The gas and dust coma of Comet C/1999 H1 (Lee)

The final version is available at: http://www.aanda.orgComet Lee (C/1999 H1) was observed on June 6, 1999 when it was at rh = 0.98 AU and Δ = 1.195 AU. The spectrophotometric observations, between 0.6 and 1 μm, were aimed at the detection of the CI(1D) doublet λλ 9823/9850 Å. The non-detection of these lines, with a 3σ flux upper limit of the order of 4.6 × 10−17 erg cm−2 s−1, confirms the CO depletion already noted by other authors. Several CN and NH2 emission bands lie in that spectral range, making it possible to derive production rates for both species as ∼3.1 × 1026 s−1 and 1.2 × 1027 s−1, respectively. The oxygen forbidden line at 6300 Å was used to obtain QH2O = (1.22 ± 0.7) × 1029 s−1. Assuming that CN and NH2 are directly produced by HCN and NH3, Comet Lee has a HCN/H2O ≈ 0.25% and NH3/H2O ≈ 1% at rh = 0.98 AU, in reasonable agreement with what has been found in other long-period comets. The structural analysis carried out on cometary images acquired with broad band R Bessel filter clearly displays two pairs of ion rays likely produced by the H2O+ doublet at 6198 and 6200 Å, wavelengths covered by the bandpass filter. Identical features are found in the images acquired with the Gunn i filter. The dust brightness profiles in the east-west direction do not deviate from a ρ−m law (with 0.7 < m ≤ 1.2) as expected for a steady state model coma with a constant dust production rate and expanding at constant velocity. The dust production rate, as obtained from the A f ρ parameter, is ∼500 cm, which compared with the gas production rate classifies this comet as a dust poor one with relatively high (6.5–11.7) gas-to-dust mass ratio. Analysis of the normalized reflectivity gradient (i.e. continuum color) as a function of ρ indicates a slight reddening of the solid component in the coma at large cometocentric distances, whereas the average dust color within an aperture of 20 000 km, centered at the nucleus, is ∼9% per 1000 Å. Mie scattering computations applied to an ensemble of particles indicate that the dust coma is haracterised by a relative broad size distribution with a typical mean size of 1 μm. These grains might be composed of a mixture of silicates and icy material.Peer reviewe

Marco Polo - a mission to return a sample from a Near-Earth Object - science requirements and operational scenarios

Marco Polo is a mission to return a sample from a Near-Earth Object of primitive type (class C or D). It is foreseen as a collaborative effort between the Japanese Space Agency (JAXA) and the European Space Agency (ESA). Marco Polo is currently in a Phase-A study. This paper focuses on the scientific requirements provided to the industrial study consortia in Europe as well as the possible mission scenario at the target object in order to achieve the overall mission science objectives. The main scientific reasons for going to a Near-Earth Object are to understand the initial conditions and evolution history of the solar nebula, to understand how major events (e.g. agglomeration, heating) influence the history of planetesimals, whether primitive class objects contain presolar material, what the organics were in primitive materials, how organics could shed light on the origin of molecules necessary for life, and what the role of impacts by NEOs would be in the origin and evolution of life on Earth

TNOs are cool: a survey of the transneptunian region

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well

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

A numerical model of cometary dust structures

Aims: The purpose of this study is to test our numerical model of cometary dust coma structures and to use the results to infer information about the nucleus surface activity of comet 9P/Tempel 1. Methods: Parameters on the activity were first estimated from simulations of ground-based observation acquired during the pre-perihelion period (January to June 2005) and compared with published results for the same period. The parameters retrieved were then used to simulate previously unpublished images of the comet acquired during the post-perihelion period (in July and August 2005). Results: Our model was able to retrieve the spin axis orientation of comet 9P/Tempel 1 as well as information on active regions at the surface of the nucleus. We could localize at least six active areas and characterize them with parameters such as the velocity of the dust particles, grain size, and activity profile. Our model confirms published results from spacecraft measurements but is also able to make realistic predictions on the evolution of the coma morphology during the post-perihelion period.Peer reviewe

The gas and dust coma of Comet C/1999 H1 (Lee)

