410 research outputs found
The Visible and Near Infrared module of EChO
The Visible and Near Infrared (VNIR) is one of the modules of EChO, the
Exoplanets Characterization Observatory proposed to ESA for an M-class mission.
EChO is aimed to observe planets while transiting by their suns. Then the
instrument had to be designed to assure a high efficiency over the whole
spectral range. In fact, it has to be able to observe stars with an apparent
magnitude Mv= 9-12 and to see contrasts of the order of 10-4 - 10-5 necessary
to reveal the characteristics of the atmospheres of the exoplanets under
investigation. VNIR is a spectrometer in a cross-dispersed configuration,
covering the 0.4-2.5 micron spectral range with a resolving power of about 330
and a field of view of 2 arcsec. It is functionally split into two channels
respectively working in the 0.4-1 and 1.0-2.5 micron spectral ranges. Such a
solution is imposed by the fact the light at short wavelengths has to be shared
with the EChO Fine Guiding System (FGS) devoted to the pointing of the stars
under observation. The spectrometer makes use of a HgCdTe detector of 512 by
512 pixels, 18 micron pitch and working at a temperature of 45K as the entire
VNIR optical bench. The instrument has been interfaced to the telescope optics
by two optical fibers, one per channel, to assure an easier coupling and an
easier colocation of the instrument inside the EChO optical bench.Comment: 26 page
Two-year observations of the Jupiter polar regions by JIRAM on board Juno
We observed the evolution of Jupiter's polar cyclonic structures over two years between February 2017 and February 2019, using polar observations by the Jovian InfraRed Auroral Mapper, JIRAM, on the Juno mission. Images and spectra were collected by the instrument in the 5‐μm wavelength range. The images were used to monitor the development of the cyclonic and anticyclonic structures at latitudes higher than 80° both in the northern and the southern hemispheres. Spectroscopic measurements were then used to monitor the abundances of the minor atmospheric constituents water vapor, ammonia, phosphine and germane in the polar regions, where the atmospheric optical depth is less than 1. Finally, we performed a comparative analysis with oceanic cyclones on Earth in an attempt to explain the spectral characteristics of the cyclonic structures we observe in Jupiter's polar atmosphere
Probing the origin of the dark material on Iapetus
Among the icy satellites of Saturn, Iapetus shows a striking dichotomy
between its leading and trailing hemispheres, the former being significantly
darker than the latter. Thanks to the VIMS imaging spectrometer on-board
Cassini, it is now possible to investigate the spectral features of the
satellites in Saturn system within a wider spectral range and with an enhanced
accuracy than with previously available data. In this work, we present an
application of the G-mode method to the high resolution, visible and near
infrared data of Phoebe, Iapetus and Hyperion collected by Cassini/VIMS, to
search for compositional correlations. We also present the results of a
dynamical study on the efficiency of Iapetus in capturing dust grains
travelling inward in Saturn system to evaluate the viability of
Poynting-Robertson drag as the physical mechanism transferring the dark
material to the satellite. The results of spectroscopic classification are used
jointly with the ones of the dynamical study to describe a plausible physical
scenario for the origin of Iapetus' dichotomy. Our work shows that mass
transfer from the outer Saturnian system is an efficient mechanism,
particularly for the range of sizes hypothesised for the particles composing
the newly discovered outer ring around Saturn. Both spectral and dynamical data
indicate Phoebe as the main source of the dark material. However, we suggest a
multi-source scenario where now extinct prograde satellites and the disruptive
impacts that generated the putative collisional families played a significant
role in supplying the original amount of dark material.Comment: 20 pages, 4 tables, 11 figures, major revision (manuscript extended
and completed, figures added and corrected, new results added), minor
revision and finalization of author list, moderate revision (update of the
manuscript following reviewer's feedback and discovery of the new Saturnian
outer ring
Saturn's icy satellites and rings investigated by Cassini - VIMS. III. Radial compositional variability
In the last few years Cassini-VIMS, the Visible and Infared Mapping
Spectrometer, returned to us a comprehensive view of the Saturn's icy
satellites and rings. After having analyzed the satellites' spectral properties
(Filacchione et al. (2007a)) and their distribution across the satellites'
hemispheres (Filacchione et al. (2010)), we proceed in this paper to
investigate the radial variability of icy satellites (principal and minor) and
