Difficulties And Anomalies Uncovered In Observing Mercury

Attempts to determine Mercury's basic physical properties led to the determination of its unexpectedly large mass and implied high density. The mass of Mercury was first derived by a German astronomer Johann Franz Encke in 1841 when he measured the perturbations produced by Mercury on a comet that has since been given his name. The measurement remained controversial until the mass and size of this body were later more accurately determined from combined ground-based and Mariner 10 observations...

Field Aligned Currents

Mhd Current

In a comparison between the terrestrial magnetosphere and that of Mercury, Hill et al, 1976 suggested that, because of the assumed weaker conductivity of the surface (and the near surface layer) of Mercury, any Field Aligned Current flows should be considerably weaker than those measured in the Earth's magnetosphere. Hill et al (1976) asserted that the solar wind induces the rapid convection leading to substorms in the tail and particle acceleration up to energies of 13 keV. Alternatively,...

References

Esposito, E. L. Lau, and G. B. Trager, The mass, gravity field, and ephemeris of Mercury, Icarus, 71, 337-349, 1987. Bowen, N.L., Papers1907-1980, Compiled by J. Snyder, Geophysical Lab, Carnegie Institute, Washington DC, 2004. Branham, The mass of Mercury, Planet. Space Sci, 42, 213-219, 1994. Chamberlain, J.W. and D.M. Hunten, Theory of Planetary Atmospheres, 2nd Ed. (Publ. Academic Press), 481 p., 1987. Colombo, G. and I. I. Shapiro. The rotation of...

Planet As A System Of Subsystems

Observations of Mercury in particular have so far allowed us to capture its essence in 'snapshot' fashion, as if the planet is frozen in time. However, observations taken over the last thirty years have indicated that Mercury interacts dynamically with its environment, the magnetosphere and exosphere, and that this environment interacts with the surface. Most likely a dynamo, indicative of ongoing activity in the interior, generates the magnetic field, which results in the presence of the...

Planned Missions And The Interior

As indicated in Chapter 2, there are presently two orbital missions to Mercury with official status (namely NASA's Mercury MESSENGER and the ESA ISAS Bepi Columbo mission) both of which could provide relevant measurements. The MESSENGER mission to Mercury (MM) (Figures 2.5 and 2.6) was launched in August of 2004. Measurements from many MM instruments (Table 2.3), including X-ray, Gamma-ray, Neutron, and Visible and infrared spectrometers, along with the Laser Altimeter, Radio Science Package...

The Bepi Colombo Mission Objectives

The objectives of Bepi Colombo focus on obtaining the kind of coverage necessary to fill in particular gaps in our knowledge of planet Mercury (Grard et al, 2000). Determining the nature of the unimaged hemisphere and polar deposits as well as composition of the entire surface Table 2-4. Proposed Payload for Bepi Colombo Table 2-4. Proposed Payload for Bepi Colombo as of 1 1 2005 3axis, nadir pointing S C, orbit 400x1500 km, periapsis anti-solar point, 1500 Gb data HiRes Stereo Cameras Vis IR...

The Nature And Composition Of Major Terranes

Three major terranes, or geochemical provinces, were observed on Mercury's heavily cratered surface by Mariner 10 (See Figure 4-12). Distinct boundaries associated with intercrater plains, small volcanic deposits, and recent impact ejecta have been identified on the basis of albedo and color ratio in the recalibrated Mariner 10 images (Robinson et al, 1997). Early on, Mercury's heavily cratered surface was inevitably compared to the lunar surface, which had been recently visited. On the other...

Nasas Ongoing Messenger Mission

MESSENGER, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging Mission, is a NASA Discovery Mission developed by the Applied Physics Laboratory of the Johns Hopkins University (Gold et al, 2001 Solomon et al, 2001). It was actually launched in August 2004 with modifications to the original scenario (Figure 2-5). After a long seven year cruise, with six challenging gravitational assists (a technique pioneered on the Mariner 10 mission ), including one at the Earth, Figure 2-5....

Current Understanding Of Source And Loss Processes

The simplest loss process is thermal release (Jeans escape), which is caused by heating of the surface due to solar radiation. Given the large surface temperature on the dayside (Chapter 1), very volatile molecules can evaporate into space with scale heights and column densities corresponding to the local surface temperature. Only H and He escape Mercury predominantly through this mechanism. Thermal vaporization is too rapid to be sustained at temperatures near the sub-solar point on Mercury...