The final version is available at: http://www.aanda.orgComet Lee (C/1999 H1) was observed on June 6, 1999 when it was at rh = 0.98 AU and Δ = 1.195 AU. The spectrophotometric observations, between 0.6 and 1 μm, were aimed at the detection of the CI(1D) doublet λλ 9823/9850 Å. The non-detection of these lines, with a 3σ flux upper limit of the order of 4.6 × 10−17 erg cm−2 s−1, confirms the CO depletion already noted by other authors. Several CN and NH2 emission bands lie in that spectral range, making it possible to derive production rates for both species as ∼3.1 × 1026 s−1 and 1.2 × 1027 s−1, respectively. The oxygen forbidden line at 6300 Å was used to obtain QH2O = (1.22 ± 0.7) × 1029 s−1. Assuming that CN and NH2 are directly produced by HCN and NH3, Comet Lee has a HCN/H2O ≈ 0.25% and NH3/H2O ≈ 1% at rh = 0.98 AU, in reasonable agreement with what has been found in other long-period comets. The structural analysis carried out on cometary images acquired with broad band R Bessel filter clearly displays two pairs of ion rays likely produced by the H2O+ doublet at 6198 and 6200 Å, wavelengths covered by the bandpass filter. Identical features are found in the images acquired with the Gunn i filter. The dust brightness profiles in the east-west direction do not deviate from a ρ−m law (with 0.7 < m ≤ 1.2) as expected for a steady state model coma with a constant dust production rate and expanding at constant velocity. The dust production rate, as obtained from the A f ρ parameter, is ∼500 cm, which compared with the gas production rate classifies this comet as a dust poor one with relatively high (6.5–11.7) gas-to-dust mass ratio. Analysis of the normalized reflectivity gradient (i.e. continuum color) as a function of ρ indicates a slight reddening of the solid component in the coma at large cometocentric distances, whereas the average dust color within an aperture of 20 000 km, centered at the nucleus, is ∼9% per 1000 Å. Mie scattering computations applied to an ensemble of particles indicate that the dust coma is haracterised by a relative broad size distribution with a typical mean size of 1 μm. These grains might be composed of a mixture of silicates and icy material.Peer reviewe

Coma Structures in Comet 73P/Schwassmann-Wachmann 3, Components B and C, Between January and May 2006

The Jupiter family comet 73P/Schwassmann-Wachmann 3 has been widely observed since 1995 after a nucleus break-up event produced at least five components labeled 73P-A to E. During the 2006 appearance, two of them (B and C) showed very strong coma activity. Our R-filter imaging of 73P-B & C from 21 January to 25 May 2006 revealed the presence of fan-like structures in the comae of both components and evidence for further fragmentation events in component B. As of early April 2006, component C showed two jets emanating from the nucleus, with one continuously visible. Through a simulation of the orbital geometry we infer that the rotation axis of 73P-C has an inclination of 20 to the orbital plane and a longitude of 45 at perihelion. The coma activity of component B was highly variable, displaying signatures of at least 3 fragmentation events. The coma was characterized by the continuous presence of a jet roughly in sunward direction, starting from the beginning of May. The first fragmentation event of component B may have happened between April 16 and April 26, leading to the presence of at least 6 fragments detected in images of May 2. The second one happened on or shortly before May 8, the third one between May 18 and 24. For the rotation axis of 73P-B we infer an inclination of 5 –15 to the orbital plane and a longitude of 20 –30 at perihelion.Peer reviewe

Marco Polo - A Mission to Return a Sample from a Near-Earth Object - Science Requirements and Operational Scenarios

International audienceMarco Polo is a mission to return a sample from a near-Earth object of primitive type (class C or D). It is foreseen as a collaborative effort between the Japan Aerospace Exploration Agency (JAXA) and the European Space Agency (ESA). Marco Polo is currently in a Phase-A study (status as of summer 2009). This paper focuses on the scientific requirements provided to the industrial study consortia in Europe as well as the possible mission scenario at the target object in order to achieve the overall mission science objectives. The main scientific reasons for going to a near-Earth object are to understand the initial conditions and evolution history of the solar nebula, to understand how major events (e.g. agglomeration, heating) influence the history of planetesimals, whether primitive class objects contain presolar material, what the organics were in primitive materials, how organics could shed light on the origin of molecules necessary for life, and what the role of impacts by NEOs would be in the origin and evolution of life on Earth