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