Giant, waterlogged "hot Saturn" hints at breadth of exoplanet diversity

Giant, waterlogged

They found very odd nature of its atmosphere. It was discovered in 2011 as part of the Wide Angle Search for Planets (WASP) project when it was observed transiting in front of its parent star.

"We need to look outward to help us understand our own Solar System", explains lead investigator Hannah Wakeford from the University of Exeter in the United Kingdom and the Space Telescope Science Institute in the USA.

An global team of astronomers have used computer time of the Hubble space telescope to observe the star WASP-39, around which the exoplanet WASP-39b. They have produced the most complete spectrum of an exoplanet's atmosphere possible with present-day technology [1]. Although this "hot Saturn" doesn't belong to our solar system, the researchers believe that it will still help them better understand how and where planets form around a star. They found a lot of water vapor and heavy metal in the atmosphere of WASP-39b. Instead, is has a puffy atmosphere that is free of high-altitude clouds, allowing Wakeford and her team to peer down into its depths.

By dissecting starlight filtering through the planet's atmosphere [2] the team found clear evidence for atmospheric water vapour. Dubbed WASP-39b, this alien world's atmosphere is estimated to have water three times more than Saturn does, but it's so extremely hot that life can not thrive on its hot and bloated surface.

Although the researchers predicted they'd see water, they were surprised by how much water they found in this "hot Saturn".

The amount of water suggests that the planet actually developed far away from the star, where it was bombarded by a lot of icy material. This kind of bombardment would only be possible if WASP-39b formed much further away from its host star than it is right now.

"WASP-39b shows exoplanets can have much different compositions than those of our solar system", said co-author David Sing of the University of Exeter. It is also expected that the exoplanet had gone through many evolutions during its journey and also destroyed many planetary objects in its path. "And that's fantastic!", adds Wakeford.

WASP-39b takes only four days to come full circle around its parent star. The planet is also tidally locked, meaning it always shows the same side to its star. Talking about its current temperature, it is 1400 degrees Fahrenheit which is 600 degrees Fahrenheit more than the Mercury's temperature. As such, this "hot Saturn" has a dayside temperature of 1,430 degrees Fahrenheit (776.7 degrees Celsius), according to NASA, with powerful winds transporting heat from the dayside to the permanent nightside, keeping it nearly as hot.

Wakeford plans to book time on NASA's James Webb Space Telescope, which is due to launch later this year, to record a more complete spectrogram of the exoplanet's atmosphere with an emphasis on how much carbon and oxygen is there so as to gain a better understanding of its formation.

This planet is from the Earth at a distance of 700 light years.

Dr. Wakeford and colleagues combined the capabilities of Hubble with those of other ground- and space-based telescopes for a detailed study of WASP-39b.

[2] When starlight passes through the atmosphere of an exoplanet, it interacts with the atoms and molecules in it. "This spectrum is thus far the most lovely example we have of what a clear exoplanet atmosphere looks like", said Wakeford.



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