Hi, my name is Amaury Triaud. I am a lecturer here at the University of Birmingham in the
School of Physics and Astronomy and I teach exoplanets. Exoplanets are planets
that orbit other stars than the Sun. It turns out this is also what I research,
so a lot of my time is spent about discovering this planet and studying
them and I share my research with students in year four and year three.
We do projects as well at the end of year four, that involve students with
current data and trying to find planets themselves. So today, what I'd like to
talk about is the heart of my research topic, which is to answer a big
question that you see on your screen which is: is there life elsewhere? It's
something that I, and many other humans, have been wondering about for a
long time. Something that has fascinated me
since I was quite small and that I have the chance and privilege to do nowadays.
This sort of question has been around for at least two and a half million years,
ever since the Greeks we have been wondering whether there is life beyond
the Earth, and I'm going to show you that we're taking active steps towards
answering this question and hopefully we will be able to know this answer within
our living times. So, the first thing that we need to do is define what we really
are searching, and by life here what I mean is this sort of organism. So,
phytoplankton plants the sort of things that on earth have radically changed
our atmosphere and, for instance, you will know that on earth about 21% of the
atmosphere of our planet is composed of oxygen and that oxygen was produced by
photosynthetic chemistry by plants. Without them, in about 10,000 years, so if
you remove all plant-based life on earth, within about ten thousand years
all the oxygen would react with the surface and disappear. And as such, the
presence of a vast amount of oxygen within the atmosphere of the earth acts as a
beacon and it shines really through space
basically saying here something funky is happening, here there is life
here there is life. So we're looking for things like this, not necessary oxygen,
other molecules as well but molecules that are produced by biological
processes and can fill an atmosphere. But at the same time, would be removed if
life were to be absent. How do you search for life elsewhere? Well the first
thing that people have thought is to search for planets that are like the
Earth, around stars that are like the Sun. While that has a certain
advantage because at least we know things have worked out here and by
looking elsewhere maybe it would work out over there too,
it has a number of problems and one of them is that we have yet to discover a
planet like the Earth orbiting a star like the Sun in the right configuration
for us to study its atmosphere, and it's still probably about two decades away.
Studying the atmosphere of that particular planet would probably take
another two to three decades more, so that pushes us quite far into the future
and if we want to understand life in the cosmos ahead of that then we need to
find a sort of shortcut. There is an inherent problem which is that it
basically assumes that life on Earth, or life in the universe rather, has to look
like life on Earth, that we need similar conditions on other planets to the
conditions that we have on Earth. There is nothing certain about this, we
don't really know what's out there and sometimes it might be good to also take
a little broader view, and the topic that I'm studying is actually looking for
planets similar to the Earth, where the stars are not like the Sun. The
stars are very small and you will see why that is important. A question
that is also I think more important rather than 'is there life
elsewhere?', is how frequently there is. And the search for life around the star like
the Sun is really to answer by yes-no, whether there is life
as well. But more important is finding out whether it's on one in ten
planets or one in a million planets and for that, we need to necessarily consider
other stellar systems and that's why my research has decided to, instead of
focusing on solar-like stars, to focus on other types of stars. That's where
Trappist-1 comes in. I don't know if you've heard of Trappist-1, you can see
it in the background. So this is the Trappist telescope which was used to
discover the Trappist-1 system, and here is a video in the background that
shows the Trappist-1 planetary system. We discovered that in about 2017 and we
found that there are seven planets, about the size of the Earth, around this star.
