Water in the Cosmos - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 5

have formed could have had liquid water on their surfaces—and so
could potentially have been habitable, even if they were far from their
parent star.
This would emphatically have been a weird universe, with matter
packed into it a million times more densely than today. Nowhere
would have been really cold , in that all-round warm blanket. It was a
short-lived state, though. After only a few million years the back-
ground temperature of the whole universe dropped below zero, so
there was not much chance for complex life to emerge before the
newly minted waters—the hypothesized newly minted waters—nearly
everywhere, froze.
In today's familiar, vastly more dilute universe, does an exploding
star literally expel steam? In reality, conditions around a nova or
(especially) a supernova are mostly too hot for that. The expelled gas
is a high-velocity plasma of separate ions. The reactions must mostly
take place later, in distant regions, as the gases expand and cool. This
is mysterious territory, where the chemical reactions of outer space
occur. It needs the most ingenious of modern instrumentation to
detect it. Fortunately, such equipment has been devised.
Herschel's Gift
A few years ago, something that looked like a large and eccentrically
sculpted trash can was launched into space. It was carefully steered
towards one of the points, 1.5 million kilometres away from Earth,
where the gravitational forces of the Earth and the Sun are balanced
by the centrifugal force of the Earth's passage around the Sun. Such
a point in space is sometimes referred to as a gravitational well, and
spacecraft can rest there without needing to use too much energy. It
is called a Lagrange point, named after their discoverer, Joseph-Louis
Lagrange. He was a mathematician so gifted and so temperamentally