36 research outputs found
DISCUS - The Deep Interior Scanning CubeSat mission to a rubble pile near-Earth asteroid
We have performed an initial stage conceptual design study for the Deep
Interior Scanning CubeSat (DISCUS), a tandem 6U CubeSat carrying a bistatic
radar as main payload. DISCUS will be operated either as an independent mission
or accompanying a larger one. It is designed to determine the internal
macroporosity of a 260-600 m diameter Near Earth Asteroid (NEA) from a few
kilometers distance. The main goal will be to achieve a global penetration with
a low-frequency signal as well as to analyze the scattering strength for
various different penetration depths and measurement positions. Moreover, the
measurements will be inverted through a computed radar tomography (CRT)
approach. The scientific data provided by DISCUS would bring more knowledge of
the internal configuration of rubble pile asteroids and their collisional
evolution in the Solar System. It would also advance the design of future
asteroid deflection concepts. We aim at a single-unit (1U) radar design
equipped with a half-wavelength dipole antenna. The radar will utilize a
stepped-frequency modulation technique the baseline of which was developed for
ESA's technology projects GINGER and PIRA. The radar measurements will be used
for CRT and shape reconstruction. The CubeSat will also be equipped with an
optical camera system and laser altimeter to sup- port navigation and shape
reconstruction. We provide the details of the measurement methods to be applied
along with the requirements derived of the known characteristics of rubble pile
asteroids.Comment: Submitted to Advances in Space Researc
Bistatic full-wave radar tomography detects deep interior voids, cracks and boulders in a rubble-pile asteroid model
In this paper, we investigate full-wave computed radar tomography (CRT) using
a rubble-pile asteroid model in which a realistic shape (Itokawa) is coupled
with a synthetic material composition and structure model. The aim is to show
that sparse bistatic radar measurements can distinguish details inside a
complex-structured rubble-pile asteroid. The results obtained suggest that
distinct local permittivity distribution changes such as surface layers, voids,
low-permittivity anomalies, high-permittivity boulders, and cracks can be
detected with bistatic CRT, when the total noise level in the data is around
-10 dB with respect to the signal amplitude. Moreover, the bistatic measurement
set-up improves the robustness of the inversion compared to the monostatic
case. Reconstructing the smooth Gaussian background distribution was found to
be difficult with the present approach, suggesting that complementary
techniques, such as gravimetry, might be needed to improve the reliability of
the inference in practice.Comment: 15 pages, 7 figures, 3 tables, Published in the Astrophysical Journa
The albedo-color diversity of transneptunian objects
We analyze albedo data obtained using the Herschel Space Observatory that
reveal the existence of two distinct types of surface among midsized
transneptunian objects. A color-albedo diagram shows two large clusters of
objects, one redder and higher albedo and another darker and more neutrally
colored. Crucially, all objects in our sample located in dynamically stable
orbits within the classical Kuiper belt region and beyond are confined to the
bright-red group, implying a compositional link. Those objects are believed to
have formed further from the Sun than the dark-neutral bodies. This
color-albedo separation is evidence for a compositional discontinuity in the
young solar system.Comment: 16 pages, 4 figures, 1 table, published in ApJL (12 August 2014), The
Astrophysical Journal (2014), vol. 793, L
TNOs are Cool: A Survey of the Trans-Neptunian Region: Radiometric properties of Trans-Neptunian Objects
The "TNOs are Cool: A Survey of the Trans-Neptunian Region" project is a Herschel Open Time Key Program awarded some 370 h of Herschel observing time. The observations include PACS and SPIRE point-source photometry on about 140 trans-Neptunian objects with known orbits. The goal is to characterize the individual objects and the full sample using radiometric techniques, in order to probe formation and evolution processes in the Solar System and to establish a benchmark for understanding the Solar System debris disk as well as extra-solar ones. We present results on a set of TNOs which were selected for the Science Demonstration and early mission phases and report on progress in deriving effective sizes, geometric albedos, and thermal characteristics. Our early sample also includes binary objects for which density estimates can be made on the basis of the derived diameters. TNO densities can provide insight into Solar-System formation scenarios
Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si
Metallic and silicate ions carry essential information about the evolution of the Earth and nearâEarth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin.Key Points:
A new data product from the Cluster mission is utilized to study heavy ions in geospace.
Traceable amounts of silicon (Si) and iron (Fe) are found in all regions of space traversed by Cluster.
The detected Si and Fe are most likely of solar wind origin.Deutsches Zentrum fĂŒr Luftâ und Raumfahrt (DLR)
http://dx.doi.org/10.13039/50110000294
Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si
Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin