The extreme ultraviolet (EUV) is an important spectral band for
planetary science as it includes many interesting emissions from
plasmas and atmospheres. However, it is not easy to observe there
because to begin with the observing site must be outside of the
Earth's atmosphere in order to avoid absorption. And because the
emissions from many of the targets are very faint, the effective
area of the detector should be as large as possible and long
observation times are required