The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society.The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9-10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences.© N. Masoumzadeh et al. 2019OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany; the CISAS University of Padova, Italy; the Laboratoire d'Astrophysique de Marseille, France; the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain; the Research and Scientific Support Department of the ESA, Noordwijk, Netherlands; the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain; the Universidad Politechnica de Madrid, Spain; the Department of Physics and Astronomy of Uppsala University, Sweden; and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Operations Centre and the Rosetta Mission Operations Centre for the successful rendezvous with comet 67P/Churyumov-Gerasimenko. This research has made use of the USGS Integrated Software for Imagers and Spectrometers (ISIS). We gratefully acknowledge the developers of SPICE and NAIF/PDS resources. This research has made use of the scientific software shapeViewer www.comet-toolbox.com.L.K.acknowledges a support from the NASA SSW grant 80NSSC17K0731

Surface evolution of the Anhur region on comet 67P/Churyumov-Gerasimenko from high-resolution OSIRIS images

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The southern hemisphere of comet 67P/Churyumov-Gerasimenko (67P) became observable by the Rosetta mission in March 2015, a few months before cometary southern vernal equinox. The Anhur region in the southern part of the comet's larger lobe was found to be highly eroded, enriched in volatiles, and highly active. Aims. We analyze high-resolution images of the Anhur region pre- and post-perihelion acquired by the OSIRIS imaging system on board the Rosetta mission. The Narrow Angle Camera is particularly useful for studying the evolution in Anhur in terms of morphological changes and color variations. Methods. Radiance factor images processed by the OSIRIS pipeline were coregistered, reprojected onto the 3D shape model of the comet, and corrected for the illumination conditions. Results. We find a number of morphological changes in the Anhur region that are related to formation of new scarps; removal of dust coatings; localized resurfacing in some areas, including boulders displacements; and vanishing structures, which implies localized mass loss that we estimate to be higher than 50 million kg. The strongest changes took place in and nearby the Anhur canyon-like structure, where significant dust cover was removed, an entire structure vanished, and many boulders were rearranged. All such changes are potentially associated with one of the most intense outbursts registered by Rosetta during its observations, which occurred one day before perihelion passage. Moreover, in the niche at the foot of a new observed scarp, we also see evidence of water ice exposure that persisted for at least six months. The abundance of water ice, evaluated from a linear mixing model, is relatively high (>20%). Our results confirm that the Anhur region is volatile-rich and probably is the area on 67P with the most pristine exposures near perihelion.© S. Fornasier et al. 2019OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Goettingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. SF acknowledges the financial support from the France Agence Nationale de la Recherche (programme Classy, ANR-17-CE31-0004). The authors thank Dr. E. Howell for her comments and suggestions which helped us to improve this article

Regional unit definition for the nucleus of comet 67P/Churyumov-Gerasimenko on the SHAP7 model

Open Acces publication. This article is available under the Creative Commons CC-BY-NC-ND license and permits non-commercial use of the work as published, without adaptation or alteration provided the work is fully attributed.The previously defined regions on the nucleus of comet 67P/Churyumov-Gerasimenko have been mapped back onto the 3D SHAP7 model of the nucleus (Preusker et al., 2017). The resulting regional definition is therefore self-consistent with boundaries that are well defined in 3 dimensions. The facets belonging to each region are provided as supplementary material. The shape model has then been used to assess inhomogeneity of nucleus surface morphology within individual regions. Several regions show diverse morphology. We propose sub-division of these regions into clearly identifiable units (sub-regions) and a comprehensive table is provided. The surface areas of each sub-region have been computed and statistics based on grouping of unit types are provided. The roughness of each region is also provided in a quantitative manner using a technique derived from computer graphics applications. The quantitative method supports the sub-region definition by showing that differences between sub-regions can be numerically justified.© 2018 The AuthorsThe team from the University of Bern is supported through the Swiss National Science Foundation and through the NCCR PlanetS. The project has also received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 686709. This work was supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 16.0008-2

