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Exploring exoplanet atmospheres in more detail was one task that planetary scientists anticipated during the long wait while the James Webb Space Telescope (JWST) was in development. Now, their patience is finally paying off. News about discoveries of exoplanet atmosphere using data from JWST seems to be coming from one research group or another almost every week, and this week is no exception. A paper published in Nature by authors from a few dozen institutions describes the atmospheric differences between the \u201cmorning\u201d and \u201cevening\u201d sides of a tidally locked planet for the first time.<\/p>\n
<\/p>\n First, let\u2019s clarify what the \u201cmorning\u201d and \u201cevening\u201d sides mean. Tidally locked planets don\u2019t spin, so one hemisphere constantly faces the planet\u2019s star. As such, there is always a part of the planet where it appears to be \u201cmorning,\u201d with the star barely peaking over the horizon. Alternatively, there\u2019s a part of the planet where it seems to be \u201cevening,\u201d where the star is again just barely peaking over the horizon, but it would appear to be setting.\u00a0<\/p>\n Typically, on Earth, we would think of the morning side as the star peaking over the eastern side, whereas the evening side would see the star setting into the western sky. However, exoplanets sometimes rotate in the opposite direction from planets in our solar system, so that mental model doesn\u2019t always work for them.<\/p>\n It\u2019s also important not to confuse the \u201cmorning\u201d and \u201cevening\u201d sides with the \u201cday\u201d and \u201cnight\u201d sides of the planet. On the day side, the full force of the star affects the planet, but on the night side, the star is never seen at all. The temperature differences on such a planet are massive, and cause much more extreme weather than anything we have experience with in our solar system.<\/p>\n That is the case for WASP-39b, one of the most studied exoplanets. It is a \u201chot Jupiter\u201d and is roughly 1.3 times the size of the largest planet in our solar system, though it only masses in at about the same size as Saturn. It\u2019s 700 light years away and is tidally locked to its star.<\/p>\n Exoplanet hunters have intently studied this exoplanet since its discovery in 2011. It was the target of JWST\u2019s first exoplanet research when it began science operations. Since then, they\u2019ve made several interesting discoveries, and the Nature paper describes a new one\u2014that the \u201cmorning\u201d side of WASP-39b is a few hundred degrees cooler than its \u201cevening\u201d side.<\/p>\n \n
Credit \u2013 NASA \/ ESA \/ CSA \/ R. Crawford (STScI)<\/figcaption><\/figure>\n<\/div>\n