577 research outputs found
Titan's atmosphere as observed by Cassini/VIMS solar occultations: CH, CO and evidence for CH absorption
We present an analysis of the VIMS solar occultations dataset, which allows
us to extract vertically resolved information on the characteristics of Titan's
atmosphere between 100-700 km with a characteristic vertical resolution of 10
km. After a series of data treatment procedures, 4 occultations out of 10 are
retained. This sample covers different seasons and latitudes of Titan. The
transmittances show clearly the evolution of the haze and detect the detached
layer at 310 km in Sept. 2011 at mid-northern latitudes. Through the inversion
of the transmission spectra with a line-by-line radiative transfer code we
retrieve the vertical distribution of CH and CO mixing ratio. The two
methane bands at 1.4 and 1.7 {\mu}m are always in good agreement and yield an
average stratospheric abundance of %. This is significantly less
than the value of 1.48% obtained by the GCMS/Huygens instrument. The analysis
of the residual spectra after the inversion shows that there are additional
absorptions which affect a great part of the VIMS wavelength range. We
attribute many of these additional bands to gaseous ethane, whose near-infrared
spectrum is not well modeled yet. Ethane contributes significantly to the
strong absorption between 3.2-3.5 {\mu}m that was previously attributed only to
C-H stretching bands from aerosols. Ethane bands may affect the surface windows
too, especially at 2.7 {\mu}m. Other residual bands are generated by stretching
modes of C-H, C-C and C-N bonds. In addition to the C-H stretch from aliphatic
hydrocarbons at 3.4 {\mu}m, we detect a strong and narrow absorption at 3.28
{\mu}m which we tentatively attribute to the presence of PAHs in the
stratosphere. C-C and C-N stretching bands are possibly present between 4.3-4.5
{\mu}m. Finally, we obtain the CO mixing ratio between 70-170 km. The average
result of ppm is in good agreement with previous studies.Comment: 51 pages, 28 figure
First results from analysis of coordinated AVIRIS, TIMS, and ISM (French) data for the Ronda (Spain) and Beni Bousera (Morocco) peridotites
Ultramafic rocks are relatively rare at the Earth's surface but constitute the vast majority of the Earth by volume. Exposures of ultramafic bodies are therefore crucial for deducing many important processes that occur in the Earth's mantle. An important science question regarding the spatial distribution, abundance, and composition of mafic minerals in ultramafic bodies that can be examined with advanced sensor data is the melting process. When a lherzolite melts, clinopyroxene (cpx) melts first and therefore variations in the modal amount of cpx remaining in the mantle are a reflection of the amount of fractional melting that has occurred. Fe goes preferentially into the melt during melting but a 20 percent batch melting (i.e. closed system) acquires less Fe relative to 20 percent fractional melting (i.e. open system). Since the strength and wavelength of diagnostic absorptions is a strong function of Fe content, it is possible to make maps of the variation in Fe:Mg ratios which can be related to the general melting process. Accurate ground-truth information about local mineralogy provides internal calibration and consistency checks. Investigations using imaging spectrometer are very complementary to field studies because advanced sensor data can provide a synoptic view of modal mineralogy and chemical composition whereas field studies focus on detailed characterization of local areas. Two excellent exposures of ultramafic lithologies are being investigated with visible to mid-infrared imaging spectrometer data: the Ronda peridotite near Ronda, Spain and the Beni Bousera ophiolitic fragment in northern Morocco. Although separated by the Alboran Sea, these bodies are thought to be related and represent fertile sub-continental mantle. The Ronda peridotite is predominantly spinel lherzolite but grades into harzburgite and shows considerable variation in major and trace element compositions. Mafic layering and dykes (i.e. olivine gabbro) are also observed. This indicates some sections of the peridotite have experienced greater degrees of partial melting. The Beni Bousera peridotite also contains mafic layers and dykes and grades into harzburgite representing similar fundamental shifts in the bulk chemistry of this ultramafic body probably related to an episode of partial melting. The specific mode of emplacement of these bodies is controversial and important for understanding the tectonic evolution of this region. Our investigations are not necessarily designed to help resolve this controversy. Rather, these exposures provide excellent and unusual examples of fertile mantle which have undergone variable degrees of partial melting
Cartographie de la péridotite de Ronda (Espagne) par télédétection hyperspectrale : données AVIRIS
La péridotite de Ronda, au sud de l’Andalousie (Espagne), a été imagée par AVIRIS en 1991 et partiellement
échantillonnée par nous-même sur le terrain à l’aide d’un spectromètre GER 3700 en 1997 dans le but d’acquérir une
expérience dans le traitement des images hyperspectrales des surfaces planétaires à l’aide de sondes telle que ISM Phobos
(1989), OMEGA Mars Express (2003) and VIMS Cassini (2004). La haute résolution spectrale des images (224 canaux
répartis entre 400 et 2 455 nm) est nécessaire à la conduite d’une analyse géologique avec identification à distance
des faciès pétrologiques. Sur Terre, il est aussi nécessaire de déterminer les espèces végétales à cause de leur grande influence
sur la cartographie des faciès pétrologiques, même dans des régions relativement arides comme celle de la péridotite
de Ronda. Cependant, la péridotite de Ronda reste un bon site test.
