With troubled planetary orbits and various stellar radiation conditions, searching for habitable zones around binary stars may not seem the best place to look for habitable exoplanets, but a new study by researchers exploring this possibility has found five double stellar systems that may be suitable for life. .
Over the past three decades exoplanetary explorers have discovered more than four thousand planets outside our Solar System and most of them have been found around single stars.
Binary or multiple star systems, however, are very common throughout the galaxy and some giant planets have been found to live in double star systems, some of which even orbit both stars, a term called circumpolar. But when it comes to finding possible habitable planets, things are not that easy.
Why? Not only does a planet have to fight against radiation from two stars, perhaps of a different spectral type, the distance from the planet to each star continues to change over time due to gravitational interactions between the planet and the two stars.
Owetu a large planet like Jupiter into the mix, and the dynamics of the system can become very unstable.
It also means that fixing the habitable zone of an exoplanet, the region where a terrestrial planet orbiting its host star can hold liquid water on its surface, is very difficult.
It would seem almost futile then to look for planets suitable for life in these systems. Not so, says an international team of researchers who have developed a new mathematical framework to explain all the dynamic variables that must surround circular planets.
In their research, the team builds on previous research to predict the existence, location, and extent of the habitable zone in binary systems with giant planets.
The calculations take into account aspects such as the class, mass, luminosity and spectral energy distribution of the stars; the added gravitational impact of the giant planet; the eccentricity (i.e. degree of ellipse of the orbit), semi-principal axis and period of the hypothetical terrestrial orbit.
The team also looked at the “climate inertia” of a hypothetical exoplanet. “Climate inertia” is the rate at which the atmosphere reacts to changes in radiation; the faster the average surface temperature changes, the lower the planet’s climatic inertia, the authors say in their research paper.
With all the data in hand, the team then analyzed the habitable zone around nine known double star systems with giant planets to determine if they were “quiet enough” to contain potentially viable worlds.
“Life most likely evolves on planets located within the Residential Zone of their system, as well as Earth. Here we investigate whether a habitable Zone exists within nine known systems with two or more stars orbiting giant planets,” says principal author of the study Dr. Nikolaos Georgakarakos, research associate of the Division of Science at New York University Abu Dhabi.
Of the nine double-star studies, all discovered with the Kepler telescope, five were found to be suitable for the bill.
“We are showing for the first time that Kepler-34, -35, -64, -413 and especially Kepler-38 are suitable for hosting terrestrial worlds with oceans,” says Georgakarakos, as they are surrounded by suitable habitable zones.
These zones are between 0.4 -1.5 Astronomical Units (or) wide starting at distances between 0.6 – 2 or from the center of mass of the binary stars the team says. For reference or is about 150 million kilometers (93 million miles) and is the distance from the Sun to our planet. Mars is 1.5 or from the Sun and Jupiter is 5.2.
The other four systems in the study did not make the cut. “In contrast, the size of the habitable zones in two additional binary systems, Kepler-453 and -1661, is about half the expected size, as the giant planets in those systems would destabilize the orbits of additional habitable worlds. For the same reason -16 and -1647 cannot host any more habitable planets at all, “says co-author Dr. Siegfried Eggl at the University of Washington.
The systems are very distant, between 2764 and 5933 light-years from Earth, in the constellations Lira and Swan, say Georgakarakos and colleagues, but the study does show that previously suspended systems in the search for life beyond the Solar System, such as multi-star systems , should no longer be discounted.
“Our best candidate to host a potentially habitable world is the binary system Kepler-38, about 3970 light-years from Earth, and known to contain a planet according to Neptune,” says Georgakarakos. “Our study confirms that even double star systems with giant planets are hot targets in the search for Earth 2.0.”, He adds.