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Two Concepts for the Terrestrial Planet Finder

Posted by timothy on from the hey-there's-on-terra dept.

EccentricAnomaly writes: "This NASA press release and this space.com story discuss two concepts for the terrestrial planet finder, a mission that will look for Earth sized planets around other stars. One concept is an infrared interferometer the will nullify starlight while amplifying the infrared light from any planets. The other concept is a visible light coronagraph - basically a larger version of Hubble that will block out the light from stars so that it can see any pale blue dots."

3 of 24 comments (clear)

  1. Infra-red? by AndrewRUK · · Score: 2, Interesting

    I might be being stoopid here (but hey, the only other psts here are a troll and two ACs posting the article) so bear with me...

    Do stars not give out any infra-red? Because, if they do, surely that would swamp any I-R detector, and the planet wouldn't be seen.

    Of course, IANAA (...astronomer) so if anyone wants to explain why I'm wrong, I'd like to know.

    1. Re:Infra-red? by RevRigel · · Score: 3, Interesting

      Actually, since stars are nearly ideal black body radiators (with the exception of some absorption lines), they have a peak frequency at which they emit radiation. For stars like the sun, this is in the ultraviolet region. It never gets as high as X-rays or gamma rays; not even in small amounts. It takes much hotter gas to emit X-rays (the sun is around 6000 K, I believe X-rays start showing up around 30000 K or 60000 K).
      The sun does emit radiation throughout the spectrum below its peak wavelength, but as the frequency approaches zero so does the energy emitted -- so you would see a fair amount of infrared, but very little ULF radio.

  2. Re:New game plan. by RevRigel · · Score: 3, Interesting

    What you're proposing is an interferometer. Radio telescopes like the Very Large Array are interferometers as well. You are correct that interferometers increase resolution to the resolution of a large telescope of the same baseline (but with the light/radio gathering power of the actual diameter of telescopes used, of course).
    In order to make an interferometer work, you have to combine the signals completely in phase (to within 1/10 wavelength, as a general rule). So if you were doing work in the 20cm band, your cable lengths from each antenna would need to be the same to within 2cm. Optionally, signals from radio telescopes can be recorded (such as those on opposite sides of the globe, for really long baseline), and lined up later, on computers. This only works because we have data acquisition systems that can work at MHz and GHz frequencies. Optical frequencies are more like 10^15 Hz.
    In order to do optical interferometry, you have to combine the light paths to within a tenth wavelength (40-50nm, or several hundred atoms). This interferometry can only be done in real time, with hard optics. At least until we get attohertz electronics and data acquisition working.

    The space interferometry mission will put an interferometer in space in the next 10 years or so, but its baseline is only 30 feet or so. Still very cool.