Monday, September 23, 2013

Detecting signs of life on far-away planets

Astrobiology has an interesting discussion of how the newest generation of telescopes could be used to detect signs of life even on extremely remote and distant planets. Earth-- the only known example of a planet supporting life-- has been extensively remodeled by its biosphere. The changes to Earth, especially to its atmosphere , (for example its high levels of atmospheric oxygen) might be detectable even at galactic distances by a sensitive enough telescope.

Recent exoplanets with earth-like sizes and properties.
Credit: Astobiology
The astrobiology article discusses the hypothetical detection of  ozone in the atmosphere of a planet orbiting a red dwarf star. Ozone is created when ultraviolet rays hit oxygen-- so the ozone signal, which could conceivably be seen by telescopes, would be both a function of oxygen on the planet and the ultraviolet production of its star.

A second discussion from last year focused on how to look for photosynthesis on a far-away planet. On our planet, photosynthetic organisms can harvest the sun's light from near-infrared wavelengths to about  400 nm (violet). In planets harboring large amounts of photosynthetic organisms, the starlight reflected from the planet's surface would be reduced in the wavelengths used. Other labs have actually modelled this effect on Earthshine. Teresstrial green plants are dominant enough that the spectrum of reflected sunshine shows a big bump in wavelengths that these plants don't use. Thus reflectance increases greatly between 670 nm and 800 nm

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