Mystery of the "cotton candy planets" solved? - WASP-107b warmer than expected
For years, exoplanets with unusually low densities have kept astronomers guessing. Now a simple explanation has been found for the first one.
Artistic representation of WASP-107b
(Image: NASA, ESA, CSA, R. Crawford (STScI))
The James Webb Space Telescope (JWST) may now have solved the mystery of the so-called "cotton candy planets", i.e. exoplanets with far too low densities. Two independent research teams have come to the conclusion that at least WASP-107b is significantly warmer than previously assumed. It is probably heated by what is known as tidal heating or tidal friction, triggered by an orbit that is not completely circular. This means that the celestial body is not as mysterious as assumed, as the density of most substances decreases with increasing temperature. Similar explanations could also be found for other extremely light exoplanets, it is assumed.
Much warmer than assumed
The "puffy planets" have been found for years, and the calculations possible up to now have resulted in densities between 0.06 and 0.31 g/cm3. This means that the exoplanets would float comfortably on a sufficiently large ocean of water, as a popular comparison goes. Earth, on the other hand, has a density of 5.5 g/cm3, while Saturn, the planet with the lowest density in the solar system, has a density of 0.69 g/cm3. However, this does not say much about the exact structure of the celestial bodies and better instruments such as the JWST can therefore overturn previous assumptions. This is now evident from the two research articles published in the scientific journal Nature.
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As those responsible for the space telescope summarize, spectral investigations of WASP-107b have revealed a surprising lack of methane, although other carbon-based molecules are present there. This indicates higher temperatures in the interior of the exoplanet, where methane is not stable. The fact that this "cotton candy planet" has such an inflated atmosphere is therefore not due to unusually extreme circumstances, but to its higher intrinsic temperature. In addition, a new way of determining the mass of the solid core has been found. It must therefore be significantly more massive than previously thought. This makes much more sense, says the team. However, it remains to be seen whether the puzzle has also been solved for other "cotton candy planets".
Tidal heating is an effect in which the orbital and rotational energy of a celestial body is released as heat in the interior of a celestial body. In the solar system, this effect is probably the cause of the unusually strong volcanism on Jupiter's moon Io. In the case of WASP-107b, the effect could now explain where the energy required to heat up the exoplanet comes from; the radiation from its star alone is not enough. It is 211 light years away from Earth, WASP-107b needs 5.7 Earth days for one orbit. There are a total of three exoplanets in the star system, each with a density of only around 0.3 g/cm3.
(mho)
