via ScienceDaily, a new record setting 5th planet (the most ever found in a single system outside our own) has been discovered in the 55 Cancri system 41 light years from our own solar system. The exciting element of the discovery is that the new planet, while a gas giant, is in the star's habitable zone where liquid water could exist. The really interesting part is the gap between the four inner worlds and the outer planet - a gap in which another, smaller and possibly rocky terrestrial type world might lie. The researchers indicate anything in this area would have to be smaller than the planet Neptune to have eluded discovery so far.
"the fifth planet is within the star's habitable zone in which water could exist as a liquid. Though the planet is a giant ball of gas, liquid water could exist on the surface of a moon or on other, rocky planets that may yet be found within the zone. "Right now, we are looking at a gap between the 260-day orbit of the new planet and the 14-year orbit of another gas giant, and if you had to bet, you'd bet that there is more orbiting stuff there."
Fischer noted that what occupies this gap has to be another planet around the size of Neptune or smaller, because anything larger would have destabilized the orbits of the other planets. All of the planets around 55 Cancri are in stable, nearly circular obits, like the eight planets in our solar system. Jupiter is located at 5.2 AU from the sun, while Mercury and Venus are closer than 0.72 AU. Earth and Mars are in the gap at 1 AU and 1.5 AU."
The 55 Cancri system's innermost planet, the size of Jupiter, was only the fourth exoplanet discovered when found in 1996, and orbits the star every 14 days. The second planet and third planets were found in 2002, the second discoverd being the outermost (14 year orbit) and four time the size of Jupiter, the third discovered about half the size of Saturn and outside the orbit of the first discovery with a 44 day orbit. The fourth planet discovered in 2004 is around the size of Neptune (14 Earth masses) and the innermost planet in the system, extremely close to the star with an orbital period of only 2.8 days.
The new planet is around half the size of Saturn, or about 45 Earth masses, and orbits the star every 260 days at around .78 astronomical units (the distance of Earth from our Sun). The new planet, along with the previous four planets, was discovered by the "wobble" technique, which analyzes the effect the planets' gravity has on the light form the star. The habitable zone around the star is slightly closer to the star than that of our own system due to the star being slightly older and dimmer than our sun.