Surface Of Trans-neptunian Objects Research Articles

Hunting for Hydrated Minerals on Trans-Neptunian Objects

We present new optical reflectance spectra of three potentially silicate-rich trans-Neptunian objects (TNOs). These spectra were obtained with the aim of confirming past hints and detections of λ ∼ 0.7 μm absorption features associated with the presence of iron-bearing phyllosilicates. Our new spectrum of 120216 (2004 EW95) presents clearly detected absorption features that are similar in shape to hydrated mineral absorption bands present in the spectra of aqueously altered outer main belt asteroids. Four new reflectance spectra of 208996 (2003 AZ84) obtained at separate epochs all appear featureless, but they vary significantly in spectral gradient (between ∼3.5%/0.1 μm and ∼8.5%/0.1 μm) on a timescale consistent with this object’s nominal rotational period. We report the first four optical reflectance spectra of 90568 (2004 GV9), finding them all to be featureless but consistent with colors previously reported for this object. We speculate that impacts are the only mechanism capable of delivering, excavating, or forming hydrated minerals at the surfaces of TNOs in detectable concentrations; as a result, any deposits of hydrated minerals on TNOs are predicted to be localized and associated with impact sites. Globally altered TNOs (as observationally suggested for 2004 EW95) plausibly formed more easily at smaller heliocentric distances (r H < 15 au) before being transplanted into the current trans-Neptunian population.

Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances

The distribution of surface classes of resonant trans-Neptunian objects (TNOs) provides constraints on the protoplanetesimal disk and giant planet migration. To better understand the surfaces of TNOs, the Colours of the Outer Solar System Origins Survey acquired multiband photometry of 102 TNOs and found that the surfaces of TNOs can be well described by two surface classifications: BrightIR and FaintIR. These classifications both include optically red members and are differentiated predominantly based on whether their near-infrared spectral slope is similar to their optical spectral slope. The vast majority of cold classical TNOs, with dynamically quiescent orbits, have the FaintIR surface classification, and we infer that TNOs in other dynamical classifications with FaintIR surfaces share a common origin with the cold classical TNOs. Comparison between the resonant populations and the possible parent populations of cold classical and dynamically excited TNOs reveal that the 3:2 has minimal contributions from the FaintIR class, which could be explained by the ν 8 secular resonance clearing the region near the 3:2 before any sweeping capture occurred. Conversely, the fraction of FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within the cold classical belt suggest that the FaintIR surface formed in the protoplanetary disk between ≳34.6 and ≲47 au, though the outer bound depends on the degree of resonance sweeping during migration. The presence and absence of the FaintIR surfaces in Neptune’s resonances provides critical constraints for the history of Neptune’s migration, the evolution of the ν 8, and the surface class distribution in the initial planetesimal disk.

A radiolytic origin of organic matter in primitive chondrites and trans-neptunian objects? New clues from ion irradiation experiments

We question here the radiolytic origin of (i) polyaromatic insoluble organic matter (IOM) recovered from primitive chondrites, and (ii) organics at the surface of reddish Trans-Neptunian Objects (TNOs), some minor planets and icy satellites. Organic synthesis by ion irradiation was investigated through experiments on a variety of targets: Polyethylene glycol 1450, lignin, cellulose and sucrose, exposed to low (C 40 keV and Ne 170 keV) and high energy (C 12 MeV, Ni 17 MeV, 78Kr 59 MeV) ions. These experiments show that all carbonaceous precursors evolve towards a sp2-rich amorphous carbon (a-C) above a critical nuclear dose of 10−7+10 eV.atom−1. A thorough review of the literature shows that this value applies for a large range of carbonaceous materials, including C-rich simple ices. Below this critical dose, irradiated targets are carbonized and transformed into cross-linked polymeric disordered solids, with abundant olefinic and acetylenic bonds, but devoid of aromatic or polyaromatic species. Ion irradiation of simple compounds, e.g. ices, is thereby not a viable process to synthesize IOM. However, in the case of aromatic-rich precursors, swift heavy ions irradiation leads to polyaromatic materials, by bridging existing aromatic or polyaromatic units. In the context of Early Solar System, i.e. Galactic Cosmic Rays (GCR) irradiation during 10–20 Myr, the formation of chondritic IOM from simple ices mixed with interstellar Polycyclic Aromatic Hydrocarbons (PAHs) appears as a plausible mechanism. This scenario, based on the recycling of existing carbonaceous interstellar grains under low-temperature conditions, would account for the heterogeneity of the D, 15N and 13C isotopic fractionations at the molecular scale, and the preservation of deuterium hot spots that are highly sensitive to high-temperature conditions (> 300 °C). At the surface of TNOs, sp2-rich amorphous carbons are formed by the implantation of GCRs and Solar wind ions. The electronic dose is also very high for an irradiation time of several Gyr (> 100 eV.atom−1), leading to the formation of reddish disordered solids, provided that the surface contains a minimum abundance of carbonaceous species. Finally, sp2-rich amorphous carbons produced in the laboratory (e.g. the ACAR compound from Zubko et al., 1996) are fair analogues of the darkening agent produced by radiolysis.

