Planetary science: Multiple data sets, multiple scales, and unlocking the third dimension Paula Martin* Department of Earth Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK Ellen R. Stofan* Proxeny Research, 20528 Farcroft Lane, Laytonsville, Maryland 20882, USA ABSTRACT ogy. The experience gained at Mars will help obtain images or analyze samples at distances us to plan and exploit the 3-D exploration of of up to several meters. Remotely sensed data Observations of the planets in our solar other planets in the future. encompass all the data collected by spacecraft in system cover a wide range of scales and are orbit around a planet, or as a spacecraft fl ies-by undertaken using a variety of techniques Keywords: planetary, Mars, surface, subsur- a planet en route to another location. In general, and platforms, resulting in extremely rich face. in-situ data provide highly detailed information data sets. This review paper provides a basic about a location that is somewhat limited in introduction to the available range of plan- INTRODUCTION size, whereas remotely sensed data provide less etary science data sets, and the combination detailed information about a location that cov- of these data sets over a range of scales, reso- Planetary science provides a basis from ers a much wider area (often >90% of an entire lutions, and techniques to address geological which to consider the formation and evolution planetary surface). In-situ data provide “ground problems. The wealth of data available and of Earth in a wider context. It can be used as truth,” which is then used to expand the interpre- the use of a selected combination of data sets a prompt to reconsider the bigger picture, and tation of remotely sensed data sets. to address geological problems are best illus- ask fundamental questions such as: Why does All of the data from NASA planetary missions trated by taking a closer look at the planet plate tectonics occur only on Earth, and not on can be accessed through the NASA Planetary Mars. As a result of the increasing preci- other planets? In the absence of plate tectonics, Data System (PDS) (for more information, see sion of spacecraft sensors, we now have data how do other planets lose their heat? What are http://pds.jpl.nasa.gov/), or by contacting your sets that cover the whole planet at spatial the major mechanisms for planetary resurfac- local NASA Regional Planetary Image Facility resolutions ranging from kilometers down ing? What geological processes operate on each (RPIF) (for more information, see http://www. to meters (e.g., Mars Global Surveyor) and planet (and how and when do they operate)? lpi.usra.edu/library/RPIF/). All of the data multiple wavelengths (e.g., Mars Reconnais- The data available to us to try to address these from ESA planetary missions can be accessed sance Orbiter), which have been collected questions can be divided into two distinct types: through the ESA Planetary Science Archive over several years. This global coverage is in-situ data and remotely sensed data. In-situ (PSA) (for more information, see http://www. complemented by surface missions that pro- data encompass all the data from the Apollo mis- rssd.esa.int/index.php?project = PSA). Data vide localized data sets down to microscopic sions to the moon, and all other data collected from each mission are made available follow- resolutions (Mars Exploration Rovers). Thus, by instruments located on the surface of planets, ing a proprietary period, which varies in length it is now possible to study geological features including both stationary landers and rovers. for each mission (but is typically a number and processes quantitatively over an impres- It should be noted that not all in-situ data are of months following initial acquisition of the sive range of scales. The combination of new obtained by instruments strictly in physical con- data), during which time the data are processed data sets from current and future missions to tact with the planetary surface. For example, all and analyzed by the team of mission scien- Mars (e.g., Mars Express and Mars Recon- imaging and geochemical instruments on board tists. Updates to the available data are made naissance Orbiter) will facilitate attempts to stationary landers and rovers are generally con- on a regular (e.g., monthly or quarterly) basis, unlock the third dimension of Martian geol- sidered to be in-situ instruments, even those that following the proprietary period, to facilitate *[email protected]; [email protected]. Geosphere; December 2007; v. 3; no. 6; p. 435–455; doi: 10.1130/GES00089.1; 18 fi gures. For permission to copy, contact [email protected] 435 © 2007 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/435/854324/i1553-040X-3-6-435.pdf by guest on 01 October 2021 Martin