An international team has discovered an extraordinarily light planet orbiting a distant star in the Milky Way that is a 50% larger than Jupiter but with a density 25 times less than that of the gas giant, suggesting that it 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 journal Nature Astronomy, challenges understanding of the formation of giant, ultralight planets.
Called WASP-193b, it 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.
A true rarity in the Milky Way
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.”
The mass of the discovered planet is equal to that of cotton candy (Image created through OpenAI DALL-E by David Berardo).
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, this is “an extreme case of a class of planets that are called ‘swollen’ or ‘spongy’“.
They have known each other for 15 years but they remain “a real mystery,” according to the researcher.
Pozuelos, an astronomer at the Andalusian Institute of Astrophysics (southern Spain), added that this planet defies 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” ahead 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 movement of the star due to the attraction of a planet orbiting around it. .
In the case of WASP-193b, the surprise was that hardly any significant changes in the star’s radial velocity were detected. “Despite its enormous size, this planet is so light that it barely exerts a detectable attraction on its star,” Pozuelos explained.
It has a mass equal to cotton candy
Gathering the data needed to obtain the mass of the new planet took almost four years. Calculations confirm that WASP-193b has a mass of approximately 0.14 times that of Jupiter and a density of 0.059 grams per cubic centimeter, considerably lower than that of Jupiter and Earth, but similar to 0.05 grams per centimeter. cubic 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, adding that the reason it resembles cotton candy is because both are practically air. “The planet is basically super fluffy.”
Artist’s impression of an extremely low-density planet (NASA ESA CSA J.OLMSTED/STSCL).
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.”
