Astronomers find exoplanet atmosphere free of clouds

May 7, 2018 , May 7, 2018 , University of Exeter

Artist rendition of 'hot Saturn' WASP-96b. A distant observer would see WASP-96b blueish in color, because sodium would absorb the yellow-orange light from the planet's full spectrum. Credit: Engine House

Scientists have detected an exoplanet atmosphere that is free of clouds, marking a pivotal breakthrough in the quest for greater understanding of the planets beyond our solar system.

An international team of astronomers, led by Dr Nikolay Nikolov from the University of Exeter, have found that the atmosphere of the 'hot Saturn' WASP-96b is cloud-free.

Using Europe's 8.2m Very Large Telescope in Chile, the team studied the atmosphere of WASP-96b when the planet passed in front of its host-star. This enabled the team to measure the decrease of starlight caused by the planet and its atmosphere, and thereby determine the planet's atmospheric composition.

Just like an individual's fingerprints are unique, atoms and molecules have a unique spectral characteristic that can be used to detect their presence in celestial objects. The spectrum of WASP-96b shows the complete fingerprint of sodium, which can only be observed for an atmosphere free of clouds.

The results are published in prestigious research journal Nature on May 7 2018.

WASP-96b is a typical 1300K hot gas giant similar to Saturn in mass and exceeding the size of Jupiter by 20%. The planet periodically transits a sun-like star 980 light years away in the southern constellation Phoenix, halfway between the southern jewels Fomalhaut (α Piscis Austrini) and Achernar (α Eridani).

It has long been predicted that sodium exists in the atmospheres of hot gas-giant exoplanets, and in a cloud-free atmosphere it would produce spectra that are similar in shape to the profile of a camping tent.

Nikolay Nikolov, lead author and from the University of Exeter said; "We've been looking at more than twenty exoplanet transit spectra. WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature, making the planet a benchmark for characterization.

A visualization of the transit of the WASP-96b in front of its host star. Credit: Ernst de Mooij

"Until now, sodium was revealed either as a very narrow peak or found to be completely missing. This is because the characteristic 'tent-shaped' profile can only be produced deep in the atmosphere of the planet and for most planet clouds appear to get in the way".

Clouds and hazes are known to exist in some of the hottest and coldest solar system planets and exoplanets. The presence or absence of clouds and their ability to block light plays an important role in the overall energy budget of planetary atmospheres.

"It is difficult to predict which of these hot atmospheres will have thick clouds. By seeing the full range of possible atmospheres, from very cloudy to nearly cloud-free like WASP-96b, we'll gain a better understanding of what these clouds are made of; " explains Professor Jonathan J. Fortney, study co-author, based at the Other Worlds Laboratory (OWL) at the University of California, Santa Cruz (UCSC).

The sodium signature seen in WASP-96b suggests an atmosphere free of clouds. The observation allowed the team to measure how abundant sodium is in the atmosphere of the planet, finding levels similar to those found in our own Solar System.

"WASP-96b will also provide us with a unique opportunity to determine the abundances of other molecules, such as water, carbon monoxide and carbon dioxide with future observations ", adds co-author Ernst de Mooij from Dublin City University.

Sodium is the seventh most common element in the Universe. On Earth, sodium compounds such as salt give sea water its salty taste and the white colour of salt pans in deserts.

In animal life, sodium is known to regulate heart activity and metabolism. Sodium is also used in technology, such as in the sodium-vapour street lights, where it produces yellow-orange light.

The team aims to look at the signature of other atmospheric species, such as water, carbon monoxide and carbon dioxide with the Hubble and James Webb Space Telescopes as well as telescopes on the ground.

'An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet ' is published in Nature on May 7 2018.

More information: N. Nikolov et al, An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet, Nature (2018). DOI: 10.1038/s41586-018-0101-7

Journal information: Nature

Provided by University of Exeter</s>London, May 8 (IANS) Astronomers have found that a planet outside our solar system, which is similar to Saturn in mass and exceeds the size of Jupiter by 20 per cent, has an atmosphere free of clouds.

The hot gas giant, WASP-96b, periodically transits a Sun-like star 980 light years away in the southern constellation Phoenix.