main rings average spectral properties. This analysis is done by using 2,264
disk-integrated observations of the satellites and a 12x700 pixels-wide rings
radial mosaic acquired with a spatial resolution of about 125 km/pixel. The
comparative analysis of these data allows us to retrieve the amount of both
water ice and red contaminant materials distributed across Saturn's system and
the typical surface regolith grain sizes. These measurements highlight very
striking differences in the population here analyzed, which vary from the
almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to
the metal/organic-rich and red surfaces of Iapetus' leading hemisphere and
Phoebe. Rings spectra appear more red than the icy satellites in the visible
range but show more intense 1.5-2.0 micron band depths. The correlations among
spectral slopes, band depths, visual albedo and phase permit us to cluster the
saturnian population in different spectral classes which are detected not only
among the principal satellites and rings but among co-orbital minor moons as
well. Finally, we have applied Hapke's theory to retrieve the best spectral
fits to Saturn's inner regular satellites using the same methodology applied
previously for Rhea data discussed in Ciarniello et al. (2011).Comment: 44 pages, 27 figures, 7 tables. Submitted to Icaru
Gas emission investigation in small bodies: case of P67/Churyumov-Gerasimenko and Ceres
In the first close up to the comet P67/Churyumov-Gerasimenko at a heliocentric distance of about 3 AU, the Visible and Infrared Thermal Imaging spectrometer (VIRTIS) on board Rosetta observed the first jet emissions from the comet's surface. The emission intensity was quite weak, as the comet was still far from the Sun. However, we expect the comet's activity to increase very fast in the incoming months. Some images of the comet's nucleus show activity, which could be ascribed to volatiles sublimation, dust upwarding or instrumental stray light. We focused on those data showing possible jet emissions from the comet's nucleus, observed both in limb and nadir viewing geometries. In this work, we propose a method to correct for the stray light, and investigate the possible emission intensity radially distributed from the point of emission. We focus in particular on the gas wavelength regions where water vapor, hydroxyl and carbon monoxide species are expected. Data are also discussed in comparison with a simple model, able to describe how the hydroxyl emission intensities vary with the heliocentric distance. A lower limit to the hydroxyl detection with VIRTIS can be inferred at the moment, while a deeper analysis is expected on the data acquired when the comet will be closer to the Sun. Similarly, Ceres has showed hydroxyl emissions in the thermal IR observed from space. The present analysis can be extended to the case of this peculiar body, which is one of the targets of the Dawn mission. The research is supported by ASI (contract ASI-INAF I/062/08/0)
Thermal maps and properties of comet 67P as derived from Rosetta/VIRTIS data
After a 10-year cruise, the Rosetta
spacecraft began a close exploration of its main target,
comet 67P/Churyumov-Gerasimenko, in July 2014.
Since then, the Visible InfraRed Thermal Imaging
Spectrometer (VIRTIS) acquired hyperspectral
images of the comet’s surface with an unprecedented
spatial resolution. VIRTIS data are routinely used to
map the surface composition and to retrieve surface
temperatures on the dayside of the comet.
The thermal behavior of the surface of comet 67P
is related to composition and physical properties that
provide information about the nature and evolution of
those materials.
Here we present temperature maps of comet 67P
that were observed by Rosetta under different illumination conditions and different local solar times
Juno's Earth flyby: the Jovian infrared Auroral Mapper preliminary results
The Jovian InfraRed Auroral Mapper, JIRAM, is an image-spectrometer onboard the NASA Juno spacecraft flying to Jupiter. The instrument has been designed to study the aurora and the atmosphere of the planet in the spectral range 2-5 μm. The very first scientific observation taken with the instrument was at the Moon just before Juno's Earth fly-by occurred on October 9, 2013. The purpose was to check the instrument regular operation modes and to optimize the instrumental performances. The testing activity will be completed with pointing and a radiometric/spectral calibrations shortly after Jupiter Orbit Insertion. Then the reconstruction of some Moon infrared images, together with co-located spectra used to retrieve the lunar surface temperature, is a fundamental step in the instrument operation tuning. The main scope of this article is to serve as a reference to future users of the JIRAM datasets after public release with the NASA Planetary Data System
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