NASA Tracks Earth’s Shifting Center of Mass with New Technique
By Sally Younger, Jet Propulsion Laboratory
Water redistribution across the planet significantly shifts Earth’s center of mass by fractions of an inch seasonally. This crucial reference point plays a vital role in satellite navigation and elevation measurements.
New Technique for Precision Measurement
A team from NASA’s Jet Propulsion Laboratory (JPL) has introduced an advanced method for calculating these seasonal oscillations, as described in a recent study published in the Geophysical Journal International. The researchers illustrate how seasonal changes—spring thaws, turbulent oceans, and heavy winter air—move large surface loads and consequently shift Earth’s center of mass.
Previous Methods and Their Limitations
Historically, several methodologies have attempted to pinpoint Earth’s center of mass, but this metric is ever-changing. Unlike a stable object, Earth’s center fluctuates due to the dynamic effects of water, ice, and air, leading to variations up to several millimeters.
Existing estimates from 2017 and 2023 diverged by 0.27 inches (7 millimeters), highlighting the inaccuracies in previous approaches.
The Role of Satellite Tracking
JPL geoscientist Donald Argus spearheaded a new measurement technique using ultraprecise satellite tracking to enhance accuracy. Satellites orbit Earth’s center of mass and provide data on small distance changes between satellites and ground stations, reflecting the planet’s shifting mass.
This method incorporates GPS tracking and data from several low Earth orbit satellites, improving the overall accuracy. It also takes into account how water and ice affect the deformation of Earth’s crust.
Research Collaborators and Findings
Collaborating with JPL’s satellite orbit determination team, the University of Nevada, the University of Montana, and the Helmholtz Centre for Geosciences in Germany, Argus notes that the new findings reveal the movement of Earth’s mass center to be about half of what was previously believed—indicating less mass movement between hemispheres.
Coauthor Felix Landerer emphasizes the importance of accurate positioning measurements for modern society, influencing everything from global shipping logistics to precision agriculture.
Seasonal Oscillations and Their Causes
The authors attributed Earth’s center of mass oscillation to three factors: oceans, atmosphere, and continental water. Key findings include:
- Snow: Maximum accumulation in North America and Eurasia in March shifts the center of mass 3 millimeters toward the North Pole.
- Rainwater: Peaks in April in the Amazon River basin at 2,400 gigatons shift it 2.2 millimeters toward South America.
- Monsoon Water: Maximum in Southeast Asia in November slightly contributes to the overall oscillation.
From late summer to fall, melting ice and rainfall cause the oceans to swell, further affecting the center of mass, especially in the South Pacific Ocean.
Further Research and Future Missions
Using a model from the European Centre for Medium-Range Weather Forecasts, the researchers also assessed atmospheric influence, noting seasonal shifts influenced by denser winter air.
Data from the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission substantiate the study’s mass calculations. The twin satellites, launched in 2018, monitor gravitational changes caused by water movement.
The upcoming GRACE-Continuity (GRACE-C) mission, set for late 2028, aims to extend nearly 25 years of data record from the GRACE series.
—Sally Younger, NASA’s Jet Propulsion Laboratory
