From Nature.com, a new paper which looks at how dry atmosphere’s of some exoplanets could cast doubt on long cherished notions about planet formation. Current mainstream thinking is that big planets form a long way out and migrate inwards. Perhaps the opposite may be the case, and ‘hot jupiters’ form near the parent star and increase the size of their orbits asthay gain angular moentum. Supporting this possibility, a recent paper by Poppenhaeger on the electromagnetic coupling of proto-planetary discs with the host star posit a slowing the stellar rotation and a shift of its angular momentum to the forming planets.
Scientists searching for worlds outside of the Solar System say that three such planets — distant gas giants that resemble Jupiter — are surprisingly dry.
The atmospheres of these exoplanets, known as ‘hot Jupiters’, contain between one-tenth and one-thousandth water vapour than predicted, measurements from the Hubble Space Telescope show. The findings, published 24 July in Astrophysical Journal Letters1, are at odds with theories of how planets form.
Madhusudhan thinks that it is possible, but not likely, that clouds are skewing his results. The particles would have to be high in the atmosphere, above the water vapour, for this to be true. That would place the clouds in the thinnest part of each exoplanet’s atmosphere, but they could be too heavy to stay aloft. The clouds would also need to survive in the wide range of temperatures the three planets’ atmospheres span — 900–2,200 ºC — which models can’t yet explain. “There is just no candidate cloud composition or physics that can do it,” he says.