832 research outputs found
Planetary internal structures
This chapter reviews the most recent advancements on the topic of terrestrial
and giant planet interiors, including Solar System and extrasolar objects.
Starting from an observed mass-radius diagram for known planets in the
Universe, we will discuss the various types of planets appearing in this
diagram and describe internal structures for each type. The review will
summarize the status of theoretical and experimental works performed in the
field of equation of states (EOS) for materials relevant to planetary interiors
and will address the main theoretical and experimental uncertainties and
challenges. It will discuss the impact of new EOS on interior structures and
bulk composition determination. We will discuss important dynamical processes
which strongly impact the interior and evolutionary properties of planets (e.g
plate tectonics, semiconvection) and describe non standard models recently
suggested for our giant planets. We will address the case of short-period,
strongly irradiated exoplanets and critically analyse some of the physical
mechanisms which have been suggested to explain their anomalously large radius.Comment: 24 pages, 8 figures, Accepted for publication as a chapter in
Protostars and Planets VI, University of Arizona Press (2014), eds. H.
Beuther, R. Klessen, C. Dullemond, Th. Henning.
A New Family of Planets ? "Ocean Planets"
A new family of planets is considered which is between rochy terrestrial
planets and gaseous giant ones: "Ocean-Planets". We present the possible
formation, composition and internal models of these putative planets, including
that of their ocean, as well as their possible Exobiology interest. These
planets should be detectable by planet detection missions such as Eddington and
Kepler, and possibly COROT (lauch scheduled in 2006). They would be ideal
targets for spectroscopic missions such as Darwin/TPF.Comment: 15 pages, 3 figures submitted to Icarus notes (10 july 2003
Thermal evolution and lifetime of intrinsic magnetic fields of Super Earths in habitable zones
We have numerically studied the thermal evolution of various-mass terrestrial
planets in habitable zones, focusing on duration of dynamo activity to generate
their intrinsic magnetic fields, which may be one of key factors in
habitability on the planets. In particular, we are concerned with super-Earths,
observations of which are rapidly developing. We calculated evolution of
temperature distributions in planetary interior, using Vinet equations of
state, Arrhenius-type formula for mantle viscosity, and the astrophysical
mixing length theory for convective heat transfer modified for mantle
convection. After calibrating the model with terrestrial planets in the Solar
system, we apply it for 0.1-- rocky planets with surface
temperature of 300~\mbox{K} (in habitable zones) and the Earth-like
compositions. With the criterion for heat flux at the CMB (core-mantle
boundary), the lifetime of the magnetic fields is evaluated from the calculated
thermal evolution. We found that the lifetime slowly increases with the
planetary mass () independent of initial temperature gap at the
core-mantle boundary () but beyond a critical value
() it abruptly declines by the mantle viscosity
enhancement due to the pressure effect. We derived as a function of
and a rheological parameter (activation volume, ).
Thus, the magnetic field lifetime of super-Earths with
sensitively depends on , which reflects planetary
accretion, and , which has uncertainty at very high pressure. More
advanced high-pressure experiments and first-principle simulation as well as
planetary accretion simulation are needed to discuss habitability of
super-Earths.Comment: 19pages, 15 figures, accepted for publication in Ap
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
A Study of the Accuracy of Mass-Radius Relationships for Silicate-Rich and Ice-Rich Planets up to 100 Earth Masses
A mass-radius relationship is proposed for solid planets and solid cores
ranging from 1 to 100 Earth-mass planets. It relies on the assumption that
solid spheres are composed of iron and silicates, around which a variable
amount of water is added. The M-R law has been set up assuming that the
planetary composition is similar to the averaged composition for silicates and
iron obtained from the major elements ratio of 94 stars hosting exoplanets.
Except on Earth for which a tremendous amount of data is available, the
composition of silicate mantles and metallic cores cannot be constrained.
Similarly, thermal profiles are poorly known. In this work, the effect of
compositional parameters and thermal profiles on radii estimates is quantified.
It will be demonstrated that uncertainties related to composition and
temperature are of second order compared to the effect of the water amount. The
Super-Earths family includes four classes of planets: iron-rich, silicate-rich,
water-rich, or with a thick atmosphere. For a given mass, the planetary radius
increases significantly from the ironrich to the atmospheric-rich planet. Even
if some overlaps are likely, M-R measurements could be accurate enough to
ascertain the discovery of an earth-like planet .The present work describes how
the amount of water can be assessed from M-R measurements. Such an estimate
depends on several assumptions including i) the accuracy of the internal
structure model and ii) the accuracy of mass and radius measurements. It is
shown that if the mass and the radius are perfectly known, the standard
deviation on the amount of water is about 4.5 %. This value increases rapidly
with the radius uncertainty but does not strongly depend on the mass
uncertainty.Comment: In press in The Astrophysical Journa
On the equilibrium rotation of Earth-like extra-solar planets
The equilibrium rotation of tidally evolved "Earth-like" extra-solar planets
is often assumed to be synchronous with their orbital mean motion. The same
assumption persisted for Mercury and Venus until radar observations revealed
their true spin rates. As many of these planets follow eccentric orbits and are
believed to host dense atmospheres, we expect the equilibrium rotation to
differ from the synchronous motion. Here we provide a general description of
the allowed final equilibrium rotation states of these planets, and apply this
to already discovered cases in which the mass is lower than twelve
Earth-masses. At low obliquity and moderate eccentricity, it is shown that
there are at most four distinct equilibrium possibilities, one of which can be
retrograde. Because most presently known "Earth-like" planets present eccentric
orbits, their equilibrium rotation is unlikely to be synchronous.Comment: 4 pages, 2 figures. accepted for publication in Astronomy and
Astrophysics. to be published in Astronomy and Astrophysic
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 à 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 caractéristiques géologiques du visible à l’infrarouge, il est alors possible de les comparer à
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
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