Granada, Spain — An international team discovered an extraordinarily light planet in orbit around a distant Milky Way star that is 50% larger than Jupiter but with a density 25 times less than that of the gas giant, suggesting which is as ethereal as cotton candy.
The discovery of this team co-led by the Spanish Andalusian Institute of Astrophysics (IAA-CSIC)which was published this Tuesday in the magazine “Nature Astronomy”, challenges the understanding of the formation of giant and ultralight planets.
Named WASP-193bit is the second lightest planet discovered to date, only surpassed by Kepler 51d, one similar in size to Neptune, IAA-CSIC researcher Francisco J. Pozuelos explained in a statement.
The dimensions of the newly discovered planet, combined with its extremely low density, make WASP-193b “a true rarity among the more than five thousand exoplanets discovered to date.”.
According to Julien de Wit, co-author of the study and associate professor in the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology, it is “an extreme case of a class of planets called 'swollen' or 'spongy' Jupiters”.
They have known each other for 15 years but they remain “a real mystery,” according to the researcher.
Pozuelos, astronomer of the Andalusian Institute of Astrophysics, added for his part that this planet challenges all current theories of planetary formation: “We cannot explain how this planet formed. “We need detailed observations of its atmosphere to understand its evolution.”
The new planet was discovered by WASP ('Wide Angle Search for Planets'), an international collaboration that jointly operates two robotic observatories in both hemispheres. Each observatory uses a set of wide-field cameras to measure the brightness of thousands of individual stars across the sky.
Based on observations obtained between 2006 and 2008, and then between 2011 and 2012, the WAPS-South observatory detected periodic decreases in the brightness of WASP-193, a Sun-like star located about 1,200 light-years from Earth.
The analysis of these periodic transits was consistent with the passage of a gigantic “super-Jupiter” in front of the star every 6.25 days.
To calculate the mass of the planet, as well as its density and possible composition, the team used the method of radial velocities.a technique that analyzes small oscillations in the motion of the star due to the attraction of a planet orbiting it.
These variations are reflected in shifts in the wavelength of the star's spectrum: The more massive the planet, the greater the observed shift in the star's spectrum.
In the case of WASP-193b, The surprise was that hardly any significant changes were detected in the radial velocity of the star. “Despite its enormous sizethis planet is so light that it barely exerts a detectable attraction on its star,” explained Pozuelos.
Gathering the data needed to obtain the mass of the new planet took almost four years.
like cotton candy
The calculations confirm that WASP-193b has a mass approximately 0.14 times that of Jupiter and a density of 0.059 grams per cubic centimeter, considerably lower than that of Jupiter and Earthbut similar to the 0.05 grams per cubic centimeter of cotton candy.
“The planet is so light that it is difficult to imagine an analogous material in a solid state,” said Julien De Wit, who added that the reason it resembles cotton candy is because both are practically air. “The planet is basically super fluffy”.
According to the authors, it is possible that WASP-193b has an atmosphere predominantly composed of hydrogen and helium, several tens of thousands of kilometers longer than Jupiter's atmosphere. Currently, no model of planetary formation can explain a planet with an atmosphere of these proportions.
Pozuelos pointed out that, of the few known ultralight planets, this is the best candidate to be studied by the James Webb space telescope and understand “how a planet as light as cotton candy can form.”