Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations

We present the first comprehensive thermal and rotational analysis of the second most distant trans-Neptunian object (225088) 2007 OR10. We combined optical light curves provided by the Kepler space telescope -- K2 extended mission and thermal infrared data provided by the Herschel Space Observatory. We found that (225088) 2007 OR10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only. The most likely light-curve solution is double-peaked with a slight asymmetry, however, we cannot safely rule out the possibility of having a rotation period of P_rot=22.40+/-0.18 h which corresponds to a single-peaked solution. Due to the size and slow rotation, the shape of the object should be a MacLaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. Its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles -- CH_4, CO and N_2 -- on the surface.Comment: Accepted for publication in AJ, 8 pages in emulateapj styl

3D image analysis of a volcanic deposit

During the last decades, X-ray micro CT has become a well established technique for non-destructive testing in a wide variety of research fields. Using a series of X-ray transmission images of the sample at different projection angles, a stack of 2D cross-sections is reconstructed, resulting in a 3D volume representing the X-ray attenuation coefficients of the sample. Since the attenuation coefficient of a material depends on its density and atomic number, this volume provides valuable information about the internal structure and composition of the sample. Although much qualitative information can be derived directly from this 3D volume, researchers usually require more quantitative results to be able to provide a full characterization of the sample under investigation. This type of information needs to be retrieved using specialized image processing software. For most samples, it is imperative that this processing is performed on the 3D volume as a whole, since a sequence of 2D cross sections usually forms an inadequate approximation of the actual structure. The complete processing of a volume consists of three sequential steps. First, the volume is segmented into a set of objects. What these objects represent depends on what property of the sample needs to be analysed. The objects can be for instance concavities, dense inclusions or the matrix of the sample. When dealing with noisy data, it might be necessary to filter the data before applying the segmentation. The second step is the separation of connected objects into a set of smaller objects. This is necessary when objects appear to be connected because of the limited resolution and contrast of the scan. Separation can also be useful when the sample contains a network structure and one wants to study the individual cells of the network. The third and last step consists of the actual analysis of the various objects to derive the different parameters of interest. While some parameters require extensive calculations, others can be obtained easily. The different parameters which can be obtained are related to the size, shape and orientation of the objects. Additionally, the connectivity of a network can be analysed by comparing the set of objects before and after separation. The size of each object can be characterized by its volume, equivalent diameter and the diameter of the maximum inscribed sphere. The surface can be determined by extracting a polygonal mesh from the volume data. Calculation of Feret’s diameter reveals information about the objects elongation. Additionally, the moments of inertia can be calculated to obtain the axes of an equivalent ellipsoid. This data can be used to determine the main axis and therefore the orientation of the object within the sample. Feret’s diameter and the equivalent ellipsoid are representative for the basic shape of the object. Additionally, using a routine that fills concave regions, the convex hull of an object can be retrieved to quantify the convexity. Different ratios can be defined, which compare the surface area with the volume of the object (sphericity) or the volume of the convex hull. These ratios and the convexity characterize the objects roughness and shape. The described parameters are used to characterize volcanic deposits found in the area west of Lac Pavin (lake in Auvergne, France). The samples are taken from the most recent ‘red scoria’ layer, which is believed to be the result of the latest eruption in Western-Europe. There is however, ambiguity on the origin of the layer in terms of age and placement. The aim is to fingerprint this layer in such a way that the various eruptions in the area can be distinguished from one another. Measurements of the vesicle density, volume and connectivity of the investigated deposits provide information about the intensity of the eruption. Additionally, vesicle geometry can be related to the magmatic permeability, which is essential to the dynamics of the eruption

Estimating Drag and Heating Coefficients for Hollow Reentry Objects in Transitional Flow Using DSMC

In NASAs Object Reentry Survival Analysis Tool (ORSAT), aerodynamic drag and aerothermal heating coefficients are computed for each of the free-molecular, continuum, and transitional flow regimes using analytical and semi-analytical methods. These methods are typically limited to convex, blunt objects (such as spheres) and are applied to other objects such as boxes and cylinders using multiplicative shape factors to account for the different behavior. Previous literature has analyzed the aerodynamic and aerothermodynamic properties of flow around sharp-edged objects like boxes and cylinders in transitional flow, though only those objects with solid external boundaries. However, many reentry objects we have encountered in real spacecraft have been hollow (i.e., with the potential to allow flow through them). We present here preliminary results from analyses performed using the NASA Direct Simulation Monte Carlo (DSMC) Analysis Code (DAC) on hollow cylinders and boxes (with varying wall thickness-diameter ratio)

Radar Cross Section of Orbital Debris Objects

This discussion is concerned with the radar-data analysis and usage involved in the building of model orbital debris (OD) populations in the near-Earth environment, focusing on radar cross section (RCS). While varying with radar wavelength, physical dimension, material composition, overall shape and structure, the RCS of an irregular object is also strongly dependent on its spatial orientation. The historical records of observed RCSs for cataloged OD objects in the Space Surveillance Network are usually distributed over an RCS range, forming respective characteristic patterns. The National Aeronautics and Space Administration (NASA) Size Estimation Model provides an empirical probability-density function of RCS as a function of effective diameter (or characteristic length), which makes it feasible to predict possible RCS distributions for a given model OD population and to link data with model from a statistical perspective. The discussion also includes application of the widely used method of moments (MoM) and the Generalized Multi-particle Mie-solution (GMM) in the prediction of the RCS of arbitrarily shaped objects. Theoretical calculation results for an aluminum cube are compared with corresponding experimental measurements

