This artist's concept illustrates two planetary systems -- 55 Cancri (top)
and our own. Blue lines show the orbits of planets, including the dwarf
planet Pluto in our solar system. The 55 Cancri system is currently the
closest known analogue to our solar system, yet there are some fundamental
differences.
The similarities begin with the stars themselves, which are about the same
mass and age. Both stars also host big families of planets. Our solar
system has eight planets, while 55 Cancri has five, making it the
record-holder for having the most known exoplanets. In fact, 55 Cancri
could have additional planets, possibly even rocky ones that are too small
to be seen with current technologies. All of the planets in the two
systems have nearly circular orbits.
In addition, both planetary systems have giant planets in their outer
regions. The giant located far away from 55 Cancri is four times the mass
of our Jupiter, and completes one orbit every 14 years at a distance of
five times that between Earth and the sun (about 868 million kilometers or
539 million miles). Our Jupiter completes one orbit around the sun every
11.9 years, also at about five times the Earth-sun distance (778 million
kilometers or 483 million miles). Fifty-five Cancri is still the only
known star besides ours with a planet in a distant Jupiter-like orbit.
Both systems also contain inner planets that are less massive than their
outer planets.
The differences begin with the planets' masses. The planets orbiting 55
Cancri are all larger than Earth, and represent a "souped-up" version of
our own solar system. In fact, this is the first star that boasts more
giant planets than our sun!
The arrangement of the planetary systems is also different. The inner four
planets of 55 Cancri are all closer to the star than Earth is to the sun.
The closest, about the mass of Uranus, whips around the star in just under
three days at a distance of approximately 5.6 million kilometers (3.5
million miles). The second planet out from the star is a little smaller
than Jupiter and completes one orbit every 14.7 days at a distance of
approximately 17.9 million kilometers (11.2 million miles). The third
planet out from the star is similar in mass to Saturn and completes one
orbit every 44 days at a distance of approximately 35.9 million kilometers
(22.3 million miles). The fourth planet is about half the mass of Saturn,
orbits every 260 days and is approximately 116.7 million kilometers (72.5
million miles) away from the star.
