174 research outputs found
Mercury's resonant rotation from secular orbital elements
We used recently produced Solar System ephemerides, which incorporate two
years of ranging observations to the MESSENGER spacecraft, to extract the
secular orbital elements for Mercury and associated uncertainties. As Mercury
is in a stable 3:2 spin-orbit resonance these values constitute an important
reference for the planet's measured rotational parameters, which in turn
strongly bear on physical interpretation of Mercury's interior structure. In
particular, we derive a mean orbital period of 87.96934962 0.00000037
days and (assuming a perfect resonance) a spin rate of 6.138506839
0.000000028 degree/day. The difference between this rotation rate and the
currently adopted rotation rate (Archinal et al, 2011) corresponds to a
longitudinal displacement of approx. 67 m per year at the equator. Moreover, we
present a basic approach for the calculation of the orientation of the
instantaneous Laplace and Cassini planes of Mercury. The analysis allows us to
assess the uncertainties in physical parameters of the planet when derived from
observations of Mercury's rotation
Spin-orbit coupling for tidally evolving super-Earths
We investigate the spin behavior of close-in rocky planets and the
implications for their orbital evolution. Considering that the planet rotation
evolves under simultaneous actions of the torque due to the equatorial
deformation and the tidal torque, both raised by the central star, we analyze
the possibility of temporary captures in spin-orbit resonances. The results of
the numerical simulations of the exact equations of motions indicate that,
whenever the planet rotation is trapped in a resonant motion, the orbital decay
and the eccentricity damping are faster than the ones in which the rotation
follows the so-called pseudo-synchronization. Analytical results obtained
through the averaged equations of the spin-orbit problem show a good agreement
with the numerical simulations. We apply the analysis to the cases of the
recently discovered hot super-Earths Kepler-10 b, GJ 3634 b and 55 Cnc e. The
simulated dynamical history of these systems indicates the possibility of
capture in several spin-orbit resonances; particularly, GJ 3634 b and 55 Cnc e
can currently evolve under a non-synchronous resonant motion for suitable
values of the parameters. Moreover, 55 Cnc e may avoid a chaotic rotation
behavior by evolving towards synchronization through successive temporary
resonant trappings.Comment: Accepted for publication in MNRA
Enceladus: Evidence for librations forced by Dione
Based on control point calculations it is shown that Enceladus experiences librations forced by Dione
The reference frames of Mercury after MESSENGER
We report on recent refinements and the current status for the rotational
state models and the reference frame of the planet Mercury. We summarize the
performed measurements of Mercury rotation based on terrestrial radar
observations as well as data from the Mariner 10 and the MESSENGER missions.
Further, we describe the different available definitions of reference systems
for Mercury, which are realized using data obtained by instruments on board
MESSENGER. In particular, we discuss the dynamical frame, the principal-axes
frame, the ellipsoid frame, as well as the cartographic frame. We also describe
the reference frame adopted by the MESSENGER science team for the release of
their cartographic products and we provide expressions for transformations from
this frame to the other reference frames
Candidate regions on titan as promising landing sites for future in situ missions
The highly successful and still on-going Cassini-Huygens mission to the Saturnian system points to the need for a return mission, with both remote and in situ instrumentation. The surface of Saturn’s moon Titan, hosts a complex environment in which many processes occur shaping its landscape. Several of its geological features resemble terrestrial ones, albeit constructed from different material and reflecting the interiorsurface-atmosphere exchanges. The resulting observed morphotectonic features and cryovolcanic candidate regions could benefit from further extensive exploration by a return mission that would focus on these aspects with adapted state-of-the-art instrumentation affording higher spectral and spatial resolution and in situ capabilities. We suggest that some features on Titan are more promising candidate locations for future landing and we present the case for Tui Regio, Hotei Regio and Sotra Patera as to why they could provide a wealth of new scientific results
Science Objectives of the Ganymede Laser Altimeter (GALA) for the JUICE Mission
Laser altimetry is a powerful tool for addressing the major objectives of
planetary physics and geodesy, and have been applied in planetary explorations
of the Moon, Mars, Mercury, and the asteroids Eros, and Itokawa. The JUpiter
Icy Moons Explorer (JUICE), led by European Space Agency (ESA), has started
development to explore the emergence of habitable worlds around gas giants. The
Ganymede Laser Altimeter (GALA) will be the first laser altimeter for icy
bodies, and will measure the shape and topography of the large icy moons of
Jupiter, (globally for Ganymede, and using flyby ground-tracks for Europa and
Callisto). Such information is crucial for understanding the formation of
surface features and can tremendously improve our understanding of the icy
tectonics. In addition, the GALA will infer the presence or absence of a
subsurface ocean by measuring the tidal and rotational responses. Furthermore,
it also improves the accuracy of gravity field measurements reflecting the
interior structure, collaborating with the radio science experiment. In
addition to range measurements, the signal strength and the waveform of the
laser pulses reflected from the moon's surface contain information about
surface reflectance at the laser wavelength and small scale roughness.
Therefore we can infer the degrees of chemical and physical alterations, e.g.,
erosion, space weathering, compaction and deposition of exogenous materials,
through GALA measurements without being affected by illumination conditions.
JUICE spacecraft carries ten science payloads including GALA. They work closely
together in a synergistic way with GALA being one of the key instruments for
understanding the evolution of the icy satellites Ganymede, Europa, and
Callisto.Comment: 10 pages, 6 figures, accepted for publication in Trans. JSASS
Aerospace Tech. Japa
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