So today we go to another far-flung planetary locale, a gas giant 150 light years away in the direction of the constellation Pegasus:
#3 HD 209458 b
HD 209458 b (the gas giant has the unofficial moniker “Osiris”. For the sake of my sanity we’re going to call it that) is another galactic object which serves as a visual totem. I can figuratively look at the planet to immediately get a great understanding of the violent processes that shape this and other hot Jovians. I read and read and read about the planet until one morning everything just clicked and I discovered that I could visualize the gas giant in great detail. Yay for paradigm shifts.
Osiris is of the Hot Jupiter order of planetary objects; heat-swollen gas giants in fast, tight orbits around their parent star. These are the most dynamic, energetic and violent planetary environments known to humanity as of 2010, and certainly the most common class of detected exoplanet. Our most successful tools for discovering exoplanets, the radial velocity and transit, are biased toward finding big planets near to their primary. Osiris is both: It was the first gas giant discovered through the transit method back in 1999.
Io? Io has plenty of big volcanoes, sure. And sure, Io’s ejected sulphur particles coats the other Galilean moons and feed into Jupiter’s frankly insane radiation belts. For the record, Io is just a little bit smaller than our own moon. Osiris has an atmospheric superstorm the size of fucking Saturn.
Orisis has a raging planetary superstorm the size as fucking Saturn. 7,000km/h winds laden with tholins and vaporized silicate and metallic compounds that are hotter than the surface of Venus.
Superstorm. Size of Saturn. Hypersonic metal winds out to eat your soul.
The picture above is deceiving; Osiris is just shy of 70% Jupiter’s mass, but the exoplanet’s volume over twice that of Jupiter. Gas expands when heated. Park an almighty ball of gas next to to a star. It gets hot. I gather from a paper I browsed that insolation from the primary doesn’t extend deep into the atmosphere. I came away with the distinct impression that if you fell or flew down deep enough into the exoplanet you would find a basically normal gas giant environment (“normal” meaning crushing pressures and temperatures). All the fun and exciting things on Osiris happen way up at the top of the atmosphere.
We learned all of these things about Osiris because after the initially discovery because astronomers don’t stick the planet’s information into a database and forget about it – they go back and observe it time and time again. First to independently confirm that it actually is there and not an imaging error or a software phantom and then to see if anything else to be learned about it. They split the light of the primary, run it through a computer program and come up with simply stunning figures on the composition (and disposition!) of Osiris’ atmosphere and nearby environment. With that in mind I’ll say that I do not necessarily want to discuss all of the dry facts on the gas giant and the processes of its discovery and remote exploration; I linked to the planet’s Wikipedia article up top (here it is again). Pick and choose: What’s salient? The superstorm. The atmosphere. The comet’s tail. And the magnetosphere.
I touched on the superstorm up above. Osiris is close enough to its primary HD 209458 so that like our own moon, the exoplanet is tidally locked; the same side of Osiris always faces the star because the length of day equals the length of the year. Unlike Earth, where the subsolar point (the point on the body nearest the star) changes minute by minute, Osiris’ subsolar point never changes. This creates an immense convection cycle as the superheated air rushes around to the far side of Osiris and cooler air comes in to replace it. A superstorm. The image below is a temperature map of the (similar to Osiris) exoplanet HD 189733 b. The big hot spot is another superstorm, one that is just a little bit smaller than Osiris’.
Unfortunately if you were hanging in space above Osiris you likely wouldn’t see any of this. The exoplanet is dark; with an atmosphere full of tholins (organic particles), Osiris only reflect 4% of the light it receives from its parent star. In visible light the planet will resemble Titan, with nothing to betray the violence of the atmosphere.
Truly a brooding and violent planet, Osiris, HD 209458 b, I salute you.