ABSTRACT

Times of impact ejection of Martian meteorites occur in clusters and correlate with petrographic classifications. The clustered or unique ejection ages apparently sample as many as seven distinct locations on Mars. All these sites, as yet not identified unambiguously, are dominated by basaltic flows or cumulate rocks formed from basaltic magmas. Except for ALH 84001, a 4.5 Ga sample of the Noachian crust, all SNCs were extracted from Amazonian volcanic terrains. Lithologies identified by landed or orbiting spacecraft are generally different from SNCs, although the distinctive mineralogic characteristics of SNCs (ferroan olivine and pyroxenes, sodic plagioclase) are commonly indicated by remote-sensing data. Aqueous alteration of SNC meteorites is limited, and light stable isotopic fractionations suggest hydrologic cycling. These meteorites reveal many geochemical, mineralogical, and chronological properties of the crust that cannot yet be measured by remote sensing.

ABSTRACT

This chapter reviews observations and interpretations since the 1990s from orbital telescopic and spacecraft observations of Mars from the extended visible to short-wave near-IR (VNIR) wavelength range. Imaging and spectroscopic measurements from the Hubble Space Telescope (HST), Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC/WA) instrument, Mars Odyssey Thermal Emission Imaging System Visible Subsystem (THEMIS-VIS), and Mars Express High Resolution Stereo Camera (MEx HRSC) and Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) have been acquired at spatial scales from global-scale ∼ 1 to hundreds of kilometers resolution to regional-scale ∼ 20–100 m resolution. Most high-albedo regions are homogeneous in color and thus, likely, composition, a supposition consistent with the long-held idea of the presence of a globally homogeneous aeolian dust unit covering much of the surface. Despite the presence and ubiquity of dust, these measurements still reveal the presence of significant VNIR spectral variability at a variety of spatial scales. For example, color variations and possibly mineralogic variations have been detected among small-scale (tens of meters) exposures of light-toned outcrop and layered materials in Meridiani Planum, Valles Marineris, and other areas. Within low-albedo regions, much of the observed color variability appears simply related to different amounts of covering or coating by nanophase ferric oxide-bearing dust and/or ferrous silicate-bearing sand. Some VNIR color units, however, in regions spanning the full range of observed surface albedos, correlate with geologic, topographic, or thermal inertia boundaries, suggesting that either composition/mineralogy or variations in physical properties (e.g., grain size, roughness, packing density) influencethe observed color.

ABSTRACT

Multispectral imaging from the Panoramic Camera (Pancam) instruments on the Mars Exploration Rovers (MERs) Spirit and Opportunity has provided important new insights about the geology and geologic history of the rover landing sites and traverse locations in Gusev crater and Meridiani Planum. Pancam observations from near-UV to near-infrared (NIR) wavelengths provide limited compositional and mineralogic constraints on the presence, abundance, and physical properties of ferric- and ferrous-iron–bearing minerals in rocks, soils, and dust at both sites. High-resolution and stereo morphologic observations have also helped to infer some aspects of the composition of these materials at both sites. Perhaps most importantly, Pancam observations were often efficiently and effectively used to discover and select the relatively small number of places where in situ measurements were performed by the rover instruments, thus supporting and enabling the much more quantitative mineralogic discoveries made using elemental chemistry and mineralogy data. This chapter summarizes the major compositionally and mineralogically relevant results at Gusev and Meridiani derived from Pancam observations. Classes of materials encountered in Gusev crater include outcrop rocks, float rocks, cobbles, clasts, soils, dust, rock grindings, rock coatings, windblown drift deposits, and exhumed whitish/yellowish sulfur- and silica-rich soils. Materials studied in Meridiani Planum include sedimentary outcrop rocks, rock rinds, fracture fills, hematite spherules, cobbles, rock fragments, meteorites, soils, and windblown drift deposits. This chapter also previews the results of a number of coordinated observations between Pancam and other rover-based and Mars-orbital instruments that were designed to provide complementary new information and constraints on the mineralogy and physical properties of Martian surface materials.

