Undreamed Shores - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 255

and Earth-like distances from their star. All five planets have closer
orbits than has Mercury to our Sun—and most (including the Earth-
sized ones) orbit much closer. These planets are Earth-sized, but
almost certainly not Earth-like. They are dry and roastingly hot and,
therefore, quite dead.
The envelope of detection continues to be pushed further. There
are now several confirmed exoplanets even smaller than Earth,
including one, a mere 33 million light years away, which has just been
discovered, quite accidentally, by the Spitzer Infra-Red Space Tele-
scope. 166 This telescope is usually used to gather further information
on exoplanets already discovered, and it was obtaining data on a
Neptune-sized exoplanet around the red dwarf star GJ 436 when it
discovered an extra 'dip' in the electromagnetic signal, which turned
out to be a 'first' for the Spitzer: an extra, and very small, planet two-
thirds the size of Earth. Again, it has a very close orbit (with a year of
1.4 Earth days): so close that rock is likely molten at its surface. The
same state is likely for Corot-7b, which may be anything between two
and eight Earth masses (estimates differ), but is also so close to its
parent star that it is likely to have a molten surface. Such exoplanets
have been termed 'lava-ocean planets': ocean worlds of a sort—but
not as we know them.
Exoplanetary Water
Water, as we have seen, is common throughout the universe, espe-
cially in its gaseous and icy forms. That is no surprise, as the H 2 O
molecule is made from two of the most common atoms in the uni-
verse, the ubiquitous hydrogen and the less common (by a factor of
1,000) but still virtually omnipresent oxygen. Water has been detected
in the comets, planets, and moons of our solar system, and as a com-
ponent of the gas and dust clouds of interstellar space, 167 and even in
intergalactic space, perhaps injected there by the enormous power of