Chapter 14: Planetary Geology: Moon, Mars and Meteorites

This book contains exercises for a physical geology lab class. It is under development, with a full 1st edition release planned for Fall 2024.

The goals of this chapter are:

  • Understand evolution of rocky planets
  • Compare various physical features seen on Earth with other planets
  • Evaluate relative ages on planets

Recent planetary missions by NASA and other space agencies have confirmed that geological processes you have investigated on Earth also help create rocky planets and moons. Common processes link the internal structure and landscapes of both rocky and icy worlds as well as volcanoes, impact craters, ice caps, dunes, faults, rivers, and oceans as features of extra-terrestrial worlds as diverse as Venus and Io. Each new mission to space reveals that many supposedly dead planetary bodies currently experience eruptions, landslides, and dust storms. Moreover, our understanding of the Solar System has increased by studying meteorites from asteroids and Mars as well as rock samples collected on the Moon.

Rocky planets (or terrestrial planets) are relatively small when compared to the Gas Giants or many of the recently discovered exoplanets. Rocky planets have solid surfaces, often pockmarked by impacts seen as craters. These don’t have rings with few or no moons. They may have evidence of past or current tectonic as well as volcanic activity. As on Earth, the rock cycle explains how the three rock types relate to each other and the process of how they change over time. We’ve spent a lot of time talking about the rocks on Earth, but do other planets have rock cycles? 

At the beginning of the semester, you may have gone over the history of the solar system and the formation of planets such as Earth. Some of the evidence for the structure of the Earth (Figure 2.2) comes from meteorites. Meteorites represent fragments of the early solar system. There are three types of meteorites: stony, iron, and stony-iron. So, how do you identify these? They are typically dense, possibly magnetic, have unusual shapes, sometimes with pits, and often have a “fusion crust” that forms when the meteorite falls through the atmosphere. Many possible meteorites are rocks, minerals, or slag left over from making steel.

  • Stony meteorites are composed of silicates and other materials. Most stony meteorites also contain both iron and nickel metal. These are by far the most common type; some 94% of all meteorites are stony.
  • Iron meteorites are composed of iron (Fe) and nickel (Ni) and sometimes cobalt (Co) and other trace elements and minerals. Iron is the predominant metal with a variable ratio of iron to nickel.
  • Stony-irons are a combination of iron and stony meteorite properties and are the rarest type of meteorite. Pallasites are simply spectacular stony irons. In a polished slice, you can see iron-nickel metal that surrounds crystals of olivine.

Exercise 14.1 – Meteorites and Internal Structure of Rocky Planets and Planetesimals

As of March 2024, 361 confirmed meteorites have been collected in Texas. Recently, some were lucky enough to witness a meteorite fall near Brownsville TX on Feb 12, 2023. Six days later meteorite hunters found pieces near El Sauz TX.

Figure 14.1 shows three different types of meteorites. Typically, any meteorite with metal is made into a polished slab (Fig 14.12 A and D)

  1. Which of these is from the core of a planetesimal?
  2. Which represents crustal material?
  3. Which represents the core-mantle boundary?
  4. Critical Thinking: What do the materials (metal, stony-metal, and stony) imply about the early processes of planet formation in terms of planetary structure? (hint: recall that oil and water do not mix but have a meniscus between them.) Do you think that silicate and metal liquids mix or not? Explain.
    Five meteorites from Texas
    Figure 14.1 Five meteorites found in Texas. A and B are iron meteorites with A as a polished slab and B unpolished piece; C is a cut slab of an aubrite; D and E are the same pallasite meteorite with D as a polished slab and E unpolished piece. Image credits: all images from Meteoritical Bulletin Database with A. Iron IIIAB found in Davis Mountains in 1903, photo by Don Edwards, ~ 1 cm across; B. Iron IIAB found in Iredell TX in 1898 photo by Don Edwards, ~1 cm across; C. Aubrite found in Pena Blanca Spring, Brewster Co TX in 1946, photo by Peter Marmet, ~3 cm across; D. Pallasite found in Sterley TX in 1950, photo by KD Meteorites, ~9 cm across; E. unpolished slab of pallasite found in Sterley TX in 1950, photo by L. Garvie, ~12 cm across.

     

Let’s look at Mars, sometimes called the Red Planet, which is the fourth planet from the Sun (Figure 14.2). Mars has some Earth-type characteristics, such as polar ice caps, mountains, sand dunes, and clouds. It is by far the planet most visited by spacecraft in our solar system. As of 2024, 21 lander missions and 8 sub-landers (rovers and penetrators) attempted to land on Mars. Of 21 landers, the Curiosity and Perseverance rovers are currently still in operation on Mars. Curiosity rover has long outlived its expected mission as it has been roaming the surface of Mars for over 11 years!

