Downloaded from http://sp.lyellcollection.org/ by guest on September 23, 2021 Volcanism and tectonism across the inner solar system: an overview T. PLATZ1,2*, P. K. BYRNE3,4, M. MASSIRONI5 & H. HIESINGER6 1Planetary Science Institute, 1700 East Fort Lowell Road, Tucson, AZ 85719-2395, USA 2Freie Universita¨t Berlin, Institute of Geological Sciences, Planetary Sciences & Remote Sensing, Malteserstrasse 74-100, 12249 Berlin, Germany 3Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA 4Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015-1305, USA 5Dipartimento di Geoscienze, Universita’ degli Studi di Padova, via G. Gradenigo 6, 35131 Padova, Italy 6Institut fu¨r Planetologie, Westfa¨lische Wilhelms-Universita¨tMu¨nster, Wilhelm-Klemm-Strasse 10, 48149 Mu¨nster, Germany *Corresponding author (e-mail: [email protected]) Abstract: Volcanism and tectonism are the dominant endogenic means by which planetary sur- faces change. This book, in general, and this overview, in particular, aim to encompass the broad range in character of volcanism, tectonism, faulting and associated interactions observed on plane- tary bodies across the inner solar system – a region that includes Mercury, Venus, Earth, the Moon, Mars and asteroids. The diversity and breadth of landforms produced by volcanic and tectonic pro- cesses are enormous, and vary across the inventory of inner solar system bodies. As a result, the selection of prevailing landforms and their underlying formational processes that are described and highlighted in this review are but a primer to the expansive field of planetary volcanism and tectonism. In addition to this extended introductory contribution, this Special Publication features 21 dedicated research articles about volcanic and tectonic processes manifest across the inner solar system. Those articles are summarized at the end of this review. Volcanic and tectonic processes have profoundly between the orbits of Mars and Jupiter, divides our shaped the surfaces of terrestrial planets in the inner solar system into inner and outer portions, it itself solar system. Even minor bodies such as asteroids is composed of asteroidal and cometary objects of and small moons, where volcanism and tectonism which a large number enter the inner solar system. have not played dominant roles, are still affected Some asteroids have received attention as the result by fracturing and faulting as a result of other pro- of spacecraft flybys or orbital operations, and for cesses like dynamic loading and gravitational col- that reason are included briefly in this volume. lapse. This Special Publication aims to encompass In this Special Publication, the journey across the broad range in character of volcanism, tecton- the inner solar system begins at the planet closest to ism, faulting and associated interactions observed the Sun. From Mercury we move to Venus; Earth on planetary bodies across the inner solar system. and its Moon are next, before we move yet further By collating observations of the Earth and other out, to Mars. This celestial journey terminates at planetary bodies, the interpretations of extraterres- the main asteroid belt (Fig. 1). trial landforms and their formational processes are The first part of this introductory chapter high- appraised in the light of our current understanding lights the current knowledge of, and recent discov- of comparable processes on Earth. eries regarding, volcanic and tectonic features and The inner solar system comprises our star, the their formational processes on the Moon, Mars, Sun, and the four terrestrial planets, Mercury, Venus, Mercury and Venus. The second part is dedicated Earth and Mars, as well as Mars’ moons Phobos to summarizing the major conclusions of articles and Deimos, and Earth’s companion, the Moon presented in this volume. In its writing, we have (Fig. 1). Although the main asteroid belt, located sought not to compose a comprehensive review From:Platz, T., Massironi, M., Byrne,P.K.&Hiesinger, H. (eds) 2015. Volcanism and Tectonism Across the Inner Solar System. Geological Society, London, Special Publications, 401, 1–56. First published online September 17, 2014, http://dx.doi.org/10.1144/SP401.22 # The Geological Society of London 2015. