IR spectroscopy of Triton, Pluto, its satellite Charon, and an important planet-crossing body (5145 Pholus) opens a window on the compositions of these primitive members of the population of left-overs from the epoch of planet formation. Current results of the spectroscopy (0.4-2.5 um) of these bodies and other planetary satellites are summarized:

Pluto (Pale Pink Dot) Surface: Near-IR spectroscopy shows that Pluto has a mostly icy surface dominated by N₂, with CH₄, CO, and H₂O detected. There are a few other weak spectral features that have not been identified. Dark regions are probably covered with organic solid material, as yet unidentified, and with no clear spectral features. Atmosphere: N₂-dominated, probably in vapor-pressure equilibrium at T=40 K (~57 µbar) CH4 probably detected, CO being sought. Atmospheric pressure probably changes with heliocentric distance; presently near maximum.

Pluto's satellite Charon (Pale White Dot) Surface: H₂O ice appears to dominate the surface, but other ices and refractory solids may exist. Atmosphere: None detected, but N₂, CO, CH₄ possible.

Triton (Pale White Dot) Surface: This satellite of Neptune is spectrally similar to Pluto, with an icy surface dominated by N₂, CH₄, CO, CO₂, and H₂O. Isotopes of C (and possibly O) are detected. Atmosphere: N₂ atmosphere detected by Voyager; vapor-pressure regulated, Ps = 16 microbar. No CH₄ or CO yet detected, but currently being sought. Photochemical haze observed by Voyager, plus plumes of particles (and gas?) rising from surface. Sublimation wind flowing from S. pole northward detected.

5145 Pholus (Pale Red Dot) Surface: Pholus has a very red reflectance in the photovisual region, H₂O ice bands ad 1.6 and 2.0 um, plus a strong absorption band at 2.27 um attributed to combinations in C-H bands in organic solids, probably light hydrocarbons ( < 400 amu; e.g., methanol, hexamethylenetetramine). Atmosphere: None detected. Cometary activity possible in the future.

Jupiter's Satellite Io: (Bright Orange Dot) Atmosphere: Transient tenuous atmosphere of SO₂, which in part freezes on surface, and part of which is swept away by the plasma flow. Ps a few microbars at most.

Jupiter's Satellite Ganymede: Surface: Mixture of H₂O ice and rocky material. O₂ detected in ice, induced by charged particle bombardment. Atmosphere: None detected

Jupiter's Satellite Europa: Surface: Dominated by nearly pure H₂O ice. Hubble Space Telescope UV spectra show a feature tentatively attributed to solid O₃ generated in the ice.

Saturn's Satellite Titan: (Pale Orange Dot) Atmosphere: N₂ + CH₄, with Ps 1.5 bar. Rich hydrocarbon inventory in stratosphere. Nearly opaque organic haze with color/optical properties matching organic solids (tholins) produced by plasma discharge in lab mixture of N₂:CH₄ = 9:1.