In Italy, What Earth Can Tell Us About Extraterrestrial Life

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To date, Earth remains the only inhabited world we know, which is why astrobiologists — loosely defined as those scientists seeking to understand the potential for life elsewhere in the universe — spend a good deal of time studying our home planet. And Italy, it seems, provides particularly fertile ground for such explorations.

For Luca Tonietti, an astrobiologist at the University of Naples, Parthenope in Italy, the quest leads to the dark recesses of abandoned mines that dot the Italian landscape. Shielded from ultraviolet radiation, poor in organic nutrients and, at times, rich in iron-bearing minerals, these lightless, underground crypts are thought to resemble conditions on Mars, where many researchers believe life might well have thrived in some distant past. If any form of life still exists on the Red Planet, Tonietti suspects it will be found beneath the surface or in deep caves — and it may rely on survival strategies similar to those of the mine-dwelling microbes he studies here on Earth.

Other researchers in the field seek to recreate extraterrestrial conditions inside the laboratory. Nicoletta La Rocca, a plant physiologist at the University of Padova, collects cyanobacteria from places like the hot springs of the Euganean Hills in northern Italy and exposes them to simulated red-dwarf starlight. Red dwarfs are the smallest, coolest, and faintest stars that burn hydrogen, and La Rocca wants to know whether photosynthetic life as we know it could thrive beneath their faint orange glow. To find out, she turns to organisms whose lineages survived the harsh conditions of early Earth — and so far, her experiments seem to suggest that photosynthesis might be more flexible than previously thought.

The discipline is similarly diverse: Some astrobiologists and allied researchers spend their careers hunting for traces of Earth’s earliest life forms, for example, so that we might better spot similar traces of life if we stumble onto them elsewhere in the universe. Other scientists focus on microbes that thrive in the harsh conditions found in the Earth’s hydrothermal vents — in the hopes of understanding how life might respond to similar conditions on Enceladus, the sixth largest moon of Saturn and a hotbed of scientific speculation around potential alien life.

“We have to use Earth as our biological model, because it’s the only one we have,” says Barbara Cavalazzi, an astrobiologist at the University of Bologna.

Scientists still disagree, of course, on how to precisely define life — intelligent or otherwise. But as the following photographs suggest, efforts to understand what “life” might look like beyond our pale blue dot are flourishing. And whether or not those efforts ultimately lead to the discovery of life elsewhere, Tonietti believes the search itself has value. “Astrobiology teaches you to ask big questions. It helps you find new perspectives.”

Into the Dark

Astrobiologist Luca Tonietti explores underground caves that are thought to resemble conditions on Mars.

Luca Tonietti collects a biofilm sample from the wall of an abandoned mine. Despite the near-total darkness, some photosynthetic organisms can grow inside these environments, challenging assumptions about the limits of life.

Dark and rich in iron-bearing minerals, some abandoned mines are natural analogues of the Martian subsurface. Before venturing into one, Tonietti pierces the darkness with a laser to estimate the depth of the entrance tunnel.

A pool inside the abandoned mine is a hotspot of microbial life. Water samples taken from the pool contain environmental DNA that can be analyzed to identify the microorganisms living there. The surrounding walls are coated with pink and golden biofilms, while a whitish microbial mat grows across the bottom.

Iron ore and a biofilm coat a portion of the wall. The blood-red color comes from iron oxides associated with certain bacteria, which use these minerals as an energy source and leave distinctive traces in the rock. Studying these microorganisms helps scientists understand what evidence of life on Mars might look like.

Among the most prized specimens in Tonietti’s rock collection is a slice of pallasite, a rare meteorite formed during the early history of the Solar System. Meteorites are a focus of astrobiology because they may have delivered the building blocks of life to Earth.

Tonietti’s collection also includes stromatolites, which are fossilized microbial structures. The many layers of rock are built by communities of cyanobacteria, which preserve some of the earliest evidence of life on Earth. Such samples may help scientists recognize evidence of life on Mars in fossils.

A Green Glow

Plant physiologist Nicoletta La Rocca grows cyanobacteria collected on Earth under simulated starlight.

