Stargazers spy retrograde planetary bloater Astronomers have spotted what they claim is the first exoplanet in a retrograde orbit around a star - a bloated body which is also the "least-dense planet currently known". Dubbed WASP-17b, the body measures 1.5-2 Jupiter radii but weighs in at just half its mass, meaning it's about a dense as polystyrene and "if you could …
I imagine it's because the super-close orbit (1/8th that of Mercury) causes both tidal effects and heating to literally inflate the planet.
What I can't picture is how it can be at 150 degrees off the orbital plane. Surely it only reaches 90 degrees off, and then it's just 90 degrees off in the other direction?
Jupiter is just that - a gas giant with a small , dense liquid core. The density of an ideal gas like hydrogen is proportional to its temperature, all other parameters being constant. This planet is so close to its sun, it must be much hotter. It probably has its core heated by gravitational and magnetic effects as well. The only surprise is that it hasn't boiled off into space. Perhaps it has only entered this orbit recently, and will be boiled away in a few (tens of ) million years.
I suppose the tidal forces causing the bloat have done something to the density of the planet. Larger (i.e. higher volume) than Jupiter, but less mass. So it must be a lot less dense than Jupiter.
I'm not a physicist, but guess that the closeness to the sun means that gravitational effects on the planet pull some of its mass away from its centre - causing those tidal forces the boffins were talking about, and reducing the density of the gas giant.
Most of Jupiter's *atmosphere* is hydrogen and helium, there's presumed to be a much denser core comprising anything between 5 and 15% if Jupiter's total mass (that's 15 to 45 Earth masses) made of elements such as silicon and iron.
If this new planet either doesn't have a rocky core, or has a very small core (like Uranus) it would have a lower density. Saturn, for instance, has a bulk density lower than water; again because it has a relatively small core.
"There are no lighter elements."
It's a matter of compression: if you squeeze hydrogen at hundreds of thousands of atmospheres pressure at some temperature, it will be more dense than hydrogen at the same pressure but a much higher temperature.
This planet is MUCH hotter than Jupiter - thus the hydrogen in this planet will be MUCH less dense than the hydrogen in Jupiter.
i dunno. something like if you have a hyperthetical ballon, and you are able to gently heat the gas inside the ballon without it bursting, then when the ballon is twice the size, it will be half the denisty for the same given mass.
so this thing is having half the mass of jupiter, is twice the size of jupiter, so maybe its structure is carrying about 4 times the heat energy of jupiter, if it has the same material composition.
given that it is so close to the sun, from what my skim reading told me, it's orbital period is under four earth days, an increase in planetary heating i'd think is a given.
but then if it had the same mass as jupiter, its gravitational effect would be twice as strong, and so it would be half its current size? ie, equal to jupiter? i dunno. maybe at room temperature, or in the bath big enough to float this monster - rather than the hostile irradiated vaccum of space maybe?.
what i think is amazing is that the planet's magnetosphere is still strong enough to maintain a gasous body this close to the star without it being blown away by the solar wind/radiation.
but then it is probably also driven by the same tidal forces from within the star that have given it such a funky orbital disposition in the first place.
but then, i have the mental capacity to be entertained by an elastic band untill home time
Ask a creationist, or scientologist. It is obviously made of elements our "handed down" science haven't found. That our creationist overlords have built in another of their "Lab worlds"
That explains it's size and composition far easier that things like tidal forces, thermic expansion or gravitational fields.
How can our puny minds comprehend this fact.
Anon in case the chuch of nut- scientology comes looking.
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