The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, ...thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•The analysis of the first couple of LEISA/New Horizons spectro-images is performed.•Qualitative distribution maps are obtained for N2, CH4, CO, H2O and the red material.•3 different types of ices ...are found: N2-rich:CH4:CO, CH4-rich(:CO:N2?) and H2O ices.•Sublimation sequence transforms N2-rich ice to CH4-rich ice through a binary mixture.
From Earth based observations Pluto is known to be the host of N2, CH4 and CO ices and also a dark red material. Very limited spatial distribution information is available from rotational visible and near-infrared spectral curves obtained from hemispheric measurements. In July 2015 the New Horizons spacecraft reached Pluto and its satellite system and recorded a large set of data. The LEISA spectro-imager of the RALPH instruments are dedicated to the study of the composition and physical state of the materials composing the surface. In this paper we report a study of the distribution and physical state of the ices and non-ice materials on Pluto's illuminated surface and their mode and degree of mixing. Principal Component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro-images from the LEISA instrument covering the whole illuminated face of Pluto at the time of the New Horizons encounter. Qualitative distribution maps have been obtained for the 4 main condensed molecules, N2, CH4, CO, H2O as well as for the visible-dark red material. Based on specific spectral indicators, using either the strength or the position of absorption bands, these 4 molecules are found to indicate the presence of 3 different types of ices: N2-rich:CH4:CO ices, CH4-rich(:CO:N2?) ices and H2O ice. The mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators. CH4 is mixed at the molecular level with N2, most probably also with CO, thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits. The occurrence of a N2-rich – CH4-rich ices mixing line associated with a progressive decrease of the CO/CH4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a N2-rich – CH4-rich binary mixture at the surface or an upper CH4-rich ice crust that may hide the N2-rich ice below. The strong CH4-rich – H2O mixing line witnesses the subsequent sublimation of the CH4-rich ice lag left behind by the N2:CO sublimation (N spring-summer), or a direct condensation of CH4 ice on the cold H2O ice (S autumn). The weak mixing line between CH4-containing ices and the dark red material and the very sharp spatial transitions between these ices and this non-volatile material are probably due to thermal incompatibility. Finally the occurrence of a H2O ice – red material mixing line advocates for a spatial mixing of the red material covering H2O ice, with possibly a small amount intimately mixed in water ice. From this analysis of the different materials distribution and their relative mixing lines, H2O ice appears to be the substratum on which other ices condense or non-volatile organic material is deposited from the atmosphere. N2-rich ices seem to evolve to CH4-dominated ices, possibly still containing traces of CO and N2, as N2 and CO sublimate away. The spatial distribution of these materials is very complex.
The high spatial definition of all these composition maps, as well as those at even higher resolution that will be soon available, will allow us to compare them with Pluto's geologic features observed by LORRI panchromatic and MVIC multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world.
Spectra taken by Cassini’s Composite Infrared Spectrometer (CIRS) between 10 and 600
cm
−1 (17–1000
μm) of surface thermal emission of Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus have been used ...to derive the thermal inertia and bolometric Bond albedo values. Only an upper limit for the bolometric Bond albedo of Iapetus’ dark leading side could be determined due to the insensitivity of the thermal model to albedo when albedos are very low. The thermal inertia in this region however is better constrained. The CIRS coverage of Enceladus is extensive enough that the latitudinal variation in these values from 60°S to 70°N has been determined in 10° wide bins. The bolometric Bond albedos determined here are consistent with literature values which show the surface of the saturnian icy moons to be covered in ice contaminated to varying degrees. The thermal inertia of the moons is shown to be in the range 9–
20
J
m
-
2
K
-
1
s
-
1
2
, approximately 2–6 times lower than that of the Galilean satellites, implying a less well consolidated and more porous surface. The thermal inertias of Iapetus and Phoebe are somewhat higher, suggesting that the very low thermal inertias of satellites from Rhea inwards may be related to their probable coating of E-ring material. Latitudinal variations on the surface of Enceladus show that the bolometric Bond albedo and thermal inertia increase towards the active plume source at the south pole.
