When
it comes to exploring exoplanets, it may be wise to take a snorkel along. A
study, published in a paper in the journal Monthly Notices of the Royal
Astronomical Society, has used a statistical model to predict that most habitable
planets may be dominated by oceans spanning over 90% of their surface area.
The author of the study, Dr. Fergus Simpson of the Institute of Cosmos Sciences
at the University of Barcelona, has constructed a statistical model – based on
Bayesian probability – to predict the division between land and water on
habitable exoplanets.
For a planetary surface to boast extensive areas of both land and water, a
delicate balance must be struck between the volume of water it retains over
time, and how much space it has to store it in its oceanic basins. Both of
these quantities may vary substantially across the full spectrum of
water-bearing worlds, and why the Earth’s values are so well balanced is an
unresolved and long-standing conundrum.
Simpson’s model predicts that most habitable planets are dominated by oceans
spanning over 90% of their surface area. This conclusion is reached because the
Earth itself is very close to being a so-called ‘waterworld’ – a world where
all land is immersed under a single ocean.
“A
scenario in which the Earth holds less water than most other habitable planets
would be consistent with results from simulations, and could help explain why
some planets have been found to be a bit less dense than we expected,” explains
Simpson.
In
the new work, Simpson finds that the Earth’s finely balanced oceans may be a
consequence of the anthropic principle – more often used in a cosmological
context – which accounts for how our observations of the Universe are
influenced by the requirement for the formation of sentient life.
“Based on the Earth’s ocean coverage of 71%, we find substantial evidence
supporting the hypothesis that anthropic selection effects are at work,”
comments Simpson.
To test the statistical model Simpson has taken feedback mechanisms into
account, such as the deep water cycle, and erosion and deposition processes. He
also proposes a statistical approximation to determine the diminishing
habitable land area for planets with smaller oceans, as they become
increasingly dominated by deserts.
Why did we evolve on this planet and not on one of the billions of other
habitable worlds? In this study Simpson suggests the answer could be linked to
a selection effect involving the balance between land and water.
“Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life,” Simpson concludes.
