Undreamed Shores - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 248

how frequently it orbits its sun (its periodicity), and on how elliptical
that orbit is.
Another surprise: Pegasi b turned out to be a giant planet, compar-
able to Jupiter. But it orbited much more closely to its sun, just 7 million
kilometres away, in a tiny orbit that gives it a very short year of just
four Earth days. So close to the sun, its surface temperature was calcu-
lated to exceed 1,000 degrees Celsius. It turned our own solar system
on its head, and so it came to be known as a 'hot Jupiter'—the first of
many such, as it turned out.
Exploiting the tiny wobble of planet-bearing stars remains a key
way of detecting exoplanets. But other techniques have been invented.
One makes use of the transit effect. As a planet passes across ('tran-
sits') the face of its star it dims the light of that star by a tiny, though
detectable, fraction. The amount of light blocked out by the planet's
transit gives a measure of the size of the planet which, if coupled with
information about its mass, can provide an indication of its density,
and thus what the planet is likely made from. The transit method can
also reveal the composition of exoplanetary atmospheres, from spec-
troscopic analysis of the starlight that passes through them.
Planets can also influence the bending of light itself. Einstein's the-
ory of relativity successfully predicted that a path of light will be bent
by the gravity of a massive object such as a star or galaxy. In 1919 the
British scientist Arthur Eddington (1882-1944) travelled to the island
of Principe off the west coast of Africa to observe the solar eclipse of
29 May that year. Eddington, a Quaker pacifist as well as a brilliant
physicist, had only just escaped imprisonment during the First World
War for his firmly held pacifist and internationalist views: he was
a conscientious objector, and advocated continuing dialogue with
German scientists. After the War, he brought Einstein's theory of gen-
eral relativity to an English-speaking audience (he was an effective
popularizer of science as well as being, reputedly, one of 'only three