Models of Rosetta/OSIRIS 67P Dust Coma Phase Function

The phase function of the dust coma of comet 67P has been determined from Rosetta/OSIRIS images. This function shows a deep minimum at phase angles near 100°, and a strong backscattering enhancement. These two properties cannot be reproduced by regular models of cometary dust, most of them based on wavelength-sized and randomly oriented aggregate particles. We show, however, that an ensemble of oriented elongated particles of a wide variety of aspect ratios, with radii r 10 μm, and whose long axes are perpendicular to the direction of the solar radiation, are capable of reproducing the observed phase function. These particles must be absorbing, with an imaginary part of the refractive index of about 0.1 to match the expected geometric albedo, and with porosity in the 60%-70% range.© 2018. The American Astronomical Society. All rights reserved..OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, in Gottingen, Germany, CISAS-University of Padova, Italy, the Laboratoire dAstrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politecnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB; grant No. 74/10: 2), and the ESA Technical Directorate is gratefully acknowledged. H.R. was also supported by grant No. 2011/01/B/ST9/05442 of the Polish National Science Center. We thank the ESA teams at ESAC, ESOC, and ESTEC for their work in support of the Rosetta mission We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC, and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. This work was supported by contracts AYA2015-67152-R and AYA2015-71975-REDT from the Spanish Ministerio de Economia y Competitividad

Solar parameters for modeling interplanetary background

The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE) Working Team of the International Space Science Institute in Bern, Switzerland, was to establish a common calibration of various UV and EUV heliospheric observations, both spectroscopic and photometric. Realization of this goal required an up-to-date model of spatial distribution of neutral interstellar hydrogen in the heliosphere, and to that end, a credible model of the radiation pressure and ionization processes was needed. This chapter describes the solar factors shaping the distribution of neutral interstellar H in the heliosphere. Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant radiation pressure force acting on neutral H atoms in the heliosphere, solar EUV radiation and the photoionization of heliospheric hydrogen, and their evolution in time and the still hypothetical variation with heliolatitude. Further, solar wind and its evolution with solar activity is presented in the context of the charge exchange ionization of heliospheric hydrogen, and in the context of dynamic pressure variations. Also the electron ionization and its variation with time, heliolatitude, and solar distance is presented. After a review of all of those topics, we present an interim model of solar wind and the other solar factors based on up-to-date in situ and remote sensing observations of solar wind. Results of this effort will further be utilised to improve on the model of solar wind evolution, which will be an invaluable asset in all heliospheric measurements, including, among others, the observations of Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).Comment: Chapter 2 in the planned "Cross-Calibration of Past and Present Far UV Spectra of Solar System Objects and the Heliosphere", ISSI Scientific Report No 12, ed. R.M. Bonnet, E. Quemerais, M. Snow, Springe

Heliolatitude and time variations of solar wind structure from in situ measurements and interplanetary scintillation observations

The 3D structure of solar wind and its evolution in time is needed for heliospheric modeling and interpretation of energetic neutral atoms observations. We present a model to retrieve the solar wind structure in heliolatitude and time using all available and complementary data sources. We determine the heliolatitude structure of solar wind speed on a yearly time grid over the past 1.5 solar cycles based on remote-sensing observations of interplanetary scintillations, in situ out-of-ecliptic measurements from Ulysses, and in situ in-ecliptic measurements from the OMNI-2 database. Since the in situ information on the solar wind density structure out of ecliptic is not available apart from the Ulysses data, we derive correlation formulae between solar wind speed and density and use the information on the solar wind speed from interplanetary scintillation observations to retrieve the 3D structure of solar wind density. With the variations of solar wind density and speed in time and heliolatitude available we calculate variations in solar wind flux, dynamic pressure and charge exchange rate in the approximation of stationary H atoms.Comment: Accepted for publication in Solar Physic

Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere

Evidence of sub-surface energy storage in comet 67P from the outburst of 2016 July 03

On 2016 July 03, several instruments onboard ESA's Rosetta spacecraft detected signs of an outburst event on comet 67P, at a heliocentric distance of 3.32 au from the Sun, outbound from perihelion. We here report on the inferred properties of the ejected dust and the surface change at the site of the outburst. The activity coincided with the local sunrise and continued over a time interval of 14-68 min. It left a 10-m-sized icy patch on the surface. The ejected material comprised refractory grains of several hundred microns in size, and sub-micron-sized water ice grains. The high dust mass production rate is incompatible with the free sublimation of crystalline water ice under solar illumination as the only acceleration process. Additional energy stored near the surface must have increased the gas density. We suggest a pressurized sub-surface gas reservoir, or the crystallization of amorphous water ice as possible causes.© 2015 The Authors.The support of the national funding agencies of Germany (DLR, grant 50 QP 1302), France (CNES), Austria, Finland and the ESA Technical Directorate is gratefully acknowledged.Peer Reviewe