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Solar System Debris Disk - S2D2 Solar System Debris Disk - S2D2 Image credit: NASA/JPL-Caltech Proposal for Science Themes of ESA's L2 and L3 Missions Ralf Srama Universität Stuttgart, Institut für Raumfahrtsysteme Raumfahrtzentrum Baden Württemberg Pfaffenwaldring 29, 70569 Stuttgart [email protected] Tel. +49 711 6856 2511, Fax +49 711 685 63596 http://www.irs.uni-stuttgart.de 2 Solar System Debris Disk - S2D2 Contributors Eberhard Grün, Max-Planck-Institut für Kernphysik, Heidelberg, Germany Alexander Krivov, Astrophysikalisches Institut, Univ. Jena, Germany Rachel Soja, Institut für Raumfahrtsysteme, Univ. Stuttgart, Germany Veerle Sterken, Institut für Raumfahrtsysteme, Univ. Stuttgart, Germany Zoltan Sternovsky, LASP, Univ. of Colorado, Boulder, USA. Supporters listed at http://www.dsi.uni-stuttgart.de/cosmicdust/missions/debrisdisk/index.html 3 Solar System Debris Disk - S2D2 Summary from direct observations of the parent bodies. The sizes of these parent bodies range from Understanding the conditions for planet Near Earth Asteroids with sizes of a few 10 m, formation is the primary theme of ESA's to km-sized comet nuclei, to over 1000 km- Cosmic Vision plan. Planets and left-over sized Trans-Neptunian Objects. The inner small solar system bodies are witnesses and zodiacal dust cloud has been probed by remote samples of the processing in different regions sensing instruments at visible and infrared of the protoplanetary disk. Small bodies fill the wavelengths, micro crater counts, in situ dust whole solar system from the surface of the analyzers, meteor observations and recent sun, to the fringes of the solar system, and to sample return missions. Nevertheless, the the neighboring stellar system. This is covered dynamical and compositional interrelations by the second theme of Cosmic Vision. between dust, interplanetary meteoroids, and Associated with the small bodies is a Debris their parent objects are still largely unknown. Disk of dust and meteoroids that are constantly No similar observations exist for the outer generated from the disintegration of their debris cloud. parent bodies due to a wide range of processes. An additional scientifically important In recent years the solar system is no longer population of dust is interstellar dust passing the only planetary system available to study. through the solar system. These grains are the An ever-growing number of extra-solar present day version of the raw material that planetary systems is being been discovered. was collected in the protoplanetary disk, Either the planets are seen directly, or the heated, mixed, and reassembled in effects of the planet on their central star or on planetesimals and planets. their environment are observed. Planets form To develop our understanding of in a protoplanetary disk from collapsing exoplanetary systems, we thus need to study interstellar material which is mixed and heated our own system. This requires two and, finally, condensed and agglomerated into complementary missions: planetesimals that accreted into planets. Material not consumed in planets remains in a · S2 : for the first time, we will have a 'bird's wide disk of planetesimals around the central eye view' of our inner debris disk in the star. infrared to examine the extent and fine Debris disks have been identified around a structure of the 'warm' zodical cloud, and significant fraction of main-sequence stars finally we may observe the 'cold' outer using the mid or far infrared excess in the Trans-Neptunian disk. spectral energy distribution of the stars. Debris disks are optically thin and mostly gas-free · D2 : an in-situ observations and sample disks of 1 µm to 100 µm-sized dust grains. return mission to probe the orbital and Such short-lived grains are continually compositional connection between the dust replenished through mutual collisions in a ring in the inner interplanetary debris disk and of unseen km-sized and bigger planetesimals. its source bodies, mapping the sky in dust. Most of the concepts required to explain This mission will provide a direct extra-solar debris disks have been developed comparison of the composition of from observations of our own solar system interstellar raw material with the more debris disk. However, the detailed processes processed material from comets and (the combination of planetary scattering and asteroids. collisional shattering) and the resulting large- The dynamical and compositional scale structure of this disk remain obscure. interrelations between dust, interplanetary Indeed, our own solar system has inner and meteoroids and their parent objects are still outer debris disks that are directly analogous largely unknown. The outer debris cloud of to those in exoplanetary systems. Moreover, our own solar system has not been observed in the best current models of the interplanetary the infrared so far, and exodisks harbor dust environment are not in agreement. unobserved planets or planetesimals, while Unlike extra-solar debris disks, knowledge their debris disks show clear features. By of the solar system debris