Mars Climate History and Habitability

Overview

Mars was not always the cold, dry desert we see today. Extensive evidence indicates that 3-4 billion years ago, Mars had a thicker atmosphere, warmer temperatures, and liquid water flowing on its surface. In this two-part lesson, students investigate what changed, why it changed, and what that means for the future of human settlement on Mars.

Background for Teachers

Mars Climate Timeline

Noachian Period (4.1 - 3.7 billion years ago):

• Thicker atmosphere with significant greenhouse warming
• Liquid water on the surface — rivers, lakes, possibly an ocean in the northern lowlands
• Active volcanism releasing gases into the atmosphere
• Magnetic field may still have been active early in this period
• Most clay minerals found on Mars date to this era

Hesperian Period (3.7 - 3.0 billion years ago):

• Climate cooling and drying
• Catastrophic floods carved massive outflow channels
• Volcanic activity produced sulfate minerals
• Atmosphere thinning as Mars lost its magnetic field and solar wind stripped gases

Amazonian Period (3.0 billion years ago - present):

• Cold, dry conditions similar to today
• Water primarily exists as ice (polar caps, subsurface)
• Thin atmosphere (6 millibars, ~0.6% of Earth’s)
• Obliquity (axial tilt) variations cause periodic climate shifts

Why Mars Lost Its Atmosphere

Mars’s core cooled and solidified, shutting down its global magnetic field approximately 4 billion years ago. Without a magnetic field, solar wind — a stream of charged particles from the Sun — directly interacts with the upper atmosphere, gradually stripping it away. NASA’s MAVEN orbiter has measured this atmospheric loss in real time and confirmed it as a major factor in Mars’s climate change.

The Pressure Problem

At Mars’s current atmospheric pressure (about 6 millibars), liquid water is unstable at most surface temperatures. At low pressure, water transitions directly between ice and vapor (sublimation) without passing through a liquid phase. This is described by the phase diagram of water, which students will explore in this lesson.

Lesson Procedure

Day 1: What Happened to Mars’s Climate? (45 minutes)

Opening Provocation (5 minutes)

Display two images side by side:

1. Artist’s rendering of ancient Mars with oceans and a blue sky
2. Current Mars surface photo from a rover — barren, red, dry

“Both images show the same planet. What happened?”

Climate Timeline Activity (20 minutes)

Provide student groups with a set of Mars Climate Timeline Cards. Each card contains one piece of evidence with a date range:

• “Valley networks carved by flowing water — 3.8 billion years ago”
• “Clay minerals formed in the presence of water — 4.0 billion years ago”
• “Sulfate minerals indicating acidic, evaporating water — 3.5 billion years ago”
• “Mars’s magnetic field shut down — 4.0 billion years ago”
• “MAVEN measures atmospheric loss to solar wind — present day”
• “Giant outflow channels from catastrophic floods — 3.2 billion years ago”
• “Polar ice caps with layered deposits — present day”
• “Methane detected in atmosphere (possible geological or biological source) — present day”

Task: Arrange cards in chronological order and create a visual timeline on chart paper. Use arrows and annotations to show cause-and-effect relationships (e.g., “magnetic field loss leads to atmospheric stripping leads to water loss”).

Class discussion: Compare group timelines. What is the overall trend? (warm and wet to cold and dry)

The Greenhouse Effect and Atmospheric Loss (20 minutes)

Mini-lecture with demonstration:

1. Explain the greenhouse effect using a simple diagram:

   • Sunlight enters atmosphere and warms the surface
   • Surface radiates heat (infrared radiation)
   • Greenhouse gases (CO2, water vapor) trap some heat
   • Result: warmer surface temperatures

2. “Mars once had a much thicker atmosphere with more CO2 and water vapor. This created a greenhouse effect that kept the planet warm enough for liquid water.”

3. What went wrong:

   • Mars is smaller than Earth, so its interior cooled faster
   • The iron core solidified, and the magnetic field died
   • Without a magnetic field, solar wind bombarded the upper atmosphere
   • Over billions of years, most of the atmosphere was stripped away
   • Less atmosphere means less greenhouse warming means colder temperatures
   • Colder temperatures mean water freezes or sublimates — it cannot remain liquid

4. Demonstration: If available, use a bell jar vacuum pump with a small container of warm water. As pressure decreases, the water begins to boil at room temperature, illustrating how low pressure destabilizes liquid water. (If no vacuum pump is available, discuss the concept using a water phase diagram.)

Day 2: Habitability Assessment and Future Settlement (45 minutes)

Water Phase Diagram (15 minutes)

Introduce a simplified water phase diagram showing the relationship between pressure and temperature:

• Solid (ice), liquid (water), and gas (vapor) regions
• The triple point: the minimum pressure at which liquid water can exist
• Mark Earth’s surface conditions (liquid water stable)
• Mark Mars’s current surface conditions (below the triple point — liquid water unstable)
• Mark ancient Mars conditions (above the triple point — liquid water stable)

Student exercise: Plot different scenarios on the phase diagram:

1. Earth sea level on a warm day
2. Top of Mt. Everest (lower pressure)
3. Mars equator at noon in summer
4. Mars polar region in winter
5. Inside a pressurized Mars habitat

Habitability Scorecard (15 minutes)

Students evaluate Mars habitability across three time periods using a structured scorecard:

For each cell, students rate the factor (available / limited / absent) and cite specific evidence.

Key insight: Ancient Mars scores surprisingly well on habitability metrics. Present Mars scores poorly for surface habitability but has resources that human technology can exploit. Future settlement requires engineering solutions for every deficit.

Engineering Solutions Discussion (10 minutes)

Brainstorm and discuss how future settlers will address each habitability challenge:

• Water: Extract from subsurface ice deposits; recycle all water in a closed-loop system
• Air: ISRU oxygen production from CO2 (MOXIE technology); plant-based oxygen supplementation
• Radiation: Underground habitats; water or regolith shielding; limit surface EVA time
• Energy: Nuclear reactors for base power; solar panels for supplemental power
• Food: Pressurized greenhouses; hydroponic and aeroponic farming; processed regolith as growing medium

Wrap-Up and Reflection (5 minutes)

“Mars lost its habitability through natural processes over billions of years. Humans have the technology to create pockets of habitability — pressurized, heated, oxygenated spaces where people can live and work. When humans reach Mars, they will not need to change the entire planet; they will need to build the right shelters and systems.”

Students write a brief reflection: “What is the most important lesson Earth can learn from Mars’s climate history?”

Assessment

• Climate timeline: Accurate chronological ordering with cause-and-effect annotations
• Phase diagram exercise: Correct plotting of conditions with explanations
• Habitability scorecard: Evidence-based ratings across all three time periods
• Reflection: Thoughtful connection between Mars’s climate history and Earth’s environmental challenges

NGSS Alignment

• MS-ESS1-4: Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth’s history
• MS-ESS2-6: Develop and use a model to describe how unequal heating and rotation of the Earth cause patterns of atmospheric and oceanic circulation
• MS-ESS3-5: Ask questions to clarify evidence of the factors that have caused the rise in global temperatures over the past century
• MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed

Extensions

• Research NASA’s MAVEN mission and its measurements of Mars atmospheric loss rates
• Model atmospheric escape: calculate how long it took for Mars to lose half its atmosphere at measured escape rates
• Compare Mars’s climate evolution with Venus — a planet that experienced runaway greenhouse warming instead of cooling
• Debate the ethics and feasibility of terraforming Mars — should humans attempt to restore Mars’s atmosphere?
• Investigate how Mars’s obliquity (axial tilt) changes over millions of years affect its climate cycles