By all counts, Earth is on a one way trip to oblivion. Our    aging Sun will see to that. Within 500 to 900 million years    from now, photosynthesis and plant life on Earth will reach a    death-spiral tipping point as the Sun continues its normal    expansion and increases in luminosity over time.  
    Trouble is, researchers are still unsure about all the grisly    endgame details, and their models of such slow motion horrors    are hard to test. But a team of researchers now say that    finding and observing nearby aging Earth-analogues, undergoing    the ravages of their own expanding sun-like stars, will help    Earth scientists understand how the stellar evolution of our    own sun will affect life here on Earth.    [Within] 500 million light years figure most plants become    extinct, although some could potentially last up to 900 million    years from now by employing more carbon-efficient    photosynthetic pathways, Jack OMalley-James, an    astrobiologist at the University of St. Andrews in the U.K.    told Forbes. At this point  
      Night sky over Death Valley. Photo Credit: Wikipedia    
    In a paper to appear in the journal Astrobiology,    OMalley-James, the lead author and colleagues, notes that as    the Suns luminosity pushes the inner edge of our solar    systems current habitable zone at 0.99 AU (or one Earth-Sun    distance) just too far out.  
    Even so, finding a planet that is a near analogue to the    far-future Earth (an old-Earth-analogue) could provide a means    to test these predictions; including declines in species    diversity, extent of habitat and ocean loss, and changes in    such planets geochemical cycles.  
    If we did find such a planet, detailed long-term studies could    give us an insight into its long-term carbon cycle, possible    showing us whether carbon dioxide (CO2) levels really will    plummet over the next billion years in the way we expect, said    OMalley-James.  
    As he explains, in Earths own far-future, plant life will be    extinct and the biosphere as we know it will have collapsed    into an unfamiliar form. Thus, even if astronomers spots such a    dying Earth, around an older sun-like star, could they    recognize any remaining signs of life there?  
    When it comes to positively identifying life on a distant    planet, it is still very early days, said OMalley-James. It    would be very difficult to pin down any remotely observable    signature that we could be 100 percent certain is caused by    life on a distant planet. However, this doesnt make work such    as this futile.  
    The hope is that if astronomers can determine the stars age    with high enough accuracy, coupled with the fact that the    planet has been in a circumstellar habitable zone for billions    of years, but is now encroaching upon the very inner-edge of    the habitable zone, then OMalley-James says future    observations of such planets could make the case that they had    observed the dying gasp of the planets biosphere.  
    The team ran simulations that placed hypothetical Earths around    six aging G spectral type stars all within some 30 light years    from Earth. OMalley-James notes that in each case, his team    used hypothetical examples of an aging Earth-like planet, all    in the inner-hot edge of their respective habitable zones.  
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Lessons From Dying Extrasolar Earths