Using the the European Southern Observatory’s Very Large Telescope in Chile, the team studied the atmosphere of WASP-96b when the planet passed in front of its host-star.

This enabled the team to measure the decrease of starlight caused by the planet and its atmosphere, and thereby determine the planet’s atmospheric composition.

“We’ve been looking at more than twenty exoplanet transit spectra. WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature, making the planet a benchmark for characterisation,” said lead author of the study Nikolay Nikolov from University of Exeter in Britain.

Just like an individual’s fingerprints are unique, atoms and molecules have a unique spectral characteristic that can be used to detect their presence in celestial objects.

The spectrum of WASP-96b shows the complete fingerprint of sodium, which can only be observed for an atmosphere free of clouds, according to the study published in the journal Nature.

It has long been predicted that sodium exists in the atmospheres of hot gas-giant exoplanets, and in a cloud-free atmosphere it would produce spectra that are similar in shape to the profile of a camping tent.

“Until now, sodium was revealed either as a very narrow peak or found to be completely missing. This is because the characteristic ‘tent-shaped’ profile can only be produced deep in the atmosphere of the planet and for most planet clouds appear to get in the way,” Nikolov added.

Clouds and hazes are known to exist in some of the hottest and coldest solar system planets and exoplanets.

The presence or absence of clouds and their ability to block light plays an important role in the overall energy budget of planetary atmospheres.

“It is difficult to predict which of these hot atmospheres will have thick clouds. By seeing the full range of possible atmospheres, from very cloudy to nearly cloud-free like WASP-96b, we’ll gain a better understanding of what these clouds are made of,” explains study co-author Jonathan Fortney, Professor at University of California, Santa Cruz (UCSC), US.</s>For the first time ever, astronomers detected sodium atoms in the atmosphere of an exoplanet, which suggests it is cloud-free.

“Hot Jupiters” aren’t the only eccentric exoplanets out there. It turns out that “hot Saturns” can be quite whimsical too. For instance, “hot Saturn” WASP-96b seems to be “entirely cloud-free,” says astronomer Nikolay Nikolov, lead author of a recent study on the atmosphere of this peculiar exoplanet.

This strange gas giant (the planet, that is) lies 980 light-years away in the Phoenix constellation. Like all “hot Saturns,” the exoplanet is similar in mass to Saturn and 20 percent bigger than Jupiter. It also orbits its parent star, WASP-96, very closely.

According to Sci-News, it only takes 3.4 days for the “hot Saturn” to complete a full orbit around WASP-96. Such close quarters with the parent star means that the exoplanet is very hot, reaching 1,881 degrees Fahrenheit (or 1,027 degrees Celsius).

Hot exoplanets, especially those as incandescent as WASP-96b, are typically known to have thick atmospheres, with plenty of clouds and hazes. The same goes for some of the coldest planets in the cosmos. However, this strange exoplanet doesn’t fit the mold, Nikolov’s team uncovered.

The researchers managed to take a close look at WASP-96b with the help of the European Southern Observatory’s Very Large Telescope (VLT) in Chile. Known as the world’s most powerful exoplanet-hunting telescope, the VLT enabled the team to gauge the composition of WASP-96b’s atmosphere as they observed the “hot Saturn” passing in front of its parent star.

Their observations pointed to a unique discovery, reveals a news release from the University of Exeter in the U.K., which led the study. For the first time ever, the astronomers found the complete fingerprint of sodium in the spectrum of an exoplanet. This discovery comes just a few days after the first-ever detection of helium in the atmosphere of exoplanet WASP-107b.

“Until now, sodium was revealed either as a very narrow peak or found to be completely missing,” said Nikolov, who is a research fellow at the British university.

Nevertheless, WASP-96b’s atmosphere was found to contain plenty of sodium, present in “levels similar to those found in our own solar system,” notes the news release.

According to the university, these high levels of sodium would make the “hot Saturn” appear bluish in color to a distant observer, because the sodium would absorb the yellow-orange light from the exoplanet’s full spectrum.

