Earth is destined to leave the Sun’s habitable zone

Nature : Each star is surrounded by a notional shell, the habitable zone, in which the star’s light is neither so strong that water on the surface of a planet would boil away nor so weak that the water would remain frozen. Without liquid water, life as we know it cannot evolve. Earth, the only planet known to harbor life, lies in the Sun’s habitable zone. In a new paper published in Astrobiology, Andrew Rushby of the University of East Anglia in the UK and his colleagues have calculated what will happen to the Sun’s habitable zone as the star ages. Because the Sun’s luminosity is set to increase, its habitable zone will expand outward. In about 1.75 billion years, according to Rushby and his colleagues, the inner surface of the Sun’s habitable zone will have moved beyond Earth. The paper’s authors also calculated Earth’s spell in the habitable zone will eventually last 6.3 billion to 7.8 billion years. Given that life began around 4 billion years ago, its span on Earth is more than half expired.