SURFACE ICES AND THE ATMOSPHERIC COMPOSITION OF PLUTO

Observations of the 1.4- to 2.4-micrometer spectrum of Pluto reveal ab sorptions of carbon monoxide and nitrogen ices and confirm the presenc e of solid methane. Frozen nitrogen is more abundant than the other tw o ices by a factor of about 50; gaseous nitrogen must therefore be the major atmospheric constituent. The absence of carbon dioxide absorpti ons is one of several differences between the spectra of Pluto and Tri ton in this region. Both worlds carry information about the compositio n of the solar nebula and the processes by which icy planetesimals for med.