Compositional Study of Trans-Neptunian Objects at λ &gt; 2.2 μm

Abstract Using data from the Infrared Array Camera on the Spitzer Space Telescope, we present photometric observations of a sample of 100 trans-Neptunian objects (TNOs) beyond 2.2 μm. These observations, collected with two broadband filters centered at 3.6 and 4.5 μm, were done in order to study the surface composition of TNOs, which are too faint to obtain spectroscopic measurements. With this aim, we have developed a method for the identification of different materials that are found on the surfaces of TNOs. In our sample, we detected objects with colors that are consistent with the presence of small amounts of water, and we were able to distinguish between surfaces that are predominantly composed of complex organics and amorphous silicates. We found that 86% of our sample have characteristics that are consistent with a certain amount of water ice, and the most common composition (73% of the objects) is a mixture of water ice, amorphous silicates, and complex organics. Twenty-three percent of our sample may include other ices, such as carbon monoxide, carbon dioxide, methane, or methanol. Additionally, only small objects seem to have surfaces dominated by silicates. This method is a unique tool for the identification of complex organics and to obtain the surface composition of extremely faint objects. Furthermore, this method will be beneficial when using the James Webb Space Telescope for differentiating groups within the trans-Neptunian population.

PHOTOMETRIC MEASUREMENTS OF H2O ICE CRYSTALLINITY ON TRANS-NEPTUNIAN OBJECTS*

ABSTRACT We present a measurement of H2O ice crystallinity on the surface of trans-neptunian objects with near-infrared narrow-band imaging. The newly developed photometric technique allows us to efficiently determine the strength of a 1.65 μm absorption feature in crystalline H2O ice. Our data for three large objects—Haumea, Quaoar, and Orcus—which are known to contain crystalline H2O ice on the surfaces, show a reasonable result with high fractions of the crystalline phase. It can also be pointed out that if the grain size of H2O ice is larger than ∼20 μm, the crystallinities of these objects are obviously below 1.0, which suggests the presence of the amorphous phase. In particular, Orcus exhibits a high abundance of amorphous H2O ice compared to Haumea and Quaoar, possibly indicating a correlation between the bulk density of the bodies and the degree of surface crystallization. We also found the presence of crystalline H2O ice on Typhon and 2008 AP129, both of which are smaller than the minimum size limit for inducing cryovolcanism as well as a transition from amorphous to crystalline phase through thermal evolution due to the decay of long-lived isotopes.

OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6 ICES IN THE NEAR- AND MID-INFRARED

ABSTRACT We present a spectroscopic study of methane–ethane ice mixtures. We have grown CH4:C2H6 mixtures with ratios 3:1, 1:1, and 1:3 at 18 and 30 K, plus pure methane and ethane ices, and have studied them in the near-infrared (NIR) and mid-infrared (MIR) ranges. We have determined densities of all species mentioned above. For amorphous ethane grown at 18 and 30 K we have obtained a density of 0.41 and 0.54 g cm−3, respectively, lower than a previous measurement of the density of the crystalline species, 0.719 g cm−3. As far as we know this is the first determination of the density of amorphous ethane ice. We have measured band shifts of the main NIR methane and ethane features in the mixtures with respect to the corresponding values in the pure ices. We have estimated band strengths of these bands in the NIR and MIR ranges. In general, intensity decay in methane modes was detected in the mixtures, whereas for ethane no clear tendency was observed. Optical constants of the mixtures at 30 and 18 K have also been evaluated. These values can be used to trace the presence of these species in the surface of trans-Neptunian objects. Furthermore, we have carried out a theoretical calculation of these ice mixtures. Simulation cells for the amorphous solids have been constructed using a Metropolis Monte Carlo procedure. Relaxation of the cells and prediction of infrared spectra have been carried out at density functional theory level.

