The Sun continues to get brighter at a rate of ~ 1 percent every hundred million years The Sun continues to get brighter at a rate of ~ 1 percent every hundred million years This should increase surface temperatures, which in turn should cause faster silicate weathering and a corresponding decrease in atmospheric CO2
1.2 b.y.: The rapid rise in surface temperature causes the stratosphere to become wet Earth’s oceans should be lost over the next few hundred million years, and all life will go extinct 1.2 b.y.: The rapid rise in surface temperature causes the stratosphere to become wet Earth’s oceans should be lost over the next few hundred million years, and all life will go extinct Is there any way to counteract these effects? Yes, one could do this by building a solar shield!
This probably isn’t a good solution to the problem of global warming, as it doesn’t solve the related problem of ocean acidification This probably isn’t a good solution to the problem of global warming, as it doesn’t solve the related problem of ocean acidification As CO2 goes down in the more distant future, however, this problem goes away
We are also interested in the possibility of finding habitable planets around other stars We are also interested in the possibility of finding habitable planets around other stars As a first step, we need to figure out where such planets might reside…
Clever biochemists have suggested that non-carbon-based, non-water-dependent life could possibly exist Clever biochemists have suggested that non-carbon-based, non-water-dependent life could possibly exist Nonetheless, the best place to begin the search for life is on planets like the Earth that have liquid water on their surfaces This means that we should look within the conventional habitable zone around nearby stars
Habitable zone (HZ) -- the region around a star in which an Earth-like planet could maintain liquid water on its surface at some instant in time Habitable zone (HZ) -- the region around a star in which an Earth-like planet could maintain liquid water on its surface at some instant in time Continuously habitable zone (CHZ) -- the region in which a planet could remain habitable for some specified period of time (e.g., 4.6 billion years)
Inner edge determined by loss of water via runaway or moist greenhouse effect Inner edge determined by loss of water via runaway or moist greenhouse effect Venus is a case in point…
Outer edge depends on how large a planet’s greenhouse effect might be Outer edge depends on how large a planet’s greenhouse effect might be Mars, at 1.52 AU, is cold and dry today but looks as if it may have been habitable in the distant past…
The ancient, heavily cratered terrain on Mars is cut through by fluvial channels The ancient, heavily cratered terrain on Mars is cut through by fluvial channels So, Mars was probably inside the habitable zone early in its history What might have kept early Mars warm?
The carbonate-silicate cycle feedback loop ensures that the habitable zone is relatively wide The carbonate-silicate cycle feedback loop ensures that the habitable zone is relatively wide We can also calculate HZs and CHZs for other types of stars…
Intriguingly, astronomers are now beginning to find planets around other stars Intriguingly, astronomers are now beginning to find planets around other stars Most of these so far have been detected using the radial velocity (or Doppler) method
708 extrasolar planets identified as of Dec. 09, 2011 708 extrasolar planets identified as of Dec. 09, 2011 Few, if any, of these planets are very interesting, however, from an astrobiological standpoint Howard et al.(2010)
600 l.y. distant 600 l.y. distant 2.4 RE 290-day orbit, late G star Not sure whether this is a rocky planet or a Neptune (RNeptune = 3.9 RE)
The real payoff will come from observing Earth-like planets directly, i.e., separating their light from that of the star, and taking spectra of their atmospheres The real payoff will come from observing Earth-like planets directly, i.e., separating their light from that of the star, and taking spectra of their atmospheres - Earth-sized planets could conceivably be detected by future 30 m-class ground-based telescopes; however, looking for biomarker gases through Earth’s atmosphere is probably impossible
Integrated light of Earth, reflected from dark side of moon; Rayleigh, chlorophyll, O2, O3, H2O Integrated light of Earth, reflected from dark side of moon; Rayleigh, chlorophyll, O2, O3, H2O
We need to preserve our environment, as Earth is the only habitable planet that we know of We need to preserve our environment, as Earth is the only habitable planet that we know of Global warming is a real problem with which we will someday have to deal There may well be other Earth-like planets around other stars. Looking for them, and looking for signs of life on them, is a scientific endeavor that is well worth undertaking
Dostları ilə paylaş: |