Mercury Science Options

[ljk4-1]

Astrophysics, abstract
astro-ph/0511419

From: Stan Peale [view email]

Date: Mon, 14 Nov 2005 22:21:56 GMT (314kb)

The proximity of Mercury's spin to Cassini state 1

Authors: S. J. Peale

Comments: 23 pages,12 figures, In press in Icarus

In determining Mercury's core structure from its rotational properties, the value of the normalized moment of inertia, $C/MR^2$, from the location of Cassini 1 is crucial. If Mercury's spin axis occupies Cassini state 1, its position defines the location of the state. The spin might be displaced from the Cassini state if the spin is unable to follow the changes in the state position induced by the variations in the orbital parameters and the geometry of the solar system. The spin axis is expected to follow the Cassini state for orbit variations with time scales long compared to the 1000 year precession period of the spin about the Cassini state because the solid angle swept out by the spin axis as it precesses is an adiabatic invariant. Short period variations in the orbital elements of small amplitude should cause displacements that are commensurate with the amplitudes of the short period terms. By following simultaneously the spin position and the Cassini state position during long time scale orbital variations over past 3 million years (Quinn {\it et al.}, 1991) and short time scale variations from JPL Ephemeris DE 408 (Standish, 2005) we show that the spin axis will remain within one arcsec of the Cassini state after it is brought there by dissipative torques. We thus expect Mercury's spin to occupy Cassini state 1 well within the uncertainties for both radar and spacecraft measurements, with correspondingly tight constraints on $C/MR^2$.

http://arxiv.org/abs/astro-ph/0511419

[ljk4-1]

Paper (*cross-listing*): gr-qc/0511137

Date: Fri, 25 Nov 2005 13:47:02 GMT (4kb)
Date (revised v2): Tue, 29 Nov 2005 11:55:15 GMT (4kb)
Date (revised v3): Thu, 1 Dec 2005 12:41:58 GMT (4kb)

Title: Can Solar System observations tell us something about the cosmological
constant?

Authors: Lorenzo Iorio

Comments: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added,
typos in the units of Lambda corrected
\\
In this note we show that the latest determinations of the residual Mercury's
perihelion advance, obtained by accounting for almost all known Newtonian and
post-Newtonian orbital effects, yields only very broad constraints on the
cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050
arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2.

The currently accepted value for Lambda, obtained from many independent
cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.

\\ ( http://arXiv.org/abs/gr-qc/0511137 , 4kb)

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Paper (*cross-listing*): gr-qc/0511138

Date: Fri, 25 Nov 2005 13:50:40 GMT (8kb)

Title: Solar System planetary motions and modified gravity

Authors: Lorenzo Iorio

Comments: Latex2e, 8 pages, 4 tables, no figures, 25 references
\\
According to the braneworld model of gravity by Dvali, Gabadadze and Porrati,
our Universe is a four-dimensional space-time brane embedded in a larger,
infinite five-dimensional bulk space. Contrary to the other forces constrained
to remain on the brane, gravity is able to explore the entire bulk getting
substantially modified at large distances. This model has not only cosmological
consequences allowing to explain the observed acceleration of the expansion of
our Universe without resorting to the concept of dark energy, but makes also
testable predictions at small scales. Interestingly, such local effects can
yield information on the global properties of the Universe and on the kind of
expansion currently ongoing. Indeed, among such predictions there are extra
precessions of the perihelia and the mean longitudes of the planetary orbits
which are affected by a twofold degeneration sign: one sign refers to a
Friedmann-Lemaitre-Robertson-Walker phase while the opposite sign is for a
self-sccelerated phase.

In this paper we report on recent observations of planetary motions in the Solar System which are compatible with the existence of a fifth dimension as predicted in the Dvali-Gabadadze-Porrati model with a self-accelerated cosmological phase, although the errors are still large. The Friedmann-Lemaitre-Robertson-Walker phase is, instead, ruled out.

\\ ( http://arXiv.org/abs/gr-qc/0511138 , 8kb)

[ljk4-1]

Mercury a Possible Hit-and-Run Planet

http://www.space.com/scienceastronomy/0601...it_and_run.html

New computer modeling shows that the planet Mercury might have formed in a
hit-and-run collision that stripped off its outer layers.