Welcome back, everyone.
So in the last lecture, we talked about the
radial velocity method for determining the existence of extrasolar planets.
And today we're going to talk about another method called planetary transits.
So this method only works if the alignment of your star and planet
system is just right, so that the planet passes in front of the star.
And when that happens, when you're lucky enough to have
that kind of alignment, there's an enormous amount of information
that can be extracted from that. In some sense, it's like an eclipse.
The even though the entire star starlight is not blocked out, enough
of the light is blocked out
for information to be extracted by astronomers.
From, how much light for example has been blotted out.
How wide, how long it takes for the light to be blotted out.
So what information can we get from these transit methods?
Well, the first thing is, as the star, or as the planet passes
in front of the star and some of that light is blocked, the, one of the
most important pieces of information we can get
is the radius, the size of the planet.
And that's a remarkable thing, because when you combine that with the
fact that from the frequency of eclipse, we can get the period.
And then using information about the star, we
can actually get the mass of the planet.
We can combine, knowing the mass of the planet, the radius of
the planet size, we can put those together to get the density.
So the density
tells us whether or not this is a
gaseous planet or whether it's a rocky planet, right?
because rocks, something like a rock, is very high, is very
dense, whereas something like a gas giant is not very dense.
So already right there, we're te-, we're able to be able to get some information
about what this planet is built out of, and what it's what its structure is.
And that is an enormously important piece of information.
Even more amazing is that when the planet passes
just in front of the star, just as it begins to
get its light begins to block out the light from the star.
Some, if there's an atmosphere, a gaseous atmosphere around the planet, some
of the light from the star passes through the limb of the planet.
Right, just right where the atmosphere is.
And, that light gets absorbed by the atmosphere
constituents and produces what we call absorption lines.
That allow us to tell what the structure in
terms of composition of the atmosphere, is.
So, so, from these transit systems, we can actually tell what kind of gases,
the atmosphere of these exoplanets, light years
away, ten, hundreds of light years away.
We can actually tell what's in those atmospheres.
Carbon monoxide, carbon dioxide.
Maybe even someday, be able to get biomarkers, things that only
gases that could only exist in the atmosphere if life existed.
So these transits are an enormously powerful tool for allowing
us to not only tell that there are exoplanets, but
begin to tell real details about the nature of those exoplanets.
Adam FrankProfessor
