So, Paul, it strikes me that spectroscopy would be really useful here as almost everything has a signature of light
that you can identify it, we can identify almost anything if we can only have a spectral of what's going on but it's not going to be easy.
Yes, because now you've not merely got to measure the total brightness, but the brightness broken down to wavelength bins.
But it has been done, so the idea is that you wait until the planet is just outside the secondary eclipse,
take a spectrum and then when it's in the secondary eclipse you take a spectrum,
so the spectrum when it's just outside will be the star light plus the planet light.
When the planet's behind it will be just the star light,
you subtract one off the other and hope that the difference is the spectrum of the actual planet. Here's one.
Okay, let's see, so this is in the infrared.
They're claiming that they see a bump here.
I see, so the idea is that you don't see anything, you don't see anything and then you see a little bump of omission of something.
You really have to be a true believer I think to believe that.
They claim it's real. Any one of these individual points is only about one arrow bar above,
so that would be a 32 percent chance it could be outside the arrow bars,
but there's quite a number of points up here, so maybe if you add them all,
but if you really believe you've got your systematic errors under control, maybe it's real.
But they claim that this is the right wavelengths to be featured from silicon,
so very suggestive from other reasons, there might be silicon clouds in these things,
it could be looking at this hot Jupiter, which actually again, has silicon, your glass or quartz clouds in the atmosphere
and what we're actually looking at is a bump in the spectrum at just below 10 microns caused by silicates.
Alright, so here we're looking in the infrared for something that is omitting in that line.
It's sort of like a neon sign omits a line of neon.
It would be nice if you can do something in absorption.
Right, that sounds easier to me.
Well first of all, because the primary eclipse effect goes in front is much deeper so you're looking at a much bigger effect.
In principle you can, I mean here's a picture of Saturn taken by the Cassini Space Probe when the sun was on the other side of it.
What you can see is a little glowing arc around the side here which is the light of the sun refracting through the atmosphere.
It's like all the sun sets on Saturn at the same time.
So, the beauty of this is you've got the light of the star shining through and, of course, when we see things like this one,
Saturn completely eclipses the sun, but in reality what you'll see is you can actually see light coming through,
you'll see the light of the star at the same time and then you'll see the absorptive fingerprint of material.
Yes, so another way of thinking of it is the radius of the star might differ as a function of wavelength
at wavelengths where the atmosphere is transparent, it will just be the radius of whatever solid or the cloud banks
and other wavelengths where the gas in the atmosphere absorbs, the radius might get a little bit bigger.
So, you'll see a bigger dip at some wavelengths than others.
So, once again, you take the spectrum when the planet is not in front of the star, it's just a star spectrum,
and when the planet's in front of the star, you'll get a star spectrum minus a bit of light from the planet
and that light you've taken off may vary as a function of wavelengths
depending on the atmosphere because of this arc around the side.
Okay, so it sounds like a promising way forward, so what have we seen?
Well, here's one result that was in a very recent paper. What we're looking at here is carbon monoxide.
So, here's a spectrum and you can see that there's a little bit of a dip along there.
Once again, it's not something you'd want to write home about. (Yes, I can see it, there's a real slide there.)
This is the simulation, it's not the real data. These are the real data.
Well, I sort of see it. I reckon that looks better to me than the previous one.
Yes, and what you're seeing here is the darkness along there. It's a sloping line.
The reason it's a sloping line is as it goes in front of the star, it's velocity is changing.
So, if it was just going straight in front on a line, the velocity wouldn't change, but it's actually doing a circle so it's going away and towards,
so we're getting a bit of a slant across here.
So, this diagram, just to be clear, is plotting how bright the area of CO is, the little signature of CO.
This is the wavelength along here.
Yes, so this is a wavelength, we're actually measuring, in some sense, the velocity
and then this is telling you what phase in the orbit it is and so we do expect there to be a change because the object is moving.
So what you're seeing is the right pattern here from the doppler effect;
as the velocity of the planet relative to the star changes, you expect this line to slope
and it slopes at exactly the right way which is looking good.