Now, this star is in the constellation of Aquarius. It's a very faint star and you
can see here the picture of the system. The seven planets here, of masses and
sizes similar to the Earth. They're also very close to their star, so the distance
between the star at the center and the outermost planet is only six percent of
the distance between the Sun and the Earth, meaning that the planets are
really hugging the star. The star itself is only 10% of the size and 10%
of the mass of the Sun, so it's very small and very cold and because it is
small and cold, although the plants are really close to
it, the planets are actually what we called temperate. It means that under
certain, and sometimes very exotic, geologic and atmospheric conditions, we
could expect water to remain liquid for billions of years on at least one part
of the surface. That's usually important for us because we're looking
for places where liquid water could exist, since water is at the heart of all
biological life on Earth, from any sort of life that we can encounter. And so
we're looking for environments where this could exist, and then our next step
would be to study those planets further to find out whether one, they have an
atmosphere. Two, whether that atmosphere allows indeed liquid water to be on the
surface. And three, whether there are traces of biological activity within
the atmospheric composition of the planet. So how did we find those planets? I
showed you the telescope already but how do we do that in practice? That
comes a bit to actually what you will do as a student, you will analyze data and
try to infer some things from it. So how did we do that?
Well, conceptually it's quite simple. We have here the Sun, and you see Venus
transiting in front of it, it's just passing in front of it - this is a video
by the way, it's footage taken from a satellite in 2012. When Venus passed
in front of the Sun in 2012, the Sun looked a little dimmer to a remote
observer. That means that we can detect that, there is a shadow that
passes and obscures it, a little bit of the star. So in our case, we don't
actually see the planet, we actually don't see the size of the Sun we
only see a dot of light. The out point will be to actually measure that
brightness very carefully, very accurately and observe a small
depression in how much flux we're getting, how much luminosity the star
has. So, if we take the case of the Sun and Trappist-1, you see here the Sun
I don't know if you see my mouse, but here you see a small planet which is the
size of the Earth that would be passing in front of the Sun. You see that it's
almost as big as some of the sunspots that we have on the Sun, so it would be
hard to distinguish the planet from these spots. However, Trappist-1 you see
here is ten times smaller than the Sun, and you see here a planet also the size
of the Earth in front of it. Comparatively, it hides more of the
stellar surface, a factor hundred times more. So it's a lot easier to detect a
small planet hiding a small star, rather than a small planet hiding a large star.
That's why stars like Trappist-1 are actually quite useful in a search for
planets the size of the Earth. It turns out that
stars the size of Trappist-1 are also about three times more frequent
then stars like the Sun. So we're looking at the most frequent type of stars and
therefore the most frequent types of planets as well.
So what does the data look like? Here you see brightness, this is a hundred per cent
this is 99 percent, and then 98 percent on the left-hand side. Each of these
dots here is basically a measurement, and we took measurements from space in
white, and from the ground using the trapeze telescope that you saw and you
can see intermittently in the background here. Each of these measurements
basically measures the luminosity of the star, and when it drops by one per cent,
we know that something ten times smaller than the star passed in front of it, and
so if we know the size of the star, we know the size of Trappist-1. Then
something ten times smaller than Trappist-1 is something that has the size of
the Earth. So here we see an eclipse of a planet the size of Earth,
obscuring Trappist-1. We measured this star for nearly three weeks, and you can
see transit, after transit, after transit. Planets covering the stellar surface
repeatedly, we'd never seen so many transits in one go, so rapidly or happening.
That's how we know that there are planets around Trappist-1, and so from
how frequently this happens, we know the orbital period of the planet and then if we
gather all these events together, we can actually make another plot which is this
one where we see here for instance, one hundred percent of the stellar light and
then the plant comes in front of the star. Then we only see a 99 percent
and then it comes out and you see only a hundred percent. That's how we know
that there are planets around Trappist-1, from the depression of light here we
measure the radius of the planet, so you see that some of the planets are smaller
and other bigger. This is bigger, this is smaller. You see that our transit
duration here is longer, that means that the planet that the further distance
from the star, it orbits slower. You can see it here, this planet goes slower around
the star, than the inner ones.
So, how can we find life from this? That's a big question. Well, what happens and
what's interesting with the trends in geometry, is that some of the starlight
now goes through the planet's atmosphere as the planet goes in front of it. And we
want to study that. Now, it's very difficult as you can see on the image
now, we don't actually really see the atmosphere of Venus. So we need to use a
little trick and we've been quite clever at that. That method is called
transmission spectroscopy, and we can explain it a little bit by using a lunar
eclipse. During a lunar eclipse, the moon is
red. And have you asked yourself why is the moon red?
