In March 2012, filmmaker James Cameron piloted a specially built submarine, the Deep Sea Challenger, to the Challenger Deep, the deepest point in the Mariana Trench. He was the first person to complete that particular dive alone.
Waiting for him when he surfaced was Kevin Hand, a NASA astrobiologist from the Jet Propulsion Laboratory. Hand had joined the expedition to study the water and sediment samples Cameron collected from the seafloor. He and Cameron had worked together before on the IMAX project Aliens of the Deep, and Cameron invited him to join this expedition as well.
Hand’s role at the time was deputy chief scientist for solar system exploration, a position focused on planets and moons rather than Earth’s own oceans. His analysis of the trench samples involved exposing them to temperatures and radiation levels similar to those measured on the icy surface of Jupiter’s moon Europa. The goal was to see how material from Earth’s deepest ocean held up under conditions that exist on a moon hundreds of millions of miles away.
The connection between Earth’s deep ocean trenches and Europa comes from a discovery made in 2003. NASA’s Galileo spacecraft confirmed that Europa, one of Jupiter’s largest moons, has a liquid water ocean beneath its icy outer shell. Researchers estimate that ocean holds roughly twice the volume of all of Earth’s oceans combined.
That finding made Europa one of the more serious candidates for supporting life beyond Earth. Because liquid water is considered a basic requirement for life, the moon became a priority for study. But an ocean sealed beneath miles of ice on a distant moon cannot be explored directly with current technology. No spacecraft exists that can drill through the ice and collect samples the way a submarine can on Earth.
Instead, researchers rely on analog environments. These are places on Earth that share enough physical similarities with distant alien oceans that studying them can reasonably inform what conditions on Europa might be like. Earth’s deep ocean trenches match several key conditions on Europa, including extreme cold, crushing pressure, and complete darkness with no sunlight reaching the bottom.
That overlap explains why a NASA astrobiologist would be present when Cameron’s submarine returned to the surface. The samples brought up from seven miles beneath the Pacific offered a physical stand-in for material that might one day be collected from an ocean no one has reached.
Cameron’s dive took two hours and 36 minutes to descend, and he spent several hours exploring terrain no one had directly observed before. The return trip took about 70 minutes. The round trip required engineering built to survive pressure that would crush an ordinary submarine hull.
Hand’s analysis focused on how the water and sediment collected from the trench held up when exposed to conditions matching what instruments have measured on Europa’s surface. This direct physical comparison between a genuine terrestrial sample and known extraterrestrial conditions is the kind of testable science that astrobiology relies on.
The approach traces back to a discovery made in 1977. Before then, most scientists believed every living thing on Earth ultimately depended on sunlight for energy. That assumption changed when researchers piloting the deep-sea submersible Alvin, operated by the Woods Hole Oceanographic Institution, descended along the Galapagos rift and found hydrothermal vents scattered across the ocean floor.
Dense communities of large, strange organisms were clustered around plumes of mineral-rich, superheated water erupting from cracks in the seafloor. The researchers had expected to study underwater volcanic activity, not biology. What they found instead were foot-long tubeworms, giant clams, and other organisms no one had seen before.
The tubeworm species later identified from these vent communities has no mouth and no digestive system. It survives through a symbiotic relationship with internal bacteria that convert vent chemicals directly into usable energy. These communities depend on a process called chemosynthesis, in which specialized bacteria convert chemicals from the vent water into energy, independent of sunlight.
That discovery mattered for astrobiology because it proved a functioning ecosystem could exist without sunlight, relying entirely on chemical energy. Scientists studying icy moons with hidden oceans recognized the implications. Those moons receive no useful sunlight beneath their ice shells, making Earth’s chemosynthesis-dependent vent communities the closest working example of the kind of life that could survive elsewhere.
Europa’s confirmed subsurface ocean turned this theoretical possibility into a funded scientific priority. It led to NASA’s Europa Clipper mission, the largest spacecraft the agency has built for a planetary science mission. Europa Clipper launched on October 14, 2024, aboard a SpaceX Falcon Heavy rocket from Kennedy Space Center in Florida. The spacecraft is expected to reach Jupiter in April 2030 after traveling roughly 1.8 billion miles.
The spacecraft carries nine science instruments covering everything from ultraviolet and thermal imaging to ice-penetrating radar and mass spectrometers. Rather than orbiting Europa directly, which would expose the spacecraft to intense radiation for long stretches, Europa Clipper will orbit Jupiter and complete 49 close flybys of Europa. Some passes will come as near as 25 kilometers above the moon’s surface.
The mission’s primary stated goal is to determine whether there are places below Europa’s surface that could support life. That is the same question Kevin Hand was investigating using Challenger Deep samples more than a decade before Europa Clipper launched.
Another icy moon has already given scientists something direct: physical samples of its hidden ocean delivered into the path of a passing spacecraft. Saturn’s moon Enceladus has geyser-like jets erupting from cracks near its south pole. NASA’s Cassini spacecraft confirmed these jets spray material from a global salty ocean hidden beneath the moon’s icy surface, shooting particles into space at roughly 800 miles per hour.
Before Cassini’s arrival, scientists had wondered why Enceladus reflected sunlight so brightly and why a faint ring of ice particles circling Saturn seemed to trace back to this one small moon. Cassini resolved both questions. Fresh ice resurfacing Enceladus and feeding that distant ring both originate from the same source: vents connected to the moon’s hidden global ocean.
