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Planet Earth will be hab­it­able for at least another 1.75 bil­lion years, say scientists

pub­lished 26 Sep­tem­ber 2013 | mod­i­fied 26 July 2014

Hab­it­able con­di­tions on Earth will be pos­si­ble for at least another 1.75 bil­lion years — accord­ing to astro­bi­ol­o­gists at the Uni­ver­sity of East Anglia (UEA).

Find­ings pub­lished on 19 Sep­tem­ber in the jour­nal Astro­bi­ol­ogyreveal the hab­it­able life­time of planet Earth — based on our dis­tance from the sun and tem­per­a­tures at which it is pos­si­ble for the planet to have liq­uid water.

Planet earth NASAThe research team, led by Andrew Rushby from UEA’s school of Envi­ron­men­tal Sci­ences, looked to the stars for inspi­ra­tion. Using recently dis­cov­ered plan­ets out­side our solar sys­tem (exo­plan­ets) as exam­ples, they inves­ti­gated the poten­tial for these plan­ets to host life. Rushby said: “We used the ‘hab­it­able zone’ con­cept to make these esti­mates — this is the dis­tance from a planet’s star at which tem­per­a­tures are con­ducive to hav­ing liq­uid water on the surface.”

“We used stel­lar evo­lu­tion mod­els to esti­mate the end of a planet’s hab­it­able life­time by deter­min­ing when it will no longer be in the hab­it­able zone. We esti­mate that Earth will cease to be hab­it­able some­where between 1.75 and 3.25 bil­lion years from now. After this point, Earth will be in the ‘hot zone’ of the sun, with tem­per­a­tures so high that the seas would evap­o­rate. We would see a cat­a­strophic and ter­mi­nal extinc­tion event for all life.”

Of course con­di­tions for humans and other com­plex life will become impos­si­ble much sooner — and this is being accel­er­ated by anthro­pogenic cli­mate change. Humans would be in trou­ble with even a small increase in tem­per­a­ture, and near the end only microbes in niche envi­ron­ments would be able to endure the heat.

“Look­ing back a sim­i­lar amount of time, we know that there was cel­lu­lar life on earth. We had insects 400 mil­lion years ago, dinosaurs 300 mil­lion years ago and flow­er­ing plants 130 mil­lion years ago. Anatom­i­cally mod­ern humans have only been around for the last 200,000 years — so you can see it takes a really long time for intel­li­gent life to develop.”

“The amount of hab­it­able time on a planet is very impor­tant because it tells us about the poten­tial for the evo­lu­tion of com­plex life — which is likely to require a longer period of hab­it­able conditions.”

“Look­ing at hab­it­abil­ity met­rics is use­ful because it allows us to inves­ti­gate the poten­tial for other plan­ets to host life, and under­stand the stage that life may be at else­where in the galaxy.”

“Of course, much of evo­lu­tion is down to luck, so this isn’t con­crete, but we know that com­plex, intel­li­gent species like humans could not emerge after only a few mil­lion years because it took us 75 per cent of the entire hab­it­able life­time of this planet to evolve. We think it will prob­a­bly be a sim­i­lar story elsewhere.”

Almost 1,000 plan­ets out­side our solar sys­tem have been iden­ti­fied by astronomers. The research team looked at some of these as exam­ples, and stud­ied the evolv­ing nature of plan­e­tary hab­it­abil­ity over astro­nom­i­cal and geo­log­i­cal time.

“Inter­est­ingly, not many other pre­dic­tions based on the hab­it­able zone alone were avail­able, which is why we decided to work on a method for this. Other sci­en­tists have used com­plex mod­els to make esti­mates for the Earth alone, but these are not suit­able for apply­ing to other plan­ets. We com­pared Earth to eight plan­ets which are cur­rently in their hab­it­able phase, includ­ing Mars. We found that plan­ets orbit­ing smaller mass stars tend to have longer hab­it­able zone lifetimes.”

“One of the plan­ets that we applied our model to is Kepler 22b, which has a hab­it­able life­time of 4.3 to 6.1 bil­lion years. Even more sur­pris­ing is Gliese 581d which has a mas­sive hab­it­able life­time of between 42.4 to 54.7 bil­lion years. This planet may be warm and pleas­ant for 10 times the entire time that our solar sys­tem has existed!”

“To date, no true Earth ana­logue planet has been detected. But it is pos­si­ble that there will be a hab­it­able, Earth-​like planet within 10 light-​years, which is very close in astro­nom­i­cal terms. How­ever reach­ing it would take hun­dreds of thou­sands of years with our cur­rent technology.”

“If we ever needed to move to another planet, Mars is prob­a­bly our best bet. It’s very close and will remain in the hab­it­able zone until the end of the Sun’s life­time — six bil­lion years from now.”

(Source: UEA press release, 19.09.2013)

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