Exoplanets The majority of the found exoplanets have larger orbital eccentricities than planets in our solar system. The solar system's eight planets all have near-circular orbits. The discovery of exoplanets demonstrates that the solar system, with its relatively low eccentricity, is rare and unique. Stars like the sun tend to have regular orbit around their centers of mass called "bodies". But many stars are not alone in this galaxy or universe, they usually travel together in a group known as a "stellar association". These groups can contain hundreds of stars with similar ages and masses from different locations in the galaxy or universe. A star may be part of more than one stellar association depending on how far it has traveled from its birthplace. A star's planetary system can influence how much energy it receives from its host star. If a planet passes directly between the star and Earth then we would see a total eclipse of the star by the planet. However, because the planet does not pass directly between the star and Earth each time it orbits the star, we see only portions of the star being eclipsed. This is why there are periods when no part of the star is completely obscured by its orbiting planet — sometimes all of it, at other times only part — and why the eclipses occur at different times each time the planet passes behind the star. The amount of energy a star emits depends on its mass.