Cassini’s instruments flew directly through these plumes multiple times. They detected water, ice, simple organic chemicals, and molecular hydrogen, a chemical signature that on Earth typically forms when hot water reacts with iron-bearing minerals inside hydrothermal vent systems. The spacecraft also detected tiny silica nanograins, a type of particle that only forms when liquid water and rock interact at temperatures above roughly 90 degrees Celsius. That provides direct physical evidence that hydrothermal chemistry is happening on Enceladus’s seafloor.
Researchers have since detected or tentatively detected all six of the basic chemical elements considered essential for building the biological molecules life depends on: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
In 2021, a team of researchers published a statistical analysis testing whether the observed rates of hydrogen and methane escaping from Enceladus’s plumes could be fully explained by ordinary rock chemistry alone. Their model found that pure rock chemistry could not fully account for the observed escape rates. The results were compatible with habitable conditions for methane-producing microorganisms, and a biological explanation scored as the most statistically likely scenario, assuming the probability of life having emerged there was reasonably high to begin with.
None of this research has produced confirmed proof that life exists on Europa or Enceladus. Scientists studying both moons have consistently described their findings as compatible with habitable conditions rather than direct evidence of living organisms.
What the research has established is that conditions capable of supporting life without sunlight exist naturally both at the bottom of Earth’s oceans and, based on physical sample data, apparently within at least one other moon orbiting a different planet. If the basic recipe for life-supporting chemistry shows up this readily in places scientists have actually sampled, it raises a serious question about how many other ocean worlds might already be meeting the same basic requirements.
A popular claim in documentaries states that humanity understands the surface of Mars better than the bottom of its own oceans. In May 2025, oceanographer Katherine Bell and colleagues published a study in the journal Science Advances to test exactly how true that claim is.
Their results showed that scientists have visually observed less than 0.001 percent of the entire deep-sea floor, an area roughly equivalent to one-tenth the size of Belgium, out of an ocean floor covering most of the planet’s surface. That number reflects actual visual observation using cameras and human eyes, a stricter standard than sonar mapping, which has covered more of the seafloor but does not show what the terrain looks like up close.
Within that tiny observed portion, researchers have documented specialized life built for extreme pressure and total darkness. In 2014, cameras lowered into the Mariana Trench recorded a pale, soft-bodied fish at a depth greater than any living fish had been filmed before. Described in 2017 as a new species, the Mariana snailfish relies on a natural compound called trimethylamine oxide to keep its proteins stable under crushing pressure.
Also found at that depth is a shrimplike creature called the supergiant amphipod, which grows up to 30 centimeters long, compared to the roughly one-centimeter size of its shallow-water relatives. Xenophyophores, single-celled organisms roughly the size of a mango, hold the record for the largest single cell known in science. Genetic studies suggest that supergiant amphipods living in trenches thousands of kilometers apart carry nearly identical DNA, hinting at a single connected population across huge stretches of the world’s deepest waters.
An additional discovery from Earth’s deep ocean concerns human impact. In 2017, a research team at Newcastle University published a study examining small scavenging creatures pulled from the Mariana and Kermadec trenches, two trench systems roughly 7,000 kilometers apart on opposite sides of the Pacific. Inside the fatty tissue of these creatures, they found high levels of polychlorinated biphenyls, banned industrial chemicals, at concentrations roughly 50 times higher than crabs studied in one of the most polluted rivers in China.
Alan Jamieson, who led the study, said publicly that his team had always assumed the deep ocean remained remote and pristine. Once pollutants sink far enough into the deepest trenches, there is nowhere left for them to go, so they accumulate indefinitely.
Explorer Victor Vescovo, who has personally piloted multiple dives to the Challenger Deep, has separately reported spotting plastic bags and food wrappers resting on the trench floor.
Meanwhile, the oceans on Europa and Enceladus remain untouched by human contamination, largely because humanity has not yet developed the technology to physically reach them.
Even before Europa Clipper’s mission concludes, NASA researchers have explored concepts for a future Europa lander. Engineers working under a project called Ocean Worlds Europa Technologies have studied designs for a spacecraft that would touch down directly on the moon’s icy surface. Because a lander could not dive beneath the ice, researchers have proposed positioning it beside an open crevasse already venting water from beneath Europa’s surface, allowing it to sample both the surface ice and any escaping ocean water without drilling through miles of ice.
Europa Clipper’s findings, once its 49 flybys wrap up after 2030, will likely shape where any future lander mission would need to land.
The broader picture involves a combination of facts. The chemistry capable of supporting life without sunlight exists naturally at the bottom of Earth’s oceans, having thrived there for billions of years. At the same time, human activity has contaminated that life-supporting environment with banned industrial chemicals before fully understanding what lived there. The deepest, most inaccessible trenches contain measurable pollution that reached them decades before most scientists thought to check.
Genuinely pristine alien oceans on Europa and Enceladus have not been contaminated, but only because the technology to reach them does not yet exist.
The evidence gathered so far indicates that the basic chemistry needed to support life appears in more places across the solar system than scientists once assumed. It also demonstrates that humanity has already contaminated the one example of that chemistry we can reach, decades before understanding what was being contaminated.
