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Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80°W and 20°S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot. reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena., Large-scale relatively bright and dark regions are present on Titan's surface. Two bright areas particularly stand out: the continent-sized Xanadu Regio centered at 110°W, 15°S and the sub-Saturnian mid-south-latitude bright [...]

Observations of the 1.4- to 2.4-micrometer spectrum of Pluto reveal absorptions of carbon monoxide and nitrogen ices and confirm the presence of solid methane. Frozen nitrogen is more abundant than the other two ices by a factor of about 50; gaseous introgen must therefore be the major atmospheric constituent. The absence of carbon dioxide absorptions is one of several differences between the spectra of Pluto and Triton in this region. Both worlds carry information about the composition of the solar nebula and the prcesses by which icy planetesimals formed., Although Pluto is usually classified as a planet, its closest relative in the solar system appears to be Triton, Neptune's largest satellite. Both of these objects evidently formed from the [...]

The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton., Voyager 2 revealed Triton as a frozen world with a relatively young and highly structured surface almost devoid of impact craters and with evidence of episodes of local and perhaps [...]

The 1.42- to 2.40-micrometer spectrum of Kuiper belt object 1993SC was measured at the Keck Observatory in October 1996. It shows a strongly red continuum reflectance and several prominent infrared absorption features. The strongest absorptions in 1993SC's spectrum occur near 1.62, 1.79, 1.95, 2.20, and 2.32 micrometers in wavelength. Features near the same wavelengths in the spectra of Pluto and Neptune's satellite Triton are due to [CH.sub.4] on their surfaces, suggesting the presence of a simple hydrocarbon ice such as [CH.sub.4], [C.sub.2][H.sub.6], [C.sub.2][H.sub.4], or [C.sub.2][H.sub.2] on 1993SC. In addition, the red continuum reflectance of 1993SC suggests the presence of more complex hydrocarbons., Ever since Kuiper (1) postulated a remnant population of solar system objects just beyond the orbit of Pluto, there has been speculation as to the existence and nature of these [...]

The article 'Telling Pluto and its partner apart' by Mark Sincell (News of the Week, 30 July, p. 649), apparently adapted from a Web site (1), reports the detection of [...]

The nature of comet studies has changed profoundly in the last two decades. From prosaic issues of the identities of parent molecules, molecular production rates, tail behavior, so forth, attention [...]

Meterites recovered on the earth represent, at least in part, fragments from collisions among the asteroids. The variety of compositional types among the asteroids, as deduced from their telescopically observed [...]

Reports on studies of the physical properties and surface composition of bodies in the outer solar system, which can yield important clues to conditions that existed in the early solar system. Detection of water ice on the surface of Centaurs and the Kuniper belt objects (KBO), which orbit beyond Neptune; Methods used in analyzing the spectra of the Centaur 1997 CU26; Determination that the Kuniper belt is the source of the Centaurs.

The article discusses research reported elsewhere in the issue by Teolis et al. on a diffuse atmosphere of carbon dioxide and oxygen that surrounds Rhea, an icy moon of Saturn. The underlying data reportedly were recorded using the Ion Neutral Mass Spectrometer housed in the Cassini spacecraft that passed Rhea in March 2010.

Reviews the present state of knowledge about comets as of March 1997, with special reference being paid to comet Hale-Bopp. Seven reports in the March 28, 1997 issue of `Science' pertaining to observations of Hale-Bopp; Importance of the study of comets to geology and biology; How comets are formed; Various observations regarding Hale-Bopp.

NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest impactor size-frequency distributions proposed for the Kuiper belt. [ABSTRACT FROM AUTHOR]