The Doppler technique has continuously improved its precision during the past two decades, attaining the level of 1 ms−1. The increasing precision opened the way to the discovery of the first extrasolar planet, and later, to the exploration of a large range of orbital parameters of extrasolar planets. This ability to detect and characterize in great detail companions down to Neptune-mass planets has provided many new and unique inputs for the understanding of planet formation and evolution. In addition, the success of the Doppler technique introduced a great dynamic in the whole domain, allowing the exploration of new possibilities.

Nowadays, the Doppler technique is no longer the only means to discover extrasolar planets. The performance of new instruments, like the High Accuracy Radial-velocity Planet Searcher (HARPS), has shown that the potential of the Doppler technique has not been exhausted; Earth-mass planets are now within reach. In the future, radial velocities will also play a fundamental role in the follow-up and characterization of planets discovered by means of other techniques—for transit candidates, in particular. We think, therefore, that the follow-up of candidates provided by, e.g., the COnvection, ROtation and planetary Transits (COROT) and Kepler space telescopes, will be of primary importance.

Human beings have long thought that planetary systems similar to our own should exist around stars other than the Sun. However, the astronomical search for planets outside our Solar System has had a dismal history of decades of discoveries that were announced, but could not be confirmed. All that changed in 1995, when we entered the era of the discovery of extrasolar planetary systems orbiting main-sequence stars. To date, well over 130 planets have been found outside our Solar System, ranging from the fairly familiar to the weirdly unexpected. Nearly all of the new planets discovered to date appear to be gas giant planets similar to our Jupiter and Saturn, though with very different orbits about their host stars. In the last year, three planets with much lower masses have been found, similar to those of Uranus and Neptune, but it is not yet clear if they are also ice giant planets, or perhaps rock giant planets, i.e., super-Earths. The long-term goal is to discover and characterize nearby Earth-like, habitable planets. A visionary array of space-based telescopes has been planned that will carry out this incredible search over the next several decades.

The host stars of extrasolar planets (ESPs) tend to be metal rich. We have examined other properties of these stars in search of systematic trends that might distinguish exoplanet hosts from the hoi polloi of the Galactic disk; we find no evidence for such trends among the present sample. The α-element abundance ratios show that several ESP hosts are likely to be members of the thick disk population, indicating that planet formation has occurred throughout the full lifetime of the Galactic disk. We briefly consider the radial metallicity gradient and age-metallicity relation of the Galactic disk, and complete a back-of-the-envelope estimate of the likely number of solar-type stars with planetary companions with 6 < R < 10 kpc.

ABSTRACT

The Mars Pathfinder Alpha Proton X-ray Spectrometer (APXS) was utilized to determine the major and minor elemental abundances of rocks and soils at the 1997 landing site in Ares Vallis. The determined abundances suggest that: (1) the rocks are covered with various amounts of soil; (2) the Soil-Free Rock (SFR) chemistry is similar to that of an evolved SNC-like (SNC – Shergottite, Nakhlite, and Chassignite) igneous tholeiitic basalt-andesite to andesite that is minimally altered (possibly similar to Type 2 TES material); (3) the carbon content is below detection limits for all samples, implying < 5% as MgCO3 (Brückner et al., 1999); (4) the α-mode oxygen abundance indicates that mineral-bound water, above the value for igneous rocks, is present in some rocks and is therefore indicative of some nonigneous alteration and therefore possibly rock-rinds that obscure the petrology of the SFR; and (5) the Pathfinder soils are similar to the Viking fines and may be composed of mafic igneous material like the SNC meteorites and of volatiles deposited from volcanic emissions, as previously suggested by Clark (1993) for the Viking soils.

