The SSDC contribution to the improvement of knowledge by means of 3D data projections of minor bodies

The latest developments of planetary exploration missions devoted to minor bodies required new solutions to correctly visualize and analyse data acquired over irregularly shaped bodies. ASI Space Science Data Center (SSDC-ASI, formerly ASDC-ASI Science Data Center) worked on this task since early 2013, when started developing the web tool MATISSE (Multi-purpose Advanced Tool for the Instruments of the Solar System Exploration) mainly focused on the Rosetta/ESA space mission data. In order to visualize very high-resolution shape models, MATISSE uses a Python module (vtpMaker), which can also be launched as a stand-alone command-line software. MATISSE and vtpMaker are part of the SSDC contribution to the new challenges imposed by the "orbital exploration" of minor bodies: 1) MATISSE allows to search for specific observations inside datasets and then analyse them in parallel, providing high-level outputs; 2) the 3D capabilities of both tools are critical in inferring information otherwise difficult to retrieve for non-spherical targets and, as in the case for the GIADA instrument onboard Rosetta, to visualize data related to the coma. New tasks and features adding valuable capabilities to the minor bodies SSDC tools are planned for the near future thanks to new collaborations

Error analysis for retrieval of Venus' IR surface emissivity from VIRTIS/VEX measurements

Venus' surface emissivity data in the infrared can serve to explore the planet's geology. The only global data with high spectral, spatial, and temporal resolution and coverage at present is supplied by nightside emission measurements acquired by the Visible and InfraRed Thermal Imaging Spectrometer VIRTIS-M-IR (1.0-5.1 μm) aboard ESA's Venus Express. A radiative transfer simulation and a retrieval algorithm can be used to determine surface emissivity in the nightside spectral transparency windows located at 1.02, 1.10, and 1.18 μm. To obtain satisfactory fits to measured spectra, the retrieval pipeline also determines auxiliary parameters describing cloud properties from a certain spectral range. But spectral information content is limited, and emissivity is difficult to retrieve due to strong interferences from other parameters. Based on a selection of representative synthetic VIRTIS-M-IR spectra in the range 1.0-2.3 μm, this paper investigates emissivity retrieval errors that can be caused by interferences of atmospheric and surface parameters, by measurement noise, and by a priori data, and which retrieval pipeline leads to minimal errors. Retrieval of emissivity from a single spectrum is shown to fail due to extremely large errors, although the fits to the reference spectra are very good. Neglecting geologic activity, it is suggested to apply a multi-spectrum retrieval technique to retrieve emissivity relative to an initial value as a parameter that is common to several measured spectra that cover the same surface bin. Retrieved emissivity maps of targets with limited extension (a few thousand km) are then additively renormalized to remove spatially large scale deviations from the true emissivity map that are due to spatially slowly varying interfering parameters. Corresponding multi-spectrum retrieval errors are estimated by a statistical scaling of the single-spectrum retrieval errors and are listed for 25 measurement repetitions. For the best of the studied retrieval pipelines, temporally varying interfering atmospheric parameters (cloud parameters, minor gas abundances) contribute errors in the order of 3%-10% of the true emissivity, depending on the surface window, the reference spectrum, and assuming statistical independence of the parameters. Temporally constant interfering parameters that spatially vary on a scale of 100 km (surface elevation, interfering emissivities) add 9%-16%. Measurement noise with a standard deviation of 10e-4 W/(m2 sr μm) leads to additional 1%-4%. Reasonable modifications of a priori mean values have negligible impacts. Retrieved maps are most reliable at 1.02 μm. There is an overall tendency for better results for cases with small cloud opacity, high surface elevation, high emissivity, and small observation angle, but this depends on the emissivity window, retrieval pipeline, and measurement repetition number. Calibration, preprocessing, and simulation errors can lead to additional errors. Based on the presented results, a subsequent paper will discuss emissivity data retrieval for a selected surface target

Characterization of the dynamics of the atmosphere of Venus with doppler velocimetry

