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posted by hubie on Sunday June 04 2023, @10:44PM   Printer-friendly
from the click-here-to-see-hot-pics dept.

JWST Scans an Ultra-Hot Jupiter's Atmosphere:

When astronomers discovered WASP-18b in 2009, they uncovered one of the most unusual planets ever found. It's ten times as massive as Jupiter is, it's tidally locked to its Sun-like star, and it completes an orbit in less than one Earth day, about 23 hours.

Now astronomers have pointed the JWST and its powerful NIRSS instrument at the ultra-Hot Jupiter and mapped its extraordinary atmosphere.

Ever since its discovery, astronomers have been keenly interested in WASP-18b. For one thing, it's massive. At ten times more massive than Jupiter, the planet is nearing brown dwarf territory. It's also extremely hot, with its dayside temperature exceeding 2750 C (4900 F.) Not only that, but it's likely to spiral to its doom and collide with its star sometime in the next one million years.

For these reasons and more, astronomers are practically obsessed with it. They've made extensive efforts to map the exoplanet's atmosphere and uncover its details with the Hubble and the Spitzer. But those space telescopes, as powerful as they are, were unable to collect data detailed enough to reveal the atmosphere's properties conclusively.

Now that the JWST is in full swing, it was inevitable that someone's request to point it at WASP-18b would be granted. Who in the Astronomocracy would say no?

[...] The researchers trained Webb's NIRISS (Near-Infrared Imager and Slitless Spectrograph) on the planet during a secondary eclipse. This is when the planet passes behind its star and emerges on the other side. The instrument measures the light from the star and the planet, then during the eclipse, they deduct the star's light, giving a measurement of the planet's spectrum. The NIRISS' power gave the researchers a detailed map of the planet's atmosphere.

With the help of NIRISS, the researchers mapped the temperature gradients on the planet's dayside. They found that the planet is much cooler near the terminator line: about 1,000 degrees cooler than the hottest point of the planet directly facing the star. That shows that winds are unable to spread heat efficiently to the planet's nightside. What's stopping that from happening?

[...] The lack of winds moving the atmosphere around and regulating the temperature is surprising, and atmospheric drag has something to do with it.

"The brightness map of WASP-18 b shows a lack of east-west winds that is best matched by models with atmospheric drag," said co-author Ryan Challener, a post-doctoral researcher at the University of Michigan. "One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery!"

[...] The researchers were also able to measure the atmosphere's temperature at different depths. Temperatures increased with altitude, sometimes by hundreds of degrees. They also found water vapour at different depths.

At 2,700 Celsius, the heat should tear most water molecules apart. The fact that the JWST was able to spot the remaining water speaks to its sensitivity.

"Because the water features in this spectrum are so subtle, they were difficult to identify in previous observations. That made it really exciting to finally see water features with these JWST observations," said Anjali Piette, a postdoctoral fellow at the Carnegie Institution for Science and one of the authors of the new research.

But the JWST was able to reveal more about the star than just its temperature gradients and its water content. The researchers found that the atmosphere contains Vanadium Oxide, Titanium Oxide, and Hydride, a negative ion of hydrogen. Together, those chemicals could combine to give the atmosphere its opacity.

[...] "By analyzing WASP-18 b's spectrum, we not only learn about the various molecules that can be found in its atmosphere but also about the way it formed. We find from our observations that WASP-18 b's composition is very similar to that of its star, meaning it most likely formed from the leftover gas that was present just after the star was born," Coulombe said. "Those results are very valuable to get a clear picture of how strange planets like WASP-18 b, which have no counterpart in our Solar System, come to exist."

Journal Reference:
Coulombe, LP., Benneke, B., Challener, R. et al. A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b. Nature (2023). https://doi.org/10.1038/s41586-023-06230-1


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  • (Score: 3, Insightful) by kreuzfeld on Monday June 05 2023, @03:36PM (3 children)

    by kreuzfeld (8580) on Monday June 05 2023, @03:36PM (#1309928)

    As a professional astronomer (co-author on the cited study, actually) I can't help but note the profusion of astro-themed posts... and how they regularly attract lower-than-average numbers of posts. Maybe these aren't particularly what the SN community is interested in...

    • (Score: 1) by dalek on Monday June 05 2023, @05:22PM

      by dalek (15489) on Monday June 05 2023, @05:22PM (#1309965)

      In many respects, this seems like an article about atmospheric dynamics, specifically the dynamics of a gas giant exoplanet. No problem; atmospheric dynamics are really interesting.

      It sounds like a significant portion of the study was to run many simulations of similar exoplanets with some sort of model, then try to replicate the characteristics of the planet with the model. The simulations that best fit the observations of the JWST would infer what the general circulation of the planet might be like. It sounds like there's little heat transfer from the day side to the night side of the planet, suggesting the lack of a significant zonal wind to advect heat and remove the thermal gradient.

      It seems like the lack of a significant zonal wind is attributed to atmospheric drag, but it's not entirely clear what would cause the high drag. If I'm understanding the article correctly, it sounds like one possible explanation is linked to a strong magnetic field. I'm not following why a strong magnetic field would contribute to high drag, or if that's really an accurate description of the theorized characteristics of this planet. The article also mentions winds flowing over the moles, which sounds like a meridional wind. There's nothing that limits heat transport by advection to the zonal wind. On Earth, the meridional wind is essential for transporting heat from tropical regions, where there is a heat surplus, toward the polar regions, where there is a heat deficit. In the presence of a strong thermal gradient from the day side to the night side, it seems like this is still a mechanism for advecting heat to the night side. But this isn't entirely clear to me from reading the article.

      I assume the original Nature article goes into considerably more detail about the theorized general circulation of this planet, but it's behind a paywall. It just doesn't seem like there's enough information to really understand the structure of the general circulation that this planet is expected to have or the processes that would give rise to the unusual characteristics that were observed. For that reason, it's difficult to write an intelligent comment about this article.

      No part of this is in any way a criticism of the work that you and the other coauthors did. I have no doubt that the Nature article has a lot more to say, and if I could read that, I'd probably have a much better understanding of this planet. I don't think the issue is necessarily with astronomy articles so much as that the Universe Today article probably doesn't provide enough detail for me to really understand what's going on with this planet. And if I don't really understand the general circulation or the relevant atmospheric processes, it's hard to write a worthwhile comment.

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      THIS ACCOUNT IS PERMANENTLY CLOSED
    • (Score: 2, Insightful) by Anonymous Coward on Monday June 05 2023, @08:27PM

      by Anonymous Coward on Monday June 05 2023, @08:27PM (#1310000)

      This kind of article is still interesting to me, even if I don't have anything to say. Keep posting them!

    • (Score: 2) by turgid on Wednesday June 07 2023, @06:46AM

      by turgid (4318) Subscriber Badge on Wednesday June 07 2023, @06:46AM (#1310294) Journal

      No, we really like them just don't always have much to add in the discussion.

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