The Curious Case for Methane on Mars: Methane and Active Organics Discovered on Mars
By: Nicole Willett
The detection of methane in the Martian atmosphere has been one of the most tantalizing and controversial discoveries in recent Mars science. Methane is a molecule of particular interest because on Earth, the vast majority of methane is produced by biological processes. The presence of methane on Mars raises the compelling question: could something be producing this gas on the Red Planet today?
The Detection of Methane
The story of methane on Mars has been marked by conflicting observations and heated scientific debate. Ground-based telescopes first reported possible detections of methane in the Martian atmosphere in the early 2000s. The Mars Express orbiter’s Planetary Fourier Spectrometer also detected what appeared to be methane, though the results were debated.
The game changed when NASA’s Curiosity rover, using its Tunable Laser Spectrometer (TLS) as part of the Sample Analysis at Mars (SAM) instrument suite, detected background levels of methane in Gale Crater, along with periodic spikes that were roughly ten times higher than the background level. These spikes appeared to follow a seasonal pattern, with higher concentrations detected during warmer months.
Possible Sources
Scientists have proposed both biological and geological explanations for Martian methane:
Biological sources: On Earth, methanogenic archaea produce methane as a metabolic byproduct. If similar organisms exist beneath the Martian surface, where liquid water may persist, they could be producing the observed methane.
Geological sources: Methane can also be produced through a process called serpentinization, where water reacts with iron-rich minerals like olivine. This process does not require life but does require liquid water, which evidence suggests may exist in the Martian subsurface.
UV degradation of organics: Ultraviolet radiation from the Sun breaking down organic molecules delivered to Mars by meteorites and interplanetary dust could release small amounts of methane.
The Organic Discovery
In addition to methane, Curiosity’s SAM instrument made another landmark discovery: the detection of organic molecules in Martian rock samples. While organic molecules can be produced by both biological and non-biological processes, their presence on Mars is significant because they are the chemical building blocks of life.
The organics were found in mudstone samples drilled from the ancient lake bed in Gale Crater. The molecules included thiophenes, benzene, toluene, and small carbon chains. These were detected after the rock samples were heated in SAM’s oven, releasing the trapped organic compounds as gases.
The Mystery Deepens
The methane story became more complex when the European Space Agency’s Trace Gas Orbiter (TGO), specifically designed to map trace gases in the Martian atmosphere with unprecedented sensitivity, failed to detect methane from orbit. This apparent contradiction with Curiosity’s surface detections suggests that methane on Mars may be a localized and transient phenomenon, possibly released from specific surface or subsurface sources and quickly destroyed by atmospheric chemistry.
Implications
Whether the methane is biological or geological in origin, its detection has profound implications. If biological, it would represent the first evidence of extant life beyond Earth. If geological, it indicates that active chemical processes involving water are occurring in the Martian subsurface today, which itself has implications for habitability.
The mystery of Martian methane remains one of the most active areas of research in planetary science. Future missions, including the European Space Agency’s Rosalind Franklin rover and eventual human missions to Mars, will carry instruments capable of providing more definitive answers about the source of this enigmatic gas.