The LAGEOS satellite, a passive laser-ranged spacecraft whose design lineage extends to LARES-2. Both satellites use arrays of retroreflectors to bounce laser pulses from ground stations, enabling millimeter-precision tracking of their orbits. Credit: NASA.
July 9, 2026 — A small Italian satellite orbiting 5,899 kilometers (3,665 miles) above Earth has delivered the most precise measurement yet of one of general relativity’s strangest predictions: that a rotating planet drags the fabric of spacetime along with it.
The result, published July 8 in Nature (doi:10.1038/s41586-026-10715-0), confirms Einstein’s theory at the one-part-in-a-thousand level — a tenfold improvement over the best previous solar system tests. The measurement places the tightest constraints yet on alternative gravity theories, including those proposed to explain dark energy.
“What we are seeing is spacetime being twisted by the rotation of the Earth,” said Ignazio Ciufolini of the University of Salento, the study’s lead author, whose team includes Nobel laureate Roger Penrose. “The effect is tiny, but LARES-2 has allowed us to measure it with extraordinary clarity.”
How frame-dragging works
Frame-dragging — also called the Lense-Thirring effect or gravitomagnetism — arises because Einstein’s equations treat mass-energy currents the way electromagnetism treats electric currents. Just as a moving electric charge generates a magnetic field, a rotating mass generates a gravitomagnetic field that twists local inertial frames.
For Earth, the effect is vanishingly small. The orbital plane of a satellite circling the planet precesses by only about 2 meters (6.6 feet) per year due to frame-dragging — roughly the width of a human hair at the satellite’s altitude. Extracting that signal from the far larger gravitational perturbations of Earth’s own lumpy shape has challenged physicists for decades.
The LARES-2 experiment
LARES-2 (Laser Relativity Satellite 2) was launched on July 13, 2022, aboard the maiden flight of the European Vega-C rocket from Kourou, French Guiana. Built by the Italian Space Agency (ASI) in cooperation with ESA, the satellite is a passive sphere 36.4 centimeters (14.3 inches) in diameter, weighing 387 kilograms (853 pounds). Its surface is covered with 303 cube-corner retroreflectors — precision mirrors that reflect laser pulses back to their source.
A global network of satellite laser ranging (SLR) stations fires pulses at LARES-2 and measures the round-trip travel time, tracking the satellite’s position to within millimeters. The team combined 3.5 years of LARES-2 data with 26 years of data from the older LAGEOS satellites (NASA, 1976, and ASI/NASA, 1992) and gravity-field models from the GRACE and GRACE Follow-On missions.
The key innovation is orbital geometry. LARES-2 flies in what is called a “supplementary orbit” to LAGEOS: their orbital planes are nearly perpendicular, with inclinations that sum to approximately 180 degrees. This configuration cancels the dominant gravitational perturbations from Earth’s equatorial bulge (the J2 harmonic), leaving the tiny frame-dragging signal exposed.
“We designed the orbit to kill the noise so the signal could shine through,” said co-author Antonio Paolozzi of Sapienza University of Rome. “It took nearly 40 years from the original proposal to get here.”
What the results mean
The measured frame-dragging agrees with general relativity’s prediction to within 0.2 percent. Beyond confirming Einstein once again, the result has sharp implications for fundamental physics.
Several alternative gravity theories — particularly Chern-Simons gravity, a scalar-tensor extension that emerges from string theory — predict frame-dragging values that differ from general relativity. The LARES-2 measurement rules out a broad class of these models, narrowing the theoretical space for explanations of dark energy and the universe’s accelerated expansion.
The data also improved measurements of Earth’s lunisolar tides — the gravitational deformation of the planet by the Moon and Sun — demonstrating that high-precision relativistic experiments can deliver geophysical dividends.
A long road from concept to orbit
The idea of using supplementary-orbit satellites to measure frame-dragging was first published in the mid-1980s, championed by Ciufolini and the late John Archibald Wheeler. The project was originally called LAGEOS-3 but was repeatedly deferred. In 2016, the Italian Space Agency revived it as LARES-2, with significantly improved technology and a dedicated launch on the new Vega-C rocket.
The satellite’s optimized design — a very low surface-to-mass ratio that minimizes drag from residual atmosphere and solar radiation pressure, plus a highly uniform retroreflector distribution — made the one-part-in-a-thousand measurement possible. Earlier tests using only LAGEOS and LARES (launched in 2012) achieved about 2 percent accuracy.
What comes next
With LARES-2 continuing to accumulate data, the team expects further improvements in precision over the coming years. The satellite carries no electronics or propulsion and has no moving parts — its design life is measured in decades. The same laser-ranging technique could be applied to future missions around other planets or the Moon, where frame-dragging effects are larger due to stronger gravitational fields.
“Every time we test general relativity more precisely, Einstein passes,” Ciufolini said. “But that is not a failure — it is a confirmation that our understanding of gravity is on the right track. And it closes the door on theories that would take us down the wrong one.”
References:
- Ciufolini, I., Paolozzi, A., Pavlis, E.C. et al. “LARES-2 satellite measures frame-dragging effect around the Earth.” Nature 655, 332-335 (2026). https://doi.org/10.1038/s41586-026-10715-0
- Ciufolini, I. et al. “First results of the LARES 2 space experiment to test the general theory of relativity.” European Physical Journal Plus 138, 1054 (2023).
- Italian Space Agency (ASI): LARES-2 mission overview. https://www.asi.it/en/earth-science/lares-2/