{"id":20540,"date":"2022-02-25T11:22:42","date_gmt":"2022-02-25T11:22:42","guid":{"rendered":"https:\/\/ounews.co\/?p=20540"},"modified":"2022-02-25T11:22:42","modified_gmt":"2022-02-25T11:22:42","slug":"ruby-clouds-and-water-behaving-strangely-what-we-found-when-studying-an-exoplanets-dark-side","status":"publish","type":"post","link":"https:\/\/www.open.ac.uk\/blogs\/news\/science-mct\/ruby-clouds-and-water-behaving-strangely-what-we-found-when-studying-an-exoplanets-dark-side\/","title":{"rendered":"Ruby clouds and water behaving strangely \u2013 what we found when studying an exoplanet\u2019s dark\u00a0side"},"content":{"rendered":"

by Joanna Barstow<\/a>, The Open University<\/em><\/p>\n

Since astronomers discovered the first planet orbiting a star other than the Sun, we have found many worlds that are very unlike the ones in our own Solar System. A large number of these \u201cexoplanets\u201d are large, gaseous planets roughly the size of Jupiter, orbiting close to their parent stars once every few days.<\/p>\n

Although we can\u2019t directly see these \u201chot Jupiters\u201d, because they are hidden in the glow from their parent stars, they are the easiest planets to detect using the transit method<\/a>. This works by inferring their presence indirectly when they pass in front of their parent star, blocking some of the starlight.<\/p>\n

During transit, we can also measure atmospheric composition by detecting different gases in the starlight that have filtered through the atmosphere. But this only tells us about conditions in one region of the planet. In a new study of the exoplanet dubbed WASP-121b, published in Nature Astronomy<\/a>, we have managed to directly investigate a hot Jupiter\u2019s global atmosphere in unprecedented detail.<\/p>\n

Planet’s “dayside” can reach extremely\u00a0 high temperatures<\/h2>\n

Planets that orbit very close to their parent stars are locked with one side in permanent daylight, and one in perpetual night. Depending on exactly how close that orbit is, the \u201cdayside\u201d can reach extremely high temperatures \u2013 sometimes even exceeding that of the coolest stars. We can measure the temperature of the dayside by working out the difference in the total amount of light between the star and the planet together and the star on its own.<\/p>\n

WASP-121b was discovered<\/a> by the SuperWASP telescope<\/a> in 2015. Its dayside reaches temperatures of over 2,500 K (2,226.85\u00b0C). Gas giant planets are largely made of molecular hydrogen and helium, with small traces of other gases, such as water vapour. However, at such extreme temperatures, molecules can start to break apart into separate atoms, and the electrons can even be ripped away from the atomic nucleus \u2013 leading to atmospheric chemistry that is drastically different from what we see on other planets.<\/p>\n

How the “night side” becomes warmer<\/h2>\n

A big question, though, is what happens on the dark \u201cnightside\u201d of an ultra-hot planet like WASP-121b. This side doesn\u2019t receive any starlight but stares forever into the freezing depths of space. The only way it can be warmed up is by winds in the planet\u2019s atmosphere carrying heat from the dayside. Even with very strong winds, though, we expect there to be enormous temperature differences between the day and night sides for the hottest planets, and that is likely to have knock-on effects for chemical processes in the atmosphere too.<\/p>\n

The only way to find out what\u2019s going on at the nightside is to try and observe the planet and star together over at least<\/a> one full orbit. We can then measure the very small changes in the light coming from the system at different wavelengths, as different faces of the planet rotate into view.<\/p>\n

This allows us to map the surface gas layer of the planet and compare the conditions during day and night. It is only possible at the moment for a handful of planets, because the signals we are looking for are so small. But we should be able to apply it more widely with the newly launched James Webb Space Telescope (JWST)<\/a>.<\/p>\n

Our team were able to make this measurement of WASP-121b by observing two full orbits of the planet using the Hubble Space Telescope. We used an instrument on Hubble that looks at the near-infrared part of the light spectrum, which is sensitive to water vapour within the planet\u2019s atmosphere. We compared the observations at each phase of the orbit with computer-generated models to measure the amount of water vapour present, and the temperature at different heights in that part of the atmosphere.<\/p>\n

Water cycle and clouds<\/h2>\n

We found that the temperatures between the day and night differed by more than 1000\u00b0C, from around 1,500K (1,226.85\u00b0C) on the nightside to well over 2,500K (2,226.85\u00b0C) at higher altitudes on the dayside. Due to the extreme temperature difference, the amount of water vapour high up on the dayside is reduced compared with the nightside \u2013 molecules are breaking up under the extreme dayside temperatures but recombining when the air cools as it moves around onto the nightside.<\/p>\n

This means that WASP-121b has something resembling a water cycle<\/a>. But instead of the water condensing into a liquid and forming clouds before evaporating as a gas, as it does on Earth, on WASP-121b it is the water molecules themselves that being destroyed and then reformed.<\/p>\n

That\u2019s not to say that there aren\u2019t clouds. On the nightside at least, the planet is cool enough for minerals \u2013 compounds that are usually found in solid rock on Earth, but have been detected as gases in the atmospheres of ultra-hot planets \u2013 to condense and form clouds. The sky on the dark side of WASP-121b may even be flecked with rubies or sapphires, since our measurements reveal the atmosphere is the right temperature for the gemstone-forming mineral corundum to condense into small, dusty particles.<\/p>\n

Observing WASP-121b\u2019s water cycle helps to confirm some of our predictions about extremely hot planets, and also provides us with the opportunity to learn more about how atmospheres behave under these conditions. The next step is to perform the same measurements for more planets and compare the results we see. We are looking forward to doing exactly that with JWST, as well as repeating our measurements for WASP-121b for an even clearer picture.\"The<\/p>\n

Joanna Barstow<\/a>, Ernest Rutherford Fellow, The Open University<\/a><\/em><\/p>\n

This article is republished from The Conversation<\/a> under a Creative Commons license. Read the original article<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

by Joanna Barstow, The Open University Since astronomers discovered the first planet orbiting a star other than the Sun, we have found many worlds that are very unlike the ones in our own Solar System. A large number of these \u201cexoplanets\u201d are large, gaseous planets roughly the size of Jupiter, orbiting close to their parent […]<\/p>\n","protected":false},"author":19,"featured_media":20543,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[14],"tags":[1525,1640],"class_list":["post-20540","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science-mct","tag-news-home","tag-ou-home"],"_links":{"self":[{"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/posts\/20540","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/users\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/comments?post=20540"}],"version-history":[{"count":0,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/posts\/20540\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/media\/20543"}],"wp:attachment":[{"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/media?parent=20540"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/categories?post=20540"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.open.ac.uk\/blogs\/news\/wp-json\/wp\/v2\/tags?post=20540"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}