Imaging Giant Extra-Solar Planets from the Ground

The ultimate solution is to get above the atmosphere by putting a large telescope in space. Unfortunately, the existing Hubble Telescope is too small, and its mirrors emit heat. The diffraction-limited resolution provided by its 2.4 m aperture is not high enough to separate star and planet in the infrared, even were it equipped with detectors in the 5 to 10 micron range, and in the visible, it simply does not collect enough light. NASA’s Next Generation Space Telescope (NGST), on the other hand, with a diameter of 8 m, is specifically targeted for observations at the right wavelengths. NGST will be able to see giant planets orbiting at large separations around other stars, but it will not be operational for about a decade. Now in the planning stages is another NASA mission called Terrestrial Planet Finder, or TPF, which will extend the search to smaller Earth-like planets, and will look for key features in the spectra of any that it finds. In the case of our Earth, the infrared spectrum shows strong features of water, indicating the presence of oceans, and ozone. As far as we know, life is the only process that can maintain such a high abundance of ozone in the atmosphere. If we found another Earth-like planet with a similar spectrum, we would strongly suspect that it also supported life.

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