Tese de doutoramento (co-tutela), Astronomia e Astrofísica, Observatoire de Paris, Universidade de Lisboa, 2013Currently the study of the Venus’ atmosphere grows as a theme of major interest among the astrophysics scientific community. The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. This work participates in the international effort to characterize the atmospheric dynamics of this planet in coordination with orbiter missions, in particular with Venus Express. The objectives of this study are to investigate the nature of the processes governing the super-rotation of the atmosphere of Venus using ground-based observations, thereby complementing measurements by orbiter instruments.This thesis analyzes observations of Venus made with two different instruments and Doppler velocimetry techniques.The first part of the thesis presents ground-based Doppler velocimetry measurements of the zonal winds based on observations carried out with the Ultraviolet and Visual Echelle Spectrograph at ESO’s Very Large Telescope. Using Doppler-shifted Fraunhofer lines from the solar spectrum, this high resolution spectrograph (R 100,000) allows to measure the velocity of Venus’ upper cloud layer with a precision of about 5 ms1. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the observations’ high spatial resolution, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. Mean zonal wind amplitudes were measured between 106 21 and 127 14 ms1 at latitudes between 18 N and 34 S, with the zonal wind being approximately uniform in 2:6 -wide latitude bands (0:3” at disk center).The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time (longitude) and in latitude. Near 50 the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by 10 ms1. Small scale wind variations with local time are also present at low and mid-latitudes (Machado et al., 2012).The second part of the thesis presents results of Venus’ mesospheric winds at cloud top level, based on ground-based Doppler velocimetry of cloud-top winds and inter comparison of cloud tracking measurements from the Venus Express spacecraft.Doppler wind velocimetry obtained with the 3.60 m Canada-France-Hawaii telescope (CFHT) and the visible spectrograph ESPaDOnS in February 2011 consisted of high-resolution spectra of Fraunhofer lines in the visible range to measure the wind velocity using the Doppler shift of solar radiation scattered by cloud top particles in the observer’s direction (Widemann et al., 2007, 2008; Machado et al., 2013). The complete optical spectrum was collected at a phase angle = (68:7 0:3) , at a resolution of about 80,000. The obtained ground-based measurements on Venus are compared with simultaneous observations using the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument from the VEx orbiter. CFHT observations included various points of the dayside hemisphere observed at a phase angle of 67 from CFHT, between +10 N and 60 S, by steps of 10 , and from sub-Earth longitude [ E ] = 0 to -50 corresponding to 7:30a - 10:50a, while VIRTIS-M UV (0.38 m) cloud tracking measurements extended on the dayside south hemisphere between 30 and 50 S and 9:05a - 10:50a at simultaneous spacecraft orbit VV1786. Doppler wind retrievals using either 1- or 2-wind circulation regimes are in good agreement with measurements based on cloud tracking from Venus Express.Were observed zonal wind field variations in the latitudinal and temporal scales within stable mean background velocities of vz = 117.35 18.0 ms1 on Feb. 19, and vz = 117.5 14.5 ms1 on Feb. 21, respectively. It is presented the first unambiguous detection from the ground of a poleward meridional wind flow on the morning dayside hemisphere, of 18.8 11.5 ms1 on Feb. 19, and 19.0 8.3 ms1 on Feb. 21. Wind temporal, local variation at the hour-scale of 18.5 ms1 were detected near morning terminator at low latitude. To provide the best description of the wind field observed, the retrieved results were compared to a series of wind circulation models and their characterization at cloud top level.The data analysis technique allowed an unambiguous characterization of the zonal wind latitudinal profile and its temporal variability, as well as an investigation of large-scale planetary waves signature and their role in the maintenance of the zonal super-rotation, and suggest that detection and investigation of large-scale planetary waves can be carried out with this technique.These studies complement the independent observations of the european space mission Venus Express, in particular as regards the study of atmospheric super-rotation, meridional flow and its variability.Fundação para a Ciência e a Tecnologia (FCT, PhD grant SFRH/BD/66473/2009

Planetary atmospheres : From Solar System to exoplanets : atmospheric characterization and search for chemical disequilibrium compounds