The Kuiper Belt hosts a swarm of distant, icy objects ranging in size from small, primordial planetesimals to much larger, highly evolved objects, representing a whole new class of previously ...unexplored cryogenic worlds. Pluto, the largest among them, along with its system of five satellites, has been revealed by NASAs New Horizons spacecraft flight through the system in July 2015, nearly a decade after its launch.
The NASA Roadmap to Ocean Worlds Hendrix, Amanda R; Hurford, Terry A; Barge, Laura M ...
Astrobiology,
01/2019, Letnik:
19, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will ...guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to "identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find." The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists.
In 2011 a thermally anomalous region was discovered on Mimas, Saturn's innermost major icy satellite (Howett et al., 2011). The anomalous region is a lens-like shape located at low latitudes on ...Mimas' leading hemisphere. It manifests as a region with warmer nighttime temperatures, and cooler daytime ones than its surroundings. The thermally anomalous region is spatially correlated with a darkening in Mimas' IR/UV surface color (Schenk et al., 2011) and the region preferentially bombarded by high-energy electrons (Paranicas et al., 2012, 2014; Nordheim et al., 2017).
We use data from Cassini's Composite Infrared Spectrometer (CIRS) to map Mimas' surface temperatures and its thermophysical properties. This provides a dramatic improvement on the work in Howett et al. (2011), where the values were determined at only two regions on Mimas (one inside, and another outside of the anomalous region). We use all spatially-resolved scans made by CIRS' focal plane 3 (FP3, 600 to 1100 cm−1) of Mimas' surface, which are largely daytime observations but do include one nighttime one. The resulting temperature maps confirm the presence and location of Mimas' previously discovered thermally anomalous region. No other thermally anomalous regions were discovered, although we note that the surface coverage is incomplete on Mimas' leading and anti-Saturn hemisphere. The thermal inertia map confirms that the anomalous region has a notably higher thermal inertia than its surroundings: 98 ± 42 J m−2 K−1 s-1/2 inside of the anomaly, compared to 34 ± 32 J m−2 K−1 s-1/2 outside. The albedo inside and outside of the anomalous region agrees within their uncertainty: 0.45 ± 0.08 inside compared to 0.41 ± 0.07 outside the anomaly. Interestingly the albedo appears brighter inside the anomaly region, which may not be surprising given this region does appear brighter at some UV wavelengths (0.338 μm, see Schenk et al., 2011). However, this result should be treated with caution because, as previously stated, statistically the albedo of these two regions is the same when their uncertainties are considered. These thermal inertia and albedo values determined here are consistent with those found by Howett et al. (2011), who determined the thermal inertia inside the anomaly to be 66 ± 23 J m−2 K−1 s-1/2 and <16 J m−2 K−1 s-1/2 outside, with albedos that varied from 0.49 to 0.70.
•The first ever maps of both bolometric Bond albedo and thermal inertia have been produced for Mimas.•The location of Mimas' thermal anomaly is confirmed, no other anomalous regions are discovered.•Thermal inertia inside the anomaly is 108 ± 34 J m−2 K−1 s-1/2, compared to 29 ± 28 J m−2 K−1 s-1/2 outside.•Albedo is 0.48 ± 0.06 inside the anomaly compared to 0.40 ± 0.07 outside it.•New thermal inertia and albedo values agree with previously published values (Howett et al., 2011, 2010).
•Pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data.•Maps of Pluto’s volatiles and non-volatiles components.•Latitudinal variations of CH4 and N2 ices consistent with differences in ...insolation.•Possible sublimation transport of N2 ice within Sputnik Planitia.•Sputnik Planitia is possibly a cold trap of volatiles.
