杏吧原创

ASTRONOMERS have finally spied a planetary system that looks something like
our own.

Most of the 70 known 鈥渆xoplanets鈥濃�攇as giants with orbits that are
either highly elliptical or very close to their stars鈥攁re nothing like
Earth. But in 1996, a planet 2.5 times the mass of Jupiter was found in a
circular 2.99-year orbit around the star 47 Ursae Majoris.

Now researchers have found a smaller sibling in a circular orbit around the
same star. The new planet has about three-quarters the mass of Jupiter, so the
pair have the same relative masses as Saturn and Jupiter
(www.exoplanets.org).

鈥淲e can make a guess that about 5 per cent of planetary systems are in
circular orbits,鈥� says Paul Butler of the Carnegie Institution of Washington
DC.