This thesis is based on an ambitious challenge: to provide useful tools in the study and characterization of planetary atmospheres, from the Solar System to exoplanets. There are four steps in the field of planetary atmospheres. Studying Earth’ atmosphere is the first step. The second is the study of Venus’ atmosphere, essential in our understanding of the origin and mechanisms that drive the superrotational atmosphere, the differences between Venus and Earth’s atmosphere and their evolution and what differentiates an Earth-like from a Venus-like exoplanets and how to model and characterize them. The Venus’ cloud-top (70 km) wind results presented in this thesis were retrieved using two techniques: 1) ground-based Doppler Velocimetry (DV), using visible high-resolution spectroscopy (CFHT/ESPaDOnS and TNG/HARPS-N observations) 2) space-based Cloud-Tracking (CT) using UV and visible imaging (VenusExpress/VIRTIS and Akatsuki/UVI observations). The most complete and precise meridional wind profile ever retrieved was based on HARPS-N observations from Gonçalves et al. (2020). Our team has also retrieved zonal wind velocities from Venus’ lower cloud deck (48 km), night-side, using CT on ground-based observations at the TNG/NICS, yielding results consistent with the data provided by space observations. The third and fourth steps of planetary atmospheres study would be the Solar System’s and exoplanet’s atmospheres, respectively. Our team is currently adapting the DV method to measure horizontal winds from Mars, Jupiter and Saturn’s atmospheres. We are also leading ESA’s space mission ARIEL scientific working group “Synergies with Solar System”. Our expertise on SS atmospheres is highly valuable in the context of building a bridge between SS and exoplanets. We are developing a tool that provides an average spectra (point source) using comprehensive coverage data of different SS planets (Venus, Jupiter and Saturn) yielding a proxy of how we would see if those were exoplanets at a chosen distance from Earth

The Venus Emissivity Mapper ─ Obtaining Global Mineralogy of Venus from Orbit on the ESA EnVision and NASA VERITAS missions to Venus.

International audienc

Understanding physical and dynamical processes in the atmosphere of the Solar System planets with ground and space based observations

The plan which gave purpose to this thesis was purposefully ambitious. Instead of focus-sing on a single theme, we chose to follow a path that would ultimately lead to a greater overall understanding of several ongoing processes within the atmospheres of planets in the Solar System. Our goal was to combine different techniques in a single project so that by the end of this PhD, not only did the candidate obtain valuable results and a worthy contribution to the scientific community, but also became proficient in multiple ways to study planetary atmospheres. With images from multiple spacecraft, we employed the Cloud-Tracking technique to study the winds on multiple layers of Venus’cloud deck, and at the tropospheric level of Jupiter’s atmosphere. We used the most modern instruments such as those on board the japanese Akatsuki mission, retrieving multiple wind profiles to study the variability and evolution of the atmosphere across several altitude layers. Along with capturing winds, we set out to gather the most complete survey of atmospheric gravity waves on the lower clouds of Venus. This effort will help not only to understand their role in powering su-perrotation but also provide general circulation models valuable data on this previously under-explored feature. From the ground we performed a unique Doppler velocimetry method to complement our analysis, proving that the wind results obtained from this method can be competitive with those gathered from spacecraft data at significantly lower costs and greater flexibility. The capabilities of the team in which I am inserted have enabled multiple collaborations on other projects, further reinforcing that science is a joint effort. In this document, I attempt to provide further proof that my contribution is not only to academia but the larger society as well.Instituto de Astrofísica e Ciências do EspaçoPrograma de Bolsas de Doutoramento da Universidade de Lisbo

Venus Atmospheric Thermal Structure and Radiative Balance

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Dynamics of Venus' atmosphere: wind characterization with Doppler velocimetry

Tese de mestrado Física (Astrofísica e Cosmologia) Universidade de Lisboa, Faculdade de Ciências, 2016The most relevant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A full characterization of the zonal winds is crucial to understand this movement and the mechanisms that maintain it. This thesis analyzes data from coordinated wind amplitude and variability measurements at Venus cloud-tops based on the two complementary techniques of Ground-based Doppler velocimetry(Widemann etal., 2007, 2008; Machado etal., 2012, 2014), using the ESPaDOnS instrument (Echelle SpectroPolarimetric Device for the Observation of Stars) at CFHT(Canada France Hawaii Telescope),and cloud-tracked winds using ESA Venus Express/VIRTIS- M (Visible and Infrared Thermal Imaging Spectrometer) imagingat0.38 µm (Drossart etal., 2007; Sánchez-Lavega etal., 2008; ?; Machado etal., 2014). We performed a new coordinated campaign in April 2014 combining both Venus Express observations and ground-based Doppler wind measurements on the dayside of Venus'cloud tops at CFHT at a phase angle ϕ =(76±0:3)ᵒ. The analysis and results show (1) additional confirmation of the complementarity, on both spatial and temporal time scales, of the two techniques ;(2) evidence of a symmetrical, poleward meridional Hadley flow in both hemispheres of vm = 22.5±15.5 ms1; (3) spatial and temporal variability of the zonal flow with latitude and local time, with a significant increase of wind amplitude near morning terminator already reported in Feb.2011observations. This work complements the independent observations of the european space mission Venus Express and is part of the effort made by the scientific community in the area of planetology to understand the dynamics of the atmosphere of Venus