and Stofan further analysis and interpretation. The total Surveyor Missions (1990s). Each of the space- missions over the past 30 yr. The Viking orbit- planetary data archive is vast; for example, the craft, landers, and rovers used in these missions ers, in the 1970s, provided grayscale images data archive for the Thermal Emission Imaging carries a wide-ranging suite of scientifi c instru- of the Martian surface at resolutions of 150 to System (THEMIS) instrument, which is just ments, including high-resolution imagers and 300 m per pixel (e.g., Fig. 1), dependent on the one of three major instruments on board the spectrometers, instruments used to identify the elevation of the spacecraft above the Martian Mars Odyssey spacecraft, is expected to grow to physical properties of the planetary surface such surface (e.g., Snyder and Moroz, 1992). More approximately 6 TB. as thermal emission and topography, and instru- recently, the Mars Orbital Camera (MOC) In this review paper, we will use the explora- ments used to investigate the geophysical prop- instrument, on board the Mars Global Surveyor tion of the planet Mars to provide examples of erties of the planet as a whole, such as gravity (MGS) spacecraft, was designed to routinely the range of planetary data that is available, the and magnetic fi elds. More recently, spacecraft acquire images at three different, complemen- range of instruments used in planetary explora- have also begun to include radar sounders to tary resolutions, using a limited number of color tion, and the range of scales that these instru- penetrate the planetary surface and attempt to fi lters: (1) global images, typically at a resolu- ments cover. We will discuss the use of plan- identify the properties of the subsurface. More tion of 7.5 km per pixel; (2) wide-angle, context etary data sets to develop our understanding of information about the different types of scien- images, typically at a resolution of 240 m per planetary surfaces and possible ways of access- tifi c instrumentation used in Mars Exploration is pixel, using red and blue fi lters; and (3) narrow- ing the third dimension on a planetary scale. available through the NASA Mars Exploration angle, high-resolution images, typically at a Web site: http://mars.jpl.nasa.gov/. resolution of 1.5 to 12 m per pixel (e.g., Fig. 2) OVERVIEW OF MARS EXPLORATION (Albee et al., 1998). Following the huge success MARS IMAGE AND COMPOSITIONAL of the MOC instrument, the Mars Reconnais- There are three spacecraft currently in orbit DATA sance Orbiter (MRO) spacecraft carries three around Mars acquiring and returning data to separate imaging instruments that operate over Earth: Mars Odyssey (2001), Mars Express The wide variety of spacecraft, landers, and a range of scales comparable with those cov- (2003) and Mars Reconnaissance Orbiter rovers involved in Mars exploration and their ered by MOC and incorporate a wider range (2006), in addition to the two Mars Explora- associated instrumentation allow us to investi- of color options (Zurek and Smrekar, 2007). tion Rovers (2003), Spirit and Opportunity, that gate the Martian surface over a wide range of Firstly, the Mars Color Imager (MARCI) takes are currently exploring the Martian surface. scales, covering many orders of magnitude. global images at fi ve visible and two ultravio- These current missions continue to acquire The rich diversity of the available data can be let wavelengths, typically at a resolution of 1 data that complement that acquired by previ- illustrated by considering the range of resolu- to 10 km per pixel (e.g., Fig. 3). Secondly, the ous missions such as Viking (1970s), and the tions, and the range of wavelengths, of imaging Context Camera (CTX) takes grayscale images, more recent Mars Pathfi nder and Mars Global instruments used by a selection of the various typically at resolutions of 6 m per pixel (e.g., Figure 1. Viking Orbiter 1 image of Meridiani Planum. The red and yellow ellipses indicate the designated landing site for the Mars Explo- ration Rover, Opportunity. The ellipses are ~71 km long; north is up. Image credit: NASA/JPL. 436 Geosphere, December 2007 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/435/854324/i1553-040X-3-6-435.pdf by guest on 01 October 2021 Planetary science Figure 2. Pair of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow-angle images showing the landing site of the Mars Exploration Rover, Opportunity, in Meridiani Planum, before and after the landing. The fi rst (top) image was acquired on 24 August 2003, fi ve months prior to the 25 January 2004 landing. The second (bottom) image was acquired on 1 February 2004, and shows Opportunity located within an ~20–m–diameter crater. In both images north is up; the second (bottom) image is ~1.4 km wide.