NASA Unveils Interactive 3D Model of Earth's Geoid, Gravity's Sculpting of the Ocean Surface

A lumpy ocean in 3D

NASA has released an interactive 3D model of Earth's geoid, giving scientists and the public a hands-on way of seeing the hidden shape that gravity gives to the ocean surface. The model, developed by NASA's Scientific Visualization Studio, turns more than two decades of satellite measurements into a detailed virtual globe. Bright colors mark places where Earth's gravitational pull is unusually strong, and pale or dark colors mark places where it is weaker. Users can rotate, zoom and tilt the model, watching the sea surface rise and fall relative to an idealized reference ellipsoid. It is one of the most accessible views yet of a fundamental but invisible feature of the planet.

The geoid is not meant to represent the real ocean as people see it. Real oceans are constantly pushed around by tides, winds and currents. The geoid strips those disturbances away. It shows how the ocean surface would look if only Earth's gravity and rotation shaped the water. Even then, the surface would not be smooth. It would resemble a lumpy potato-shaped surface, with lows of more than 100 meters and highs that reflect the uneven distribution of mass inside Earth, from deep mountain belts to dense mantle rocks.

What the geoid tells us about Earth

The concept dates back more than a century, when geodesists began trying to define what "sea level" really meant. Surveyors needed a stable reference surface, but the ocean is never perfectly flat. The geoid became that practical compromise: an equipotential surface of Earth's gravity field, following the direction of gravity at every point. It is the surface that a still ocean would settle into, and every elevation measurement on land is ultimately referenced to it.

The new NASA visualization makes those variations easy to see. Regions such as the Indian Ocean geoid low, a vast depression centered south of Sri Lanka, sink tens of meters below the reference ellipsoid. The low is associated with unusually weak mantle density and deep density anomalies below the region. Elsewhere, strong features appear around Iceland, the Andes, the western Pacific and the Himalayan ranges, where massive continental crust and subduction zones create concentrated gravitational attraction. For close observers, the model is also a window into plate tectonics and mantle convection, since the gravity field is an aggregate signature of Earth's deep interior.

The satellite record behind the model

The interactive product is not a single satellite image but a synthesis of decades of gravity observations. The most important data has come from NASA's Gravity Recovery and Climate Experiment (GRACE) mission, which operated from 2002 to 2017, and its successor, GRACE Follow-On, launched in 2018. The two GRACE satellites orbited Earth one after the other, measuring tiny changes in the distance between their centers as they passed over regions with slightly different gravity. Those measurements made it possible to map both time-invariant features of Earth's gravity field and changes over time, including melting ice sheets, groundwater depletion and shifting ocean currents.

European gravity data also contributed, notably from the European Space Agency's GOCE satellite, which mapped gradients of the gravity field and measured the shape of the geoid to high precision along with global ocean circulation. Radar altimetry from the Jason series and other ocean-observing satellites had already given geodesists a highly accurate picture of sea-surface height. Combining altimetry, gravity measurements and geophysical models allowed NASA's visualizers to produce a global geoid with remarkably fine detail. The agency said in the release that the model can be used for education, research and public engagement. "The geoid is the shape the ocean surface would have if gravity alone were the only force acting on it," NASA explained.

Why the geoid matters for navigation and climate science

The geoid is far from an abstract curiosity. It is the foundation for a vertical measurement system used across surveying, construction and civil engineering. Elevation, altitude and even the datum used by smartphones to determine altitude are tied to the geoid. A precise geoid model turns raw GPS readings, which are tied to an ellipsoid, into meaningful heights above sea level. Without a good geoid model, flood defenses, roads, drainage systems and airport runways cannot be designed with accurate vertical control.

The geoid also matters to oceanographers. When scientists subtract the geoid from satellite measurements of sea-surface height, what remains is ocean surface topography — the part of sea level caused by currents, eddies and other dynamic processes. That has helped reveal the paths of the Gulf Stream, the Antarctic Circumpolar Current and smaller mesoscale eddies that redistribute heat around the planet. The more accurate the geoid, the more confident those estimates become.

For climate science, the geoid has another underappreciated role. As ice sheets and glaciers melt, the redistribution of mass from land to ocean causes Earth's gravity field to change. As a result, sea-level rise is not uniform: in some places, ocean water is actually pulled away from a melting ice sheet because the ice's gravitational attraction weakens; in other places, sea levels rise more than the global average. This "sea-level fingerprint" effect is essential for coastal planning and detailed regional sea-level projections. A clear model of the present-day geoid helps scientists identify those gravitational fingerprints and predict how they will evolve.

A model built for exploration

NASA intends the interactive 3D model to be accessible, not just to researchers but to anyone interested in how the planet works. Through the agency's Scientific Visualization Studio portal, users can explore the globe without specialized software. The color scales show the range of geoid anomalies, and overlays identify coastlines and underlying geological features. This makes it easier to connect abstract data with something tangible, such as why the sea level around some islands is not the same as sea level measured from shore.

The interactive visualization also has practical potential in classrooms and museums, where the geoid has historically been difficult to explain due to its complexity. Instead of viewing a flat map or a static chart, students can manipulate the planet with the same tools scientists use. NASA hopes the model supports teaching in geodesy, geology, geophysics and oceanography, as well as broader interest in space-based Earth observation.

What comes next

The geoid map is not a final view. Earth's gravity field continues to change as ice melts, groundwater is withdrawn and large geological structures slowly shift. GRACE Follow-On remains active, providing a continuous record of mass change that scientists use to update geoid models. NASA and its international partners are discussing next-generation gravity missions to ensure that critical climate observations do not end with the aging spacecraft. Future missions could improve spatial resolution and extend the record, allowing researchers to measure the gradual motion of hot material in the mantle and follow short-term changes in water stored on land.

For now, the new interactive 3D model puts one of planetary science's most important concepts into public hands. It is a reminder that even what appears to be a flat surface can be shaped by a hidden world of mass and motion deep inside Earth. The geoid is not just a line on an engineering chart; it is the dynamic grain of the planet itself.