at a recently discovered gas giant in a very close orbit to the star. Wasp-39b is about the size of Saturn, and it’s just 0.05 AU from Wasp-39; that’s 20 times closer than Earth is to the Sun. Such a close orbit – taking just four days to complete – leaves Wasp-39b tidally locked, with the star-facing side baking at a blisteringly hot 776°C. Powerful, fast winds distribute this heat evenly all the way around its atmosphere. It’s likely that Wasp-39b formed much further out in the system and – like that other class of gas giant exoplanets, ‘hot Jupiters’ – migrated in to its current position at some point in its past.

Wasp-39b has been described as a ‘wet gas giant’, however, because water has been detected in its atmosphere; water that may well have come from collisions with comets and other bodies earlier in its history. Spectra taken with the Hubble and Spitzer Space Telescopes discovered the presence of huge amounts of water in the upper atmosphere; in fact, three times as much water as exists on Saturn. This is certainly a most curious prospect.

I wonder what sounds might be created by a world described as a ‘wet gas giant’. The sloshing and gurgling of a planetarygrade orbiting laundrette? Perhaps combined with the eerily evocative sound of shortwave radio signals or Morse code, and the mating call of a Megalodon? It’s a whimsical idea at least, a part of the Universe that could well have been conjured up by Douglas Adams.

Stopping the Perihelion 1.2 million km from the planet – the same distance that Titan orbits Saturn – I am rewarded with an arresting view of Wasp-39b. It has the gentle appearance of a vanilla-flavoured gas giant, garlanded with coffee-coloured parallel shades of beige and off-white, but I bet it smells of hot Brasso.

We’re familiar with Jupiter’s shades of ochre, steel blue and silvery white. The texture of Wasp-39b’s atmosphere follows similar if much softer patterns, with curves and swirls of more delicate shades. The bands appear as though they could have been made by a creative barista using the soft hues of a Dulux colour chart.

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