Now, the secondary transit stuff is all very difficult,
I mean, you're looking at, even though the original transits are too small to see from the ground
and in this case you're trying to find secondary transits at slight slopes, it's very, very tough.
Yes, well it tikes me, Paul, that maybe we're looking in the wrong place in the spectrum,
because in an optical light, the planets like Jupiter are just reflecting the sun, so they're going to be very, very faint.
But, if you have a Jupiter in close it's going to be hot and glowing on its own.
Now, it might be in the infrared, but if we look at the infrared,
it strikes me that we're going to maybe have some bigger signals to get our hands on.
Yes, so here's the spectrum in wavelength going from something with maybe a temperature of 6000 degrees
like a sun-like star and in this case it peaks at visible wavelengths.
But, if you look at something that's maybe at a thousand Kelvin, like one of these hot planets
they also will glow but the glow might be out at your three microns, five microns, which is what we call infrared light.
So, if we look at visible light like Kepler does or the Hubble Space telescope do,
we're looking in the worst place where the light of the star completely dwarfs the planet.
But if we go out, the actual green curve here is grossly exaggerated, it wont actually be as high as the red curve,
but nonetheless the ratio is going to get much better in our favour, the effects are going to be much bigger.
Right, well that sounds good, the problem is that observing in the infrared is hard.
On the ground, the whole atmosphere glows and if there's anything I hate doing,
it's going to the telescope and observing in the infrared because it's just so hard.
Yes, you're struggling with the glow because, of course, your telescope is glowing with these wavelengths.
These atmosphere is glowing and also the atmosphere is largely opaque because of the greenhouse effect on Earth.
You've got lot's of particularly water vapour absorption which blocks you in a very unpredictable way and constantly changing.
So, trying to do this from the ground, even though it's a bigger effect, is going to be hopeless.
So, what we need is an infrared space telescope.
Exactly, so fortunately NASA has provided us with the Spitzer Telescope.
This is one of the great observatories and was done in the series
that brought us the Hubble Space telescope and also the Chandra X-ray telescope.
Spitzer is a space based infrared telescope and even though it's mission,
it needed to operate very cool to do it's most precise measurements.
Yes, it's primary mission had a huge spacely tank of coolant that kept the detectors and the mirror very, very cold.
That eventually, after many years, boiled off, but nonetheless, at wavelengths of a few microns, it can still work very nicely,
out at near 20 microns and so on, it can't work anymore since the coolant boiled off.
But those few microns were good for looking at ten things with a temperature of maybe 1000 degrees,
which is exactly what we're looking for for these transiting planets.
So, a great resource for for us to go out and look at these things.
It's not going to find them in the first place, but if you found them by some other method,
whether it be Kepler or a ground-based survey, this is a great telescope for following them up.
Because it's in space, it has a sensitivity and also because nothing is changing for it,
it doesn't have to worry about day and night and varying amounts of water vapour and everything else, it can look for very small changes.
Okay, so what have we seen?
Well, the question we're dealing with here is "what might the weather be like on hot Jupiters?"
If we look at the weather on Earth, it's driven by the fact that more sunlight falls near the equator than near the poles,
and so it's very hot here and that causes wind from the equator or equatorial regions to rise and move out and fall down.
Because it's spinning, that produces sideways motion, the trade wind.
You can see all of these storms around the centre which is the air rising up and then it moves further out and distributes heat away.
If it was just an equilibrium, if heat couldn't move from the equator to the poles, the temperature difference at the moment,
or it may be typically 30 degrees near the equator and minus 20 or 30 near the poles, so maybe a 60 degree difference.
If it wasn't for the atmosphere, it would be more like a 200 degree difference.
Oh, okay so, very substantial, yes.
So, what's happening is a large amount of heat is being carried by atmospheric currents and ocean currents as well on the Earth
from the hot regions to the cold regions, so the temperature gap is nothing like as big as it would be if we didn't have an atmosphere.
Alright, so all we have to do is look at one of these Jupiters
and see how it behaves and we can, you think, get a sense of its weather.
Yes, now Jupiters would have very different weather because they almost certainly are tidally locked, as talked about before.
They would tend to face the same side towards the star.
So, we've got a star over here and we've got a hot Jupiter and this side is always going to face it,
so as it goes around the star, it is always going to look at the star.
So, we are going to have a hot side and a cold side then.
Yes, so the orange and the blue side, as I've drawn it here,
and the question is going to be "is there any weather to carry the heat from the hot side around to the cold side?"
If there's not many winds going from one side to the other, assuming that they're gassy things,
maybe the gas on this side is just sitting there incredibly hot,
and the gas on that side is maybe sitting there incredibly cold and nothing's transferring.
Or maybe, like on Earth, you've got winds, but with a pretty different pattern
because it's spinning only every few days as it goes around the star,
but it might still be enough to drive some quite interesting weather patterns.
The answer is, well at the time of producing this video, there are about three systems which have these data.
This will go up dramatically, probably even by the time this course goes live, so it's probably out of date even today.
One of them is new Andromedae, which is, we've already talked about the one with the first one they discovered three things,
that a hot Jupiter and two eccentric giants further out.
In this case, there's a huge day and night temperature difference.
So, that's sort of telling us that there's not a lot of wind there to redistribute things.
Or maybe the winds are just doing loop-de-loops around the hot air but not carrying too much heat around the cold
and, well, to others finding similar sorts of results where there seems to be a huge gap in temperature between day and night.
Alright, so these may be kind of boring places, but is that always the same?
Do we get the same answer wherever we look?
Well, here's another one which is a different answer.
Here we've got the overall light curve of the main transit and the secondary transit and again you see a little slope up here.
You can see how much bigger that transit here is compared to that one.
Remember in the previous ones, you couldn't even have these ones on the same scale but in infrared, you can suddenly see them.
That's the power of the method.
If we zoom in, you can see this clear change here and what you're seeing is the difference in brightness there and there,
it's telling you the difference in heat between the day and night side of the planet and the dip here is when you lose the entire planet.
So, if the gap there is telling you how much radiation you get from the day side,
and the gap from the bottom there to here is telling you how much radiation you got on the dark side.
So, even the dark side, this one is glowing quite a lot. It's hotter in the day than in the night, but not very much.
In this case we may be talking maybe a 200 degree difference,
so maybe you're 1200 degrees in the day side and 1000 on the night side.
So, in this case, there does seem to be some sort of wind, 200 degrees would need a wind to carry it around.
So, somehow the heat is getting moved from the day side to the night side in this particular case.
Okay, so not everything is the same. We seem to, again, have a very large range of phenomenon.
This pattern is maybe slowly becoming clear here.
It kind of looks like if when you find the planets that are really close in the very classical hot Jupiters.
In those cases there seem to be very big day to night temperature differences.
But when you get the ones that are a little bit further out,
some of them still have the very big temperature differences, but some of them have much smaller ones.
So, it looks like that maybe there's something about being very close in that actually stops winds.
Maybe it's just such a big difference and maybe the tidal force in the star, I don't know what could be doing it,
seems to shut down this heat transfer, but the ones a little further out can do more like the Earth do
and have currents that carry the heat from day to night.
But it's still early days, we only have a handful of these, so we'll learn more as we get more data.