Pluto is the only major solar system object that has not been explored
with spacecraft. Triton was photographed from Voyager yielding a puzzling
surface of nitrogen, methane and carbon dioxide ices and strange atmospheric
plumes [ Stone and Miner, 1989]. By chance, Pluto, in its very eccentric
orbit, happens to be at Triton's distance of about 30 AU (heading outward) and
is apparently a very similar object. The Pluto atmosphere will freeze out in a
few decade and our opportunity to study its composition will be lost for over a
century. Solid nitrogen and methane had been detected on Triton by Dale
Cruikshank and his coworkers before the Voyager encounter and they have
recently detected solid CO and CO
on Triton's surface [ Cruikshank, et
al, 1993]. Owen, et al. [1993] have detected the ices of nitrogen and
methane on the surface of Pluto which leads them to conclude that the major
gases in the (current) atmosphere are the vapor phases of these molecules,
with nitrogen being a factor of about 50 more abundant. It is not clear that
CO ice was detected on Pluto, but it is certainly not as abundant as on Triton.
It follows that CO must be abundant in Triton's atmosphere and is probably
present in Pluto's. Carbon Monoxide and methane provide excellent tracer
gases for the remote study of these atmospheres in the submillimeter microwave
spectrum, but the next generation of instruments will be required to exploit
this circumstance. The study of Pluto and Triton are vital in bridging the gap
between the solar system, the comet forming region, and the nearby galactic
molecular clouds.