L’image AVIRIS de Ronda est d’abord analysée par photo-interprétation. Des compositions colorées (affichées
sur les canaux rouge, vert et bleu visibles) sont construites Ă partir de 3 canaux visibles et/ou infrarouge choisis parmi
les 150 canaux utiles (le dernier détecteur AVIRIS ne fonctionnant pas en 1991). Ces compositions colorées permettant
de visualiser les principales caractĂ©ristiques gĂ©ologiques du visible Ă l’infrarouge, il est alors possible de les comparer Ă
des cartes géologiques, puis aux mesures de terrain de la campagne de juillet 1997. Cette analyse visuelle permet de distinguer
très facilement le massif de péridotite de ses roches avoisinantes (gneiss, marbres, grès et calcaires) ainsi que de
mettre en évidence une nette zonation en serpentine habituellement non cartographiée.
Ce travail faisant suite à celui de Chabrillat et al. [2000] nous avons pris le parti d’explorer une autre voie que
celle des analyses en composantes principales en cherchant à retirer couche par couche les différents éléments à l’origine
de la réponse spectrale de la péridotite de Ronda. Nous avons aussi pris le parti de ne nous fier qu’aux mesures de
terrain et de ne jamais avoir recours à des échantillons d’image pour effectuer des classifications car notre expérience du
terrain nous a clairement montré qu’aucun pixel n’était constitué d’une seule composante à 100 %
Frontiers of the physics of dense plasmas and planetary interiors: experiments, theory, applications
Recent developments of dynamic x-ray characterization experiments of dense
matter are reviewed, with particular emphasis on conditions relevant to
interiors of terrestrial and gas giant planets. These studies include
characterization of compressed states of matter in light elements by x-ray
scattering and imaging of shocked iron by radiography. Several applications of
this work are examined. These include the structure of massive "Super Earth"
terrestrial planets around other stars, the 40 known extrasolar gas giants with
measured masses and radii, and Jupiter itself, which serves as the benchmark
for giant planets.Comment: Accepted to Physics of Plasmas special issue. Review from
HEDP/HEDLA-08, April 12-15, 200
Titan Science with the James Webb Space Telescope (JWST)
The James Webb Space Telescope (JWST), scheduled for launch in 2018, is the
successor to the Hubble Space Telescope (HST) but with a significantly larger
aperture (6.5 m) and advanced instrumentation focusing on infrared science
(0.6-28.0 m ). In this paper we examine the potential for scientific
investigation of Titan using JWST, primarily with three of the four
instruments: NIRSpec, NIRCam and MIRI, noting that science with NIRISS will be
complementary. Five core scientific themes are identified: (i) surface (ii)
tropospheric clouds (iii) tropospheric gases (iv) stratospheric composition and
(v) stratospheric hazes. We discuss each theme in depth, including the
scientific purpose, capabilities and limitations of the instrument suite, and
suggested observing schemes. We pay particular attention to saturation, which
is a problem for all three instruments, but may be alleviated for NIRCam
through use of selecting small sub-arrays of the detectors - sufficient to
encompass Titan, but with significantly faster read-out times. We find that
JWST has very significant potential for advancing Titan science, with a
spectral resolution exceeding the Cassini instrument suite at near-infrared
wavelengths, and a spatial resolution exceeding HST at the same wavelengths. In
particular, JWST will be valuable for time-domain monitoring of Titan, given a
five to ten year expected lifetime for the observatory, for example monitoring
the seasonal appearance of clouds. JWST observations in the post-Cassini period
will complement those of other large facilities such as HST, ALMA, SOFIA and
next-generation ground-based telescopes (TMT, GMT, EELT).Comment: 50 pages, including 22 figures and 2 table
Super-Earths: A New Class of Planetary Bodies
Super-Earths, a class of planetary bodies with masses ranging from a few
Earth-masses to slightly smaller than Uranus, have recently found a special
place in the exoplanetary science. Being slightly larger than a typical
terrestrial planet, super-Earths may have physical and dynamical
characteristics similar to those of Earth whereas unlike terrestrial planets,
they are relatively easier to detect. Because of their sizes, super-Earths can
maintain moderate atmospheres and possibly dynamic interiors with plate
tectonics. They also seem to be more common around low-mass stars where the
habitable zone is in closer distances. This article presents a review of the
current state of research on super-Earths, and discusses the models of the
formation, dynamical evolution, and possible habitability of these objects.
