Five double-star systems, each with a planet capable of supporting life, have been discovered by a team of scientists using data from NASA‘s Kepler space telescope.
University of Illinois scientists used the Kepler data to create a new methodology that can identify systems with two stars that could host habitable Earth-like planets.
Luke Skywalker’s view of two suns from his aunt and uncle’s moisture farm in the first-released Star Wars film is fictional, but this research suggests that five known systems have double-star planets like Tatooine.
The team used information on the mass of the two stars, how bright they were and the location of planets within the system to determine their habitability.
Habitability is defined in this research as planets, like Skywalker’s home and Earth, that have liquid water somewhere on their surface and one system fits the bill.
Kepler-38, a binary system with one Earth-like and one smaller star is 3,970 light years away and while so far only one Neptune-sized world has been spotted orbiting the larger star, it is predicted there are rocky worlds in the habitable zone.
Five double-star systems, each with a planet capable of supporting life, have been discovered by a team of scientists using data from the Kepler space telescope
Luke Skywalker’s view of two suns from his aunt and uncle’s moisture farm in the first-released Star Wars film is fictional, but this research suggests that five known systems have double-star planets like Tatooine (pictured)
The researchers investigated the effects of double-star and giant planets on habitable zones of nine systems observed by the Kepler mission.
Each of the systems they selected had at least one large planet at least as big as Neptune in the solar system.
They did this as they wanted to demonstrate the presence of a large planet doesn’t preclude the chance for habitable worlds to develop in the goldilocks zone – the area where liquid water can flow on the surface of a planet.
Not so close to the star, it escapes as vapour, but not so far away it completely freezes.
‘Life is far most likely to evolve on planets located within their system’s Habitable Zone, just like Earth,’ says corresponding author Dr Nikolaos Georgakarakos, a research associate from the Division of Science at New York University Abu Dhabi.
Kepler-34, 35, 38, 64, and 413 were promising targets – with Kepler-38 being the best candidate for hosting Earth-like worlds with oceans, they found.
These are all multi-star systems that have configurations that support a permanent ‘habitable zone’ that won’t be ‘pushed out’ by the gravitational pull of the stars.
They all have two stars in one configuration or another, apart from Kepler-64, which despite having four suns, could be home to a habitable rocky world.
Kepler-38 is a binary system in the constellation of Lyra about 3,970 light years away, with one large star 95 per cent the mass of the Sun and a smaller star 25 per cent the Sun’s mass.
So far, a Neptune-sized planet has been found orbiting the larger star but it is thought there are more planets within the habitable zone not yet discovered.
Eggl said the methodology they developed is based on analytical equations rather than computer simulations that have to run day and night for months.
‘There are some parts that use numerical models to feed in information, such as the way that the atmosphere interacts to different amounts and spectra of sunlight.
‘That’s really difficult to figure out analytically so we used pre-computed atmospheric models for that,’ Eggl explained.
This is an artist impression of a planet orbiting the binary system Kepler-38, which researchers say is the best candidate for an Earth-like habitable world
‘The benefit of our approach is that anyone can take our equations and apply them to other systems to determine where to best look for Earth-like worlds.’
The Earth’s orbit around the Sun is nearly circular, ensuring that the planet receives an almost constant amount of radiation on a permanent basis.
But that isn’t true for planets that orbit two suns as the second star would provide an additional source of radiation and gravitational pull.
Even if a planet’s orbit is initially circular around the two stars, it will become elliptic over time due to the push and pull of both parental bodies.
This is an artist impression of a planet orbiting the two stars of Kepler-35, one of the candidates for an Earth-like rocky habitable planet
Because of this, Eggl said dynamical stability is a necessary condition for habitability of a two-sun planet, but it is not the only one.
‘If a planet comes too close to its suns its oceans could boil away. If the planet is too far out, or even ejected from a system, water on its surface will ultimately freeze, as will the atmosphere itself, like CO2 that forms seasonal polar caps on Mars.
‘Once we confirm that a potentially habitable planet is on a stable orbit, we can proceed to investigate how much radiation it receives from the two stars over time.
‘By modeling the evolution of the stars and planetary orbits we can estimate the actual amount or radiation the planet receives.’
This is an artists impression of a planet within a binary star system with two stars of different sizes
The Kepler mission has spotted thousands of exoplanets since 2014, with 30 planets less than twice the size of Earth now known to orbit within the habitable zones of their stars
In Eggl’s doctoral dissertation, he developed an analytic framework to determine habitable zones in double-star systems.
He said subsequent research and this new work ‘completes the picture,’ adding: ‘We know that planets can form in these systems and now we know they can actually retain water on the surface, and it’s pretty awesome.’
‘Our study confirms that even binary star systems with giant planets are hot targets in the search for Earth 2.0. Watch out Tatooine, we are coming,’ said Georgakarakos.
The findings have been published in the journal Frontiers in Astronomy and Space Science.