So Amaury, last year there was an
important discovery in the world of
astronomy, three planet circling a star
30 light-years from the earth. You stayed
on this area to examine it further and
you've made quite important discovery
that there are more planets. How many and
what size are they?
So in total now we now we that the system has seven
planets - we started by thinking they were
three but one of them we were a bit mistaken
so we found essentially we have two
well-defined and then we can add now
another five, where we're pretty sure that
existing in the system. And they're circling the
particular star called Trappist one
described that star how did it compare
to the Sun? Yeah it's very odd it's a star
that is roughly ten percent of the size
of the sun so ten times smaller.
It's about the size of Jupiter slightly
larger than Jupiter. It's got a
temperature which is rather cold, we call
that an Ultra Cool Dwarf in our jargon. The
star is more than twice cooler than the
Sun. It means that the star looks very
red and for planet detection it's really
good
the smaller size helps us find small
planets like the one we found.
So from what you know so far about this
solar system, what would the
star look like them from any of these
planets.
Oh the view would be quite
remarkable how very different from what
we have here on earth. The star would
look much bigger you have to imagine an
enormous orb into the sky.
Itself, the star would appear quite
faint because it emits most of its light
in a regime of light very red as we will
perceive heat but not see much light and
then the other planets in the system the
closest next planet in the system could
appear as biggest twice the size of the
moon in the sky so a very beautiful sight.
With a small telescope if they're were
cities, you'd be able to see cities it's
remarkable to think of it.
Searching for exoplanets is notoriously
difficult, how did you go about actually
discovering that there were these extra
planet's orbiting this
particular star? So the method that
we use is what we call the transit
method we wait for the planet to pass in
front of the star, this creates, a transit.
And during the transit the planet
would cast a shadow and so if you have a
big planet on a certain star it would cast
a bigger shadow than a small planet. But
similarly a small planet will cast a
small shadow on the big star but a
much bigger shadow on a smaller star and
so because we have such a small star it was
easier to find things like a planet the
size of the earth. If we had selected and
instead investigated stars like the Sun
it would have been a hundred times
fainter a signal to detect. So we were
helped by the fact that the star was so
small. The star is much smaller than the
Sun so would it give off enough energy
to sustain life on any of these planets?
We claim that it could be liquid
water - life
we don't know yet that's for the future
that's why we're excited and with that
system it's really for the future. So the
fact that the story is smaller and
colder means that for water to be liquid
on a given planet needs to be closer a
bit like putting your hand next to a
very powerful light or weaker light you
would see it to feel the same heat you
need to be much closer so compared to
say the distance where the earth is from
the Sun it takes a year to go around. Planets
in the trappist one system need to be on
orbits of order seven days to 12 days and
so about order of the week for the
conditions to be correct for liquid
water to exist. And do you think that's
that's happening in this case? That again is
something where we are a bit uncertain, we
know that the distance is correct but
eventually whether there is water
depends on whether well there is water
in the first place.
It also depends on the atmospheric
conditions because you know greenhouse
gases can heat up the planet and remove
the liquid water or equally geologic
conditions depending
on how hot the planet's surface as well
is, so these are elements that we will
find out in the future we already
investigating some of them but the
planets are the right distance that if
there is water on them and it looks the
atmospheric conditions would look like
the earth, then it would be in the liquid
form. Without being able to observe
closely the surface of these planets, how
would you determine that there was
liquid? That's a very good question,
so we go back here to the transit
method as the planet goes in front of
the star, some of the star light will
shine through the planet's atmosphere. It
basically makes a shadow within the
shadow and from that we deduce what's
within the atmosphere of the planet. We
deduce the chemical makeup we can also
extract information such as cloud cover
vertical structure of the atmosphere and
all these will tell us whether the
conditions of correct. And then there is
a chance to see the planet as it goes
behind the star and then as it just
about to leave from behind the star we
get a view very good view of its lit
surface of the dayside of the planet and
that will give us an indication of the
temperature of the planet and so also
information on its surface as well but that
comes in the future and not quite now.
So from what we know of these seven planets
and the Trappist one star, how does this
differ from our own solar system?
The planets are very similar to the planets
of the solar system but their star is so
very different and that has implications.
The planets are much closer to the star
they're much closer to one another and it
means that probably they would have also
constant daylight and constant nightside.
So the planets are locked what we call a
bit like the moon is locked towards the Earth
showing always the same face.
The planets will always see the sun
at the same position in the sky.
And that will effect the climate
very much and we do not know exactly how.
And on a personal level, how
exciting is this for you?