JWST maps DAWN & DUSK on Exoplanets!

[00:00:00]Are you a morning person or a night person?

[00:00:04]What if you could float right on the boundary between day and night? On the exoplanet Wasp 121b, also known as Tylos, you literally can. But your experience will be wildly different depending on which way you look. At dawn, you might be watching clouds of liquid sapphire form in the skies.

[00:00:25]Whilst at dusk that heat will be so violent it literally rips apart water molecules. Until now astronomers thought that these twilight zones were identical. But JWST now allows us to resolve the atmosphere longitude by longitude.

[00:00:43]Hey space cats. I'm Dr. Maggie Lou.

[00:00:45]Let's talk about how we resolve dawn and dusk on an exoplanet.

[00:00:54]Tylos is an ultra hot Jupiter-like planet located 900 lighty years away in the constellation of Pupus.

[00:01:03]It is tidily locked to its host star Dilman, meaning that one side of the planet experiences a forever daytime with scorching hot temperatures reaching over 2,500° C, whilst that other side sits in this neverending darkness. Now, naturally, we would want to know what the weather is like on a world that is this extreme.

[00:01:29]And to do that, we have to look at its shadow.

[00:01:34]We can probe an exoplanet's atmosphere when it transits in front of its host star, creating a dip in its light curve.

[00:01:42]If a planet was just bare rock with zero atmosphere, it would block the exact same amount of light at every single wavelength, and that dip would be perfectly flat. But if a planet has a thick atmosphere, gases will absorb specific wavelengths of light, causing a deeper dip at those specific colors.

[00:02:04]It's important to note that this technique only measures the terminator line. That's the boundary separating day from night. When we watch a transit, the core of the planet blocks out the entirety of the light. It's only that very edge of the planet silhouette that lets starlight filter through. So, every chemical fingerprint or water signal that we detect comes exclusively from that twilight ring. Up until now, because a transit lasts a few hours, astronomers blended all of that data together. This meant that the light that came from the dawn terminator and the light that came from the dusk terminator was mixed into a single average signal.

[00:02:45]On paper, everyone assumed that these boundaries were symmetrical. If the planet wasn't spinning, air would just blow straight from that scorching hot dayside over the edges and meet at the center of the night side. It's just standard convection, hot to cold. Now, you're probably thinking, "But Tylos isn't spinning, right? It's tidily locked." However, this would be a mistake. Even though Tylos is tidily locked to its host star, it still rotates relative to Earth here on Earth.

[00:03:19]A full orbit around its star takes around 30 hours, but a transit takes about three. This means that whilst crossing the face of the star, that planet actually rotates by about 30 degrees across our line of sight. At the start of the transit, JWST got a clear view of the dawn terminator. And by the end of it, the planet had turned, exposing the dusk terminator.

[00:03:47]By breaking the transit down minute by minute instead of averaging it, they effectively sliced the planet's twilight zone into half. And what they found has completely changed our understanding of alien weather. Instead of a simple day toight breeze, the planet's rotation actually whips the atmosphere into a state of atmospheric super rotation. You see, the intense heating at the equator creates largecale atmospheric waves.

[00:04:15]These waves act like a giant mechanical pump. As they interact with the planet's rotation, they systematically steal momentum from the high latitudes, the poles, and pump it directly into the equator. This continuous pumping mechanism accelerates the equatorial air faster and faster until it forms a single screaming supersonic jet stream traveling at speeds of up to 33,000 km hour. This is a phenomenon called atmospheric super rotation. And since the planet is spinning, the corololis effect bends those winds sideways.

[00:04:55]Together, these lock the planet's weather into a one-way highway of wind.

[00:04:59]Since the jetream only flows in one direction, the two terminators are completely different. By analyzing the light curve variations minute by minute instead of averaging them, astronomers using JWST were able to map how the depth of the dip shifted for water and carbon monoxide as dawn swap places with dusk. What they found was that on the evening side, the water signal had dramatically dropped at the evening terminator. Massive winds would flow from the hot dayside to the cooler night side, making it so much hotter. It's literally a blast furnace so intense that water molecules are literally ripped apart, causing the atmosphere here to puff up and expand. Meanwhile, on the morning side, this was significantly colder than any of our standard atmospheric models have ever predicted. To explain that sudden drop in temperature, the team realized that there must be something that is able to shield the morning terminator from the dayside's heat. A thick high alitude blanket of mineral clouds, effectively meaning that it could be raining liquid sapphires and rubies at dawn. And this actually kind of makes sense if the winds continue onto the night side and cool down as they head towards that morning terminator because this side is significantly cooler. Water molecules can reform and even get cool enough here for vaporized rock to condense into gemstone like clouds. Isn't it just so insane that we can learn so much about a planet that is 900 lighty years away just by monitoring the starlight of its host star? Anyway, that is all I have time for this week. Thank you to my YouTube perks members for supporting this video. If you enjoyed it, please don't forget to leave me a like, share, and subscribe.

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