Finding sodium in WASP-96’s atmosphere led to another breakthrough. Since the spectral characteristics of sodium atoms can’t be observed in planets with thick atmospheres because their clouds would obscure the view — the element’s “tent-shaped” profile can only be spotted deep in a planet’ atmosphere, notes Nikolov — the team deduced that WASP-96b’s atmosphere has no clouds.

“WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature, making the planet a benchmark for characterization,” Nikolov pointed out.

This exoplanet’s “spectrum is in excellent agreement with cloud-free, solar-abundance models,” his team wrote in their paper, published yesterday in the journal Nature.

This important discovery has now given astronomers the opportunity to observe the full range of possible atmospheres on other planets, which can help shed more light into cloud formation and composition, noted Nikolov.

“WASP-96b will also provide us with a unique opportunity to determine the abundances of other molecules, such as water, carbon monoxide and carbon dioxide with future observations,” said study co-author Dr. Ernst de Mooij, from Dublin City University in Ireland.</s>Scientists have detected an exoplanet atmosphere that is free of clouds, marking a pivotal breakthrough in the quest for greater understanding of the planets beyond our solar system.

An international team of astronomers, led by Dr. Nikolay Nikolov from the University of Exeter, have found that the atmosphere of the ‘hot Saturn’ WASP-96b is cloud-free.

Using Europe’s 8.2m Very Large Telescope in Chile, the team studied the atmosphere of WASP-96b when the planet passed in front of its host-star. This enabled the team to measure the decrease of starlight caused by the planet and its atmosphere, and thereby determine the planet’s atmospheric composition.</s>An important arm of exoplanet research involves the study of the atmospheres that surround these distant worlds. The molecules they hold can reveal valuable insights into what kind conditions can be found there – along with ones that cannot. Such is the case for scientists studying WASP-96b, who are now claiming to have discovered the first exoplanet to be free of clouds.

Described as a "hot Saturn," WASP-96b circles a Sun-like star around 980 light years away in the constellation of Pheonix. Astronomers at the University of Exeter and Dublin City University were observing the planet with the Very Large Telescope in Chile, studying its atmosphere as it passed in front of its host star.

This technique is known as the transit method and involves detecting the dimming of a host star by an exoplanet passing in front of it. NASA's Kepler Space Telescope has discovered the presence of thousands of exoplanets using this method, but by looking at what kind of light that makes its way through, scientists can also draw conclusions about a planet's atmosphere.

This is because an atmosphere will block certain wavelengths of light depending on the kinds of molecules and atoms within it, creating a unique spectrum for that planet. And it just so happens that the unique signature of WASP-96b contains the complete fingerprint for sodium, a chemical element that produces a tent-shaped spectra and can only be seen in atmospheres without clouds.

"Until now, sodium was revealed either as a very narrow peak or found to be completely missing," says Nikolay Nikolov, lead author from the University of Exeter. "This is because the characteristic 'tent-shaped' profile can only be produced deep in the atmosphere of the planet and for most planets clouds appear to get in the way."

The team was also able to measure the abundance of sodium in the atmosphere of WASP-96b, observing levels similar to those found in our own Solar System. Its presence suggests that the exoplanet WASP-96b has an atmosphere free of clouds, which not only furthers our understanding of the universe, but also clears the way for further inspection.

"WASP-96b will also provide us with a unique opportunity to determine the abundances of other molecules, such as water, carbon monoxide and carbon dioxide with future observations," says co-author Ernst de Mooij, from Dublin City University.</s>Astronomers have detected an exoplanet whose sodium-rich atmosphere is completely devoid of clouds—a strange celestial feature that until this point only existed in theory.

The planet is called WASP-96b, and it’s located about 980 light-years from Earth. This distant world is what astronomers call a hot-Saturn—a planet with a mass comparable to our own Saturn (even though this one is 20 percent larger than Jupiter), but with considerably hotter surface temperatures (in this case, temperatures can exceed 1,000 degrees Celsius). A year on WASP-96b only lasts about three days, which should give you a sense of how close it is to its host star.

