The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69’s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

Abstract. Contrary to assumptions often made in the literature, explosive volcanic eruptions are capable of transporting significant amounts of water into the stratosphere. In addition to the magmatic water component, atmospheric water vapor is entrained by the column at lower levels. A theoretical model for the conservation of mass, momentum, and thermal energy of four separate components (dry air, water vapor, liquid condensates, and solid particles) is used to determine the extent of atmospheric water redistribution. We examine the effects of water vapor condensation on dynamical characteristics and ambient water vapor transport. A simple technique is presented for deriving canonical forms for the complex system of ordinary differential equations governing the column components. Solutions of this model are presented that show the influence of different volcanic boundary conditions and a range of ambient water vapor distributions on transport of the buoyant column. We show that the water component (vapor + liquid) of small eruption columns rising through a wet atmosphere is dominated by entrained water, whereas larger columns are dominated by the magmatic water. This is due, in part, to the proportionately smaller entrainment surface area in relation to the control volume for the larger columns.We also show that a maintained column with an initial mass flux of 2.7 x 108 kg s -• erupted into a wet atmosphere would inject 96 Mt of water vapor into the stratosphere over 24 hours, comparable to the annual input from methane oxidation or 100 midlatitude thunderstorms. This increase may accelerate the conversion of simultaneously erupted volcanic SO 2 into sulfuric acid.

Fifteen Landsat Thematic Mapper (TM) images of L•scar volcano (Chile), recorded between December 1984 and April 1992, document the evolution of a lava dome within the summit crater. Four of the scenes were acquired at night. In every image, the two short-wavelength infrared bands, 5 and 7, have detected thermal radiation from the volcano. As a consequence of the Planck distribution function, the relative response of these two channels depends on the proportions of very hot (> 600øC) surfaces occupying tiny pixel areas and broader regions at moderate temperatures (< 280øC). Intercomparison of bands 5 and 7 thereby provides a means for interpreting TM thermal anomalies even in the absence of ground observations. Pronounced changes in the configuration and intensity of the L•scar anomaly suggest that the volcano has experienced at least two cycles of lava dome activity since 1984. The first of these progressed through a "cooling" period, possibly reflecting a reduced flux of magmatic volatiles at the surface, and culminated in an explosive eruption on September 16, 1986, which appears to have completely destroyed the inferred lava dome. The TM data indicate that a new dome had been emplaced by November 1987, more than 15 months before it was first discovered by local observers. Lfiscar's style of cyclical effusive and explosive activity is typical of many volcanoes, and the remote sensing techniques presented herein could be applied elsewhere. INTRODUCTION Satellite remote sensing can serve volcanological inquiry in various ways. Preliminary investigations have demonstrated the utility of spaceborne infrared sensors for observing volcanic thermal phenomena such as lava flows and lava lakes[Rothery etal., 1988], fumarole fields [Oppenheimer and Rothery, 1991], and crater lakes [Oppenheimer, 1993]. Detection of new thermal anomalies, or of changes in existing ones, can be of especial value for hazard evaluation. In addition, thermal measurements can illuminate the physical processes that trigger eruptions and influence the behavior of erupted materials. Data from the Landsat Thematic Mapper (TM) enabled Pieri et al. [1990] and Oppenheimer [1991] to infer thermal properties of lava flows. Although orbital remote sensing offers a continuity of observation difficult to achieve by other means at many volcanoes worldwide [Francis, 1979], previous studies have tended to concentrate on techniques for analyzing individual "snapshot" TM images. Thermal anomalies in TM data can be difficult to identify. While a long thermal signature extending radially from a volcano summit is very likely to represent a lava (or possibly pyroclastic) flow, confined lava bodies and high-temperature fumarole fields can be indistinguishable, on spatial grounds, in satellite data. The 30 x 30 m TM pixels often cover substantial portions of such features and the strongest sources of short-wavelength infrared (SWIR) radiation may occupy only tiny fractions (< 0.1%) of pixel areas [Oppenheimer, 1991; Oppenheimer et al., 1993]. Rothery et al. [1988], i...

[1] The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth-and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

[1] We use the Mars Global Surveyor and Viking data sets to compare and contrast the geomorphology of four large Martian landslides located in Valles Marineris to fluidized ejecta of seven fresh Martian craters located in Lunae Planum. Both mass movements have flowed over the Martian surface and possess characteristics seen in terrestrial mass movements. We combine these comparisons with simple flow models to determine how the planar geometry of landslides and the cylindrical geometry of ejecta can generate different topographic expressions for the same input constraints. Our purpose is to better understand the emplacement processes of both types of mass movements. Our geomorphic analyses are consistent with previous views that the large Martian landslides resemble large terrestrial long-run-out flows. The planar flow model supports this inference: Martian landslides probably flowed as a basal glide, where motion is limited to a narrow interface at the base of the mass movement. Geomorphic investigations of fresh multilayered ejecta indicate that their inner portions with their subtle rampart probably flowed like their landslide counterparts as a basal glide. Distal pronounced contiguous ramparts, however, resemble features akin to terrestrial debris flows. The cylindrical flow model shows that differences in geometry can mask the dynamics of flow emplacement. This model suggests, as expected, a basal glide origin for the inner portions of the ejecta. Surprisingly, basal glide also best explains the topography of the distal ejecta ramparts.