From rogue worlds that roam the cosmos alone to Tatooines that orbit two suns, astronomers are expanding our definition of habitable exoplanets
Life
26 August 2020
IN A dark and seemingly barren universe, our pale blue dot of a world is a beacon of hope that life is possible. The confluence of factors that help sustain life here are astonishing: from the planet’s rocky crust, broken into tectonic plates that help maintain a breathable atmosphere by releasing and trapping gases, to its distance from the sun. Earth orbits at the inner edge of a Goldilocks region called the habitable zone: a narrow ring that is neither too hot nor too cold to allow liquid water to exist. Every living thing we know of, from a bacterium to a blue whale, needs water to survive.
Given this, it is no surprise that our efforts to find life elsewhere have focused on spotting a carbon copy of our world. Frustratingly, these seem to be few and far between. Of the thousands of exoplanets discovered to date, only a handful are thought to have conditions remotely like ours. Most orbit either scorchingly close to their host star or keep a frosty distance. Others move in loops around two stars, circle long-dead suns or wander the cosmos alone, without the benefit of stellar heat at all. Life on such planets would once have been considered impossible – but that view is changing.
Recent research suggests that these weird and wonderful worlds could be capable of sustaining life after all. It is time to tear up the rulebook and go on an incredible interplanetary journey.
HELL OR HEAVEN?
Table of Contents
Planets in searing proximity to their stars
Evidence that planets very different from Earth could nevertheless be balmy havens for life might …