The temperatures on this blazingly hot world may be unbearable, but visitors to this exoplanet wouldn’t have to worry about any clouds or haze obstructing their view of the heavens. As new research published in Nature shows, WASP-96b’s atmosphere has no clouds. Not a single one—not a fluffy cumulus, a hazy stratus, or wafting cirrus. Not even haze exists on this world. The reason has to do with the atmosphere’s primary ingredient: gaseous sodium. The ubiquitous presence of this element makes it impossible for haze or clouds to form and remain stable.

Prior to this discovery, astronomers had predicted that some gas giants with an overabundance of atmospheric sodium would be cloud-free. These latest observations are now the first to prove it. Sodium is the seventh most common element in the Universe, and it’s previously been detected around Mercury, within cometary tails, and in the atmospheres of some exoplanets. But WASP-96b’s “absolute sodium abundance” precludes the possibility of clouds.

Astronomers have known about Wasp-96b since 2013, but a recent survey of this planet and the atmospheres of 20 similar worlds led to the cloud-free discovery. The scientists couldn’t actually see the cloud-free skies of the planet. Instead, using the Very Large Telescope in Chile, a research team led by Nikolay Nikolov from the University of Exeter captured the planet’s spectral signature as it passed in front of its host star. The incoming wavelength pointed to sodium, and with a spectrum that was in “excellent agreement” with a pristine, cloud-free environment.

“WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature, making the planet a benchmark for characterization,” said Nikolov in a statement. “Until now, sodium was revealed either as a very narrow peak [as seen in the spectral graph] or found to be completely missing. This is because the characteristic ‘tent-shaped’ profile can only be produced deep in the atmosphere of the planet, and for most [planets] clouds appear to get in the way.”

It’s an important discovery, because clouds have a profound effect on a planet’s climate, blocking out light, absorbing aerosols, and sometimes producing rain that falls on the surface. Trouble is, knowing which planets are capable of producing thick clouds isn’t easy, given the vast distances involved. WASP-96b will now provide a good model for researchers as they move forward. For the next stage of this research, the scientists are hoping to determine how much water, carbon monoxide, and carbon dioxide exists on WASP-96b, offering a fuller picture of this world and its unique atmosphere.

Correction: An earlier version of this article incorrectly equated sodium with salt (salt is actually sodium with chloride). Sorry for the error.</s>Out in the cold, dark cosmos, a team of astronomers has discovered an exoplanet that is completely cloud-free.

The Kepler Space Telescope has contributed a great deal to astronomy, revealing thousands of strange exoplanets against the backdrop of the blackness of space.

And, sometimes, it helps astronomers find a particular planet that, to those of us on Earth, sounds truly alien.

The latest one to join that list is a ‘hot Saturn’ dubbed WASP-96b, analysed in detail by a team of international astronomers led by Dr Nikolay Nikolov from the University of Exeter and including Dr Ernst de Mooij from Dublin City University’s School of Physical Sciences.

Publishing their findings to Nature, the team revealed that a unique set of circumstances mean that WASP-96b has an atmosphere completely free of clouds.

Using the European Southern Observatory’s Very Large Telescope in Chile, the team studied the atmosphere of WASP-96b when the planet passed in front of its host star. This allowed them to measure the decrease of starlight caused by the planet and its atmosphere, thereby determining the planet’s atmospheric composition.

In the same way that a person’s fingerprints can reveal their identity, atoms and molecules can be identified through spectral analysis. In the case of WASP-96b, the results showed sodium.

This was important in determining the planet’s chemical composition because sodium can only be detected on a cloud-free planet.

WASP-96b has a sweltering average temperature of more than 1,000C and a mass similar to Saturn, but it is about 20pc larger than Jupiter.

It was the only planet out of 20 analysed during the study to show a cloud-free atmosphere.

“Until now, sodium was revealed either as a very narrow peak or found to be completely missing,” Nikolov said.

“This is because the characteristic ‘tent-shaped’ profile can only be produced deep in the atmosphere of the planet and for most [planets] clouds appear to get in the way.”

Speaking of its importance to our understanding of similar planets, de Mooij of DCU said: “WASP-96b will also provide us with a unique opportunity to determine the abundances of other molecules such as water, carbon monoxide and carbon dioxide with future observations.”
Scientists discover that WASP-96b has an atmosphere that is free of clouds.