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So yesterday I talked a lot about , but that's not actually what I work on the most right now! Until we get JWST data I'm over in land, a previous space telescope that is unfortunately no longer operational.

Even though it's not actively collecting data, there is still so much we can do with what exists! 🔭

I have a grant from NASA to uniformly reanalyze ALL of the Spitzer phase curve data:

So what's a phase curve and why do we care?

Well first we need to talk a little bit about this really weird type of exoplanet called a Hot Jupiter.

In our Solar System we have a relatively well ordered set of planets. There are 4 rocky planets closer to the Sun and 4 gaseous planets further from the Sun. For a long time we expected all planetary systems to look like this too!

But as it typically goes with science, once we started finding planets around other stars it turned out that many of them are nothing like we expected

The very first exoplanets we found were about the size of Jupiter and REALLY REALLY REALLY close to their stars!

Mercury is the closest planet to the Sun and it orbits in about 88 days. But some of these new exoplanets we were finding orbit their stars in *only a few days* 🔥

The temperature of a planet generally scales with the distance it is from the star (with a few exceptions I won't get into here).

Think about it like standing next to a bonfire, the closer you are the more heat you'll feel.

So these Jupiter sized planets weren't only really close to their star, they were REALLY REALLY hot!

I'm talking more than 1000 degrees Celsius! Meanwhile the dayside temperature of Mercury is *only* about 450 degrees Celsius

This completely changed our view of how and where planets of that size can form and exist!

One particularly interesting result of being this close to the star is that the planet is "locked" to the star due to tides. This is the same reason why we always see the same side of the moon!

So not only is the planet getting absolutely *blasted* with heat, it's only getting blasted on one side of it.

This led to lots of new questions about how atmospheres in these extreme conditions move heat around

Conveniently, the fact that these planets are so close to their star and so hot makes them easier for us to study to answer our questions!

First of all, it doesn't take so long for the planet to orbit the star, so it's reasonable to point a telescope at it for the entire length of the orbit.

Second of all, it's really hot, which means it's brighter! A brighter planet means it's easier to detect.

Enter the now inoperable space telescope!

When we observe a planet over the entire length of its orbit, we're observing what we call a "phase" curve.

Just like how the moon goes through different phase depending on how the Sun is illuminating it, we can watch a planet go through different phases as we see it orbit its star.

But remember these planets are locked to their star, so sometimes we will see the dark nightside and sometimes we will see the permanent dayside. Over the course of the entire orbit we see the whole planet!

During this observation we also see the "transit", which I talked about yesterday and is when the planet crosses between us and the star and blocks out some light.

But we also see the "eclipse", which is the reverse, when the planet goes behind the star and the star blocks the light from the planet! This is often a much much smaller signal because the planet is so much dimmer and smaller than the star, but for these bright Hot Jupiters, we can still measure it!

So with the Spitzer space telescope, we are able to stare at the system and observe the total amount of light from the planet + star as the planet moves around.

This can teach us about how hot not only the dayside of the planet is, but also how hot the nightside is. Remember, the nightside never gets starlight though! So together this tells us about how the winds on the planet help move heat from the dayside to the nightside 💨

And because of this big difference between the permanent day and nightsides, the winds on Hot Jupiters can be THOUSANDS of miles per hour. 😱

These are truly extreme planets that even have weird things like clouds made of ROCKS! Yes, they're so hot that even rocks melt and form clouds.

So back to Spitzer and why I joke that I'm "stuck" in Spitzer land right now.

Spitzer, like basically every telescope in existence right now, was not designed with exoplanets in mind.

Our observations have to be more precise than others, and the telescope also has to stable over long time scales. This includes keeping the telescope pointed perfectly at the same area of the sky, and also making sure the temperature of the telescope itself doesn't change because this can add noise

And unfortunately Spitzer, while it's good at staring at the same point of the sky, it also has some weird things going on with the pixels on the detector. For Spitzer the size of these extra noise sources can be ten times larger than the planet signal.

This makes data analysis HARD and leaves a lot of biases in our results.

Enter me I suppose? I'm leading a program to improve how we remove systematics in Spitzer data so we can compare results about different planets better!

We're trying to uncover trends in the atmospheres of Hot Jupiters. Which ones have the strongest winds? Where does weird physics happen? How can we explain their properties with climate models?

This will help us better select targets to observe in the future because we'll be better able to predict which ones will have the types of features we want to study in more detail.

Next week I'll be presenting my most recent publication on my Spitzer data analysis program at the biggest Exoplanet conference in the world! We're still working on the data analysis for the entire program, so I don't have any exciting trends to talk about yet other than to tease that we're finding more unexpected things! 😉

But stay tuned for next week because I plan to bring some of the ground breaking results I learn about at the conference here!

@_astronoMay Are they still thinking late June / early July for first data from jwst?

@jarmer Yes! The preliminary schedule has gone out to the people getting data this Cycle and it looks like the first week in July or so will be the first data! It'll take a few weeks for us to process things before there are public results though

@_astronoMay ohhhhh very exciting news! Okay so I'm looking forward to the end of July then :) I think we're going to have a party to celebrate all this new data that could potentially revolutionize our thinking. Thank you for the info!

