Comparison of Mercury and the Moon: A conference

Environmental Effects on Volcanic Eruptions, 2000

The Moon and Mercury have a generally similar surface morphology, with their ancient landscapes characterized by heavily cratered terrain, impact basins, and expanses of smooth plains (Murray et al., 1981; Taylor, 1982; Strom, 1987). In addition, volcanism is known (in the case of the Moon) and thought to have been (in the case of Mercury) an important part of their surface evolution. Volcanic processes on these bodies are likely to have shared some important attributes because of the ancient nature of the geologic record (e.g., early thermal evolution phases) and the lack of an atmosphere (e.g., the style of cooling of lava flows, influencing the distribution of volcanic ejecta). But what about the fundamental differences between the Moon and Mercury, and the lack of knowledge about their consequences? Should Mercury, with its very high surface temperatures, Mars-like surface gravity, and very large iron core, be characterized by volcanic activity that is similar to that of the Moon? Or do these variations dictate that volcanism should be manifested differentially on the two bodies? It is generally thought that the Moon formed very early in solar system history when a Mars-sized object impacted Earth, ejecting crust and upper mantle material that reaccreted in Earth orbit. The energy associated with accretion caused large-scale melting, and this was accompanied by density segregation of the melt and formation of a low-density, plagioclaserich crust. The solidification of the global crust was accompanied by, and succeeded for several hundred million years by, a massive influx of projectiles producing impact craters of many sizes and obscuring the record of any early volcanism, although some evidence of the eruptions in the latest part of heavy bombardment is described below. The formation of the Environmental Effects on Volcanic Eruptions: From Deep Oceans to Deep Space.

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

Space Science Reviews, 2014

Mercury's regolith, derived from the crustal bedrock, has been altered by a set of space weathering processes. Before we can interpret crustal composition, it is necessary to understand the nature of these surface alterations. The processes that space weather the surface are the same as those that form Mercury's exosphere (micrometeoroid flux and solar

Planetary and Space Science, 2011

In this paper we present a crater age determination of several terrains associated with the Raditladi and Rachmaninoff basins. These basins were discovered during the first and third MES-SENGER flybys of Mercury, respectively. One of the most interesting features of both basins is their relatively fresh appearance. The young age of both basins is confirmed by our analysis on the basis of age determination via crater chronology. The derived Rachmaninoff and Raditladi basin model ages are about 3.6 Ga and 1.1 Ga, respectively. Moreover, we also constrain the age of the smooth plains within the basins' floors. This analysis shows that Mercury had volcanic activity until recent time, possibly to about 1 Ga or less. We find that some of the crater sizefrequency distributions investigated suggest the presence of a layered target. Therefore, within this work we address the importance of considering terrain parameters, as geo-mechanical properties and layering, into the process of age determination. We also comment on the likelihood of the availability of impactors able to form basins with the sizes of Rachmaninoff and Raditladi in relatively recent times.

2009

In this paper we present a new method for dating the surface of the Moon, obtained by modeling the incoming flux of impactors and converting it into a size distribution of resulting craters. We compare the results from this model with the standard chronology for the Moon showing their similarities and discrepancies. In particular, we find indications of a non-constant impactor flux in the last 500 Myr and also discuss the implications of our findings for the Late Heavy Bombardment hypothesis. We also show the potential of our model for accurate dating of other inner Solar System bodies, by applying it to Mercury.

Earth and Planetary Science Letters, 2009

The first MESSENGER flyby of Mercury obtained images of 21% of the surface not seen by Mariner 10, including the center and western half of the Caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains. These new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on Mercury and the distribution of volcanic materials. Data from the Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft have shown the following: (1) Numerous volcanic vents, in the form of irregularly shaped rimless depressions, are concentrated around the interior edge of the Caloris basin. (2) These vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions. (3) Lobate margins of plains units, seen previously in Mariner 10 data, are documented in MESSENGER images with more clarity and are often distinctive in morphology and color properties, supporting the interpretation that these features are the edges of lava flow units. (4) The interior of the Caloris basin is filled with plains units spectrally distinctive from the rim deposits, and comparison with the lunar Imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin; detailed differences in the mineralogy of lava flow units, so prominent in Imbrium, are not seen in the Caloris interior. (5) Some of the smooth plains surrounding the exterior of the Caloris basin show distinct differences in color and morphological properties, supporting a volcanic origin. (6) Some smooth and intercrater plains units distant from the Caloris basin show evidence of flooding and embayment relations unrelated to Caloris ejecta emplacement; local and regional geological and color relationships support a volcanic origin for these plains. (7) Large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes. (8) Crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers. (9) Impact crater size-frequency distributions for Caloris exterior deposits, including the facies of the Caloris Group and relatively high-and low-albedo smooth plains, show that they are younger than plains interior to Caloris and thus must be dominantly the product of post-Caloris volcanism. These new data provide evidence that supports and confirms earlier hypotheses from Mariner 10 data that volcanism was important in shaping the surface of Mercury. The emerging picture of the volcanic style of Mercury is similar to that of the Moon, the other small, one-plate planetary body: there are no major shield volcanoes (e.g., comparable to Tharsis Montes on Mars), shallow magma reservoirs are rare, and there is little evidence for surface deformation or long-lived volcanic sources related to sites of upwelling mantle. The close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of Mercury.

Planetary Science Inst Report, 1987

Vents and deposits attributed to explosive volcanism occur within numerous impact craters on both the Moon and Mercury. Given the similarities between the two bodies it is probable that similar processes control this spatial association on both. However, the precise morphology and localization of the activity differs on the two bodies, indicating that the nature of structures beneath impact craters and/or volcanic activity may also be different. To explore this, we analyze sites of explosive volcanism within complex impact craters on the Moon and Mercury, comparing the scale and localization of volcanic activity and evidence for post-formation modification of the host crater. We show that the scale of vents and deposits is consistently greater on Mercury than on the Moon, indicating greater eruption energy, powered by a higher concentration of volatiles. Additionally, while the floors of lunar craters hosting explosive volcanism are commonly fractured, those on Mercury are not. The most probable explanation for these differences is that the state of regional compression acting on Mercury's crust through most of the planet's history results in deeper magma storage beneath craters on Mercury than on the Moon. The probable role of the regional stress regime in dictating the depth of intrusion on Mercury suggests that it may also play a role in the depth of sub-crater intrusion on the Moon and on other planetary bodies. Examples on the Moon (and also on Mars) commonly occur at locations where flexural extension may facilitate shallower intrusion than would be driven by the buoyancy of the magma alone.

Recently acquired altimetry data from laser altimeters are used to assess the morphometry of impact craters. Data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft are used to measure the depths and diameters of 537 craters at the high northern latitudes on Mercury, including 42 polar-deposit-hosting craters (PDCs) which host material that is bright to earth-based radar observations. A comparative analysis suggests that the radar-bright material forms a thin (< 20 m) layer emplaced preferentially in comparatively young craters, contradicting an earlier morphometric study that indicated that PDCs contained a thick layer of water ice and dust. Topographic datasets from the lunar surface, collected by the Lunar Orbiter Laser Altimeter onboard the LRO spacecraft, are also used to evaluate the morphometry of 1,356 lunar craters. We study the morphologic change between the simple and complex crater regime, a manifestation of the transition between gravity-dominated an...