Undreamed Shores - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 261

of them out there. Most stars have them. The overwhelming majority
of them are very unlike Earth, or many are well outside the range of
anything we see in the solar system, and many planets have unstable
orbits prone to dramatic reorganization. However, if even one planet
in a thousand is broadly Earth-sized and within the habitable zone,
then there might be as many as a billion potentially habitable planets
with plentiful water out there, just in our galaxy. It gives pause for
thought.
Where Next?
We can detect ever-increasing numbers of exoplanets and we can spec-
ulate from the mass and radius of these planets—and thus from their
density—that there are planets with liquid water. We can find water in
the atmosphere of a hot Jupiter. As ever, we need to look closer.
There is a monster that is currently growing in the NASA work-
shops—and eating up most of even that large organization's money.
It is the James Webb Telescope. Three times the size of the Hubble,
with powers to match, it will see farther, more clearly, and bring the
universe into much sharper focus than before. 176 Fingers are crossed
that all will go well with the launch (set for 2018). If all does go well,
and it arrives safely at 'Lagrange point 2', a million and a half kilo-
metres from Earth, then it can get to work (see Plate 10).
The James Webb is designed as a multi-purpose telescope, like the
Hubble, so it will do far more than just look for planets. But its poten-
tial is already making exoplanet scientists impatient for the years of
waiting to be over. Its giant eye will— should —have the capacity to
gaze uninterrupted at Earth-sized planets orbiting small suns within
the habitable zone, and to 'sniff' the composition of the atmospheres
looking for water vapour, carbon dioxide, and gases. Then we will be
much closer to detecting distant Earth-style oceans.