The Astronomy Book

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have proved to be false positives
but, after three years of analysis,
the program had identified 1,284
exoplanets, with more than 3,000
stars left to examine. The statistics
for the exoplanets in the Kepler field
are striking—most stars are part
of a planetary system. This means
that the number of planets in the
universe is likely to exceed the
number of stars.
The amount of dimming during
a transit gives an indication of how
big an exoplanet might be, but the
study of an exoplanet’s size and
characteristics is still in its early
stages. The light reflected from
a planet is about 10 billion times
fainter than the star it orbits.
Astronomers are waiting for the
James Webb Space Telescope in
2018 and the European Extremely
Large Telescope in 2024 to image
this light directly and analyze the
chemistry of exoplanets. Until then,
they have to speculate using very
little data: an approximate mass
of the planet, its radius, the orbital

distance, and the temperature

of the star. This tells them what

the planet is probably made of

and allows them to conjecture

what the surface conditions are

likely to be.

Hot and super Jupiters

The exoplanets discovered so far

have added a host of weird worlds

to the neat family portrait that is

the sun’s planetary system. For

THE TRIUMPH OF TECHNOLOGY

example, 51 Pegasi b was the first

of many “hot Jupiters.” These have

a mass similar to Jupiter’s and a

large size that shows that they are

mostly made of gas. 51 Pegasi b is

half as massive as Jupiter, but is

slightly larger. This gas giant orbits

its sunlike star every four days.

That means it is much closer to

its star than Mercury is to the sun.

Such proximity means it is tidally

locked to the star—one side always

faces the scorching stellar surface,

and the other always faces away.

Many hot Jupiters have been found.

They have confounded scientists,

who are trying to understand how

gas planets can exist so close to

a star without evaporating. Some

exoplanets are dozens of times

more massive than Jupiter, and

are known as “super-Jupiters.” ❯❯

We were not expecting

to find a planet with a

4-day [orbital] period. No

one was expecting this.

Michel Mayor

The “super-Jupiter” Kappa

Andromedae b, shown here in an

artist’s render, has a mass of 13 times

Jupiter’s. It glows a reddish color, and

may yet be reclassed as a brown dwarf.