Scientists have found a new clue in the hunt for planets just like Earth in other solar systems, suggesting that giant planets could be somewhat key to habitability.
A study, published in The Astrophysical Journal, suggests that worlds 10 to 1,000 times as large as our planet could affect the habitability of other planets in their system. They may dictate whether a world becomes an “Earth 2.0” or not.
The team from New York University Abu Dhabi and NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California looked at 147 other solar systems that contained giant planets. In most cases, they found the presence of a giant planet reduced the chances of habitability.
This is because giant planets can gravitationally pull other worlds, reducing their chances of having a stable orbit and climate that could support liquid water and thus life. The closer a planet is to a gas giant, the worse it gets. And they can also change the orbits of asteroids and comets, sending them flying towards other worlds.
However, this wasn’t always the case. The team found that in certain scenarios, gas giants actually increased the habitable zone of an extrasolar system, allowing Earth-like worlds to form. One particularly good example would be, say, our own Solar System, where we happily co-exist with Jupiter and Saturn.
“While in the majority of investigated systems the presence of the gas ‘giants’ shrank the habitable zone, they still left sufficient room for habitable Earth-like planets to be there,” Nikolaos Georgakarakos from NYU Abu Dhabi said in a statement.
“This is an important insight to inform follow-up investigations. It would not make sense to search for Earth 2.0 in a system where a giant planet stirs the orbit of any neighboring terrestrial planet in the habitable zone so much that its climate collapses.”
In particular, they found that systems where gas giants that are in tight orbits around their stars – known as hot Jupiters – or in distant orbits (cold Jupiters) have the best chance of increasing the habitability of planets. Thus, these systems may be some of the best places to look for Earth 2.0. We're yet to find a world exactly like our own.
Hot Jupiters are seen as alluring because their proximity to the star means they have almost circular orbits, which are unlikely to perturb other rocky worlds in the system. If rocky planets form here, then these scorching gas giants could make “excellent neighbors for habitable worlds,” the researchers note in their paper.
While they haven’t identified any specific systems that should be studied, the team hope their research could help us find potentially habitable worlds in the future.