New study explores how life on one exoplanet could spread to its neighbor
- By David Rothery, The Conversation on December 7, 2015
- Imagine two nearby exoplanets orbiting the same sun, each with its own indigenous civilisation. They’re going through history either as companionable neighbours or deadly rivals. This is a familiar situation in science fiction, but could it ever happen?
With the rapidly growing number of habitable exoplanets being discovered, this scenario may seem plausible. Now a new scientific study, to be published in the Astrophysical Journal, explores this issue by examining some of the conditions affecting life in a solar system with two habitable planets.
The researchers were inspired by NASA’s discovery of Kepler 36b and Kepler 36c, the two known planets of the star Kepler 36. The orbital distances of these planets from their star differ by only 10%, making them extremely close neighbours.
The inner planet completes seven orbits in the time that it takes the outer planet to complete six orbits (a situation described as 7:6 mean motion resonance). This means that once in every six or seven of your years (depending on which planet you live on), your neighbouring planet passes close by.
Wild wobbles?
The researchers first of all wondered if these periodic close passages would affect the tilt of either planet’s axis. This is important in the context of life because large fluctuations in axial tilt would lead to drastic variations in climate. While not fatal for microbial life, it could reduce the chances of complex life emerging and make it very hard for any intelligent life that did evolve to establish a long-lasting civilisation.
In the case of Kepler 36b or Kepler 36c, it is highly unlikely that life could exist, because they are too close to their star and have surface temperatures approaching 1000C. The researchers therefore analysed a hypothetical pair of Earth-like planets in 3:2 resonance, both within their star’s habitable zone where liquid water would be stable on their surfaces.
Reassuringly for the prospects of complex life, they found that neither planet’s axial tilt was driven to vary wildly as a result of their closeness.
