The ISO spectra of Uranus and Neptune between 2.5 and 4.2 mu m: constraints on albedos and H-3(+) (vol 358, pg L83, 2000)

Spectra of Uranus and Neptune were recorded in May 1997, between 2.5 and 4. 2 mum, using the ISOPHOT-S instrument. The two planets were detected at 2.7 5 mum, with geometric albedos of 0.0015 and 0.0052 for Uranus and Neptune r espectively. In the case of Uranus, the shape of the CH4 absorption is cons istent with a reflection over the 3 bar-level cloud level, presumably due t o H2S: in the case of Neptune, the reflection seems to take place above the CH4 cloud at about 0.3 bar. Two ISO-SWS spectra of Uranus, recorded around 3.3 mum in April and May 1998, show the presence of four H-3(+) emission l ines. From the May 1998 data, the inferred H-3(+) column density is 0.1 - 4 0 x 10(12) cm(-2), and the rotational temperature is 600 +/- 200 K. The obs erved H-3(+) emission is significantly stronger than previous ground-based determinations, obtained in 1992 and 1995.