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Planets begin as dense
knots in a cloud of gas and dust swirling around a
star. But how do they go from something like this ....
... to something like this. With the James
James Webb Space Telescope, astronomers will be able to study how planets
come to be and how they change as get older.
After centuries of searching, astronomers are finding
exoplanets ... just about everywhere.
ranging from giant planets with masses much greater than
Jupiter's ... to worlds only a few times more massive than Earth.
But where do the planets we know
best fit into the menagerie of worlds astronomers are finding?
How did our solar system come to be the way it is?
Why is Earth a balmy, water-rich world -- and are there
others like it elsewhere in the galaxy?
These are the kinds of questions astronomers will address
with Webb.
For planets that pass directly in front of their stars,
Webb will search for chemical "fingerprints," identifying
atmospheric gases like water vapor, carbon dioxide and
methane that absorb specific wavelengths of the star's light.
Webb will also study the dusty disks where new
planets form, revealing how the chemical compositions of younger and older
disks change with time and identifying
how these changes are reflected in the planets we find.
Such studies will be revolutionary in their own right.
And by applying Webb's capabilities closer to home, astronomers
will better understand planetary systems.
For example:
How do our asteroids, comets, and other small bodies like Pluto
relate to the objects that create the dusty disks around other stars?
The Webb telescope will determine the chemical and physical
properties of these bodies with unprecedented sensitivity in
in wavelengths unavailable to telescopes on the ground.
By learning more about the small bodies in our solar system,
scientists will be able to address questions about the solar system's past
and compare it to other planetary systems we find in similar
phases of construction. For example,
did Earth's oceans arrive by impacts with small icy bodies?
If so, is the same process happening elsewhere
-- and can we find those locations?
Webb also will study the outer planets and their moons.
Of particular interest is Titan, the largest
moon of Saturn. Now being explored by NASA's Cassini spacecraft,
Titan is as big as the planet Mercury, possesses
an atmosphere half again as thick as Earth's, and frigid surface
with lakes of liquid hydrocarbons. Webb
will map Titan's chemical makeup with six times Cassini's
resolution and monitor the moon's seasonal changes over a decade
or more. Next stop: Uranus.
When Voyager 2 returned this image in 1986, the
planet's south pole was facing the sun. Few clouds could be seen.
But as Uranus neared its equinox in 2007
brightclouds suddenly materialized. So far,
scientistsare at a loss to explain this profound seasonalchange."
During Voyager's visit, the northern
hemispheres of Uranus' big moons were all in shadow.
. But when Webb begins service, the moons' northern halves
will face the sun and give astronomers abundant new real estate
to explore.
Three years later, in 1989, Voyager 2 passed
Neptune and imaged its strange dark spot.
Over the following years, astronomers have seen the dark spot disappear ...
and then reappear. Voyager easily picked
out clouds despite Neptune's greater distance from the sun.
Why is weather on Uranus and Neptune so different?
Neptune's big moon Triton is unusual, too.
Nitrogen-spewing volcanoes and other geological
forces reshape this frozen surface in ways we're just
beginning to understand.
Comets. Asteroids.
The outer planets and their moons -- and beyond them, the icy
the icy bodies of the Kuiper Belt. These objects provide us with
the closest and most detailed look at how our own solar system evolved.
The James Webb Space Telescope
makes it possible to take that understanding a step farther
-- to probe the makeup of nearby planetary systems at comparable
distances from their stars. Webb
will allow astronomers to directly compare the chemical and physical
properties of our outer solar system with similar zones
around nearby stars.
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