disk comes mostly studying the interaction (compositionally and 4 Solar System Debris Disk - S2D2 dynamically) between dust and these parent 1. Introduction bodies, we learn about the exodisks as well as about our own solar system. To date, no 1.1. Extra solar debris disks compositional and density “map” exists of the debris disk of the Sun and the existing Debris disks were first discovered by IRAS meteoroid models do not provide reliable in 1984. Since then, a significant fraction of answers for meteoroid fluxes further away main-sequence stars have been found to harbor from the Sun as 1 AU. such disks. They are usually identified by the If we want to understand exoplanetary mid or far infrared excess in the spectral systems, we must start at "home". S2D2 will energy distribution of the stars (Wyatt 2008, shed light on all these questions by mapping Krivov 2010), which is interpreted as our solar system in dust, using the unique originating from cold dust located at tens to combination of in-situ dust measurements, hundreds of AU from the central star. Debris analyses of returned samples, and a bird’s eye disks consist largely of 100 µm to 1 mm-sized view for infrared observations of our outer dust grains, and are optically thin and mostly “home” debris disk and beyond. This will gas-free. provide links between interplanetary Circumstellar dust is short-lived because it meteoroids and their parent objects, teaching strongly interacts with the electromagnetic and us about hidden planetesimals in exodisk corpuscular radiation of the central star. debris clouds and much more. The wealth of Therefore, the mere existence of these disks is science return of a mission like S2 and D2 is evidence that dust-producing bigger objects large: S2D2 therefore covers nearly all topics are still present in mature stellar systems. of the first and second cosmic vision themes, Short-lived grains must be continually providing valuable information for astronomy, replenished by mutual collisions in a ring of exoplanet sciences, solar system formation, unseen km-sized and bigger planetesimals. planetary sciences, astrobiology and make Hence, debris disks are believed to be the human interplanetary spaceflight safer by aftermath of planet formation, and to have better understanding the meteoroid formed within this process. Even after planet environment. formation has long been completed, they continue to evolve collisionally and dynamically, are gravitationally sculptured by Science goals planets, and produce dust through ongoing −−− Determine the extent and fine collisional cascades. Therefore, debris disks structure of the solar system can serve as indicators of directly invisible debris disk small bodies and planets, and are tracers of −−− Establish the dynamical and their formation and evolution. They are an compositional relationships important component of planetary systems. The dust around almost all Vega-like stars between micrometeoroids and is so cold that it must be orbiting with semi- their parent bodies major axes of 50 AU or more from the central −−− Characterize similarities and star. Thus, the debris disks are mostly differences of micron to mm- considered analogs of the Sun’s Kuiper Belt. sized meteoroids flux The incidence rate of debris disks, about one- −−− Determine compositional fifth for solar-type stars, is roughly differences between interstellar, comparable to the frequency of exoplanet comet, and asteroid dust detections with current techniques (Eiroa et al. 2013). Several tens of extrasolar systems are −−− Link samples returned and known to harbor both planets and debris disks. analyzed to meteor streams and Spatially resolved images of about 70 debris parent objects disks have been obtained (Fig. 1); several of those possibly show the effects of planetary interactions. Gaps, clumps, warps, and sharp edges in the disks may indicate the existence of planets that sculpt these disks and are waiting to be discovered. 5 Solar System Debris Disk - S2D2 their parent bodies. In contrast, in the solar system we know the distribution of the source bodies, TNOs, comets and asteroids, but the link to their dust is still obscure (e.g., Vitense et al. 2012). Therefore, a deeper insight into the solar system debris disk and its interrelation with its parent objects will provide an important step towards the understanding of the formation of our own planetary system and of planetary systems in general. 1.2. Exploration of the solar system debris disk Figure 1. The Debris ring around Our own solar system debris disk must be Fomalhaut is located between about 130 observed using very different techniques. The and 160 AU from the star. The inset shows major difference is we must observe the dust the location of planet Fomalhaut b imaged from a location within the disk. We do have by Hubble Space Telescope's coronagraph. observations that define the disk itself – such The interrelation of the planet with the as zodiacal light and infrared observations. debris disk is still unclear. (NASA, ESA, However, we also have measurements of and P.
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