Of the several thousand exoplanets known today, some stand out sharply against the general background. So was the giant WASP-193b, discovered 1200 light years away. With a mass of only 0.13 of the mass of Jupiter, it is almost one and a half times larger than it in radius. Thus, the density of this planet is only about a percent of the density of the Earth. This is described in an article by European scientists, which is still being prepared for publication, but already available in the online library of preprints arXiv.
Exoplanet WASP-193b is located near the solar-type star WASP-193: it is 1.1 times more massive and 1.2 times larger than our star, close to it in brightness and age. However, WASP-193b’s orbit is much tighter than that of any planet in the solar system. It passes one annual turnover in just 6.25 days. Khalid Barkaoui of the University of Liege and colleagues estimated the mass and size of the planet by calculating its density.
This value was only about 0.059 grams per cubic centimeter. For comparison: the average density of the Earth is 5.51 g/cm3; “loose” Jupiter – 1.33 g / cm3, bottle cap – 0.2 g / cm3, and sweet cotton candy – 0.05 g/cm3. Thus, WASP-193b turned out to be several times lighter than cork and slightly denser than cotton candy. However, this is still not a new record. Planets with lowest known density known in the Kepler-51 system, the density of two of them is even lower – about 0.03 g/cm3.
Planets with extreme characteristics are rare and remain exceptions. However, they allow us to understand the general “galactic context” in which our solar system exists, to better understand the processes that lead to the emergence of worlds with different properties. So, it is assumed that such “loose” planets can be formed due to too close approach of the gas giant with its star, which leads to heating and “inflating” of its outer shells.
On the other hand, such a mechanism does not allow “loose” planets to exist for a long time. Fluxes of particles and radiation should lead to erosion of their atmosphere in a matter of tens of millions of years. Therefore, theoretically, worlds like WASP-193b should only be found in very young stars, while WASP-193 is already about six billion years old. Perhaps this contradiction can be considered an argument in favor of an unusual hypothesis, according to which the very existence of extremely “loose” exoplanets is only an illusion associated with the presence of a system of rings.
