WEBVTT

00:00:00.000 --> 00:00:08.010 align:middle line:90%


00:00:08.010 --> 00:00:10.470 align:middle line:84%
How do we learn about
a planet's atmosphere?

00:00:10.470 --> 00:00:14.770 align:middle line:90%


00:00:14.770 --> 00:00:18.270 align:middle line:84%
How do we know what's in the
atmosphere of an exoplanet?

00:00:18.270 --> 00:00:20.280 align:middle line:84%
The majority of
known exoplanets have

00:00:20.280 --> 00:00:22.290 align:middle line:84%
been discovered because
they partially block

00:00:22.290 --> 00:00:24.120 align:middle line:90%
the light of their host star.

00:00:24.120 --> 00:00:26.970 align:middle line:90%
This is called a transit.

00:00:26.970 --> 00:00:28.950 align:middle line:84%
During a transit some
of the star's light

00:00:28.950 --> 00:00:31.860 align:middle line:84%
travels through the planet's
atmosphere and gets absorbed.

00:00:31.860 --> 00:00:34.440 align:middle line:84%
The light that survives
carries information

00:00:34.440 --> 00:00:36.990 align:middle line:84%
about the planet across
light years of space

00:00:36.990 --> 00:00:39.120 align:middle line:90%
where it reaches our telescopes.

00:00:39.120 --> 00:00:43.020 align:middle line:84%
However, the planet is very
small relative to the star.

00:00:43.020 --> 00:00:45.570 align:middle line:84%
So it is still very
difficult to detect,

00:00:45.570 --> 00:00:47.670 align:middle line:84%
which is why we
need a big telescope

00:00:47.670 --> 00:00:50.800 align:middle line:84%
to be sure to capture
this tiny bit of light.

00:00:50.800 --> 00:00:54.510 align:middle line:84%
So how do we use a telescope
to read transit light?

00:00:54.510 --> 00:00:56.820 align:middle line:84%
Stars emit light at
many wavelengths.

00:00:56.820 --> 00:00:59.700 align:middle line:84%
Like a prism makes a rainbow,
we can separate light

00:00:59.700 --> 00:01:01.410 align:middle line:90%
into its separate wavelengths.

00:01:01.410 --> 00:01:03.600 align:middle line:90%
This is called a spectrum.

00:01:03.600 --> 00:01:05.489 align:middle line:84%
Visible light
appears to our eyes

00:01:05.489 --> 00:01:07.110 align:middle line:90%
as the colors of the rainbow.

00:01:07.110 --> 00:01:10.110 align:middle line:84%
But beyond visible light there
are many wavelengths we cannot

00:01:10.110 --> 00:01:12.730 align:middle line:90%
see.

00:01:12.730 --> 00:01:15.780 align:middle line:84%
Now back to the
transiting planet.

00:01:15.780 --> 00:01:18.300 align:middle line:84%
As light as traveling through
the planet's atmosphere,

00:01:18.300 --> 00:01:20.830 align:middle line:90%
some wavelengths get absorbed.

00:01:20.830 --> 00:01:23.850 align:middle line:84%
Which wavelengths get absorbed
depends on which molecules

00:01:23.850 --> 00:01:25.590 align:middle line:90%
are in the planet's atmosphere.

00:01:25.590 --> 00:01:28.320 align:middle line:84%
For example, carbon
monoxide molecules

00:01:28.320 --> 00:01:29.880 align:middle line:84%
will capture
different wavelengths

00:01:29.880 --> 00:01:33.450 align:middle line:90%
than water vapor molecules.

00:01:33.450 --> 00:01:35.960 align:middle line:84%
So when we look at that
planet in front of the star,

00:01:35.960 --> 00:01:37.760 align:middle line:84%
some of the wavelengths
of the starlight

00:01:37.760 --> 00:01:40.460 align:middle line:84%
will be missing depending
on which molecules

00:01:40.460 --> 00:01:43.580 align:middle line:84%
are in the atmosphere
of the planet.

00:01:43.580 --> 00:01:45.740 align:middle line:84%
Learning about the
atmospheres of other worlds

00:01:45.740 --> 00:01:49.130 align:middle line:84%
is how we identify those that
could potentially support life,

00:01:49.130 --> 00:01:52.310 align:middle line:84%
bringing us another step closer
to answering one of humanity's

00:01:52.310 --> 00:01:55.840 align:middle line:90%
oldest questions, are we alone?

00:01:55.840 --> 00:02:11.000 align:middle line:90%