[meteorite-list] Researchers Claim Planets Can Support Life Up To Ten Times Further Away From Stars Than Previously Thought

[Ron Baalke]

http://www.dailymail.co.uk/sciencetech/article-2535900/Forget-Goldilocks-Zone-planets-support-life-TEN-times-away-stars-previously-thought.html

Forget the 'Goldilocks Zone' - planets can support life up to TEN times 
further away from stars than previously thought

By Ellie Zolfagharifard
Mail Online
8 January 2014

Scientists may not have found extra-terrestrial life yet, but they now 
claim there are far more aliens out there than first believed.

Researchers in Scotland believe that Earth-sized planets can support life 
at least ten times further away from stars than previously thought.

This means that cold rocky planets previously considered uninhabitable 
may be teeming with life beneath the surface.

Academics at the University of Aberdeen and University of St Andrews claim 
the definition of the "Goldilocks" zone -  the area of space around a 
star, or sun, which can support life - is flawed.

They argue this definition fails to take into account life that can exist 
beneath a planet's surface.

"As you get deeper below a planet's surface, the temperature increases, 
and once you get down to a temperature where liquid water can exist - 
life can exist there too," said Aberdeen University PhD student Sean McMahon.

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WHAT IS THE GOLDILOCKS ZONE?

The Goldilocks zone is the belt around a star where temperatures are ideal 
for liquid water to pool on a planet's surface.

To determine the location of a star's habitable zone, scientists have 
to first learn how much total radiation it emits. 

Knowing precisely how far away a habitable zone needs to be from a star 
also depends on chemistry. 

For example, molecules in a planet's atmosphere will absorb a certain 
amount of energy from starlight and radiate the rest back out.

How much of this energy is trapped can mean the difference between a turquoise 
sea and erupting volcanoes.

Researchers in Scotland now claim that Earth-sized planets could support 
life at least 10 times further away from stars than first thought.

-----------------------------

In a galaxy of 200 billion stars of various types, scientists estimate 
there are 11 billion potentially habitable planets in the Goldilocks zone 
as it is currently defined.

Factor smaller, dimmer red dwarf stars, and the number of planets with 
mild temperatures similar to Earth rises to 40 billion. 

Researchers in Aberdeen claim the figure is much higher. Mr McMahon told 
MailOnline the number was "probably several times" larger but added that 
the is difficult to quantify. 

Mr McMahon's team created a computer model that estimates the temperature 
below the surface of a planet of a given size, at a given distance from 
its star.

"The deepest known life on Earth is 5.3 km below the surface, but there 
may well be life even 10 km deep in places on Earth that haven't yet been 
drilled," he said.

"Using our computer model we discovered that the habitable zone for an 
Earth-like planet orbiting a sun-like star is about three times bigger 
if we include the top five kilometres below the planet surface."

The model shows that liquid water could survive 5km below the Earth's 
surface even if the Earth was three times further away from the sun.

"If we go deeper, and consider the top 10 km below the Earth's surface, 
then the habitable zone for an Earth-like planet is 14 times wider," said 
Mr McMahon.

The current habitable zone for our solar system extends out as far as 
Mars, but this re-drawn habitable zone would see the zone extend out further 
than Jupiter and Saturn.

The findings also suggest that many of the so-called "rogue" planets drifting 
around in complete darkness could be harbouring life..

"Rocky planets a few times larger than the Earth could support liquid 
water at about 5 km below the surface even in interstellar space, even 
if they have no atmosphere because the larger the planet, the more heat 
they generate internally," said Mr McMahon.

"It has been suggested that the planet Gliese 581 d, which is 20 light 
years away from Earth in the constellation Libra, may be too cold for 
liquid water at the surface.

"However, our model suggests that it is very likely to be able to support 
liquid water less than 2 km below the surface, assuming it is Earth-like."

Another paper published by the same team suggests there could be more 
life below the surface of the continents on Earth than there is below 
the seafloor.

Mr McMahon hopes the studies will encourage other researchers to consider 
how life on other planets might be detected.

"The surfaces of rocky planets and moons that we know of are nothing like 
Earth," he said.

"They're typically cold and barren with no atmosphere or a very thin or 
even corrosive atmosphere.

"Going below the surface protects you from a whole host of unpleasant 
conditions on the surface. So the subsurface habitable zone may turn out 
to be very important.

"Earth might even be unusual in having life on the surface."