Topography of Mars
Figure 14.2 – Global false-color topographic views of Mars from the Mars Orbiter Laser Altimeter (MOLA). The vertical accuracy is less than 5 meters. The right-hand image view features the Hellas impact basin (in purple) and Elysium Mons (isolated white region). The left-hand features the Tharsis topographic rise (in red and white) and Valles Marineris (linear blue region): Image Credit: NASA Public Domain

 

Exercise 14.2 – Martian Rock Cycle

Today, Mars is no longer volcanically or tectonically active. However, remnants of Mars’ massive volcanoes remain (Figure 14.3). Its most recent eruption is estimated to have occurred only 50,000 years ago near Elysium Mons. In fact, some attribute recent Mars quakes to movement of magmas. To distinguish features on planets from those on Earth, mountains are called Mons (singular) or Montes (plural).

Map of volcanoes on Mars
Figure 14.3 – Map of Olympus Mons and Tharsis Montes region on Mars. Image credit: Sémhur, CC BY-SA.
  1. Tharsis Montes are three enormous volcanoes located within the Tharsis region of Mars. These volcanoes form a straight line each other and align with other volcanoes in the region such as Ceraunius Tholus and Uranius Mons. What does this chain of volcanoes in the Tharsis region suggest about volcanic and tectonic history of this region?
  2. Figure 14.4 is a picture of an igneous rock taken by NASA’s Curiosity Mars rover. The light-colored, elongated crystals are likely feldspar; some are 1 cm in size. The dark-colored matrix surrounding the feldspar is pyroxene.
    1. Describe the texture and cooling history of the rock.
    2. Is this rock felsic, intermediate, mafic, or ultramafic? How can you tell?
      Igneous rock from Mars
      Figure 14.4 – Martian rock ‘Harrison’ from inside Gale crater on the lower slope of Mount Sharp. Created by merging images from two cameras on NASA’s Curiosity Mars rover. Annotated figure includes a scale bar in the upper right. Image credit, NASA, Public Domain.
  3. Figure 14.5 is a picture of a sedimentary rock taken by NASA’s Curiosity rover.
    1. Describe the texture of the rock.
    2. How much energy is needed to transport the pebbles?
    3. Today, the main mechanism for sediment transport on Mars is wind. What features do you see that either support or don’t support this method of sediment transport?
    4. If this rock were from Earth, what type of environment would you find it?
    5. What does this imply about Mars’s geologic history?
    6. At present, could there be water on Mars?
      Image of Martian rock
      Figure 14.5 – Image of the Martian rock “Link” taken by the Mars Curiosity Rover. The color was changed to resemble conditions on Earth. Image credit: NASA, Public Domain.
  4. Do you think we could find metamorphic rocks on Mars? Use Figures 14.6 to help.
    Satellite image of a Martian impact crater
    Figure 14.6 – A photograph of an impact crater from Mars taken form the European Space Agency’s Mars Express spacecraft. Image credit. ESA/DLR/FU Berlin, CC BY-SA IGO.

     

  5. Meteorites also hold clues about metamorphism of our solar system and Mars. Figure 14.7 shows two different meteorites from Mars; one which originated from Mars during an impact about 700,000 to 1.1 million years ago and another which fell to the surface of Mars. Both of these images record possible metamorphic changes. Can you identify these processes?
    Two martian meteorites - one fell on Earth and the other on Mars
    Figure 14.7 – Two photos of Martian meteorites. A. Tissint meteorite that witnesses watched fall onto the Moroccan desert.  B. Curiosity rover has discovered several meteorites on the surface of Mars including “Egg Rock”. Several small white pits show where the rover analyzed the rock confirming it is an iron-nickel meteorite. Also, there are abundant white veins made of calcium sulfate (anhydrite, bassanite, and perhaps gypsum). Image credit: Annotated photos of Tissint meteorite James St. John and Egg Rock meteorite NASA, Public Domain.
  6. Another way to investigate planetary surfaces is to use satellites equipped with spectrometers such as CRISM (Compact Reconnaissance Imaging Spectrometer for Mars). CRISM uses detectors that see in visible, infrared and near-infrared wavelengths to map the minerals that have water in their structure. This spectrometer surveyed the surface of Mars from March 2006 until January 2023. Figure 14.8 shows a geologic map of the Terra Sirenum region with relative ages based on impact relationships. Also shown are some of the CRISM results showing mineral locations for both minerals in igneous rocks (primary minerals) as well as secondary minerals formed by either metamorphism, hydrothermal activity or evaporite (lake systems).
    1. Look at the distribution of primary minerals. Do they occur only in impact craters? What is their age?
    2. Look at the distribution of secondary minerals. Do they occur only in impact craters? What is their age?
    3. The presence of gypsum (a common variety of polyhydrated sulfate) may indicate evaporite deposits. Do these occur only in impact craters? What is their age?
    4. Critical thinking: According to Viviano et al. (2023), this region has 30% more secondary minerals than other areas on Mars. Why do you think this area has more secondary minerals?
Geologic and mineral map of the Terra Sirenum region, Mars
Figure 14.8 Geologic map and mineral map in the Terra Sirenum region of Mars which is southwest of Arsia Mons (Figure 14.3). In part A, geologic units are Amazonian-Hesperian impact (AHi) 3.7 Ga to present, and Noachian (mNh, middle Noachian highlands, lNh, late Noachian highlands, eNh, early Noachian highlands) 4.1 to 3.7 Ga. These relative ages are from Tanaka et al. (2014). In part B, primary minerals indicate the presence of mafic igneous rocks with olivine and pyroxene (low calcium LCP and high calcium HCP). Secondary minerals include metamorphic chlorite, prehnite, epidote, mica (biotite), clay (kaolinite) and gypsum (polyhydrated sulfate). White arrows indicate a new discovery of kaolinite identified recently using CRISM data. Image Credit: Viviano et al. (2023), CC BY.

 

Next, let’s explore Earth’s moon. You may have heard the fanciful saying that the moon is made of Swiss-cheese. Well, what looks like holes are actually the sites of impact craters. There are thousands of craters on both the moon and Mars and only ~190 on Earth. Planetary scientists use the law of superposition with these craters to determine relative ages of the moon and other planets. The lunar geological timescale has five periods: the Copernican, Eratosthenian, Imbrian, Nectarian, and Pre-Nectarian. The absolute ages for these periods have been constrained by radiometric dating of samples obtained from the lunar surface.

Exercise 14.3 – Lunar Geology and relative time

Head to this interactive map of the Moon created from images with the Lunar Reconnaissance Orbiter Camera.

  1. Separate the moon’s surface into different types using any criteria. What are the criteria you used and why?
  2. Share your criteria with the class and compare answers.

Hopefully, you picked up on the distinction between two different colors on the Moon’s surfce: a lighter shade of white or gray and darker colored areas. The lighter areas are the lunar highlands and are composed of anorthosite, a special type of granite with mostly calcium-rich feldspar. The darker areas are the lunar mare or maria, composed of a special type of basalt called KREEP, which has high concentrations of potassium (K), rare-earth elements (REE), and phosphorus (P).

  1. Describe the distribution of craters on the moon. Is there any distinction between the highlands and the maria?
  2. You may have heard about recent attempts to land on the South Pole of the moon with two failed missions from Japan and Russia and two successful missions including India’s Chandrayaan-3 and the short-lived Odysseus mission by Houston based Intuitive Machines . NASA has proposed that the first Artemis III flight land in this region in 2026. Describe the landscape in this region. Why is there renewed interest in landing in this region?
  3. Critical Thinking: Some areas of the moon have more craters than others. Why? Note: Under the layers tab > ACT Layers, turn on TerrainHillshade to really see the difference.

As you found out in Chapter 10 on geologic time, cross-cutting relationships is a principle in geology used to decipher the relative ages of rocks and geologic features. This principle is based on the concept that a rock or feature must be younger than any rock or feature it cuts across. We can apply this principle to determine the relative ages of features on other planetary bodies. In this exercise, we will look at images of the surface of Mars and apply the principle of cross-cutting relationships to determine their relative ages. However, unlike Earth, planets do not have fossils to help determine relative ages.

What else can substitute for fossils on other rocky worlds? As you saw on the Moon, that something else is impact craters. This works except when they’ve been obliterated by active geology as Venus, Io, Europa, Titan, and Triton. We use craters to establish relative age dates in two ways. If an impact event was large enough, its effects were global in reach. For example, the Imbrium impact basin on the Moon spread ejecta all over the place. Any surface that has Imbrium ejecta lying on top of it is older than Imbrium. Any craters or lava flows that happened inside the Imbrium basin or on top of Imbrium ejecta are younger than Imbrium. Imbrium is therefore a stratigraphic marker — something we can use to divide the history of the Moon. The second method is that they may also crosscut each other. For example, the surface of Mercury has many landforms including ridges (rupes) and craters. Figure 14.7 shows that the ridges may be younger than some craters yet older than others. In fact, there are craters that crosscut other craters!

False-color image of ridges and craters on Mercury
Figure 14.9 – A false-color image of Mercury showing Carnegie Rupes (ridge), a large tectonic landform, which cuts through Duccio crater. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Public Domain.

Exercise 14.4 – Relative Dating on Mars

Figure 14.10 is a Google Earth image from Mars that shows craters, fractures, and river channels. Use the principle of cross-cutting relationships to answer the following questions.

