Lesson 4 of 6 · Where did the atmosphere go?
Where did the atmosphere go?
10 minute lesson · 3 checks along the way
Your goal for this lessonTrack atmospheric material through multiple reservoirs and distinguish a budget from a unique history.
Follow a linked name to explore its archive card. “Back to your lesson” brings you to the same part of the reading.
Words with a dotted underline open a short definition right here in the lesson.
A thin atmosphere is still an atmosphere
Mars’s present atmosphere is thin and dominated by carbon dioxide. Pressure and temperature together make long-lived exposed liquid water difficult to maintain across most of the surface. This does not mean Mars has no atmosphere, no weather, or no water. Winds move dust, temperatures vary, and water exists as ice and vapor. Ancient rivers and lakes point to environments different from many of those seen today.
Reconstructing those environments requires several connected questions. How much gas was present? Which gases contributed to warming? How did surface conditions vary by location and season? How persistent were wet intervals? An atmospheric inventory alone does not determine temperature, because sunlight, greenhouse properties, clouds, dust, and surface conditions also matter. Models must explain geological evidence without assuming that one climate state persisted everywhere for all early Martian history.
Escape leaves measurable clues
MAVEN investigated how the upper atmosphere interacts with the Sun and loses material to space. Energetic radiation and particles can drive escape processes. Different isotopes of an element can escape at different rates, changing the mixture left behind. Measurements of that mixture help constrain past loss when combined with a physical model. The inference depends on which gas and process are being studied.
A present-day escape rate is not automatically the average rate over billions of years. The young Sun and the Martian atmosphere differed from today, and several loss mechanisms operate. Nor does losing a global magnetic field imply that every gas molecule immediately escaped. A useful history must account for changing conditions, uncertainties, and material stored elsewhere. The observations support substantial loss while leaving details of its timing and partitioning under investigation.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Rocks and ice belong in the accounting
Carbon dioxide can leave the air without leaving the planet. Carbon-bearing material may be incorporated into carbonate minerals, while ice reservoirs also exchange material with the atmosphere. In results reported in April 2025, Mars Science Laboratory Curiosity identified the iron carbonate in samples from three drill sites in sulfate-rich layers. That finding adds evidence for carbon stored in rock.
Those local measurements do not close the global carbon budget. How widespread are similar deposits, how thick are they, and which episodes formed them? Orbital spectra can miss a mineral that is obscured by other materials. Combining local mineral identification with regional mapping is therefore essential. A discovery can reveal an important missing reservoir while still leaving much of an ancient atmospheric inventory unexplained.
Check 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Work through a decision
Work the evidence: keep every reservoir
Use an invented carbon budget in consistent units of carbon amount. Start with 100 units in the atmosphere and add 20 through . Suppose net transfers remove 60 to space, 35 into rocks, and 5 into ice. The final atmospheric amount is 100 + 20 − 60 − 35 − 5 = 20 units. Across all listed destinations, the accounted total remains 120.
The atmosphere fell from 100 to 20, an 80-unit net decrease, yet only 60 units escaped the planet. Calling all 80 “lost to space” confuses reservoirs. Many different timings could also produce this same final budget. To distinguish histories, seek dated mineral formation, evidence, and models of changing escape conditions. This exercise conserves carbon amount; it is not a measurement of Mars or an equation converting atmospheric carbon directly into a surface temperature.
Keep all carbon destinations in the budget
Original invented carbon accounting, not measured Martian reservoir sizes. All entries use the same units of carbon amount and represent the stated net transfers. The final air inventory is 100 + 20 − 60 − 35 − 5 = 20 units. Only the 60-unit transfer to space leaves the planet.
Open full-size diagram in a new tab: Keep all carbon destinations in the budgetCheck 3 of 3
10 pointsUse the reading above. You can try again without losing points.
Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
Go to the source
Explore the evidence behind this lesson. These optional readings and videos open in a new tab.
- Read: NASA: MAVEN’s atmospheric-loss evidenceIsotope measurements and model-based inference; argon is not a direct percentage measurement of every gas.
- Read: NASA JPL: siderite in Curiosity drill samplesApril 2025 evidence for rock storage, with explicit limits on global extrapolation.
- Read: NASA: seasonal atmospheric exchangesCarbon-dioxide frost and pressure connect the atmosphere to another reservoir.