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 #Spitzer 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.