Pulled by this
unseen planet, the star 51 Pegasi approaches and recedes from Earth
every 4.2 days. The planet, a gas giant like our Jupiter or Saturn,
is called 51 Peg b for its parent star. Its 4.2 day orbit is an
orbit incredibly close for a gas planet and, as noted, most of the
exoplanets so far found are large gas planets, with the exception
of a few, like Gliese 581.
Theorists believed that, like Jupiter, giant
gas planets would only be found far from their stars in orbits taking
years to complete. But as astronomers have watched more stars, more
gas planets have been turning up in extremely close orbits or on
wildly eccentric paths, some in weirdly
elongated orbits and others so close to their star that they circle
it in days or even hours.
These worlds are called ROASTERS or ECCENTRIC