Signal strength of Europa in the two-dimensional spectral images. (a) Europa’s signal strength extends in the wavelength direction. The flux distribution was extracted to produce two-dimensional spectra with a width of 40 pixels (see the narrow yellow rectangle). (b) Close-up of the two-dimensional spectra of Europa, corresponding to the range of the small blue rectangle in panel (a). Two-dimensional, 1.6-pixel-wide spectra were extracted in the direction of the slit length. Yellow dashed lines enclose sections with a width of 1.6 pixels each, corresponding to the spatial resolution of the Subaru AO system (∼0.″087).