NASA’s SWOT Satellite Just Revealed Thousands of Hidden Mountains Beneath the Ocean

We know more about the Moon’s surface than Earth’s ocean floor — but that’s changing fast.

A NASA-supported team used a groundbreaking satellite called SWOT to map the seafloor in unprecedented detail. This space-based data reveals hidden underwater mountains and hills, offering insights into deep-sea currents, tectonic shifts, and even potential mineral hotspots. With this leap in technology, scientists are racing to complete the most comprehensive map of the ocean floor ever created, unlocking secrets of Earth’s geology and ecology that were once invisible.

Mapping the Unknown Ocean

We have more detailed maps of the Moon’s surface than of Earth’s ocean floor. For decades, scientists have been working to change that. Now, a NASA-supported team has taken a major step forward by releasing one of the most detailed seafloor maps to date. The map was created using data from the SWOT (Surface Water and Ocean Topography) satellite, a joint mission between NASA and the French space agency CNES (Centre National d’Études Spatiales).

While ships equipped with sonar can produce highly accurate maps of the seafloor, only about 25% of the ocean has been mapped this way. To fill in the gaps and build a global view of the ocean floor, researchers have increasingly turned to satellite data.

Why Seafloor Maps Matter

High-resolution maps of the ocean floor are vital for many practical uses, from navigating ships and laying submarine cables to detecting hazards and supporting military operations. “Seafloor mapping is key in both established and emerging economic opportunities, including rare-mineral seabed mining, optimizing shipping routes, hazard detection, and seabed warfare operations,” said Nadya Vinogradova Shiffer, who leads physical oceanography programs at NASA Headquarters.

Accurate seafloor maps are also important for an improved understanding of deep-sea currents and tides, which affect life in the abyss, as well as geologic processes like plate tectonics. Underwater mountains called seamounts and other ocean floor features like their smaller cousins, abyssal hills, influence the movement of heat and nutrients in the deep sea and can attract life. The effects of these physical features can even be felt at the surface by the influence they exert on ecosystems that human communities depend on.

This animation shows seafloor features derived from SWOT data on regions off Mexico, South America, and the Antarctic Peninsula. Purple denotes regions that are lower relative to higher areas like seamounts, depicted in green. Eötvös is the unit of measure for the gravity-based data used to create these maps. Credit: NASA’s Scientific Visualization Studio

The Role of the SWOT Satellite

Mapping the seafloor isn’t the SWOT mission’s primary purpose. Launched in December 2022, the satellite measures the height of water on nearly all of Earth’s surface, including the ocean, lakes, reservoirs, and rivers. Researchers can use these differences in height to create a kind of topographic map of the surface of fresh- and seawater. This data can then be used for tasks such as assessing changes in sea ice or tracking how floods progress down a river.

“The SWOT satellite was a huge jump in our ability to map the seafloor,” said David Sandwell, a geophysicist at Scripps Institution of Oceanography in La Jolla, California. He’s used satellite data to chart the bottom of the ocean since the 1990s and was one of the researchers responsible for the SWOT-based seafloor map, which was published in the journal Science in December 2024.

How It Works

The study authors relied on the fact that because geologic features like seamounts and abyssal hills have more mass than their surroundings, they exert a slightly stronger gravitational pull that creates small, measurable bumps in the sea surface above them. These subtle gravity signatures help researchers predict the kind of seafloor feature that produced them.

Through repeated observations — SWOT covers about 90% of the globe every 21 days — the satellite is sensitive enough to pick up these minute differences, with centimeter-level accuracy, in sea surface height caused by the features below. Sandwell and his colleagues used a year’s worth of SWOT data to focus on seamounts, abyssal hills, and underwater continental margins, where continental crust meets oceanic crust.

Previous ocean-observing satellites have detected massive versions of these bottom features, such as seamounts over roughly 3,300 feet (1 kilometer) tall. The SWOT satellite can pick up seamounts less than half that height, potentially increasing the number of known seamounts from 44,000 to 100,000. These underwater mountains stick up into the water, influencing deep sea currents. This can concentrate nutrients along their slopes, attracting organisms and creating oases on what would otherwise be barren patches of seafloor.

Looking Into the Abyss

The improved view from SWOT also gives researchers more insight into the geologic history of the planet.

“Abyssal hills are the most abundant landform on Earth, covering about 70% of the ocean floor,” said Yao Yu, an oceanographer at Scripps Institution of Oceanography and lead author on the paper. “These hills are only a few kilometers wide, which makes them hard to observe from space. We were surprised that SWOT could see them so well.”

Abyssal hills form in parallel bands, like the ridges on a washboard, where tectonic plates spread apart. The orientation and extent of the bands can reveal how tectonic plates have moved over time. Abyssal hills also interact with tides and deep ocean currents in ways that researchers don’t fully understand yet.

Toward a Complete Seafloor Map

The researchers have extracted nearly all the information on seafloor features they expected to find in the SWOT measurements. Now they’re focusing on refining their picture of the ocean floor by calculating the depth of the features they see. The work complements an effort by the international scientific community to map the entire seafloor using ship-based sonar by 2030. “We won’t get the full ship-based mapping done by then,” said Sandwell. “But SWOT will help us fill it in, getting us close to achieving the 2030 objective.”

Reference: “Abyssal marine tectonics from the SWOT mission” by Yao Yu, David T. Sandwell and Gerald Dibarboure, 12 December 2024, Science.
DOI: 10.1126/science.ads4472

More About SWOT

The Surface Water and Ocean Topography (SWOT) satellite is a groundbreaking international mission designed to measure the height of water across nearly all of Earth’s surface—including oceans, rivers, lakes, and reservoirs—with unprecedented detail. SWOT is a collaboration between NASA and the French space agency CNES, with contributions from the Canadian Space Agency (CSA) and the UK Space Agency.

The U.S. portion of the mission is led by NASA’s Jet Propulsion Laboratory (JPL), managed by Caltech. NASA provided several key instruments, including the Ka-band Radar Interferometer (KaRIn), a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and oversight of U.S. instrument operations.

CNES contributed the satellite platform, ground operations, and systems such as the Doppler Orbitography and Radioposition Integrated by Satellite (DORIS) and the Poseidon dual-frequency altimeter, developed by Thales Alenia Space. The KaRIn radio-frequency subsystem was jointly developed by Thales Alenia Space and CNES, with support from the UK. The KaRIn high-power transmitter assembly was provided by CSA.

Together, these contributions enable SWOT to deliver high-resolution measurements of water surfaces, helping scientists better understand Earth’s water cycle, ocean currents, and even the topography of the ocean floor.

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