On July 14th 2015, NASA’s New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Pluto’s encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large scale latitudinal variations of methane and nitrogen ices and aims at setting observational constraints to volatile transport models. Specifically, we find three latitudinal bands: the first, enriched in methane, extends from the pole to 55°N, the second dominated by nitrogen, continues south to 35°N, and the third, composed again mainly of methane, reaches 20°N. We demonstrate that the distribution of volatiles across these surface units can be explained by differences in insolation over the past few decades. The latitudinal pattern is broken by Sputnik Planitia, a large reservoir of volatiles, with nitrogen playing the most important role. The physical properties of methane and nitrogen in this region are suggestive of the presence of a cold trap or possible volatile stratification. Furthermore our modeling results point to a possible sublimation transport of nitrogen from the northwest edge of Sputnik Planitia toward the south.
A multiwavelength regionally dependent photometric analysis of Pluto's anti-Charon-facing hemisphere using images collected by New Horizons' Multispectral Visible Imaging Camera (MVIC) reveals large ...variations in the absolute value and spectral slope of the single-scattering albedo. Four regions of interest are analyzed: the dark equatorial belt, Pluto's north pole, nitrogen-rich regions, and the mid-latitude terrains. Regions dominated by volatile ices such as Lowell Regio and Sputnik Planitia present single-scattering albedos of ∼0.98 at 492 nm, almost neutral across MVIC's visible wavelength range (400-910 nm), indicating limited contributions from tholin materials. Pluto's dark equatorial regions, informally named Cthulhu and Krun Maculae, have single-scattering albedos of ∼0.16 at 492 nm and are the reddest regions. Applying the Hapke radiative transfer model to combined MVIC and Linear Etalon Imaging Spectral Array (LEISA) spectra (400-2500 nm) of Cthulhu Macula and Lowell Regio successfully reproduces the spectral properties of these two regions of dramatically disparate coloration, composition, and morphology. Since this model uses only a single coloring agent, very similar to the Titan-like tholin of Khare et al., to account for all of Pluto's colors, this result supports the Grundy et al. conclusion that Pluto's coloration is the result of photochemical products mostly produced in the atmosphere. Although cosmic rays and extreme ultraviolet photons reach Pluto's surface where they can drive chemical processing, observations of diverse surface colors do not require different chemical products produced in different environments. We report a correction scaling factor in the LEISA radiometric calibration of 0.74 0.05.
The New Horizons spacecraft flew past the Kuiper Belt object (486958) Arrokoth (also known as 2014 MU69) in January 2019. Because of the great distance to the outer Solar System and limited ...bandwidth, it will take until late 2020 to downlink all the spacecraft's observations back to Earth. Three papers in this issue analyze recently downlinked data, including the highest-resolution images taken during the encounter (see the Perspective by Jewitt). Spencer et al. examined Arrokoth's geology and geophysics using stereo imaging, dated the surface using impact craters, and produced a geomorphological map. Grundy et al. investigated the composition of the surface using color imaging and spectroscopic data and assessed Arrokoth's thermal emission using microwave radiometry. McKinnon et al. used simulations to determine how Arrokoth formed: Two gravitationally bound objects gently spiraled together during the formation of the Solar System. Together, these papers determine the age, composition, and formation process of the most pristine object yet visited by a spacecraft.
► A thermally anomalous region is discovered on Tethys. ► The anomaly is very similar in location and diurnal temperature to Mimas’. ► Anomaly is in a region preferentially bombarded by MeV ...electrons. ► Provides strong evidence that MeV electrons can significantly alter icy surfaces.
New Cassini observations show that Saturn’s moon Tethys, like Mimas, has a region of anomalously high thermal inertia at low latitudes centered on its leading hemisphere. Derivation of the thermophysical properties of the surface across three representative regions indicate that the bolometric Bond albedo across Tethys’ leading hemisphere remains constant, within error, whilst the thermal inertia increases from 5±1Js−1m−1K−1 outside of the anomalous region to 25±3Js−1m−1K−1 inside. The thermally anomalous region is spatially correlated with a decrease in the IR/UV surface coloration. The discovery greatly strengthens the hypothesis that high-energy electrons, which preferentially bombard the leading hemispheres on both satellites, produce dramatic alterations in surface texture.
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