EX PLANET EX­CUR­SIONS

Jon vis­its a world very much like Venus, but also mer­ci­fully very dif­fer­ent

Sky at Night Magazine - - EXOPLANET EXCURSIONS - JON CULSHAW’S Jon Culshaw is a co­me­dian, im­pres­sion­ist and guest on The Sky at Night

Af­ter the seren­ity of the TRAPPIST-1 sys­tem, 39 lightyears from Earth, I thought that my ship and I would ben­e­fit from a jour­ney some­where far­ther afield. And I’ve got the per­fect des­ti­na­tion in mind: Ke­pler 1649b.

This world holds a par­tic­u­lar fas­ci­na­tion for me be­cause of the sim­i­lar­i­ties it shares with Venus. It or­bits the star Ke­pler 1649, which is 219 lightyears away in Cygnus. Ke­pler 1649 is smaller than our Sun, around a quar­ter of its size and mass. It’s a faint lit­tle star that shines at mag. +17.3, so a rather sub­stan­tial scope would be re­quired to ob­serve it from Earth.

The planet, which is an es­ti­mated 1.08 Earth radii, re­ceives the same amount of starlight as Venus does from the Sun, which makes me won­der. How sim­i­lar to our hellish, sul­phuric acid rain­ing, run­away green­house ef­fect, evil sib­ling Venus is it?

For all the sim­i­lar­i­ties, there are some im­por­tant dif­fer­ences too. The planet is much closer to its star than Venus is to the Sun, just 0.05 AU, com­plet­ing an or­bit ev­ery nine days. It re­ceives lower lev­els of ra­di­a­tion than Venus, since its home star emits en­ergy at lower fre­quen­cies than the Sun. Ke­pler 1649b is also cooler than the Sun (ther­mally, not cul­tur­ally) at around 3240 Kelvin. Such a close or­bit has tidally locked this world. The planet also ap­pears to have some quite ro­bust ge­o­log­i­cal ac­tiv­ity go­ing on. Ev­i­dence of vol­canic ac­tiv­ity like Io’s can be seen: yel­low, shin­ing, vein-like growths flecked across the night side of the planet. Tidal heat­ing could well be tak­ing place here.

There are breaks in what ap­pears to be a thin at­mos­phere en­velop­ing the planet. The breaks fit to­gether in a for­ma­tion like a pas­try lat­tice, giv­ing tan­ta­lis­ing views of the planet’s sur­face be­low. Un­like molten plan­ets, Ke­pler 1649b looks hard-baked and smoul­der­ing.

Al­low me to be tan­gen­tial for a mo­ment. As a seven-year-old I was fas­ci­nated by a gi­ant, in­dus­trial boiler at a mush­room farm where my dad worked. It had an outer view­ing tube which al­lowed the fe­roc­ity of the fire in­side to be seen. This was amaz­ing to watch. I thought of the ma­chine as be­ing like an in­door, man-made vol­cano. One mo­ment there’d be the daz­zling, solid yel­low light of the fire vis­i­ble through this tube. When the fir­ing cy­cle ended, there’d be a bright am­ber heat shine grad­u­ally fad­ing from yel­low to orange to red, then brown – like moon­rise in re­verse. The sur­face of Ke­pler 1649b ap­pears very much like this. Patches of vary­ing heat in­ten­sity, blended to­gether like gi­raffe mark­ings. An in­cred­i­ble and un­usual plan­e­tary sur­face to be­hold.

I hover the Per­i­he­lion at a point on the planet’s night side where I can safely ob­serve. The sky is over­cast and what ap­pears to be deep red cot­ton wool. Be­low that is a clear zone of vivid orange like a glass­blower’s oven with the area lead­ing to the hori­zon, as well as the hori­zon it­self, fes­tooned with gold sparks of dis­tant vol­canic ac­tiv­ity. It’s like a soothed ver­sion of Venus. Less vi­o­lent and more beau­ti­ful.

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