@_astronoMay reading your toots is like I've hit the jackpot. I love this stuff.
Thanks for sharing your insights.

@_astronoMay this was really interesting. Thank you for sharing

@_astronoMay Are you also using data from the newer CHEOPS (ESA) satellite for (exo-) planet hunting?

@_astronoMay Is it likely our own Jupiter-esque planets started life as similarly hot and migrated outward?

@David_Kelly_SF the other way around! We expect hot Jupiters formed further out in the planet forming disk where it was cool enough for them to grow as big as they are, then they've migrated inwards over time. Jupiter probably formed pretty close to where it is now

@_astronoMay Interesting. I thought I'd read somewhere about the larger planets in our solar system possibly moving outward. So maybe that wasn't accurate. Thanks!

@David_Kelly_SF the great thing is we really don't know! We can fine-tune planet formation models to give us the Solar System, but then they can't explain things we've observed elsewhere and vice versa! I don't think any of my planet formation friends have made the jump yet but hopefully some of them migrate here soon!

@_astronoMay We need a time machine lol But seriously that's one of the things that makes science and astronomy so interesting - there's always more to learn 🙂

@_astronoMay Have you made it out to JPL yet? If you're doing Spitzer + Exoplanets, it seems like you're an ideal visitor

@thomasconnor Considering I started working on Spitzer about 4 months before the pandemic, no I haven't! Maybe I'll make it out once seminar travel happens again :)

@_astronoMay Is the detector pixel noise much higher than originally expected? Or is this as-designed and we just need to deal with it?

@tsturm Unfortunately this is a common "feature" of the type of detector they are. For most use cases it's fine - what happens is the amount of light you measure changes by several percent depending on where your star falls within a *single* pixel. But for exoplanets our signals are generally less than 1% of the total light, so this pixel problem is important!

@_astronoMay That's very cool. I really enjoy when a scientist describes their technical challenges and I realize that how I imagined the problem is by several orders of magnitude easier than the real challenge. 😅​

@_astronoMay ESA's CHEOPS space telescope, recently launched, is for exoplanets. 👍

@_astronoMay I'm sure they never mention that in their tourism brochure. 😆​

@_astronoMay
What does a light curve differ from? I'm not on planetary science so maybe I'm just not used to the vocabulary?

@_astronoMay
And also, when you say the planet is locked, and that you're able to see the whole planet, you mean that it "behaves" like the Moon? I mean, its rotation matches its traslation period always (why would this be true)? Sorry my science English is rusty 🤭.

@Maya yes, the rotation rate of the planet is the same as it's orbital period! 1 year = 1 day on these planets.

@_astronoMay Makes me think of a toasted marshmallow. Says the non-astronomer Seth

@seth Wait until you hear about the class of planets that we call "Super Puffs" that are about the same density as a marshmallow 😉

@_astronoMay Oh nice it reminds me a lot about the WASP-121b, it even contains water 👌🏾 👍🏾

@_astronoMay now you’ve got me wondering whether there could be tidally locked rocky planets close to their stars with thin enough atmospheres to be habitable only along the terminator 🤯

@noleli Yes! planets in the habitable zone of smaller stars like M-dwarfs are also likely to be tidally locked. So all the TRAPPIST-1 planets which are big targets for biosignatures probably *are* tidally locked!

@_astronoMay @noleli

Science fiction writers have been speculating about this literally since before the Second World War. You can find stories set in the hypothetical, habitable Twilight Zone of Mercury, which at the time was believed to be tidally locked.

@_astronoMay I don't think a "Hot Jupiter" could form so close to its host star. It must have formed much further out and is slowly migrating inward. I'd like to see if 51 Pegasi b, for example, is on that slow spiral and will one day crash into the star Pegasi itself. Or get ripped apart when it gets a little bit closer than it is now. A four day orbital period is ridiculous.

@_astronoMay oh and I didn't mean to imply you said hot Jupiters "form" near their stars. Sometimes I get too excited about this stuff. Lol

@_astronoMay I've always wondered about that; were their local stars siphoning gas from them at that distance?

@_astronoMay I assume we can't really measure the rotation of exoplanets yet but is there any informed guess about how fast a planet that orbits its star in a few days would spin?

@_astronoMay ...and that means wicked-ass New Year's Eve parties and even more wicked-ass hangovers.

@_astronoMay ...but then, I suppose it's even worse on Jupiter where, if you can't get your New Year's Eve plans together, you're totally screwed (assuming you're even alive at the right time).

@_astronoMay for those of you speaking German: The Austrian Astronomy #Podcast #DasUniversium has a longer feature about Hot Jupiters in their latest episode. It highlights the discovery of the very first exoplanet orbiting 51 pegasi. dasuniversum.podigee.io/51-du0

@_astronoMay What algorithms do you use for light curve fitting? I've experimented with doing this kind of thing, but the methods I used were quite crude - just trying a lot of frequencies.

gitlab.com/bashrc2/ngtsscan

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