ABSTRACT

The reflection of visible and near-infrared light from Mars can vary significantly depending on the directional scattering characteristics of surface materials. Observations acquired under a range of illumination and viewing angles can be input to radiative transfer models to constrain the albedo, surface roughness, grain size, and/or porosity of these materials. This chapter reviews multiangular measurements of Mars obtained by Earth-based telescopes (including the Hubble Space Telescope), orbiters (Mariner, Viking, Mars Express), landers (Viking, Mars Pathfinder), and rovers (Mars Exploration Rovers), and how the photometric analyses of these datasets have been used to understand the surface properties of local and regional geologic units and terrain types. Although acquisition of data covering sufficient incidence, emission, or phase angles to fully constrain all parameters within photometric models is challenging, a common theme among these studies is the dominantly backscattering nature of the Martian surface, the magnitude of which is often related to the presence of high-albedo aeolian dust. The local and regional photometric variability observed in these data encourages further refinement of radiative transfer methods and atmospheric correction algorithms to provide additional tools with which to categorize and map distinct photometric units on Mars, particularly to provide support for ongoing and upcoming orbital and landed missions.

ABSTRACT

The polar caps are the most active regions on Mars. The annual cycling of atmospheric CO2 into the seasonal CO2 ice caps is a driving force of the Martian climate. The polar layered deposits (PLDs), with thousands of layers whose thickness is only resolvable with sub-meter spatial resolution from orbit, may contain a record of past climates. The polar regions contain the majority of known H2O ice deposits, distributed between the residual caps and near-surface ice in the regolith. In this chapter, we synthesize results from missions and instruments largely presented in detail elsewhere in this book, and consider the implications for Martian polar processes and the areas for future research. The focus here is on presenting evidence for and interpretations concerning the CO2 cycle and other related polar processes. Implications for water-ice in the subsurface are examined with respect to its effects on the CO2 cycle. Comparisons of water-ice abundance to the mass and distribution of seasonal CO2 ice are also explored. While the amount of available data has increased exponentially, our knowledge and understanding of Martian polar processes has increased much more gradually. As each question about the polar regions of Mars is answered, several new questions are brought to light. Many of the processes that occur in the polar regions of Mars do not have direct analogs on Earth, but do have analogs in other parts of the Solar System.

ABSTRACT

The Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS) mapped the surface, atmosphere, and polar caps of Mars from 1997 through 2006. TES provided the first global mineral maps of Mars, and showed that the surface is dominated by primary volcanic minerals (plagioclase feldspar, pyroxene, and olivine) along with high-silica, poorly crystalline materials. Differences in the abundances of these minerals were initially grouped into two broad compositional categories that correspond to basalt and basaltic andesite. Additional analysis has identified four surface compositional groups that are spatially coherent, revealing variations in the composition of the primary crust-forming magmas through time. In general, plagioclase, high-Ca clinopyroxene, and high-silica phases are the dominant mineral groups for most regions, with lesser amounts of orthopyroxene, olivine, and pigeonite. One of the fundamental results from the TES investigation was the identification of several large deposits of crystalline hematite, including those in Meridiani Planum, that were interpreted to indicate the presence of liquid water for extended periods of time. This interpretation led to the selection of Meridiani as the target for the Opportunity rover, the first time that a planetary landing site was selected on the basis of mineralogic information. Aqueous weathering may have formed some of the high-silica phases seen in TES spectra at high latitudes, and the Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) spectrometer has detected phyllosilicates and sulfates, typically formed by aqueous weathering and deposition, in several locations.

ABSTRACT

Two Miniature Thermal Emission Spectrometers (Mini-TES) operated successfully onboard the two Mars Exploration Rovers (MER) on the Martian surface, one at Gusev crater and the other at Meridiani Planum. Designed to provide remotely sensed information on the bulk mineralogy of surface materials, the Mini-TES instruments served to guide the rovers to targets of interest and extrapolate the observations made by the rovers' mechanical-arm-mounted instruments. The Mini-TES on the Spirit rover in Gusev crater observed a flat plain covered by rocks with an olivine-rich ((Mg,Fe)2SiO4) mineralogy and a soil-like unit mantled by airfall dust occurring between the rocks. The dust is a spectral match to dust observed at Meridiani Planum and across the globe. The soil is basaltic in composition, dominated by plagioclase (NaAlSi3O8–CaAl2Si2O8), pyroxene (Ca(Mg,Fe)Si2O6–(Mg,Fe)SiO3), and olivine that probably was produced in part from the breakdown of local rocks. Approximately 2.5 km from the Spirit lander, the Columbia Hills contain a remarkably diverse set of rocks distinct from the plains. Basaltic glass appears to dominate the mineralogy of various outcropping rocks while plagioclase dominates the float rocks that cover most of the north side of Husband Hill, the tallest of the Columbia Hills. Numerous exotic (out of place) rocks dot the hillside that likely were emplaced as impact ejecta in some cases and perhaps as volcanic intrusions in other cases. Onboard the Opportunity rover in Meridiani Planum, the Mini-TES observed a nearly rock-free plain covered in hematite (Fe2O3) spherules and basaltic sand.

