Scientists have suspected Mars has had liquid bodies of water for decades, but it was difficult to say the Earth's smaller sister planet had ever experienced warm weather.
The climate of early Mars was subject to intermittent periods of warmth from the rise of greenhouse gases caused by meteorites and volcanism — in between longer bouts of cold — which opened pathways for microbial life to evolve while also challenging it to survive frigid periods on the Red Planet, according to a new study published in the journal Nature Geoscience.
Reconciling Mars' geology and models of atmospheric evolution
The study authors — who worked under the leadership of Harvard University's Professor Robin Wordsworth — emphasized the need to reconcile the geology of Mars with models of atmospheric evolution. This is extremely difficult, since Martian geology involves past evidence for temporary bodies of liquid water, in addition to geochemistry suggesting a slow and intermittent shift from wetter to drier — with increasingly oxidized surface conditions.
The research team used a "coupled model of episodic warming, oxidation and geochemical transitions on early Mars" to curate a new model integrating the randomized injection of greenhouse gases — in addition to oxidation from atmosphere-escaping hydrogen — to evaluate the conditions responsible for the uncommonly diverse geological observations.
"Mars was intermittently warmed when its atmospheric composition was altered by the input of gases derived from volcanism and meteorite impactors," said Joel Hurowitz, an associate professor in Stony Brook University's Department of Geosciences in the college of arts and sciences, according to a Phys.org report. "These climate optima allowed water to flow across the surface, forming rivers and lakes, and the rocks and minerals we associate with water on Mars."
Hurowitz is also a member of the team executing research on NASA's Perseverance rover — and is one among the scientists who worked on the Planetary Instrument for X-ray Lithochemistry (PIXL) that's equipped on the rover's arm.
Large-scale changes on Red Planet's surface mineralogy explained by three primary causes
"This paper proposes a model for climate variation on Mars that can be tested with measurements of the chemistry and mineralogy of rocks by PIXL and the Perseverance rover in Jezero Crater," added Hurowitz.
The climate model projects a generally cold early Mars, with a mean yearly temperature below 240 degrees Kelvin (-28°F, or -33.33°C). When reducing gas release rates reached their peak, and background carbon dioxide levels rose to sufficient levels, the plant would reach intervals of climate warm enough to degrade crater walls, connect valley networks, and create other, various fluvial (or lacustrine) geographic features.
The researchers also said the model predicts a temporary buildup of oxygen in the Martian atmosphere — which would help explain the presence of oxidized mineral types like manganese oxides, which were observed in Gale Crater via the Curiosity rover. The research team also added that large-scale temporal changes in the Red Planet's surface mineralogy may be explained by three combined phenomena.
They are: planetary oxidation, a reduction in the availability of groundwater, and a waning flux of meteorite impacts — which together dramatically slowed the remobilization and thermochemical annihilation of sulfates on Mars' surface.
Life on Mars may have emerged 'during warm, wet intervals'
Some believe the presence of oxygen on planets (like Earth) might serve as a biomarker gas in the search for life on exoplanets. Not necessarily, write the study's authors: "Our model predicts long-lived, relatively oxygen-rich atmospheres for Mars in the middle period of its history without requiring the presence of life, indicating that oxygen detection alone can be a 'false positive' for life in some circumstances."
"Because prebiotic chemistry does not occur in highly oxidizing environments, this work places constraints on the time periods and locations in which life could have originated and persisted on early Mars."
However, this new climate model suggests unprecedented opportunities for the "emergence of life during warm, wet intervals when reducing conditions would have favored prebiotic chemistry," write the authors. But with new opportunities comes the challenge for possible life on Mars in persisting during frequent and increasingly-lengthy intervals of cold, dry oxidizing climates.
This was a breaking story and was regularly updated as new information became available.