ESA Science & Technology - Publication Archive
Published online 14 April 2015 in Science ExpressKnowledge of the magnetization of planetary bodies constrains their origin and evolution, as well as the conditions in the solar nebular at that time. Based on magnetic field measurements during the descent and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko, we show that no global magnetic field was detected within the limitations of analysis. The ROMAP suite of sensors measured an upper magnetic field magnitude of less than 2 nT at the cometary surface at multiple locations with the upper specific magnetic moment being < 3.1·10-5 Am2/kg for meter-size homogeneous magnetized boulders. The maximum dipole moment of 67P/Churyumov-Gerasimenko is 1.6·108 Am2. We conclude that on the meter-scale, magnetic alignment in the pre-planetary nebula is of minor importance.
Rosetta is ESA's comet-chasing mission to 67P/Churyumov-Gerasimenko. Launched on 2 March 2004, the spacecraft travelled for 10 years and required three gravity-assist flybys at Earth and one at Mars before homing in on its target.
Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission could be the key to unlocking the history and evolution of our Solar System.
Table of contents:
- Europe's comet-chaser
- The long trek
- A human endeavour
- Rendezvous with a comet
- Pull-out poster: Rosetta mission selfie
- Landing on a comet
- The Rosetta orbiter
- The Philae lander
- Getting to know the comet
- An evolving story
- An international enterprise
- Join the adventure
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This document presents the results of a study, performed by ESA's Concurrent Design Facility (CDF) in 2014, that analysed the feasibility of a 150 kg-class rover compliant with a potential Mars Sample Return mission and its "FAST" mobility performance requirements. The rover is also able to provide in-situ science for supporting future Mars robotic exploration. For this study, a landing platform delivered by NASA/JPL was considered, in the view of a possible ESA/NASA cooperation in the 2024 timeframe.
ESA's Concurrent Design Facility (CDF) have completed a study of a Next Generation-Cryogenic cooled InfraRed Telescope (NG-CryoIRTel). The purpose of this study is to support the European and Japanese science community in defining a post-SPICA mission for the Cosmic Vision M5 call. Full details of the study can be found in this report.
Context. The European Space Agency Rosetta mission reached and started escorting its main target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, at the beginning of August 2014. Within the context of solar system small bodies, satellite searches from approaching spacecraft were extensively used in the past to study the nature of the visited bodies and their collisional environment.
Aims. During the approaching phase to the comet in July 2014, the OSIRIS instrument onboard Rosetta performed a campaign aimed at detecting objects in the vicinity of the comet nucleus and at measuring these objects' possible bound orbits. In addition to the scientific purpose, the search also focused on spacecraft security to avoid hazardous material in the comet's environment.
Methods. Images in the red spectral domain were acquired with the OSIRIS Narrow Angle Camera, when the spacecraft was at a distance between 5785 km and 5463 km to the comet, following an observational strategy tailored to maximize the scientific outcome. From the acquired images, sources were extracted and displayed to search for plausible displacements of all sources from image to image. After stars were identified, the remaining sources were thoroughly analyzed. To place constraints on the expected displacements of a potential satellite, we performed Monte Carlo simulations on the apparent motion of potential satellites within the Hill sphere.
Results. We found no unambiguous detections of objects larger than ~6 m within ~20 km and larger than ~1 m between ~20 km and ~110 km from the nucleus, using images with an exposure time of 0.14 s and 1.36 s, respectively. Our conclusions are consistent with independent works on dust grains in the comet coma and on boulders counting on the nucleus surface.
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Context. We investigate the dust coma within the Hill sphere of comet 67P/Churyumov-Gerasimenko.
Aims. We aim to determine osculating orbital elements for individual distinguishable but unresolved slow-moving grains in the vicinity of the nucleus. In addition, we perform photometry and constrain grain sizes.
Methods. We performed astrometry and photometry using images acquired by the OSIRIS Wide Angle Camera on the European Space Agency spacecraft Rosetta. Based on these measurements, we employed standard orbit determination and orbit improvement techniques.
Results. Orbital elements and effective diameters of four grains were constrained, but we were unable to uniquely determine them. Two of the grains have light curves that indicate grain rotation.
Conclusions. The four grains have diameters nominally in the range 0.14–0.50 m. For three of the grains, we found elliptic orbits, which is consistent with a cloud of bound particles around the nucleus. However, hyperbolic escape trajectories cannot be excluded for any of the grains, and for one grain this is the only known option. One grain may have originated from the surface shortly before observation. These results have possible implications for the understanding of the dispersal of the cloud of bound debris around comet nuclei, as well as for understanding the ejection of large grains far from the Sun.
The Microwave Instrument on the Rosetta Orbiter (MIRO) has been observing the coma of comet 67P/Churyumov-Gerasimenko almost continuously since June 2014 at wavelengths near 0.53 mm. We present here a map of the water column density in the inner coma (within 3 km from nucleus center) when the comet was at 3.4 AU from the Sun. Based on the analysis of the H216O and H218O (110-101) lines, we find that the column density can vary by two orders of magnitude in this region. The highest column density is observed in a narrow region on the dayside, close to the neck and north pole rotation axis of the nucleus, while the lowest column density is seen against the nightside of the nucleus where outgassing seems to be very low. We estimate that the outgassing pattern can be represented by a Gaussian distribution in a solid angle with FWHM ≈ 80°
Titan's polar surface is dotted with hundreds of lacustrine depressions. Based on the hypothesis that they are karstic in origin, we aim at determining the efficiency of surface dissolution as a landshaping process on Titan, in a comparative planetology perspective with the Earth as reference. Our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies. The model depends on the solubility of solids in liquids, the density of solids and liquids, and the average annual net rainfall rates. We compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over Titan and Earth timescales. We then investigate the denudation rates of a superficial organic layer in liquid methane over one Titan year. At this timescale, such a layer on Titan would behave like salts or carbonates on Earth depending on its composition, which means that dissolution processes would likely occur but would be 30 times slower on Titan compared to the Earth due to the seasonality of precipitation. Assuming an average depth of 100 m for Titan's lacustrine depressions, these could have developed in a few tens of millions of years at polar latitudes higher than 70°N and S, and a few hundreds of million years at lower polar latitudes. The ages determined are consistent with the youth of the surface (<1 Gyr) and the repartition of dissolution-related landforms on Titan.