[Background Sound]
This exo-planet in the distant solar system appears to have features very similar to our
own Earth. It has continents, oceans, and clouds.
This star has another planet. This one appears to be a gas giant not unlike Jupiter in our
own Solar System.
As we move farther away, the two planets disappear into the glare of their sun. The star now
looks like the all the other stars in the night sky. How will we ever see these planets,
we cannot yet travel there? For the distances that even the closest stars are well beyond
humanity's current capability to traverse in our lifetimes. We will have to rely on
a "space telescope."
Housed inside this telescope is a science instrument called a "coronagraph" that is
designed to separate starlight from reflected planet light. As the light makes its way to
the coronagraph, we also noticed signs of small distortions picked-up when the light
reflected off the tiniest of imperfections in the telescope's large mirrors. With the
coronagraph not yet activated, we see on the monitor what the star looks like through a
telescope. No matter how large and perfect the telescope is, it turns into what once
a point of light in space into a round disc surrounded by concentric rings. The effect
is what is known as "defraction."
Somewhere behind the rings of light are the two faint planets. As you're about to see,
a coronagraph helps directly image faint planets by doing 3 things:
First, a coronagraph blocks most of the incoming starlight using a mass with a dark central
region. The mass is carefully designed to redirect the starlight that is not blocked
off to the edges of the beam. As we see on the monitor, the inserted mass has already
decreased much of the central starlight.
Secondly, the coronagraph removes the effects from defraction. When something that looks
like a washer that is placed into the lightpath, it blocks the light in edges of the beam,
and the rings disappear.
We have now managed to removed almost all of the starlight and are now able to view
objects more than a million times fainter than the star.
But what happens to the light from a planet? Why doesn't it also get blocked by the mass?
Because the telescope is pointing directly at the star, the planets' light comes in at
an angle--misses the mass, and passes through the center of the washer. But we are still
unable to see the planets? If we look closely at the monitor, when we turn up the image
signal by collecting more light, what appears to have been a blank field, actually consists
of blobs of leftover starlight. This scattered light, due to minute imperfections in the
telescope's optics is still hiding the faint planets. So this takes us to the third and
last element of the coronagraph. The removal of the scattered blobs.
A special mirror is used with hundreds of tiny pistons behind it that can change its
shape so as to correct the distortions in the light beam. As the mirror deforms, the
blobs of light as seen on the monitor slowly begin disappearing finally revealing the brighter
of the two planets. Afterwards, the fainter planet also comes into view.
We can now start to see objects more than billion times fainter than the star. Deep
within the glare of their star. We have discovered our two planets.
And if the light from these is past through a prism. We will see the light spread out
into rainbows of color. But when looking closely, some colors are missing. They were absorbed
by gases from each planet's atmosphere-- giving us important clues about their composition.
The search for life in the universe has taken a new step forward.
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