E-TRoll: Tactile sensing and classification via a simple robotic gripper for extended rolling manipulations

Robotic tactile sensing provides a method of recognizing objects and their properties where vision fails. Prior work on tactile perception in robotic manipulation has frequently focused on exploratory procedures (EPs). However, the also-human-inspired technique of in-hand-manipulation can glean rich data in a fraction of the time of EPs. We propose a simple 3-DOF robotic hand design, optimized for object rolling tasks via a variable-width palm and associated control system. This system dynamically adjusts the distance between the finger bases in response to object behavior. Compared to fixed finger bases, this technique significantly increases the area of the object that is exposed to finger-mounted tactile arrays during a single rolling motion (an increase of over 60% was observed for a cylinder with a 30-millimeter diameter). In addition, this paper presents a feature extraction algorithm for the collected spatiotemporal dataset, which focuses on object corner identification, analysis, and compact representation. This technique drastically reduces the dimensionality of each data sample from 10×1500 time series data to 80 features, which was further reduced by Principal Component Analysis (PCA) to 22 components. An ensemble subspace k-nearest neighbors (KNN) classification model was trained with 90 observations on rolling three different geometric objects, resulting in a three-fold cross-validation accuracy of 95.6% for object shape recognition

Formulation and implementation of mathematical models suitable for deformation analysis of structures

Deformation monitoring is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stresses induced by applied loads. Deformation monitoring is a major component of logging measured values that may be used for further computation, deformation analysis, predictive maintenance and alarming. The main purpose of structural deformation monitoring scheme and analysis is to detect any significant movements of the structure. An effective approach is to model the structure by using well-chosen discrete points located on the surface of the structure which, when situated correctly, accurately depict the characteristics of the structure. The problem of Engineering Geodesy is the formulation of the Mathematical model that will reveal the characteristic of the structure being monitored. In this paper, the mathematical model that reveals the changes in shape of a circular reservoir structure is formulated and applied numerically. A numerical solution was carried out using the Mathematical model formulated.Keywords: Accuracy, deformation, diameter, Monitoring, Mathematical mode

Physical Properties of Asteroid (308635) 2005 YU55 derived from multi-instrument infrared observations during a very close Earth-Approach

The near-Earth asteroid (308635) 2005 YU55 is a potentially hazardous asteroid which was discovered in 2005 and passed Earth on November 8th 2011 at 0.85 lunar distances. This was the closest known approach by an asteroid of several hundred metre diameter since 1976 when a similar size object passed at 0.5 lunar distances. We observed 2005 YU55 from ground with a recently developed mid-IR camera (miniTAO/MAX38) in N- and Q-band and with the Submillimeter Array (SMA) at 1.3 mm. In addition, we obtained space observations with Herschel/PACS at 70, 100, and 160 micron. Our thermal measurements cover a wide range of wavelengths from 8.9 micron to 1.3 mm and were taken after opposition at phase angles between -97 deg and -18 deg. We performed a radiometric analysis via a thermophysical model and combined our derived properties with results from radar, adaptive optics, lightcurve observations, speckle and auxiliary thermal data. We find that (308635) 2005 YU55 has an almost spherical shape with an effective diameter of 300 to 312 m and a geometric albedo pV of 0.055 to 0.075. Its spin-axis is oriented towards celestial directions (lam_ecl, beta_ecl) = (60 deg +/- 30deg, -60 deg +/- 15 deg), which means it has a retrograde sense of rotation. The analysis of all available data combined revealed a discrepancy with the radar-derived size. Our radiometric analysis of the thermal data together with the problem to find a unique rotation period might be connected to a non-principal axis rotation. A low to intermediate level of surface roughness (r.m.s. of surface slopes in the range 0.1 - 0.3) is required to explain the available thermal measurements. We found a thermal inertia in the range 350-800 Jm^-2s^-0.5K^-1, very similar to the rubble-pile asteroid (25143) Itokawa and indicating a mixture of low conductivity fine regolith with larger rocks and boulders of high thermal inertia on the surface.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 10 figure

`Oumuamua as a messenger from the Local Association

7 pages, one table, two figures, accepted for publication by ApJL. © 2018. The American Astronomical Society. All rights reserved.With a hyperbolic trajectory around the Sun, 'Oumuamua is the first confirmed interstellar object. However, its origin is poorly known. By simulating the orbits of 0.23 million local stars, we find 109 encounters with periastron less than 5 pc. 'Oumuamua's low peculiar velocity is suggestive of its origin from a young stellar association with similar velocity. In particular, we find that 'Oumuamua would have had slow encounters with at least five young stars belonging to the Local Association, thus suggesting these as plausible sites for formation and ejection. In addition to an extremely elongated shape, the available observational data for 'Oumuamua indicates a red color, suggestive of a potentially organic-rich and activity-free surface. These characteristics seem consistent with formation through energetic collisions between planets and debris objects in the middle part of a young stellar system. We estimate an abundance of at least 6.0 × 10 -3 au -3 for such interstellar objects with mean diameter larger than 100 m and find that it is likely that most of them will be ejected into the Galactic halo. Our Bayesian analysis of the available light curves indicates a rotation period of 6.96 +1.45 -0.39, which is consistent with the estimation by Meech et al. and shorter than those in other literature. The codes and results are available on GitHub (https://github.com/phillippro/Oumuamua).Peer reviewe