Aims. The goal of this work is to characterize the ensemble thermal properties of the Centaurs / trans-Neptunian population. Methods. Thermal flux measurements obtained with Herschel/PACS and ...Spitzer/MIPS provide size, albedo, and beaming factors for 85 objects (13 of which are presented here for the first time) by means of standard radiometric techniques. The measured beaming factors are influenced by the combination of surface roughness and thermal inertia effects. They are interpreted within a thermophysical model to constrain, in a statistical sense, the thermal inertia in the population and to study its dependence on several parameters. We use in particular a Monte-Carlo modeling approach to the data whereby synthetic datasets of beaming factors are created using random distributions of spin orientation and surface roughness. Results. Beaming factors η range from values <1 to ~2.5, but high η values (>2) are lacking at low heliocentric distances (rh < 30 AU). Beaming factors lower than 1 occur frequently (39% of the objects), indicating that surface roughness effects are important. We determine a mean thermal inertia for Centaurs/ TNO of Γ = (2.5 ± 0.5) J m-2 s−1/2 K-1, with evidence of a trend toward decreasing Γ with increasing heliocentric (by a factor ~2.5 from 8–25 AU to 41–53 AU). These thermal inertias are 2–3 orders of magnitude lower than expected for compact ices, and generally lower than on Saturn’s satellites or in the Pluto/Charon system. Most high-albedo objects are found to have unusually low thermal inertias. Our results suggest highly porous surfaces, in which the heat transfer is affected by radiative conductivity within pores and increases with depth in the subsurface.
We report here the first detection of hectometer-size objects by the method of serendipitous stellar occultation. This method consists of recording the diffraction shadow created when an object ...crosses the observer's line of sight and occults the disk of a background star. One of our detections is most consistent with an object between Saturn and Uranus. The two other diffraction patterns detected are caused by Kuiper Belt objects beyond 100 AU from the Sun and hence are the farthest known objects in the solar system. These detections show that the Kuiper Belt is much more extended than previously believed and that the outer part of the disk could be composed of smaller objects than the inner part. This gives critical clues to understanding the problem of the formation of the outer planets of the solar system.
Photometric and spectroscopic observations of Centaur Chiron have been obtained at the ESO/Very Large Telescope (VLT), both in optical and near-infrared spectral ranges, on 12–14 June 2001. ...Photometric optical data reveal that Chiron had reached a high activity level at that time. No absorption feature could be seen on the spectra; especially, no water ice could be detected.
Context. Physical characterization of trans-Neptunian objects, a primitive population of the outer solar system, may provide constraints on their formation and evolution. Aims. The goal of this work ...is to characterize a set of 15 scattered disk (SDOs) and detached objects, in terms of their size, albedo, and thermal properties. Methods. Thermal flux measurements obtained with the Herschel-PACS instrument at 70, 100 and 160 μm, and whenever applicable, with Spitzer-MIPS at 24 and 70 μm, are modeled with radiometric techniques, in order to derive the objects’ individual size, albedo and when possible beaming factor. Error bars are obtained from a Monte-Carlo approach. We look for correlations between these and other physical and orbital parameters. Results. Diameters obtained for our sample range from 100 to 2400 km, and the geometric albedos (in V band) vary from 3.8% to 84.5%. The unweighted mean V geometric albedo for the whole sample is 11.2% (excluding Eris); 6.9% for the SDOs, and 17.0% for the detached objects (excluding Eris). We obtain new bulk densities for three binary systems: Ceto/Phorcys, Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to observational bias, we find significant correlations between albedo and diameter (more reflective objects being bigger), and between albedo, diameter and perihelion distance (brighter and bigger objects having larger perihelia). We discuss possible explanations for these correlations.
