• An Earth-sized ‘Tatooine’ like planet could be quite hospitable if located at the right distance from its two stars, according to a new study.
• With two suns in its sky, Luke Skywalker’s home planet Tatooine in “Star Wars” looks like a parched, sandy desert world.
• “In real life, thanks to observatories such as NASA’s Kepler space telescope, we know that two-star systems can indeed support planets, although planets discovered so far around double-star systems are large and gaseous,” researchers said.
• Scientists wondered if an Earth-size planet orbiting two suns could support life.
• They found that such a planet could be quite hospitable if located at the right distance from its two stars, and would not necessarily even have deserts.
• In a particular range of distances from two sun-like host stars, a planet covered in water would remain habitable and retain its water for a long time, researchers said.
• “This means that double-star systems of the type studied here are excellent candidates to host habitable planets, despite the large variations in the amount of starlight hypothetical planets in such a system would receive,”
• In reality, the stellar pair Kepler 35A and B host a planet called Kepler 35b, a giant planet about eight times the size of Earth, with an orbit of 131.5 Earth days.
• For their study, researchers neglected the gravitational influence of this planet and added a hypothetical water- covered, Earth-size planet around the Kepler 35 AB stars.
• They examined how this planet’s climate would behave as it orbited the host stars with periods between 341 and 380 days.
• In exoplanet research, scientists speak of a region called the “habitable zone,” the range of distances around a star where a terrestrial planet is most likely to have liquid water on its surface.
• In this case, because two stars are orbiting each other, the habitable zone depends on the distance from the centre of mass that both stars are orbiting.
• To make things even more complicated, a planet around two stars would not travel in a circle; instead, its orbit would wobble through the gravitational interaction with the two stars.
• Researchers found that on the far edge of the habitable zone in the Kepler 35 double-star system, the hypothetical water-covered planet would have a lot of variation in its surface temperatures.
• Since such a cold planet would have only a small amount of water vapour in its atmosphere, global average surface temperatures would swing up and down by as much as 2 degrees Celsius in the course of a year.
• “This is analogous to how, on Earth, in arid climates like deserts, we experience huge temperature variations from day to night,”

Source: The Hindu