Astronomers have discovered a new planetary oddity beyond the solar system, as soft and light as cotton candy.
The extrasolar planet, or “exoplanet,” called WASP-193 b, is about 1.5 times as wide as Jupiter but has just over one-tenth the mass of the gas giant in the solar system. This makes it the second lightest planet in the exoplanet catalogue, which contains more than 5,400 records. Only the Neptune-like world, Kepler 51 d, is lighter than WASP-193 b.
Located about 1,200 light-years from Earth, WASP-193 b orbits its star at a distance of about 6.3 million miles; this is approximately 0.07 times the distance between the Earth and the sun. This means that its Sun-like star WASP-193 completes its orbit in just 6.2 Earth days.
The discovery of WASP-193 b adds to the vast and wonderful diversity of planets outside the solar system and could help scientists redefine models of how planets form.
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“It is really rare to find these giant objects with such small density,” discovery team co-leader and Massachusetts Institute of Technology (MIT) postdoctoral researcher Khalid Barkaoui said in a statement. said. “There’s a class of planets called puffy Jupiters, and what they are has been a mystery for 15 years. And this is an extreme example of that class.”
Bubbly world is an ‘outlier’ in planet formation models
The MIT team found WASP-193 b using the Wide Angle Search for Planets (WASP) system, which consists of two robotic observatories and telescope arrays, one in the northern hemisphere and the other in the southern hemisphere.
WASP detected the bloated gas giant planet using tiny dips in starlight that occur as it passes, or “transits,” across the face of the star. These transits also allowed researchers to determine the planet’s plus-Jupiter size and orbital period (how long it takes to complete one orbit around its star).
WASP-193 b’s mass was determined by observing the gravitational pull it exerts on its star as it orbits. This causes a “wobble” in the star’s motion, which manifests itself as a shift in the wavelengths of light coming from it. The magnitude of the distortion gives scientists an idea of the planet’s mass. However, in this case, WASP-193 is so light that its pull on its star cannot be detected using this “radial velocity” method.
“Generally, large planets are pretty easy to detect because they are usually very large and exert a large gravitational pull on their stars,” said team member Julien de Wit, an assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences. said. “But what was misleading about this planet was that although it was large – huge – its mass and density were so low that it was actually very difficult to detect using radial velocity techniques alone. It was an interesting twist.”
It took four years of observations with WASP to pick up a small but detectable “wobble” signal from this star and determine the mass of the orbiting gas giant exoplanet. This confirmed that WASP 193 b is so “puffy” that it defies concepts of planet formation.
“We were getting extremely low intensities in the beginning, which was very hard to believe at the beginning,” said team co-leader Francisco Pozuelos, a senior researcher at the Andalusian Institute of Astrophysics. “We don’t know where to put this planet in all the formation theories we have now because it’s an outlier of all of them.
“We cannot explain how this planet was formed according to classical evolutionary models.”
To understand how light and soft WASP-193 b is, we can say that the Earth has a density of 5.5 grams per cubic centimeter, while the gas giant Jupiter in the solar system has a density of about 1.3 grams per cubic centimeter. The density of WASP-193 b is only 0.059 grams per cubic centimeter. It is roughly similar to cotton candy because it has a density of about 0.05 grams per cubic centimeter.
“The planet is so light that it is difficult to think of a similar, solid-state material,” Barkaoui said. he explained. “The reason it’s close to cotton candy is because they’re both mostly composed of light gases rather than solids. The planet is basically super soft.”
The team thinks WASP-193 b consists mostly of hydrogen and helium, like Jupiter and other gas giants. They suggest that these gases form a hyperinflated atmosphere tens of thousands of miles wider than Jupiter’s atmosphere.
While the puffy atmosphere is likely a result of radiation bombardment from WASP-193 b’s nearby star, what the team does not yet know is exactly how this super-puffy nature is maintained by WASP-193 b. planet formation models do not take this into account.
“A closer look at its atmosphere will allow us to obtain the evolutionary path of this planet,” Pozuelos said. said.
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To gather information about WASP-193 b’s atmosphere and uncover the secrets of its origin, the team will turn to a technique developed by de Wit. The technique also uses dips in starlight caused by a planet as it passes across the face of its star to determine atmospheric properties such as temperature, composition, and pressure at various depths.
The team also thinks WASP-193 b could be an ideal exoplanet target for the James Webb Space Telescope (JWST).
“The larger a planet’s atmosphere, the more light can pass through,” de Wit concluded. “So it’s clear that this planet is one of the best targets we have for studying atmospheric effects. It will be a Rosetta Stone to try to solve the mystery of puffy Jupiters.”
The team’s research was published Tuesday (May 14) in the journal Nature Astronomy.