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on September 23, 2021 2 T. PLATZ ET AL. Downloaded from http://sp.lyellcollection.org/ by guest on September 23, 2021 VOLCANISM AND TECTONISM ACROSS THE INNER SOLAR SYSTEM: AN OVERVIEW 3 per se but, rather, to provide a detailed introduction Volcanism to the diversity of observed volcanic and tectonic processes present throughout the inner solar sys- The three flybys of Mercury by the Mariner 10 space- tem, from which the interested reader may explore craft in 1974–1975 returned images that raised the further – and farther. prospect of volcanism on the innermost planet. Smooth plains deposits were identified across the approximately 45% of the planet observed during Mercury that mission; some workers interpreted their large volumes, together with their embayment relation- Until very recently, Mercury (Fig. 1c) was the most ships with, and spectral distinctiveness from, sur- enigmatic of the inner solar system’s planets. Its rounding terrain, as evidence for a volcanic origin proximity to the Sun rendered telescopic obser- for these deposits (Murray et al. 1975; Strom et al. vations of Mercury from Earth difficult, and the 1975; Dzurisin 1978; Kiefer & Murray 1987; planet’s location in the Sun’s gravity well chal- Robinson & Lucey 1997). Yet, others argued that lenged mission designers. It was not until NASA’s Mercury’s smooth plains units were morphologi- Mariner 10 spacecraft flew past the planet in the cally similar to lunar highland plains, which were 1970s that the surface of Mercury was imaged shown to have been emplaced as fluidized ejecta directly for the first time and, even then, only a (Wilhelms 1976; Oberbeck et al. 1977). The pro- single hemisphere was observed. Those early data venance of smooth plains on Mercury therefore showed the planet’s surface to resemble superfi- remained unresolved until the three flybys of the cially that of the Moon, with ancient, cratered plains MESSENGER spacecraft in 2008–2009 (Fig. 1c). interspersed with expanses of younger smooth plains. Yet, unlike its larger terrestrial counterparts, Mercury does not have primary volcanic features, Smooth plains. MESSENGER imaged almost the such as the giant shield volcanoes that dominate entire surface of Mercury during its flybys, and the Tharsis province on Mars. The volcanic charac- showed the smooth plains to be a globally present ter of Mercury, therefore, remained an open ques- unit, the majority of which is volcanic in nature tion until the planet was visited by the MErcury (Fig. 2). This inference is based on superposition Surface, Space ENvironment, GEochemistry, and relations indicative of the sequential embayment of Ranging (MESSENGER) mission. However, the impact basins and ejecta, as well as spectral homo- tectonics of Mercury were readily visible from the geneity but colour variation, partially buried impact outset of its exploration by spacecraft. Long, cliff- structures, and thicknesses of hundreds to thou- like escarpments were observed across the Mariner sands of metres (Head et al. 2008, 2009; Denevi 10 hemisphere, with wrinkle ridges akin to those et al. 2009). Observations made after MESSENGER in lunar maria populating the planet’s smooth plains entered orbit about the planet in March 2011 have units. Even so, the spatial extent, styles and amount allowed for the spatial extent of Mercury’s smooth of tectonic deformation of Mercury are questions plains to be quantified (Denevi et al. 2013): these that could only be fully explored from orbit. This plains are now known to occupy some 27% of the section describes the current state of knowledge of surface of Mercury (Fig. 2). Notably, the single Mercury’s volcanic and tectonic character, places largest contiguous smooth plains unit on the planet these findings in the context of how our understand- has been identified at high northern latitudes (Head ing of the innermost planet has evolved, and high- et al. 2011). Occupying around 6% of the total planet lights key aspects of the geological development surface, this region has been termed the northern of Mercury that have yet to be answered. volcanic plains (NVP) (Fig. 3a). Fig. 1. The principal components of the inner solar system include the four terrestrial planets, Mercury, Venus, Earth and Mars, as well as Earth’s moon and the two moons of Mars. The main asteroid belt separates the inner and outer portions of the solar system. On a yet smaller scale are objects that come close to Earth’s neighbourhood (on astronomical scales) or cross Earth’s orbit; these are collectively termed Near Earth Objects (NEO). At time of writing, there are 11 057 NEAs, of which 861 are larger than 1 km in diameter. (a) View of the inner solar system from above the ecliptic plane. The yellow dots denote Near Earth Asteroids; white triangles denote Near Earth Comets (courtesy of P. Chodas; 1 April 2014; NASA/JPL; http://neo.jpl.nasa.gov). (b) View of the inner solar system from the edge of the ecliptic plane. The orange line represents Jupiter’s orbit (courtesy of P. Chodas; 1 April 2014; NASA/JPL; http://neo. jpl.nasa.gov). (c) Enhanced colour mosaic of Mercury in orthographic projection centred at 08 (wide-angle camera of the Mercury Dual Imaging System; NASA/John Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington). (d) Global view of Venus centred at 1808E (Magellan Synthetic Aperture Radar Mosaic; NASA/JPL). (e) Nearside view of the Moon (Lunar Reconnaissance Orbiter wide-angle camera mosaic; NASA/GSFC/Arizona State University). (f) Global view of Mars centred at 208N, 3008E (Viking Orbiter 1 mosaic; NASA/JPL/USGS). 4 Downloaded from http://sp.lyellcollection.org/ T.