Terrestrial Analogues - Parallels between two worlds

All data sets used in planetary geology have limited resolution, and many also have incomplete coverage. Planetary geologists are required to make predictions from geologicaldata that are often sparsely distributed or incomplete. Interpreting planetary (as well as terrestrial) geological data is typically an under-constrained problem (e.g., Bond et al., 2007). Therefore, the knowledge of terrestrial analogues and the ability to apply them to "planetary" problems is an important aspect of planetary geology. It is well recognized that interpretations of Mars must begin with the Earth as a reference. The most successful comparisons have focused on understanding geologic processes on the Earth well enough to extrapolate to Mars'' environment (e.g., see reviews by Farr et al. [2002] and Farr [2004].

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Figure 1: Analogs used in morphological, physical, chemical, mineralogical and exobiologic studies related to the Martian surface. Note that this list is not intended to include all analogs used so far in Mars studies (which would far exceed the scope of this document), but to provide a few selected examples.
valley networks volcanoes dunes polygonal pattern rock glaciers outflow channels gullies impact craters hemalite marbles mafic minerals phyllosilicates sulphates moats wind tails

Several aspects of terrestrial analog studies have been pursued and are continuing (Table 1/Fig. 1). These studies include field workshops, characterization of terrestrial analog sites (e.g., Fig. 2), instrument tests, laboratory measurements (including analysis of Martian meteorites), and computer and laboratory modeling.The combination of all these activities allows scientists to constrain the processes operating in specific terrestrial environments and extrapolate how similar processes could affect Mars. Analogs are also a powerful tool for education or public outreach activities, because people will often gain access to scientific questions if confronted with something they are familiar with (Fig. 3).

  Analog Mars Earth
Morphological Fluvial
Periglacial
Volcanic
Impact		 Outflow Channels
Polygonal patterns
(e.g., in Utopia Planitia)
Low shield volcanoes
Impact craters		 Channeled Scablands (Washington State, USA)
Ice-wedge polygons (e.g., Siberia)
Snake River Plains (Idaho, USA)
Roter Kamm (Namibia)
Physical Ice stability
Rover operations
Thermal studies		 Near surface ice
Soil at Mars landing sites
Possible Martian caves		 Buried ice in Antarctica
Field sites for rover testing
Terrestrial caves
Chemical Oxygen isotopes (as possible biosignature) Mafic and ultramafic rocks Carbonate cements in ophiolite
Mineralogical Primary igneous rocks
Alteration minerals
Mineral assemblages		 Basalts
Hydrated sulfates
MER results in Meridiani Planum		 Basalts
Evaporites
Rio Tinto (Spain)
Climatic Dry environments
Cold environments		 Mars surface
Mars surface		 Atacama Desert (Chile)
Antarctic Dry Valleys
Biologic Organisms
Environments		 Possible Martian organisms
Possible Martian habitats		 Extremophiles (e.g., endolithic)
Extreme habitats (e.g., Antarctica)
Figure 2: Earth or Mars? Blueberry-size concretions of haematite found by the MER rover Opportunity (left) have been interpreted as products of diagenesis on the basis of their analogy to haematite "marbles" found in Utah (right). From Catling [2004].
Figure 2: Earth or Mars? Blueberry-size concretions of haematite found by the MER rover Opportunity (left) have been interpreted as products of diagenesis on the basis of their analogy to haematite "marbles" found in Utah (right). From Catling [2004].
Figure 3: The comparison of planetary features with well-known terrestrial analogs helps to raise public interest in planetology and will allow immediate access to scientific questions. The caldera of Olympus Mons on Mars (left; simulated 3D-view derived from HRSC stereo images) can be directly compared to the caldera of Mauna Loa (Hawaii, USA; photo by D.W. Peterson), which is known to many people by media or even by personal experience from a visit.
Figure 3: The comparison of planetary features with well-known terrestrial analogs helps to raise public interest in planetology and will allow immediate access to scientific questions. The caldera of Olympus Mons on Mars (left; simulated 3D-view derived from HRSC stereo images) can be directly compared to the caldera of Mauna Loa (Hawaii, USA; photo by D.W. Peterson), which is known to many people by media or even by personal experience from a visit.

A broad community survey of the current state of solar system exploration, initiated by the US National Research Coucil at the request of NASA to provide recommendations for the coming decade, has considered sidered the following two key questions related to analog studies [Farr, 2004]:

  1. How do terrestrial analog studies tie in to the Mars science questions about life, past climate, and geologic evolution of Mars?
  2. How can future instrumentation be used to address these questions?

Last update: 31/05/2010 14:06