Given the recent advances in detection techniques, the detectability of
super-Earths is also discussed, and a review of the prospects of their
detection in the habitable zones of low-mass stars is presented.Comment: A (non-technical) review of the literature on the current state
ofresearch on super-Earths. The topics include observation, formation,
dynamical evolution, habitability, composition, interior dynamics, magnetic
field, atmosphere, and propsect of detection. The article has 44 pages, 27
figures, and 203 references. It has been accepted for publication in the
journal Contemporary Physics (2011
Comparing HARPS and Kepler surveys: The alignment of multiple-planet systems
Aims. We study a subset of the planetary population characterized both by
HARPS and Kepler surveys. We compare the statistical properties of planets in
systems with m.sin i >5-10 M_Earth and R>2 R_Earth. If we assume that the
underlying population has the same characteristics, the different detection
sensitivity to the orbital inclination relative to the line of sight allows us
to probe the planets' mutual inclination.
Methods. We considered the frequency of systems with one, two and three
planets as dictated by HARPS data. We used Kepler's planetary period and host
mass and radii distributions (corrected from detection bias) to model planetary
systems in a simple yet physically plausible way. We then varied the mutual
inclination between planets in a system according to different prescriptions
(completely aligned, Rayleigh distributions and isotropic) and compared the
transit frequencies with one, two or three planets with those measured by
Kepler.
Results. The results show that the two datasets are compatible, a remarkable
result especially because there are no tunable knobs other than the assumed
inclination distribution. For m.sin i cutoffs of 7-10 M_Earth, which are those
expected to correspond to the radius cutoff of 2 R_Earth, we conclude that the
results are better described by a Rayleigh distribution with mode of 1 deg or
smaller. We show that the best-fit scenario only becomes a Rayleigh
distribution with mode of 5 deg if we assume a rather extreme mass-radius
relationship for the planetary population.
Conclusions. These results have important consequences for our understanding
of the role of several proposed formation and evolution mechanisms. They
confirm that planets are likely to have been formed in a disk and show that
most planetary systems evolve quietly without strong angular momentum exchanges
(abridged).Comment: 10 pages, 6 figures, 4 tables, accepted for publication in Astronomy
& Astrophysic
Cassini/VIMS hyperspectral observations of the HUYGENS landing site on Titan
Titan is one of the primary scientific objectives of the NASA ESA ASI Cassini
Huygens mission. Scattering by haze particles in Titan's atmosphere and
numerous methane absorptions dramatically veil Titan's surface in the visible
range, though it can be studied more easily in some narrow infrared windows.
The Visual and Infrared Mapping Spectrometer (VIMS) instrument onboard the
Cassini spacecraft successfully imaged its surface in the atmospheric windows,
taking hyperspectral images in the range 0.4 5.2 ?m. On 26 October (TA flyby)
and 13 December 2004 (TB flyby), the Cassini Huygens mission flew over Titan at
an altitude lower than 1200 km at closest approach. We report here on the
analysis of VIMS images of the Huygens landing site acquired at TA and TB, with
a spatial resolution ranging from 16 to14.4 km/pixel. The pure atmospheric
backscattering component is corrected by using both an empirical method and a
first-order theoretical model. Both approaches provide consistent results.
After the removal of scattering, ratio images reveal subtle surface
heterogeneities. A particularly contrasted structure appears in ratio images
involving the 1.59 and 2.03 ?m images north of the Huygens landing site.
Although pure water ice cannot be the only component exposed at Titan's
surface, this area is consistent with a local enrichment in exposed water ice
and seems to be consistent with DISR/Huygens images and spectra
interpretations. The images show also a morphological structure that can be
interpreted as a 150 km diameter impact crater with a central peak
- …