Chapter 1: What are the bizarre clouds found on WASP-94A b?
Hey, it's Flora, and you're listening to Science Friday. It seems like every week a new exoplanet drops. NASA counts 6,000 official alien worlds, with around 8,000 more suspected. They're stuck on the wait list till more research can be done to confirm them.
One way to spot an exoplanet is to use a telescope to carefully look at the light of a star, watching for a tiny periodic dip in brightness as a planet crosses in front of it. But now researchers say that using this transit method, they detected not just a planet, but its clouds. And the clouds on this one gas giant, some 700 light years away, are super weird. They're made of rock.
Here to tell us more is Dr. David Singh. He's a Bloomberg Distinguished Professor of Earth and Planetary Sciences at Johns Hopkins. Hey, David.
Hello. Thank you for having me.
Thanks for being here. Tell us about this planet that you've been looking at and what the weather's like.
Well, this is a planet, what we call a hot Jupiter. It's a gas giant, much like Jupiter, but it's orbiting very close to a host star. And as a result, it's heated up to very high temperatures, up to 1,500 degrees Kelvin. And at those temperatures, what we normally experience as, say, rocks, actually can form clouds in the atmosphere.
Like they're being boiled off the surface?
Well, this is a gas giant, so there's no surface, but indeed, if you get hotter than about 1500, these rocks are actually in vaporous form. And as it gets colder, they can condense into solid, small particles.
Yeah, how should I be imagining these clouds? Are they puffy like our clouds, or are they filled with little granules?
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Chapter 2: How do astronomers detect clouds on exoplanets?
And so the planet must have actually very vigorous mixing, turbulent mixing to keep those sand clouds that high in the atmosphere. It's really surprising.
What would they, you know, if I could bubble up below them, I guess, what would they look like in the sky? Is it like a haze or a fog or are they, you know, like a cumulus cloud here on Earth?
It would look like a very actually thick, dense cloud. So on this particular planet, the clouds are actually even confined to the morning side of the planet. So the morning side is completely cloudy and the evening side is actually completely clear. It's much hotter and those clouds can't form.
And so I kind of imagine it sort of like you're in San Francisco and in the morning it's all cloudy and you can't see anything anymore. And then by the afternoon, they've all boiled off and you can see the clear sky.
They burn off, as we say. How do you get enough resolution to be able to see the clouds? I mean, that seems amazing.
Yeah, well, we've been studying exoplanets through the transit technique for nearly 25 years, and we've been mainly using the Hubble Space Telescope during that time. But now we have the powerful JWST telescope, and that's given us actually two important advances to be able to make this measurement. The one is... Hubble is in low Earth orbit.
It's orbiting around the Earth about every 90 minutes. And so it spends half of its time on the day side of our planet and half of it on the night side. Well, when we look at these transit events of these exoplanets, you know, we're looking at it over the course of several hours. But that means the Hubble is actually spending half of its time on the wrong side of our planet.
And so actually, you can't even observe the full transit event continuously, which kind of prevents this measurement from being made. But JWST is out beyond the Earth and the Moon, and it can stare continuously for hours or even days. So... That's one key aspect of JWST that's important. And the other is that the telescope, JWST, is just so much bigger.
It has seven times the light collecting ability. So that means what took Hubble more than an hour to make a measurement, now JWST can do in, say, 10 minutes. And actually that sort of 10-minute timeframe is really important because in order to separate out
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Chapter 3: What makes the clouds on WASP-94A b unique?
Absolutely. So there's kind of two key questions we can start to unravel because we've been looking at these planets for quite some time and we see molecules and their atmospheres and the clouds together. But now we can separate these out quite cleanly and we can look, for instance, at the clear atmosphere and what its chemical composition is. And these gas giants are...
basically like fossilized records for when the planet formed. So we want to use these as basically records to figure out how these planets formed and evolved. And many of these types of planets we do not have in our own solar system, like hot Jupiters or sub-Neptunes. And some of these types of planets are actually the most common forms
found throughout the galaxy, yet we don't really have a good idea how they form or evolved. And so by measuring the chemical composition cleanly with this technique, we can start to unravel that mystery. And there's another important aspect was actually just studying these clouds themselves.
So clouds and modeling them are the biggest uncertainty we have in studying and modeling atmospheres, and that includes our own Earth's atmosphere. And with these exoplanets, we're actually using the same models that are used to measure the weather and predict the weather on Earth. So it actually turns out that we don't know the physics of cloud formation and how it interacts that well.
So by measuring how clouds are formed and the dynamics in these different extreme environments, we can actually improve the physics of our overall models.
That's wild. So alien clouds could help us understand our own clouds better.
Yeah, absolutely.
Are clouds common on exoplanets? Is this a feature every planet has?
For most planets, indeed. It's very common for all exoplanets that we almost see. There's a few out there that are just so, so hot. They're mostly cloud-free, but those are kind of a tip-of-the-iceberg, extreme planets.
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Chapter 4: How does the atmosphere on WASP-94A b support cloud formation?
And part of that is sort of the radars are very sensitive, but there's a lot of noise on the signal. And so there has to be sort of sufficient signal, sufficient density of insects for our methods to be able to differentiate and say, okay, this is real insects, right?
Can you tell which species of insects you're looking at?
No, not at all. The radar totally doesn't know and doesn't care. And that's an interesting thing about this tool. It's really good for quantifying abundances and looking at a standardized way of measuring how many insects are out there. It's the same tool. across all these different radars across different regions across the entire United States.
But if you wanted to know more about what's happening specifically with this population or that, then you need to combine it with sort of local surveys or citizen science or other types of tools that we have.
You looked at a 10-year period from 2011 to 2021. Did you see any big trends?
Yeah, interestingly, we sort of expected everyone's been really worried about insect declines. Obviously, there's a lot of studies demonstrating that insect biodiversity is going down, and in many species, insect abundances have been declining over the past 10-something years. And so we sort of expected to find widespread declines, and instead we found that
At the continental scale, insect abundances are pretty stable. There's areas where they're declining and there's areas where they're increasing. And it sort of offsets each other that over the 10-year period, we don't see a strong trend.
Although we don't know which insects, right? So we could be sort of compensating for the loss of some insects with the gain in other insects.
That's exactly right. You've got winners and losers, probably. Some species doing really well. And the species that we know sort of don't handle anthropogenic change so well maybe are declining. And so there's a balancing act happening of increases and declines in different species that results in this stable trend.
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Chapter 5: What is the significance of the James Webb Space Telescope in exoplanet research?
I'm Flora Lichtman, and thank you for listening. On Science Friday, we talk about the science, tech, and health stories changing our world, from a pancreatic cancer vaccine, to data centers in space, to AI in art, to the real science behind cold plunges. We talk with world experts on issues listeners really care about.
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