Unraveling the Red Planet's Atmospheric Secrets
Once thought to be a simple, dry world, Mars is now revealing a complex volatile history that may hold clues to its potential for life.
The Martian landscape today is a cold, barren desert with an atmosphere less than 1% as dense as Earth's, but multiple lines of evidence point to a dramatically different past. River valleys, lakebeds, and mineral formations suggest that liquid water once flowed freely across the Martian surface, indicating a previously thicker atmosphere capable of sustaining warmer conditions.
Current Martian atmospheric density compared to Earth
What happened to this ancient atmosphere? The answer lies in understanding Martian volatiles—elements and compounds that vaporize at relatively low temperatures, such as water, carbon dioxide, nitrogen, and noble gases. The ongoing quest to decode the evolution of these volatiles not only reveals Mars' history but also provides crucial insights into planetary evolution and the potential for life beyond Earth.
Evidence of river valleys and lakebeds suggests Mars once had flowing water
Multiple processes led to the depletion of Mars' once-thicker atmosphere
Planetary scientists have long debated the origins of Martian volatiles, with two primary sources under consideration: the solar nebula (the primordial cloud of gas and dust from which our solar system formed) and chondritic meteorites (primitive meteorites that contain volatile elements).
Conventional theory suggested that planets first incorporated volatiles from the solar nebula into their molten interiors, which later degassed to form atmospheres, with meteorites delivering additional volatiles later. However, recent evidence has overturned this simplistic narrative, pointing toward a more complex hybrid origin for Martian volatiles 4 .
Once acquired, Martian volatiles faced numerous challenges. Over billions of years, Mars lost significant portions of its atmosphere to space through various escape processes:
Multiple lines of evidence point toward substantial loss of the martian atmosphere from its earliest history to the present time 1 . Isotopic measurements provide crucial evidence for this escape—lighter isotopes escape more readily, leaving behind a higher proportion of heavier isotopes.
A groundbreaking study led by Dr. Sandrine Péron at UC Davis utilized a novel approach to address the question of Martian volatile origins by examining the Chassigny meteorite—a rare meteorite that fell in France in 1815, believed to represent the interior of Mars .
Obtaining samples of the Chassigny meteorite, classified as a chassignite and thought to originate from the Martian mantle
Using the UC Davis Noble Gas Laboratory to make extremely precise measurements of minute quantities of krypton isotopes in the meteorite samples
Comparing the isotopic signatures from the meteorite with known solar and chondritic compositions to determine the origin of the volatiles
Contrasting these interior measurements with known Martian atmospheric compositions from previous missions
The krypton isotope measurements from the Chassigny meteorite yielded surprising results that contradicted current thinking about planetary formation. Contrary to expectations, the krypton isotopes in the Martian interior matched those originating from chondritic meteorites, not the solar nebula .
This finding was revolutionary because it meant that meteorites were delivering volatile elements to the forming Mars much earlier than previously thought—while the solar nebula was still present.
| Reservoir | Krypton Isotope Source | Implications |
|---|---|---|
| Martian Interior | Chondritic (meteoritic) | Early delivery of volatiles by meteorites during formation |
| Martian Atmosphere | Solar (nebular) | Atmosphere acquired from solar nebula after mantle cooling |
Motivated by the disparate inferences about Martian volatile sources, scientists have developed a hybrid origin model for the Martian atmosphere. This model proposes that Mars' primordial atmosphere formed as a mixture of outgassed volatiles from the planetary interior and gases captured from the solar nebula 4 .
In this hybrid scenario, a high molecular weight outgassed component (CO2-rich) mixed with the low molecular weight H2-rich nebular atmosphere during the lifetime of the solar nebula. Calculations show that mixing an outgassed component enhances the nebular captured gas inventory by approximately 1-3 orders of magnitude relative to "pure" nebular capture 4 .
| Stage | Process | Key Features |
|---|---|---|
| Stage 1 | Early Accretion | Chondritic volatiles delivered by meteorites incorporated into mantle |
| Stage 2 | Hybrid Atmosphere Formation | Outgassed chondritic volatiles mix with captured solar nebula gases |
| Stage 3 | Atmospheric Processing | Hydrodynamic escape and other processes fractionate volatiles |
| Stage 4 | Modern Era | Distinct interior (chondritic) and atmospheric (solar) signatures remain |
Analysis of other Martian meteorites provides additional evidence for this hybrid model. Studies of the Tissint meteorite, which fell in Morocco in 2011, reveal evidence of alteration by fluid processes—surprising for a meteorite from what is thought to be Mars' current dry period 3 .
Similarly, investigations of carbon-rich inclusions in Martian meteorites of various ages (Tissint, Dhofar 019, Nakhla, Lafayette, Chassigny, and NWA 7034) show that carbon has been present ubiquitously across the Martian globe throughout its history, with potential sources being either carbon-rich meteorites or the Martian mantle itself 3 .
Cutting-edge research on Martian volatiles relies on sophisticated analytical equipment capable of detecting minute quantities of elements and precise isotopic ratios.
Measures water content and D/H ratios in mineral types
Determines mineral structure and magnitude of shock pressure
High-resolution isotopic imaging of geological samples
Measures composition and structure of upper atmosphere
Identifies molecular structures and organic compounds
The study of Martian volatiles has undergone a remarkable transformation in recent years, with new evidence challenging long-standing theories about the planet's formation and evolution. The emerging picture suggests a hybrid origin for Martian volatiles, with planetary interiors preserving chondritic signatures while atmospheres retain solar nebula components—a finding that may have implications for understanding the formation of all terrestrial planets.
Current and future missions, including NASA's Mars 2020 Perseverance rover and the ESA ExoMars program, continue to investigate Martian volatiles, bringing us closer to understanding not only the Red Planet's history but also the fundamental processes that shape planetary environments throughout our solar system and beyond.
NASA's ongoing mission to collect samples and analyze Martian geology
ESA's mission to search for signs of past life on Mars
The ongoing research into Martian volatiles represents more than just planetary science—it's a quest to understand how planets form, evolve, and potentially become habitable. Each meteorite analysis and each atmospheric measurement brings us closer to answering fundamental questions about our place in the cosmos and the potential for life beyond Earth.