It may come as a shock that the depths of Earth’s oceans are more alien to scientists than the surface of the moon, 240,000 miles away in space.

But it’s true: With cameras and sensors, spacecraft have mapped lunar landscape features over the decades. Meanwhile, charting the ocean floor has presented its own daunting challenges. The intense water pressure found deep in the abyss can crush most equipment, and the seafloor is essentially hidden from view under miles upon miles of water, which absorbs light and becomes opaque. That makes direct observations especially difficult. 

A new effort using data from a NASA-led satellite is helping to change that, providing one of the most detailed maps of the bottom of the world’s oceans ever created. The SWOT satellite, short for Surface Water and Ocean Topography, is a collaboration between NASA and its French counterpart, the Centre National d’Études Spatiales. 

“This satellite is a huge jump in our ability to map the seafloor,” said David Sandwell, a geophysicist at Scripps Institution of Oceanography, in a statement. 

Launched in December 2022, the satellite actually was built to measure water height across the planet’s oceans, lakes, and rivers. Though not designed for seafloor mapping, scientists have found its advanced technology can help them estimate the size and shape of structures underwater more precisely.

Scientists of many disciplines say knowing what’s down there is important. Maps help ships navigate around safety hazards and guide engineers in laying underwater communication cables. They also play a role in studying deep-sea currents, tides, and the movements of Earth’s tectonic plates, those massive puzzle pieces of Earth’s crust that shift over millions of years. 

Experts have been working on mapping the ocean floor with traditional methods, sending ships across the water with sonar technology — sound waves that bounce off the bottom — to measure depth. But the process has moved at a snail’s pace: Ships can only cover small areas at a time, leaving much of the ocean uncharted. 

That slow progress means scientists may not meet their goal of having a complete seabed map by 2030. 

Though satellites are swarming in low-Earth orbit, most have a resolution that isn’t as good as sonar. But the new data from SWOT is about twice as detailed as older satellite maps, making it easier to see previously unknown features. A new SWOT-based seafloor map was published in the journal Science in December. 

NASA created an animation, posted above,  of some of the new information revealed in the SWOT data, including in regions off Mexico, South America, and the Antarctic Peninsula. Purple areas highlight lower regions around higher underwater elevations, shown in green. 

The satellite’s new type of radar technology has allowed it to detect seamounts less than half the size of those previously mapped, potentially increasing the number of known seamounts from 44,000 to 100,000. These underwater mountains affect ocean currents and can create nutrient-rich areas that attract marine life.

“We won’t get the full ship-based mapping done by” 2030, Sandwell said. “But SWOT will help us fill it in.”

Here’s how the technology works: The satellite detects tiny changes in the height of the water. Rather than a glass-like sheet all around the globe, the sea is uneven. Submerged mountains and other geological features with more mass than their surroundings cause bumps due to slightly stronger gravitational pulls. Those slight variations can be measured with SWOT’s instruments. The satellite sweeps over 90 percent of the planet as it orbits every 21 days.

The SWOT satellite sweeps over 90 percent of the planet as it orbits every 21 days.
Credit: NASA / JPL-Caltech / CNES / Thales Alenia Space illustration

SWOT apparently collected more detailed data than 30 years’ worth of older satellite missions in just one year, according to the Science paper. The new map has a resolution of about 5 miles, meaning scientists are detecting things that eluded them in the past.

The clarity has allowed scientists to detect underwater ridges known as “abyssal hills,” carved in long rows by slow tectonic shifts. They’re the most common topographical feature on Earth, covering about 70 percent of the ocean floor — whose water, by the way, covers about 70 percent of the planet. Because they’re smaller than seamounts, past satellites have struggled to find them.

The enhanced maps could lead to new geological discoveries, such as locating active underwater volcanoes and previously unknown fault lines. There could even be rediscoveries of lost ancient lands that weren’t always hidden by water. 

And there’s something in it for astrobiologists, too. Many researchers have posited that the chemistry needed to start life on this planet began at mid-ocean ridges, where tectonic plates have moved apart. This activity sometimes creates hydrothermal vents, a key environment of superheated water, rich in minerals. SWOT data may help scientists pinpoint new underwater hot springs for future study, which could help scientists better understand the recipe for life, perhaps even beyond Earth.