The composition of “ultra-red” TNOs and centaurs

We present an analysis of the colors available for seven trans-neptunian objects (TNOs) and three centaurs among the reddest known, aimed at characterizing their surface chemical properties. In particular we seek to obtain evidence in support of the proposed correlation between the visible coloration of the surface of TNOs and their surface compositions (Brown, M.E., Schaller, E.L., Fraser, W.C. [2011]. Astrophys. J. 739, L60).The analysis focuses on nine available colors in the visible–near IR (0.3–4.5μm) spectral range scaled to the V albedo to provide a proxy for the spectral shape of the objects. The colors include Spitzer IRAC data never published before, key in providing an effective constraint in the discrimination of ices contributing to the surface composition of the objects.Compositions are obtained by comparing the data to a grid of radiative transfer models convolved by the filter response functions of the colors adopted in the spectrum-proxies to match the resolution of the observations. We find evidence suggesting the presence of hydrocarbons and/or methanol on the surfaces of most objects in our sample, supporting the hypothesis by Brown et al. (Brown, M.E., Schaller, E.L., Fraser, W.C. [2011]. Astrophys. J. 739, L60) that the coloration of red TNOs could be linked to their methanol content.From our finding of methanol/hydrocarbon ices on the surfaces of the objects in our sample of very red TNOs and centaurs we infer that ultra-red objects in general might contain these ices and therefore might have formed in the outer part of the Solar System. We also deduce that the surfaces of most of the very red TNOs in our dataset are probably still quite pristine, and that their organic materials could have been produced by irradiation of the volatile ices whose traces are still present on their surface. Although our sample is small, we infer that the irradiation process is still in progress, as hinted by the centaurs’ slightly elevated organic amounts at smaller perihelion distances. However, considering the relatively similar amounts of organics found in our data at a wide variety of perihelion distances, we also infer that it could have started before Neptune’s migration.The technique used to constrain the composition described as part of this study introduces a new approach at investigating the surface chemistry of the very small and numerous objects that constitute the bulk of the TNO and centaur populations. This innovative method has the potential to provide constraints for irradiation theories and for models of dynamical and chemical evolution of the Solar System.

Photometry and taxonomy of trans-Neptunian objects and Centaurs in support of aHerschelkey program

Context. The investigation of Centaurs and trans-Neptunian objects (TNOs) provides essential information about the early conditions and evolution of the outer solar system. The radiometric technique combines measurements in the visible and thermal infrared; with these one can estimate the size and albedo of Centaurs and TNOs. Aims. Our aim is to obtain visible photometry of a sample of Centaurs and TNOs, a subset of the targets of the “TNOs are cool” key program at the Herschel Space Observatory. Methods. We carried out visible photometry of Centaurs and TNOs, making use of the DOLORES instrument at the Telescopio Nazionale Galileo (TNG, La Palma, Spain). Results. We report photometric observations of 20 objects and present the computed absolute magnitudes. We derive the taxonomy of our targets (nine are classified for the first time, the results for five objects agree with the literature, the other targets are tentatively classified based on incomplete datasets) and combine the results with the literature, searching for correlations between taxonomy and dynamics. We look for comet-like activity in our Centaur sample, including (248835) 2006 SX368, which was previously described as active. Conclusions. We provide an accurate determination of the absolute magnitude and of the relative error for each of our targets. These values can be readily used in combination with thermal infrared data. The surface of TNO (65489) Ceto seems to be heterogeneous. Our results seem to support an evolutionary origin for the color dichotomy of Centaurs, and the occurrence of a strong mixing after the TNO formation. No evident cometary activity is detected around the five Centaurs in our sample; assuming that an unresolved coma is present around (248835) 2006 SX368, we use the “photometric model” to derive the possible dust production rate, finding that Qdust is in the range 1–31 kg/s.

A compositional interpretation of trans-neptunian objects taxonomies

Trans-neptunian objects (TNOs) are a population of small objects orbiting the Sun beyond Neptune. Because of their distance they are difficult to observe spectroscopically, but a large body of photometric observations is available and growing. TNOs are important tracers of the evolution of the outer Solar System and key when testing current dynamical evolution theories. Previous statistical studies of the colors of TNOs have yielded useful but limited results regarding the chemical history and evolution of these bodies.With the aim at obtaining compositional information on the small and distant TNOs we introduce a statistical cluster analysis (labelled albedo) based on colors and published albedos of TNOs. We compare it to a previous taxonomy, to illustrate the significance of including the albedo information when determining the composition of the objects. When the albedo contribution is removed from the data, the new taxonomy (now labelled classical) is in general agreement with the published ones, supporting the applicability of our approach. Making use of modeled reflectance spectra of a variety of plausible mixtures found on the surface of TNOs, we extract the average surface composition of each taxon, for both the classical and the albedo taxonomy, in a statistically consistent fashion.Differently from previous and classical, the albedo taxonomy establishes a direct link between the colors and albedos of the objects and their surface composition, allowing, for the first time, a quick assessment of the chemical history of TNOs. In fact, under closer examination the taxa show trends in composition that might be evolutionary in nature. If a simple ‘snow lines’ model is adopted, we can infer that albedo taxa relate the current objects’ locations to their original ones, prior to the migration of the outer planets. We regard the large population that characterizes the darkest classes spread at a variety of semi-major axis distances as one of the intriguing results of this work.

Near-infrared laboratory spectra of H2O trapped in N2, CH4, and CO: hints for trans-Neptunian objects' observations

Context. Recent mid-infrared spectroscopic observations of Pluto and Triton suggest a wide distribution of H2O ice into surface regions containing more volatile species such as N2 ,C H4, and CO. This disagrees with the common idea that because of their typical surface temperature, water should not be involved in volatile transport processes, standing easily segregated from the more volatile species. Aims. We analyse infrared H2O band profiles when water is diluted in solid matrices dominated by methane, carbon monoxide, and/or molecular nitrogen. We also show the results of temperature-related diffusion processes of solid N2 into H2O ice deposited at different temperatures. Finally, we analyse ion irradiation effects for some of the mixtures considered. Methods. Solid samples were analysed by infrared (1.0‐16.0 µm) transmission and reflectance spectroscopy at different temperatures (15‐150 K), before and after ion irradiation with 200 keV protons. Results. When water is highly diluted in solid matrices, the profile of its near-infrared bands is strongly modified. Two narrow bands appear around 1.89 µm and 1.39 µm instead of the well known pure water ice bands at 2 µm and 1.5 µm, respectively. Furthermore, the peak position and width of the 1.89 and 1.39 µm bands depend on the initial mixture water is embedded in. The intensity of these bands decreases after ion irradiation. Conclusions. Since the mixtures considered closely resemble the surface composition of trans-Neptunian objects, experiments here discussed show that the bands around 1.89 µm and 1.39 µm are appropriate to investigating the presence of diluted water regions on their surface. In fact, the irradiation dose required for a significant decrease in their intensity would be accumulated on a timescale larger than the timescale for resurfacing processes on the surfaces of trans-Neptunian objects. Results shown here will contribute in a strong way to the interpretation of New Horizons near-infrared observations.

Observations of the Trans‐Neptunian Objects 1993 SC and 1996 TL \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $_{66}$ \end{document} with theInfrared Space Observatory

Observations at 90 μm of the trans-Neptunian objects (TNOs), 1993 SC and 1996 TL66, using the Infrared Space Observatory (ISO) are reported. Five individual observations of 1993 SC were acquired giving a 2.7 σ detection (a confidence level of 99.6%). The signal level of 11.46 ± 4.24 mJy has been modeled using a standard thermal model (STM) and gives an effective radius of 164 km and a geometric albedo of 0.022. Estimated radii and albedos using the fast rotator approximation and the thermophysical model are also presented. Two individual observations of 1996 TL66 are also reported. A clear signal of 39.77 ± 11.62 mJy at 90 μm was recorded. However, the position of the signal on the detector does not correspond to the position expected. A detailed investigation has not revealed a satisfactory explanation. Assuming that ISO was mispointed and that the origin of the signal is 1996 TL66, application of the STM gives an effective radius of 316 km and a geometric albedo of 0.030. This is in good agreement with expectations based on the assumption that the surfaces of TNOs are similar to those of cometary nuclei. The results for 1996 TL66 and 1993 SC indicate that TNOs are large, spherical, and very dark objects. A main-belt asteroid, 1997 SU15, was also detected giving an effective radius of 1.13 ± 0.04 km and a geometric albedo of 0.25 ± 0.02. An estimate of the relative dependence of the zodiacal light background in the ecliptic on elongation angle at 90 μm was also determined.

The Extraordinary Colors of Trans-Neptunian Objects 1994 TB and 1993 SC

We present B–V and V–R colors for trans-neptunian objects (TNOs) 1994 TB and 1993 SC. We have found that these TNOs have colors almost as red as 5145 Pholus which are therefore consistent with surfaces rich in complex organic molecules. We have measured B–V colors of 1.10 ± 0.15 and 1.27 ± 0.11 for 1994 TB and 1993 SC, respectively, as well as V–R colors of 0.68 ± 0.06 and 0.70 ± 0.04 for 1994 TB and 1993 SC, respectively. Currently, there are only four TNOs with published broadband colors (1992 QB1, 1993 FW, 1993 SC, and 1994 TB). TNO colors range from solar (a single V–R measurement of 1993 FW in the literature) to nearly the reddest objects in the solar system (our measurements of 1993 SC and 1994 TB). Although we have concluded 1993 SC is a very red TNO, a measurement in the literature has suggested that there is nothing special about the color of 1993 SC. Because there are so few TNOs with color measurements and because colors for 1993 SC are inconsistent, we cannot say yet with any certainty whether the surfaces of TNOs exhibit a diversity of colors and hence a diversity of surface compositions.