Magnetopause Structure

Slavin 2004 Mercury Magnetosphere

Mariner 10 data indicated that the Mercurian magnetopause had a significant aberration in the ecliptic plane as well as equator-pole asymmetries. Ness et al (1975) computed the shape of the magnetopause for the case where the solar wind was incident on a Mercury-centered magnetic dipole orthogonal to the solar wind flow. The theoretical position of the bow shock was determined for the case of aligned flow, in which the upstream magnetic field and solar wind velocity were deemed to be parallel....

The Exosphere Concept

An exosphere is an ensemble of atoms or molecules above a planet's surface or atmosphere for which the mean free path is greater than the scale height (the e-folding height for density). Because collisions are rare in an exosphere, each constituent maintains its own distribution, defined by its unique combination of source energy and distribution, mass, radiation pressure and loss processes (e.g. Jeans escape, photo-dissociation adsorption ionization surface chemistry). Killen and Ip (1999)...

The Selective Accretion Model

Selective Accretion relies on differences between the aerodynamic and mechanical properties of metals in the inner Solar System (where the gas densities were relatively great and the time scale short) sufficient to support dynamic sorting leading to iron enrichment (Weidenschilling, 1978). Metal silicate fractionation might have resulted from the Selective Accretion of the cores of differentiated asteroids. This process would require the original composition of the asteroids to be at least as...

Understanding The Planet Mercury

Thirty years have elapsed since the one and only mission to Mercury, Mariner 10, performed three flybys of the planet, capturing moderate-resolution (100 m at best) images of one hemisphere (45 of the surface) and discovering that Mercury could be the only other terrestrial planet to have a global magnetic field and core dynamo analogous to the Earth's. At the time of this writing, the MESSENGER mission to Mercury has been launched. We are still a couple of years away from the first of the next...

Ground Based Observations Of Sodium And Potassium

Well after the Mariner 10 flybys, a fortuitous observation led to the identification of sodium and potassium exospheres at Mercury. These first observations were made using ground based instrumentation consisting originally of single-slit, spectrographs (Potter and Morgan, 1985, 1986). Later, an image slicer technique was introduced (Potter and Morgan, 1990). An account of this latter method is contained in Pierce (1965). (Briefly, an image slicer placed at the entrance to the Echelle...

Magnetosphere Structure

Mercury Plasma Propulsion

Many workers have modeled the dimensions of the dayside magnetosphere based on the Mariner 10 magnetopause and bow shock transit measurements (Ness et al, 1974 Ogilvie et al, 1977 Russell, 1977 and Slavin and Holzer, 1979a, 1979b). A straightforward way to understand Mercury's magnetosphere is to scale the Earth's magnetosphere to be equivalent to Mercury's. This is done by decreasing the radius of Earth's magnetosphere by a factor of 8 relative to the radius of the planet and then decreasing...

Direct Accretion Of Reduced Components

Ringwood (1966) and Wanke (1981) modeled Mercury's initial composition using two chemically distinct components, one highly reduced and moderately refractory, the other highly oxidized. Modeling based on chemistry when applied to the Earth and Mars, display a trend that predicts Mercury to be extremely reduced (Dreibus and Wanke, 1984, 1985). In the case of Mercury itself, the models generated are consistent with the implied reduced state of the planet's interior because of the absence of a...

Summary

Mercury is in a unique position to provide understanding of planetary magnetospheres. The planet has a simple magnetosphere formed by the solar wind, which shapes it the interplanetary magnetic field (IMF), which activates it an interior magnetic dipole, which structures it and the planet itself which anchors it. These are the basic ingredients. All other known magnetosphere-bearing planets have added complexities, such as additional sources of plasmas or current systems, that encumber the...

Mercurys Exosphere After Sodium And Potassium Detection

Following the ground based discovery of sodium and potassium in the Hermean atmosphere, Hunten et al (1988) produced an excellent review of the state of knowledge concerning Mercury's exosphere. These authors pointed out that, although Mercury's atmosphere is technically an exosphere, the gas-surface interaction is very different from the interaction of an exosphere in contact with an underlying atmosphere. Mercury's exosphere is the observable result of a dynamically coupled system, with the...