Time filter

Source Type

Ehrenfreund P.,Leiden Institute of Chemistry | Ehrenfreund P.,Space Policy Institute | Ulamec S.,German Aerospace Center | Barucci M.A.,LESIA Observatoire de Paris | And 9 more authors.
Proceedings of the International Astronautical Congress, IAC | Year: 2012

MarcoPolo-R is a sample return mission to a primitive Near-Earth Asteroid (NEA) selected in February 2011 for the Assessment Study Phase in the framework of ESA's Cosmic Vision 2 program. MarcoPolo-R is a European mission and takes advantage of three completed industrial studies. MarcoPolo-R will rendezvous with a unique kind of target, the primitive binary NEA (175706) 1996 FG3. The MarcoPolo mission will scientifically characterize the binary NEA system at multiple scales, and return a unique pristine sample to Earth unaltered by the atmospheric entry process or terrestrial weathering. The binary target provides enhanced science return: precise measurements of the mutual orbit and rotation state of both components can be used to probe higher-level harmonics of the gravitational potential, and therefore the internal structure. The main goal of the MarcoPolo-R mission is to return unaltered NEA material for detailed analysis in ground-based laboratories which will allow scientists to study the most primitive materials available to investigate early Solar System formation processes. Copyright © (2012) by the International Astronautical Federation.

Thebault P.,LESIA Observatoire de Paris | Marzari F.,University of Padua | Augereau J.-C.,Joseph Fourier University
Astronomy and Astrophysics | Year: 2010

Context. Debris disc analysis and modelling provide crucial information about the structure and the processes at play in extrasolar planetary systems. In binary systems, this issue is more complex because the disc should also respond to the companion star's perturbations. Aims. We explore the dynamical evolution of a collisionally active debris disc for different initial parent body populations, diverse binary configurations, and optical depths. We focus on the radial extent and size distribution of the disc in a stationary state. Methods. We numerically followed the evolution of 10 5 massless small grains, initially produced from a circumprimary disc of parent bodies following a size distribution in dN propto s -3.5ds. Grains were submitted to both stars' gravity and radiation pressure. In addition, particles were assigned an empirically derived collisional lifetime. Results. For all the binary configurations, the disc extends far beyond the critical semi-major axis a crit for orbital stability. This is due to the steady production of small grains, placed by radiation pressure on eccentric orbits reaching beyond a crit. The amount of matter beyond a crit depends on the balance between collisional production and dynamical removal rates: it increases for more massive discs, as well as for eccentric binaries. Another important effect is that, in the dynamically stable region, the disc is depleted from its smallest grains. Both results could lead to observable signatures. Conclusions. We have shown that a companion star can never fully truncate a collisionally active disc. For eccentric companions, grains in the unstable regions can contribute significantly to the thermal emission in the mid-IR. Discs with sharp outer edges, especially bright ones such as HR4796A, are probably shaped by other mechanisms. © ESO, 2010.

Vincent J.-B.,Max Planck Institute for Solar System Research | Schenk P.,Lunar and Planetary Institute | Nathues A.,Max Planck Institute for Solar System Research | Sierks H.,Max Planck Institute for Solar System Research | And 11 more authors.
Planetary and Space Science | Year: 2014

Orbiting asteroid (4) Vesta from July 2011 to August 2012, the Framing Camera on board the Dawn spacecraft has acquired several tens of thousand images of the asteroid surface, revealing a complex landscape. The topography is dominated by craters of all sizes and shapes, from fresh, simple, bowl-shaped craters to giant basins, as seen in the southern hemisphere. Craters of different ages or states of degradation can be seen all over the surface; some have very sharp rims and simple morphology, whereas others are highly eroded and have sometimes been filled by landslides and ejecta from nearby craters. The general depth/Diameter (d/D) distribution on Vesta is similar to what has been observed on other small rocky objects in the Solar System with a distribution peaking at 0.168±0.01 in the range 0.05-0.35. However, the global map of d/D reveals important geographic variations across the surface, unlike any other asteroid. The northern most regions of Vesta show d/D values comparable to other asteroid surfaces, with a mean d/D of 0.15±0.01, and a steep cumulative distribution. Craters in the regions affected by the giant southern impacts are deeper (mean d/D=0.19±0.01) and show less erosion. It can be interpreted as the southern surface being younger than the rest of the asteroid, or made of a material which either allows the formation of deeper features or prevents their erosion. This picture is consistent with the idea of a southern Vestan hemisphere resurfaced relatively recently by the giant impact that created the Rheasilvia basin. The analysis of depth-to-Diameter variations over the whole surface also brings some insight into the transition regions between different cratering regimes: about 20 km for the strength-to-gravity dominated regime, and 38 km for the beginning of the simple-to-complex transition. © 2013 Elsevier Ltd. All rights reserved.

Harris A.W.,German Aerospace Center | Barucci M.A.,LESIA Observatoire de Paris | Cano J.L.,Deimos Space | Fitzsimmons A.,Queens University of Belfast | And 10 more authors.
Acta Astronautica | Year: 2013

Although discussions are underway within the Action Team 14 of the United Nations COPUOS, there is currently no concerted international plan addressing the impact threat from near-Earth objects (NEOs) and how to organize, prepare and implement mitigation measures. We report on a new international project to address impact hazard mitigation issues, being the subject of a proposal submitted to the European Commission in response to the 2011 FP7 Call "Prevention of impacts from near-Earth objects on our planet". Our consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The primary aim of the project, NEOShield, is to investigate in detail the three most promising mitigation techniques: the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Furthermore, we will investigate options for an international strategy for implementation when an actual impact threat arises. The NEOShield project was formally accepted by the European Commission on 17 November 2011 and funded with a total of 5.8 million Euros for a period of 3.5 years. The kick-off meeting took place at the DLR Institute of Planetary Research, Berlin, in January 2012. In this paper we present a brief overview of the planned scope of the project. © 2012 IAA. Published by Elsevier Ltd. All rights reserved.

Yang P.,CAS Shanghai Institute of Optics and fine Mechanics | Yang P.,Max Planck Institute for Astronomy | Yang P.,University of Chinese Academy of Sciences | Hippler S.,Max Planck Institute for Astronomy | And 9 more authors.
Optics Express | Year: 2013

The adaptive optics system for the second-generation VLT-interferometer (VLTI) instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope (VLT). Feeding the GRAVITY wavefront sensor with light in the 1.4 to 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. In this paper, we present the development of a quantitative near-infrared point diffraction interferometric characterization technique, which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat. The technique can be readily applied to quantitative phase measurements in the near-infrared regime. Moreover, by employing a slightly off-axis optical setup, the proposed method can optimize the required spatial resolution and enable real time measurement capabilities. The feasibility of the proposed setup is demonstrated, followed by theoretical analysis and experimental results. Our experimental results show that the phase error repeatability in the nanometer regime can be achieved. © 2013 Optical Society of America.

Discover hidden collaborations