Both physical and dynamical properties must be considered to constrain the origins of the dynamically excited distant solar system populations. We present high-precision (g-r) colors for 25 small (Hr ...> 5) dynamically excited trans-Neptunian objects (TNOs) and centaurs acquired as part of the Colours of the Outer Solar System Origins Survey. We combine our data set with previously published measurements and consider a set of 229 colors of outer solar system objects on dynamically excited orbits. The overall color distribution is bimodal and can be decomposed into two distinct classes, termed gray and red, that each has a normal color distribution. The two color classes have different inclination distributions: red objects have lower inclinations than the gray ones. This trend holds for all dynamically excited TNO populations. Even in the worst-case scenario, biases in the discovery surveys cannot account for this trend; it is intrinsic to the TNO population. Considering that TNOs are the precursors of centaurs, and that their inclinations are roughly preserved as they become centaurs, our finding solves the conundrum of centaurs being the only outer solar system population identified so far to exhibit this property. The different orbital distributions of the gray and red dynamically excited TNOs provide strong evidence that their colors are due to different formation locations in a disk of planetesimals with a compositional gradient.
Context.
A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have ...resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers.
Aims.
We have made observations to determine sizes and geometric albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities.
Methods.
We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter.
Results.
The detected Haumea family members have a diversity of geometric albedos ~0.3–0.8, which are higher than geometric albedos of dynamically similar objects without water ice. The median geometric albedo for accepted family members is
p
V
= 0.48
−0.18
+0.28
, compared to 0.08
−0.05
+0.07
for the dynamical interlopers. In the size range
D
= 175−300 km, the slope of the cumulative size distribution is
q
= 3.2
−0.4
+0.7
for accepted family members, steeper than the
q
= 2.0 ± 0.6 slope for the dynamical interlopers with
D
< 500 km. The total mass of Haumea’s moons and family members is 2.4% of Haumea’s mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21–0.50.
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•Thin-walled Ti6Al4V parts were produced by Selective Laser Melting.•Several laser power and scan speed combinations were tested in the production.•Four models on the thickness of ...these thin-walled parts were developed.•All models exhibit complex correlations of SLM parameters, with non-linear equations.•These models can be used to optimize the manufacture of Ti6Al4V thin-walled parts.
Selective Laser Melting (SLM) is an extremely versatile technology especially suited for the manufacturing of thin-walled parts. Micro-sized parts are highly influenced and dependent on the SLM processing parameters; thus being indispensable to assess the influence of processing parameters on SLM fabrication, as isolated parameters but also their interactions. In this study, the influence of SLM laser power and scanning speed on Ti6Al4V micro-pillars and micro-plates thickness was assessed by applying response surface methodology (RSM). These analyses resulted in four models that exhibit complex correlations of SLM process parameters, with non-linear equations, having coefficients of determination that assess the quality of the models. These developed models are accurate tools that can be used to optimize the micro manufacture of Ti6Al4V thin-walled parts by SLM.
Transneptunian objects and Centaurs are supposed to be among the most pristine bodies of the Solar System. To investigate their physical properties and their surface composition, an ESO large program ...at the Very Large Telescope was carried out. In this paper we present photometric and spectroscopic near-infrared data of two Centaurs (1998 SG35 and 2000 QC243) and one transneptunian object (47171 1999 TC36). For 47171 1999 TC36 and 1998 SG35 visible photometry is also presented. Models of the surface composition of these objects are presented and discussed. By including a small percentage of water ice in our geographical mixtures, we obtain a better agreement with the observations in the H and K bands.
•Space debris detection;•Payload camera breadboard for space surveillance;•Star tracking and space debris detection algorithms;•Hybrid time-index image algorithm.
Space debris threatens space ...activities, demanding continuous observation and tracking by the Space Surveillance Network (SSN) to secure the Earth’s orbits. However, SST efforts are limited by the size and brightness of the debris, detecting only a small amount of the total. Seeking to overcome such limitations, this study proposes an alternative payload camera capable of extracting the attitude of a satellite in orbit and detecting under-catalogued debris. This work is a sequential study of previous research, where the camera breadboard was designed and implemented. The contribution of this paper is the evaluation of star tracking and space debris algorithms to be implemented in the payload camera, the development and implementation of a new hybrid algorithm and the elaboration of performance metrics for comparison between the algorithms. The observation data of the previous research was used as input for the algorithms’ tests. For star identification and, consequently, attitude extraction, the chosen algorithm was Tetra. The results were compared to the standard star identification software, Astrometry.net, to assess the attitude accuracy. For debris detection, ASTRiDE and the Hybrid time-index image algorithms were used. A comparison of the results was made to establish a performance evaluation metric in terms of detectability, time, and computational cost.
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