157 research outputs found
Librations and Obliquity of Mercury from the BepiColombo radio-science and camera experiments
A major goal of the BepiColombo mission to Mercury is the determination of
the structure and state of Mercury's interior. Here the BepiColombo rotation
experiment has been simulated in order to assess the ability to attain the
mission goals and to help lay out a series of constraints on the experiment's
possible progress. In the rotation experiment pairs of images of identical
surface regions taken at different epochs are used to retrieve information on
Mercury's rotation and orientation. The idea is that from observations of the
same patch of Mercury's surface at two different solar longitudes of Mercury
the orientation of Mercury can be determined, and therefore also the obliquity
and rotation variations with respect to the uniform rotation. The estimation of
the libration amplitude and obliquity through pattern matching of observed
surface landmarks is challenging. The main problem arises from the difficulty
to observe the same landmark on the planetary surface repeatedly over the MPO
mission lifetime, due to the combination of Mercury's 3:2 spin-orbit resonance,
the absence of a drift of the MPO polar orbital plane and the need to combine
data from different instruments with their own measurement restrictions. By
assuming that Mercury occupies a Cassini state and that the spacecraft operates
nominally we show that under worst case assumptions the annual libration
amplitude and obliquity can be measured with a precision of respectively 1.4
arcseconds (as) and 1.0 as over the nominal BepiColombo MPO lifetime with about
25 landmarks for rather stringent illumination restrictions. The outcome of the
experiment cannot be easily improved by simply relaxing the observational
constraints, or increasing the data volume.Comment: 30 pages, 6 figures, 2 table
Exoplanet interiors and habitability
More than 1000 exoplanets with a radius smaller than twice that of the Earth are currently known, mainly thanks to space missions dedicated to the search of exoplanets. Mass and radius estimates, which are only available for a fraction (⌠10%) of the exoplanets, provide an indication of the bulk composition and interior structure and show that the diversity in exoplanets is far greater than in the Solar System. Geophysical studies of the interior of exoplanets are key to understanding their formation and evolution, and are also crucial for assessing their potential habitability since interior processes play an essential role in creating and maintaining conditions for water to exist at the surface or in subsurface layers. For lack of detailed observations, investigations of the interior of exoplanets are guided by the more refined knowledge already acquired about the Solar System planets and moons, and are heavily based on theoretical modelling and on studies of the behaviour of materials under the high pressure and temperature conditions in planets. Here we review the physical principles and methods used in modelling the interior and evolution of exoplanets with a rock or water/ice surface layer and identify possible habitats in or on exoplanets
Titan's Obliquity as evidence for a subsurface ocean?
On the basis of gravity and radar observations with the Cassini spacecraft,
the moment of inertia of Titan and the orientation of Titan's rotation axis
have been estimated in recent studies. According to the observed orientation,
Titan is close to the Cassini state. However, the observed obliquity is
inconsistent with the estimate of the moment of inertia for an entirely solid
Titan occupying the Cassini state. We propose a new Cassini state model for
Titan in which we assume the presence of a liquid water ocean beneath an ice
shell and consider the gravitational and pressure torques arising between the
different layers of the satellite. With the new model, we find a closer
agreement between the moment of inertia and the rotation state than for the
solid case, strengthening the possibility that Titan has a subsurface ocean.Comment: 11 pages, 4 figure
Obliquity of the Galilean satellites: The influence of a global internal liquid layer
The obliquity of the Galilean satellites is small but not yet observed.
Studies of cycloidal lineaments and strike-slip fault patterns on Europa
suggest that Europa's obliquity is about 1 deg, although theoretical models of
the obliquity predict the obliquity to be one order of magnitude smaller for an
entirely solid Europa. Here, we investigate the influence of a global liquid
layer on the obliquity of the Galilean satellites. Io most likely has a fully
liquid core, while Europa, Ganymede, and Callisto are thought to have an
internal global liquid water ocean beneath an external ice shell. We use a
model for the obliquity based on a Cassini state model extended to the presence
of an internal liquid layer and the internal gravitational and pressure torques
induced by the presence of this layer. We find that the obliquity of Io only
weakly depends on the different internal structure models considered, because
of the weak influence of the liquid core which is therefore almost impossible
to detect through observations of the obliquity. The obliquity of Europa is
almost constant in time and its mean value is smaller (0.033-0.044 deg) with an
ocean than without (0.055 deg). An accuracy of 0.004 deg (about 100 m on the
spin pole location at the surface) would allow detecting the internal ocean.
The obliquity of Ganymede and Callisto depends more on their interior structure
because of the possibility of resonant amplifications for some periodic terms
of the solution. Their ocean may be easily detected if, at the measuring time,
the actual internal structure model lead to a very different value of the
obliquity than in the solid case. A long-term monitoring of their shell
obliquity would be more helpful to infer information on the shell thickness.Comment: 27 pages, 6 tables, 7 figure
Pre-mission InSights on the Interior of Mars
Abstract The Interior exploration using Seismic Investigations, Geodesy, and Heat Trans-
port (InSight) Mission will focus on Marsâ interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moonâs much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of 3â10Ă relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars
Jovian tidal dissipation from inner satellite dynamics
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Jovian tidal dissipation from inner satellite dynamics
International audienceNot Availabl
Librations and Polar Motion of Titan
We study the influence of the presence of a global subsurface ocean on the three-dimensional rotation of large icy satellites such as Europa, Callisto, Ganymede and Titan
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