Shape and Orientation of Mercury from Radar Ranging Data

Space Science …, 2007

Icarus, 2012

Mapping tectonic features using MESSENGER data mainly acquired at high Sun incidence angle (>50°) reveals previously undetected structures. The analysis of the latter features determines an upward revision of measurements of density and spatial distribution of tectonism and thus of estimates of average contractional strain and planetary radius decrease. We calculated an average surface contraction of $0.23-0.30% ($0.28% for fault dip angle h = 30°) within an area corresponding to 21% of the planet. This strain, extrapolated to the entire surface, corresponds to a decrease in radius of about 2.4-3.6 km ($3.0 km for h = 30°). These values are three-four times higher with respect to previous estimates and are compatible with results from thermomechanical models.

Reports on Progress in Physics, 2002

The planet closest to the Sun, Mercury, is the subject of renewed attention among planetary scientists, as two major space missions will visit it within the next decade. These will be the first to return to Mercury, after the flybys by NASA's Mariner 10 spacecraft in 1974-5. The difficulties of observing this planet from the Earth make such missions necessary for further progress in understanding its origin, evolution and present state. This review provides an overview of what is known about Mercury and what are the major outstanding issues. Mercury's orbital and rotation periods are in a unique 2:3 resonance; an analysis of the orbital dynamics of Mercury is presented here, as well as Mercury's special role in testing theories of gravitation. These derivations provide a good insight into the complexities of planetary motion in general, and how, in the case of Mercury, its proximity to the Sun can be described and exploited in terms of general relativity. Mercury's surface, superficially similar to that of the Moon, presents intriguing differences, representing a different, and more complex history in which the role of early volcanism remains to be clarified and understood. Mercury's interior presents the most important puzzles: it has the highest uncompressed density among the terrestrial planets, implying a very large, mostly iron core. This does not appear to be the completely solidified yet, as Mariner 10 found a planetary magnetic field that is probably generated by an internal dynamo, in a liquid outer layer of the large iron core. The current state of the core, once established, will provide a constraint for its evolution from the time of the planet's formation. Mercury's environment is highly variable. There is only a tenuous exosphere around Mercury; its source is not well understood, although there are competing models for its formation and dynamics. The planetary magnetic field appears to be strong enough to form a magnetosphere around the planet, through its interaction with the solar wind. This magnetosphere may have similarities with that of the Earth, but is more likely to be dominated by global dynamics that could make it collapse at least at the time of large solar outbursts. The future understanding of the planet will now await the arrival of the new space missions. The review concludes with a brief description of these missions.

Science (New York, N.Y.), 2009

Mapping the distribution and extent of major terrain types on a planet's surface helps to constrain the origin and evolution of its crust. Together, MESSENGER and Mariner 10 observations of Mercury now provide a near-global look at the planet, revealing lateral and vertical heterogeneities in the color and thus composition of Mercury's crust. Smooth plains cover approximately 40% of the surface, and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically. A low-reflectance, relatively blue component affects at least 15% of the surface and is concentrated in crater and basin ejecta. Its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron- and titanium-bearing oxides.

Space Science Reviews, 2007

Mariner 10 and Earth-based observations have revealed Mercury, the innermost of the terrestrial planetary bodies, to be an exciting laboratory for the study of Solar System geological processes. Mercury is characterized by a lunar-like surface, a global magnetic field, and an interior dominated by an iron core having a radius at least three-quarters of the radius of the planet. The 45% of the surface imaged by Mariner 10 reveals some distinctive differences from the Moon, however, with major contractional fault scarps and huge expanses of moderate-albedo Cayley-like smooth plains of uncertain origin. Our current image coverage of Mercury is comparable to that of telescopic photographs of the Earth's Moon prior to the launch of Sputnik in 1957. We have no photographic images of one-half of the surface, the resolution of the images we do have is generally poor (∼1 km), and as with many lunar telescopic photographs, much of the available surface of Mercury is distorted by foreshortening due to viewing geometry, or poorly suited for geological analysis and

Journal of Geophysical Research, 2009

Science, 2012

Geophysical Research Letters, 2019

Geodetic analysis of radio tracking measurements of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft while in orbit about Mercury has yielded new estimates for the planet's gravity field, tidal Love number, and pole coordinates. The derived right ascension (𝛼 = 281.0082 • ± 0.0009 • ; all uncertainties are 3 standard deviations) and declination (𝛿 = 61.4164 • ± 0.0003 • ) of the spin pole place Mercury in the Cassini state. Confirmation of the equilibrium state with an estimated mean (whole planet) obliquity 𝜖 of 1.968 ± 0.027 arcmin enables the confident determination of the planet's normalized polar moment of inertia (0.333 ± 0.005), which indicates a high degree of internal differentiation. Internal structure models generated by a Markov Chain Monte Carlo process and consistent with the geodetic constraints possess a solid inner core with a radius (r ic ) between 0.3 and 0.7 that of the outer core (r oc ).

Space Science Reviews, 2007

Mercury’s surface is thought to be covered with highly space-weathered silicate material. The regolith is composed of material accumulated during the time of planetary formation, and subsequently from comets, meteorites, and the Sun. Ground-based observations indicate a heterogeneous surface composition with SiO2 content ranging from 39 to 57 wt%. Visible and near-infrared spectra, multi-spectral imaging, and modeling indicate expanses of feldspathic, well-comminuted surface with some smooth regions that are likely to be magmatic in origin with many widely distributed crystalline impact ejecta rays and blocky deposits. Pyroxene spectral signatures have been recorded at four locations. Although highly space weathered, there is little evidence for the conversion of FeO to nanophase metallic iron particles (npFe0), or “iron blebs,” as at the Moon. Near- and mid-infrared spectroscopy indicate clino- and ortho-pyroxene are present at different locations. There is some evidence for no- or low-iron alkali basalts and feldspathoids. All evidence, including microwave studies, point to a low iron and low titanium surface. There may be a link between the surface and the exosphere that may be diagnostic of the true crustal composition of Mercury. A structural global dichotomy exists with a huge basin on the side not imaged by Mariner 10. This paper briefly describes the implications for this dichotomy on the magnetic field and the 3 : 2 spin : orbit coupling. All other points made above are detailed here with an account of the observations, the analysis of the observations, and theoretical modeling, where appropriate, that supports the stated conclusions.

Advances in Space Research, 2013

Earth-based radar observations of the rotational dynamics of Mercury (Margot et al. 2012) combined with the determination of its gravity field by MESSENGER (Smith et al. 2012) give clues on the internal structure of Mercury, in particular its polar moment of inertia C, deduced from the obliquity (2.04 ± 0.08) arcmin. The dynamics of the obliquity of Mercury is a very-long term motion (a few hundreds of kyrs), based on the regressional motion of Mercury's orbital ascending node. This paper, following the study of Noyelles & D'Hoedt (2012), aims at first giving initial conditions at any time and for any values of the internal structure parameters for numerical simulations, and at using them to estimate the influence of usually neglected parameters on the obliquity, like J 3 , the Love number k 2 and the secular variations of the orbital elements. We use, for that, averaged representations of the orbital and rotational motions of Mercury, suitable for long-term studies. We find that J 3 should alter the obliquity by 250 milli-arcsec, the tides by 30 milli-arcsec, and the secular variations of the orbital elements by 10 milliarcsec over 20 years. The resulting value of C could be at the most changed from 0.346mR 2 to 0.345mR 2 .