Nicoletta La Rocca holds one of hundreds of cyanobacterial cultures growing in her laboratory. Some cyanobacteria can remodel their photosynthetic machinery to harvest wavelengths of light that most photosynthetic organisms barely use.

Researcher Elisabetta Liistro holds up a cyanobacteria culture to green light. These conditions minimize photosynthesis while allowing researchers to observe the culture, preserving the experimental conditions for subsequent tests.

La Rocca’s team simultaneously cultivates several batches of microorganisms while varying the type of light, temperature, atmosphere, and nutrient availability. They also test the organisms’ ability to capture carbon dioxide, a process that could support future space missions.

Microalgae under a microscope. After light-exposure experiments, researchers examine the cells for changes in morphology, pigments, and the organization of their photosynthetic machinery.

Researcher Beatrice Boccia exposes cyanobacteria to ultraviolet radiation simulating stellar flares. The goal is to understand which adaptations may have allowed microorganisms to survive on early Earth before the planet had a protective atmosphere.

According to La Rocca, this is the world’s only red dwarf star light simulator, mounted on a chamber that can replicate atmospheres ranging from Mars to early Earth. Red dwarfs are the most common stars in our galaxy, and nearly all potentially habitable exoplanets discovered so far orbit one. Studies by La Rocca’s team found that cyanobacteria and microalgae can grow and photosynthesize under the light of a red dwarf star, suggesting that photosynthetic life could exist beyond our Solar System.

Evidence Locked in Stone

Astrobiologist Barbara Cavalazzi examines traces of some of Earth’s earliest life, preserved from an age when our planet resembled a young Mars. 

Barbara Cavalazzi examines a drill core from Buch Reef Chert, South Africa. Future missions to Mars may bring back similar rock core samples for study.

Researcher Alice Tarozzi places a fragment of fossilized microbial mat — layered communities of microorganisms that grow on wet sediments or rocks — on a specimen holder for analysis in a scanning electron microscope.

A thin section of a fossilized microbial mat shows its layered structure. Scientists compare such samples with their living counterparts to estimate how well traces of microbial life can be preserved.

One of the oldest records of life on Earth: a thin section of rock containing 3.42-billion-year-old filamentous microbes. By studying fossils like these, Cavalazzi is building a database to help scientists recognize evidence of life on Mars.

Researcher Rebecca Martellotti removes a fragment from a fossil hydrothermal sample. Analyzing the fossil’s microstructure and chemical composition can help scientists determine whether the fossil structures were formed through biological or geological processes.

Life From Below

Astrobiologist Mattia Esposito seeks out extremophiles that inhabit geothermal springs, like Italy’s Grande Inferno.

Mattia Esposito, an astrobiologist at Ca’ Foscari University of Venice, studies microbes from hydrothermal vents to understand conditions thought to exist on Enceladus, one of Saturn’s moons. Esposito and fellow biologist Matteo Selci carry sampling equipment to the Grande Inferno geothermal spring to collect water and sediment.

Esposito measures physical and chemical properties of Grande Inferno, or the “Great Hellhole,” a geothermal spring straddling the border between Lazio and Campania. Its gurgling water smells of rotten eggs and gasoline, and locals have long believed that bathing in the water can remedy skin issues.

Esposito and Selci collect water samples from the Grande Inferno. Geochemical and environmental DNA analyses will tell them how the spring’s chemistry shapes its microbial communities — and how those microbes, in turn, may alter the surrounding environment.

In the Grande Inferno, a biofilm of extremophilic bacteria coats rocks and submerged vegetation. Its composition helps microbes survive the harsh geothermal conditions. The biofilm also fosters interactions among the microbes themselves and between the microbes and the surrounding environment.

Mattia Esposito measures the temperature of a hydrothermal spring in Campania, southern Italy. Its highly acidic waters support unique microbial communities, including extremophilic species like Acidithiobacillus ferrooxidans, which may be able to extract metals from Martian rocks.

Andrea De Giovanni is a photojournalist, filmmaker, and science communicator based in Italy.