Giant planets like Jupiter and Saturn may make Earth-like worlds in their star systems more hospitable to life. A study comparing more than 140,000 simulated planetary systems, each with two gas giants, found that while many of them wouldn鈥檛 allow any habitable Earth-like worlds, some resulted in 鈥渦ltra-habitable鈥� systems.
Planets are said to be habitable when they orbit their stars in a particular zone 鈥� close enough to allow liquid water on their surfaces but far enough away that it doesn鈥檛 all evaporate immediately. There are many factors that affect the habitability of a system, including the presence of giant planets, which can keep asteroids away and direct the orbits of other planets in the system. But we didn鈥檛 know how such giants might affect the orbit of an Earth-like planet in a habitable zone.
and at the University of Chicago simulated 147,456 planetary systems, each consisting of a sun-like star and two giant planets, to evaluate which of these systems would allow a habitable Earth-sized world. In their simulations, the gas giants ranged from 0.1 to 10 times the mass of Jupiter, and had orbits of different shapes and sizes. They measured whether an Earth analogue would survive in the habitable zones of these systems or whether it would be destroyed by crashing into the system鈥檚 star, colliding with either of the gas giants, or even being flung out of the system altogether.
Advertisement
They let the simulations run for 5 billion orbits of the innermost giant planet and calculated the relative habitability of each system. A score of 0 indicated that there is practically no possibility a habitable Earth-like planet could exist there for any significant length of time. A score of 1 meant that the system would be as good for an Earth analogue as one with no other planets to disturb its orbit. A score above 1 suggested that the giant planets would increase the habitable zone or stabilise the orbit of the Earth-like planet.
About 60 per cent of their simulated systems had a relative habitability of 0. There were eight systems in their data with giant planets similar to Jupiter and Saturn, with habitability scores ranging from 0 to 0.93.
Most of the rest had scores between 0 and 1, but 253 of the systems had relative habitability scores above 1 鈥� meaning the giant planets actually enhanced the habitability of the system, resulting in what the researchers dubbed ultra-habitable systems. 鈥淭he absolute most habitable system was one with relatively low-mass giant planets, a tenth of a Jupiter mass or so, located relatively far out in the system with nearly circular orbits,鈥� says Bailey.
This may mean that exoplanet systems with pairs of relatively small gas giants orbiting at a great distance are the best ones in which to look for habitable worlds. However, it is definitely not a guarantee.
鈥淚t鈥檚 incredibly complex the number of factors that come into play,鈥� says Bailey. 鈥淚n this work, we completely ignored the process of planet formation, and giant planets could be necessary for the formation of a terrestrial planet.鈥� We don鈥檛 understand all the effects giant planets can have on smaller ones, even in our own relatively well-studied solar system, but this work is a step towards being able to evaluate that, she says.
Reference: arXiv,
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
