Laguna Caliente may not be the hottest lake on Earth. It may not be the most acidic, either. But the lake — a steaming turquoise menace near the summit of Costa Rica's Poás Volcano — is certainly among the world's most mercurial.
Tepid as bathwater on Monday, it might be an acid-spiked steam pot by Wednesday. And then there are the geysers, spewing scalding acid whenever water from the lake meets magma from the chambers that run underneath it.
So, who would want to visit a place such as Laguna Caliente? People who are interested in "pushing the fringes of what Earth life can tolerate," Brian Hynek said.
Hynek, a planetary scientist and astrobiologist in the Department of Geological Sciences and Laboratory for Atmospheric and Space Physics at the University of Colorado, searches planet Earth for places that resemble planet Mars — not as it is today, but as it was billions of years ago, when volcanoes steamed up natural cauldrons of water above and below ground.
Like Hynek's other favored destinations — Iceland, Nicaragua, Hawaii, Patagonia — Laguna Caliente is a time machine and spaceship in one. It takes scientists back in time and to another world, on a journey to answer the Big Question: Could there have once been life on Mars?
In many ways, Laguna Caliente is a dead ringer for ancient Mars. The hydrothermal minerals that cover the Costa Rican crater match those seen in parts of Mars and may have once been hydrothermal systems. But because Laguna Caliente is remote, dangerous and protected, no one had ever checked to see if anything was living in its noxious water.
So, in November 2013, Hynek and his team donned helmets, gas masks and other protective gear and trekked from the edge of the crater down to the shore of the lake, about an hour's journey. There, they filled up sample tubes with lake water, then scrambled to the (relative) safety of a nearby ledge to do on-the-spot analysis.
Everything had to be done fast.
"If we're down at the lake shore and one of these eruptions happen, it's light out," he said. Though he checked in regularly with Costa Rican researchers who monitor the volcano's activity, the eruptions aren't perfectly predictable. "It's a bit of Russian roulette."
Safely back home in Colorado, Hynek extracted any DNA and sent the samples off to a collaborator for genetic sequencing. The result: There is life in Laguna Caliente, but just barely. The genetic analysis revealed only one microbe species living in the lake water.
"That is extremely rare on Earth," he said.
Most Earth species live in ecosystems containing scores of other species, woven together in a web of delicate dependencies. In fact, there is only one other known place on Earth — a South African gold mine some two and a half miles deep — where a single species lives all alone.
So, what's living in Laguna Caliente? Hynek's team is still working that out. Based on the genetic analysis the team has done so far, it thinks that it is a previously unknown species of bacteria. Like many of its acid-loving cousins, it probably gets energy from sulfur in the rocks and minerals being cycled in the lake.
Mars life, if it ever existed, may have used a similar strategy. Though planetary scientists think that Mars once had lakes and rivers, hydrothermal systems such as Laguna Caliente may have persisted for longer, perhaps billions of years, Hynek points out. That ups the odds that life could have taken hold there. With that in mind, Hynek hopes that planners working on Mars 2020, NASA's next Mars rover, will send the wheeled robot to one of Mars' "dried-up Yellowstones" to search for signs of past life.
But should the solitary species at Laguna Caliente inspire hopes for Mars life, or dash them? "We found very little life at a Mars analog. On that side of the coin, it's bad," Hynek said. "But this is such an extreme environment. That there's anything there, that's the positive. Life could have tolerated almost anything."