The configuration is the following. We have the Sun, and we have the Earth and
then the moon in a direct line. The only light that reaches the moon
is in the cone of shadow from the Earth, the only line that reaches the moon is
sunlight through the atmosphere of the Earth. It got imprinted by
atmospheric features, for instance, the atmosphere of the Earth scatters blue
light. It creates a blue sky at midday, but then there's no more blue light when you
reach sunset and sunrise which are on the edge of the earth here. That's
why sunsets and sunrises are red. And so the light that is on a moon during a
lunar eclipse is the light of the south and sunrises and sunsets. Essentially
sunlight transformed by the atmosphere of the Earth, exactly like what we want
to do on an exoplanet. And we have measured that, so for
instance, you can see here a video that was taken by astronauts on
Apollo-12 in 1969 as they returned to Earth. They became the only three people
to see a lunar eclipse from the moon pretty much. You can see here they
basically shot this video through the window of the spacecraft and we can see
that the Sun is a little red, and it's red because it's actually not sunlight
let we see, it's sunlight transformed by the Earth's atmosphere. If the
astronauts had an instrument called a spectrograph and had analyzed this ring
of light here, which is our atmosphere, they would have noticed notably the
presence of oxygen and would have been able to deduce that there is life on
Earth. So how do we do this on exoplanets? We
don't see a crescent, we don't see really a star, we only see a dot of light. And we
definitely don't see the planet. The way we do it is by being a little clever, so
if we have a star in a planet like this, and a planet passes in front of the star,
you are the observer on the right-hand side of the screen. Then you measure the
deficit of light and it tells you the size of the star. That's a transit and you've
seen that before. Now if the planet has an atmosphere, it
will scatter blue light like an atmosphere like the Earth. And so if we
basically have blue light going in front of the planet and then we measure a
certain size and we measure the planet, it's actually big because the blue light gets
stopped by the atmosphere and the planet and the atmosphere looks opaque. Red light,
however, goes through the atmosphere. That happens in sunrises and sunsets, it's what
reaches the moon, and under this condition we would measure an
apparent size for the planet that is slightly smaller in redder wavelength. So by
carefully measuring the size of the planet as a function of wavelength or
color, then we know opacity sources within the atmosphere notably without
the atmosphere has a property similar to the Earth, that it
scatters blue light and has blue sky. But also whether it has oxygen or
methane, any molecule that could be of biological of geological origin. That's
something that we want to do with the James Webb Space Telescope, which will
normally be launched in Spring 2021. Unfortunately the current condition of
Covid-19 has delayed the launch, and we are hoping that work can resume on
preparing the spacecraft for launch. Soon enough we will have data on exo-
planetary atmospheres of Trappist-1 and others. So this is Trappist-1 small
telescope, it's about only 40 centimetres, about this size of a mirror.
It's in Chile, the reason why we go to Chile is because the skies were
absolutely fantastic. We see stars right at the bottom of the horizon and in a
dry desert on a high plateau and so we are in a very good situation to measure
starlight very precisely and detect
planets. This is a full night taken from Paranal Observatory in northern
Chile. This is really gorgeous, we see here the Milky Way. The beam that you see
every now and then shooting from the mountain is a laser that we use to make
our images a bit finer, this is the sea here that we just about see.
The light that is dashing every now and then here, are aeroplanes.
These sights absolutely fantastic, I encourage you, if you go to South America,
to stop by the deserts of Chile and observe the sky.
Now there is a website for Trappist-1 if you want to know more about it, please
tune into www.trappist.one in order to find a lot more information. And on
that note, I will leave you. Our telescopes are actually scanning the sky now
for more planets than that, we have a new set of telescopes in Chile and we're
hoping in the next 10 years to detect another 20 systems like Trappist-1. Now
if you join us in Birmingham, you will have the chance to work on this kind of
data and discover planets. So get a chance to discover planets yourself.