In the middle of the tropical greenery of Costa Rica, a smoking crater encloses a landscape that seems torn from another planet. There, where the air burns with sulfur and the water has the acidity of battery acid, a way of life that defies logic thrives.
The Poás volcano is not only one of the most active in the country: it has become a unique natural laboratory to understand how life could arise on Mars when it was still a humid and volcanic planet.
A terrestrial lake with a Martian soul
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In the center of the Poás crater is the Laguna Caliente, a superacid lake whose chemical composition is reminiscent of the ancient hydrothermal systems of early Mars. Its pH is around the values of sulfuric acid, and its waters concentrate dissolved metals, sulfur and volcanic gases.
Despite this, in this extreme environment a unique microbial community survives: a small group of bacteria adapted to toxic and changing conditions. For astrobiologists, studying their metabolism can offer clues about how life might have originated—or endured—on other planets.
“We have a very human bias about what we consider a habitable environment,” says Rachel Harris, a microbial ecologist with NASA. “But for a microbe adapted to heat, acid and toxic metals, Poás is paradise.”
This is how the camera of the National Seismological Network of the University of Costa Rica captured the eruption of the Poás volcano tonight. The column of ash heads towards the west of the colossus. pic.twitter.com/6cY3bbFrCi
— Delfino.CR (@delfinocrc) April 26, 2025
An active volcano and a living laboratory
Poás is a stratovolcano with more than a million years of geological history. Its activity continues: in recent decades it has recorded multiple eruptions, ash columns and gas emissions that have forced the evacuation of nearby areas.
This geothermal dynamism explains the extreme chemistry of the lake. The continuous filtration of volcanic gases turns its waters into a sulfurous broth where conditions change unpredictably. Precisely for this reason, scientists consider it a terrestrial analogue of ancient Martian hydrothermal environments.
Satellite images captured in 2025 show the fascinating contrast: a caldera of ocher and greenish tones, as if a fragment of the red planet had made its way into the heart of Central America.
The bacteria that does not appear in any record
In 2018, an international team led by Brian Hynek, a researcher at the University of Colorado at Boulder, undertook an expedition to Poás to collect microbial samples. The objective: analyze the DNA of the organisms that survive in Laguna Caliente and compare them with known lineages.
The result was disconcerting. Only a single, extremely specialized bacterial species was found in the water, which uses sulfur from the environment as a source of energy. This metabolism, based on chemosynthesis rather than sunlight, matches theoretical models of early life that could have existed on Mars.
But the most surprising thing is that, after genetic sequencing, the bacteria did not match any known species.
“Maybe it had never been identified before, and that’s why it doesn’t appear in the databases,” Hynek explained. “This place has the same chemistry and minerals as the hydrothermal systems on Mars 3.5 billion years ago. Studying it is like going back in time.”
Researchers suspect this is a unique lineage, possibly isolated for thousands of years, that could rewrite what we know about the limits of life.
A model of what Mars could have been
The link between Poás and Mars is not new. Already in 2009, rocks analyzed by the Spirit rover in a region called Home Plate showed traces of ancient acidic hydrothermal systems. The similarities with the chemistry of Poás are so notable that many scientists consider it the best Earth model to study Martian biology.
If a form of life can exist in a lake as corrosive as Laguna Caliente, it is plausible that Mars also hosted microorganisms in the past, when it still had liquid water and a denser atmosphere.
Even if they have already disappeared, their traces – biomarkers, microscopic fossils or chemical remains – could still be hidden in the Martian subsoil.
“Mars is still a great natural laboratory,” says Hynek. “To look for life there is to look for a story that began billions of years ago… and that perhaps has not yet ended.”
A tropical crater that explains the cosmos
The recent eruptions of Poás forced the suspension of new expeditions, and the lake even temporarily disappeared due to evaporation and underground drainage. Still, scientists plan to return when the environment stabilizes.
For them, this Central American volcano is not only a geological curiosity, but a door to humanity’s oldest questions: how life began and how far it can go.
The Poás demonstrates that biology does not depend on comfort, but on adaptation.
And perhaps, to understand other worlds, we must first look closely at the most inhospitable places in our own.
Source: Infobae.
