More planets could harbour life
New computer models
suggest there could be many more habitable planets out there than previously
thought.
Scientists have
developed models to help them identify planets in far-away solar systems that
are capable of supporting life.
Estimates of habitable
planet numbers have been based on the likelihood of them having surface water.
But a new model allows
scientists to identify planets with underground water kept liquid by planetary
heat.
The research was
presented at the British Science Festival in Aberdeen.
Water is fundamental
for life as we know it.
Planets too close to
their sun lose surface water to the atmosphere through evaporation.
Surface water on
planets located in the more frigid distant reaches from their sun is locked
away as ice.
The dogma was, for
water to exist in its life-giving liquid form, a planet had to be the right
distance from its sun - in the habitable zone.
As Sean McMahon, the
PhD student from Aberdeen University who is carrying out the work explained:
"It's the idea of a range of distances from a star within which the
surface of an Earth-like planet is not too hot or too cold for water to be
liquid.
"So traditionally
people have said that if a planet is in this Goldilocks zone - not too hot and
not too cold - then it can have liquid water on its surface and be a habitable
planet"
But researchers are
starting to think that the Goldilocks theory is far too simple.
Planetary
heat
• A planet is warmed
by two sources of heat - solar energy and internal heat
• The further away a
planet is from its sun the less energy it receives and surface water freezes
• As the distance
increases underground water also starts to freeze
• But if the planet is large enough and
produces enough internal heat, it could still contain deep reservoirs of liquid
water capable of supporting life, no matter how far away from the sun
Planets can receive
two sources of heat - heat direct from the star and heat generated deep inside
the planet.
As you descend through
the crust of the Earth, the temperature gets higher and higher. Even when the
surface is frozen, water can exist below ground.
Immense quantities of
water in fact - teeming with primitive life.
As Prof John Parnell,
also from Aberdeen University said: "There is a significant habitat for
microorganisms below the surface of the Earth, extending down several
kilometres.
"And some workers
believe that the bulk of life on Earth could even reside in this deep biosphere."
So the Aberdeen team
are developing models to predict which far-flung planets might harbour
underground reservoirs of liquid water with the possibility of alien life.
Explaining their
rationale, Mr McMahon said: "If you take into account the possibility of
deep biospheres, then you have a problem reconciling that with the idea of a
narrow habitable zone defined only by conditions at the surface."
As you move away from
the star the amount of heat a planet receives from the star decreases and the surface
water freezes - but any water held deep inside will stay liquid if the internal
heat is high enough - and that water could support life.
Even a planet so far
from the star that it receives almost no solar heat could still maintain
underground liquid water.
According to Mr
McMahon, "There will be several times more [habitable] planets".
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