In a protoplanetary disk that is sufficiently cold and massive, gravitational instabilities (GIs) will lead to the development of dense spiral waves on a dynamic time scale. For sufficiently short cooling times, comparable to about half a rotation period, an unstable disk will fragment into dense clumps that could be the precursors of gas giant protoplanets. At moderate cooling rates, the strong spiral waves which permeate the disk do not fragment, but nevertheless generate significant mass and angular momentum transport. I will review recent research on GIs with an emphasis on several critical questions: Do GIs cause planets to form? How fast do they transport mass? When do they occur? How do they affect the solids in the disk? The physical processes that are central to answering these questions are radiative and possibly convective cooling, irradiation of the disk, and gas-solid interactions. I conclude that, while it is unlikely that gas giant planets are formed directly by disk instability, GIs may substantially accelerate both planetesimal formation and core accretion.

ABSTRACT

The Gamma Ray Spectrometer (GRS) onboard the Odyssey spacecraft has made the first global measurements of the elemental composition of the Martian surface using gamma rays measured from polar orbit. We report results for Si, Fe, K, Th, Cl, and H. The nominal spatial resolution is 450 km in diameter. Gamma Ray Spectrometer data show that the Martian surface is chemically heterogeneous. Elemental concentrations vary across the surface, including variations within high-albedo areas that are presumably covered with dust. Fe concentrations are uniformly high, in accord with the compositions of Martian meteorites and most rock samples analyzed in situ. K/Th is variable, but 95% of the surface has a weight ratio between 4000 and 7000. The mean (5300) is double that in terrestrial crustal rocks and in the inferred bulk silicate Earth. Cl varies substantially, with the highest values in the region west of the Tharsis Montes. Surface Types 1 and 2 (ST1 and ST2), identified from the Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS), are indistinguishable except in the amount of K and Th they contain: ST2 is enriched in both elements by about 30% relative to ST1, while both types have similar K/Th ratios. The H2O mass fraction (stoichiometrically derived from the H content) in equatorial regions ranges from about 1.5%–7%, indicative of the presence of hydrous minerals.

ABSTRACT

Mars Global Surveyor (MGS) discovered intense magnetization in the Mars crust. The planet, which today lacks a dynamo, somehow acquired a crust with at least 10, and perhaps as much as 100 times the volume magnetization intensity of Earth's crust. Interpretation of these data has provided a new and unique window into the origin and evolution of the planet. In this chapter we consider the implications of these discoveries for the understanding of processes that may have led to the minerals and geology that are observed on Mars' surface today. We also include relevant work associated with Earth's magnetic minerals and magnetic and mineralogical characteristics of SNC (SNC – Shergottite, Nakhlite, and Chassignite) meteorites. There is widespread agreement that the Martian dynamo ceased operation within < 500 Myr of accretion and core formation, exposing the atmosphere to erosion by ion-pickup processes in the solar wind for > 4 Gyr. This may constitute an important additional constraint on the minerals and geochemistry observed to date. There is less agreement on whether the magnetic record requires an early era of plate tectonics on Mars. A complete understanding of the crustal magnetic record remains as one of the most significant challenges in Martian geophysical research, one with great potential for understanding not only Mars' evolution but also many aspects of that of the terrestrial planets, asteroids, and the Moon.