Earth is only the habitable planet in our solar system. But other planetary systems could have as many as seven habitable worlds in the absence of a gas giant like Jupiter, according to a new study.

Published in the Astronomical Journal, the new study, led by UC Riverside astrobiologist Stephen Kane, concludes that other stars can hold multiple habitable planets in their Goldilocks zone.

The discovery of life in outer space usually focuses on what scientists call the "habitable zone," the region around a star that may have liquid oceans in an orbiting planet, a condition for life as we know it.

Kane had been researching a nearby solar system called Trappist-1 which has in its habitable zone three Earth-like planets. Which made him think about the actual number of habitable planets a star should have, and why our star has only one.

His team developed a model system in which planets of different sizes were projected around their stars. A gravitational force algorithm helped to check how the planets interacted for millions of years. Many stars might support up to seven, and a star such as our Sun could support six planets with liquid water.

"More than seven, and the planets become too close to each other and destabilize each other's orbits," Kane said.

How then would our solar system have only one habitable planet, if it can sustain six? This helps to avoid near interaction and to maintain steady orbits if the rotation of the planets is circular rather than oval or irregular.

It could be potentially due to Jupiter too, according to Kane, which has a mass two and a half times that of all the other planets combined in the solar system, limited the habitability of our system.

It's estimated that only a handful of stars have several planets in their habitable zones. Kane wants to look for additional stars which are absolutely surrounded by smaller planets. These stars will be the perfect candidates for direct imaging with NASA telescopes, such as the one at the Habitable Exoplanet Observatory at the Jet Propulsion Laboratory.

Kane's analysis found one such star, Beta CVn, at 27 light years away, which is fairly close by. Since it does not have a planet like Jupiter, it will be included as one of the stars tested for multiple habitable zone planets.

Future studies will also include the development of new models to study atmospheric chemistry in other star systems for habitable zones. Initiatives like these deliver more than just new paths in our quest for finding intelligent life. We also give researchers insight into factors that might one day transform life on our own planet.