Because the plate is flat, it can be made of plastic and folded up for launch. Using a zone plate instead of a mirror gets around this. The formation would have to fly with a precision of a few billionths of a metre. An array is needed because a single mirror big enough to do the job of separating star from planet would be too large to launch. But existing plans to photograph extrasolar planets in this way involve orbiting arrays of reflecting telescopes all pointing in exactly the same direction. Space telescopes are nothing new, of course, and several more are in the works (see article).
#Alien on tiny planet free
Free of the confounding effects of the Earth's own atmosphere, it will be able to isolate images of alien planets, make spectra of the light from their air, and examine those spectra for the characteristic dark lines that are caused by part of the light being absorbed by particular gases-oxygen among them. But Dr Koechlin does not worry about that, because his Fresnel telescope will be in space. And this is where Fresnel comes in.įresnel telescopes have not been developed in the past because the image formed by one that was large enough to rival a useful-sized reflecting telescope would be several kilometres from the zone plate. Stars are so much brighter than the planets which orbit them that their light overwhelms the small amount reflected from a planet's surface. Looking at such an atmosphere, though, is tricky.
That would almost certainly mean something akin to photosynthesis was going on, for no known non-biological process can produce oxygen from common materials in sufficient quantity. Seeing oxygen in another planet's atmosphere would be a giveaway of biological activity because the gas is so reactive that it needs to be continuously renewed.
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