  1. Which is older, Crater A or Fracture A? How can you tell?
  2. Which is older, Crater B or Channel A? How can you tell?
  3. Is Crater C younger or older than Crater B? How can you tell?
  4. If Channel B cuts through both Crater B and Fracture A, is Crater A younger of older than Crater B?
  5. Look at Figure 14.11. Arrange the craters in relative order from oldest to youngest.
Satellite image of Martian geomorphology
Figure 14.10 – Surface image from Mars. Approximate coordinates are 18.38° N 76.75° E. Image credit: adapted from Google Earth.
Satellite image of Mars
Figure 14.11 – Surface image from Mars. Image credit: adapted from Google Earth.

As you learned in the landscape chapter, dunes are classified by the amount of sand and wind direction (Figure 13.X). On Earth, vegetation also influences dune morphology, but in the rest of the solar system, vegetation is not an issue. Sand refers to grain size and is just a small solid particle, which can be basaltic (Mars) or even solid methane if you are in the outer solar system (Titan and Pluto).

Planetary geologists have identified dunes on Earth, Venus, Mars, Titan (moon of Saturn), Triton (moon of Neptune), Io (moon of Jupiter), and Pluto as well as one comet. To interpret these, look for shadows on the dunes. This is the steep versus gentle slope on the dune. The steep side will be the downwind side for barchan, transverse, barchanoid, and star dunes. When looking at these images, you must ignore the features that are not dunes, such as hills, mesas, buttes, craters, etc.

Exercise 14.5 – Winds and Dunes in our Solar System

As you learned in the landscape chapter, dunes are classified by the amount of sand and wind direction (Figure 13.X). On Earth, vegetation also influences dune morphology, but in the rest of the solar system, vegetation is not an issue. Sand refers to grain size and is just a small solid particle, which can be basaltic (Mars) or even solid methane if you are in the outer solar system (Titan and Pluto).

  1. Figure 14.12 shows several dunes from Mars. On each image, use arrows to show the direction(s) of the wind. Also mark a spot where you might land to explore this region.  For each image, determine the dune type, number of wind directions, and relative amount of sediment.
  2. Complete Table 14.1. For each image, determine the dune type, number of wind directions, and relative amount of sediment.
    Table 14.1 – Martian Dune Data
    Location Dune type(s) # of wind directions Sediment amount
    A. Summer dunes (43° N)
    B. Dunes in crater (12° S)
    C. Winter Dunes (76° N)
    D. Chasma Boreale (85° N)
    Four images of Martian dunes
    Figure 14.2 – Four false-color images of Martian dunes. A. Dunes sitting on white ridges of gypsum that are deposited on basalt. B. Dunes formed within an impact crater with mound in the center that appears to have blocked the wind. C. Dunes with frost. Image collected on Martian winter solstice (7/22/22). This frost is mixture of carbon dioxide and water ice. D. Dunes on Mars from the north polar ice cap in the Chasma Boreale region.  The white areas show irregular polygonal patterns developed in carbon dioxide ice (dry ice). The dunes are made of basalt and gypsum grains. Image credit: False-color HiRISE image from NASA/JPL-Caltech/UArizona Public domain.
  3. Now that you’ve analyzed dunes from several places on Mars, let’s see if you make any generalizations about winds and sediment supply on the Mars. Do these all places have only one direction of wind.
  4. Does the number of wind directions change with distance from the Martian equator?
  5. Is the sediment supply the same in the different Martian examples? Rank them from most to least amount of sediment.
  6. Critical Thinking: Which of these dunes fields is where you would like to go explore?  Just choose one and explain why you chose that place.

Additional Information

Exercise credit

Virginia Sisson, Kaitlin Thomas, and Daniel Hauptvogel

References 

Hare, T.M, R.K. Hayward, J.S. Blue, and B.A. Archinal, 2015, Image mosaic and topographic map of the moon, 2 sheets, U.S. Geological Survey Scientific Investigations Map 3316, doi:10.3233/sim3316

Tanaka, K.L., Robbins, S.J., Fortezzo, C.M., Skinner, J.A., Jr., and Hare, T.M., 2014, The digital global geologic map of Mars: Chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history, Planetary and Space Science, v. 94, p. 11-24., doi:10.1016/j.pss.2013.03.006

Viviano, C.E., Beck, A.W., Murchie, S.L., Dapremont, A.M., and Seelos, F.P., 2023, Heterogeneity of the Noachian crust of Mars Using CRISM multispectral mapping data, Geophysical Research Letters Volume 50, Issue 5 e2022GL102711: doi:10.1029/2022GL102711

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Investigating the Earth: Exercises for Physical Geology Copyright © by Daniel Hauptvogel; Virginia Sisson; and Michael Comas is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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