So, the planet looks like it has CO in it.
But there's a surprise in here, it turns out that the velocity, the one that's sloping, is not quite in the right place.
It's a bit different from the velocity of the star by about two kilometres a second, that's about 7000 kilometres an hour.
What it seems to be is that the CO is not just sitting on the planets atmosphere,
it's actually moving from the hot side to the cold side at about seven or eight thousand kilometres an hour.
Wow, so our jet stream is maybe 350 kilometres per hour, so this is 20 times faster than the fastest stuff we see on Earth.
Yes, it is indeed seven or eight times faster than the winds on Jupiter, which are much stronger than the winds on Earth.
Jupiter's orbiting very quickly, so this is pretty funny.
Yes, it looks like, at least at the altitude where you're getting carbon monoxide,
we're seeing an incredibly fast wind from the day side to the night side in this case.
Here's another surprising case. In this case, the planet causes a typically sort of half percent dip,
but if you look not at the general optical wavelength, you could look at the wavelength where you get absorption from hydrogen.
This is actually in ultraviolet so it's supposed to be done with the Hubble Space Telescope
because the ultraviolet can't penetrate the Earth's atmosphere.
But if it were the Lyman-alpha line which is where an electron jumps from level two to one of hydrogen
which is in the ultraviolet, 121.6 nanometers, something I've spent a lot of my life working on,
instead of blocking half a percent of the light, this thing is blocking 15 percent of the light of the star when it goes in front.
So, it can't be that its atmosphere puffs up to 15 percent of the radius of the star, that seems crazy.
Yes, so maybe that will be able to do it if you've got a planet that's got an atmosphere this big of hydrogen,
but more likely, at atmosphere that big of hydrogen wouldn't stay there, it would get blown away.
So, our best guess is that what's actually happening is an evaporating planet.
It's losing huge amounts of hydrogen and producing an almost cometary tail of the stuff.
As it goes in front, you get this huge amount of hydrogen absorption
plus a small amount of absorption at all solid wavelengths caused by that stuff.
Oh, okay so this planet sounds to me like it's going to be doomed if it's losing too quickly.
I guess it really depends on how quickly it really is losing it, because hydrogen and that Lyman-alpha line is so sensitive
that you just need a little bit of hydrogen and it really is good at taking out all the light.
Yes, so we've had a planet with incredible winds, we've got an evaporating planet,
but even, it turns out, that seeing nothing can be interesting at times.
Here, remember we had two possible models for these Super-Earths that might be a potential water planet,
one of which had a hydrogen-helium atmosphere, one of which was mostly water and water vapour all the way out.
For one of these things, people have tried to measure the transits at different wavelengths so you can see that going from the red,
well these are actually all red wavelengths, but slightly less red to slightly more red
and you can see the dip of the transit and you can compare the shapes of all these different wavelengths here.
So, what they've done is that they've fitted the average of all these things and taken it off
and what you can see is that the transit actually looks exactly the same all the way from 1000 nanometers down to 780 nanometers.
Okay, so that means that the planet is really exactly the same colour at all these different wavelengths.
That's kind of, well, it is interesting.
Well, if we've got a water surface or a cloud surface, that's fine. Clouds absorb or solid surfaces absorbs at more wavelengths.
But if it had mostly a hydrogen atmosphere, it would not be like this, it would absorb more at some than others.
Right, because hydrogen ends up having this signature of, in this case, scattering at some point so it would change things.
Okay, so that's telling us that this object is interesting.
Perhaps, maybe, it has a dense shroud of clouds,
you know, interestingly enough, clouds turn out very conveniently for astronomers because they're around,
they really have no colour to them, so when we looks through the atmosphere,
they are effectively a neutral density filter that you would use on your camera, it doesn't change the colour.
So, whatever it is in this particular possibly water world, it certainly has the right density to be a water world,
I don't know, whatever it is in it's atmosphere so that it doesn't have different effects at different wavelengths.
So, not conclusive yet, but it did give us some interesting results.
Okay, that would be interesting to see if there are more of these.