Albert Einstein's general theory of relativity predicts that a rotating mass like Earth drags spacetime along for the ride - a phenomenon called frame dragging, or the Lense-Thirring effect. Measuring it around our pale blue dot has been tricky, since Earth is millions of times lighter than a typical black hole and rotates at a leisurely pace. But a team led by Ignazio Ciufolini of the Wuhan Institute of Physics and Mathematics has now measured the effect with just 0.2 percent uncertainty, thanks to a satellite that looks like a golf ball crossed with a disco globe.

The satellite, LARES-2 (Laser Relativity Satellite 2), built by the Italian Space Agency, is a solid sphere of Inconel 718 alloy covered in 303 retroreflectors. It has no thrusters, solar panels, or electronics - just mass. At 294.8 kilos and a bit over 40 centimeters across, it boasts the lowest area-to-mass ratio of any satellite in medium-Earth orbit, minimizing non-gravitational forces like photon pushes. Launched in July 2022, it sits at about 12,265 kilometers altitude.

The team fired ground-based lasers at LARES-2, whose retroreflectors bounce light straight back. About 200,000 observations from July 2022 to June 2025 pinpointed its position to within 1 millimeter. But Earth's equatorial bulge creates Newtonian forces that dwarf frame dragging. Ciufolini's solution: use two satellites in supplementary orbits - LARES-2 and its older cousin LAGEOS (launched in 1976) - whose orbital inclinations sum to 180.01 degrees. The Newtonian perturbations cancel out, while the relativistic signal adds up.

Even then, the K1 lunisolar tide - a gravitational disturbance from the Moon and Sun - threatened accuracy. The team collected data over one complete 1,050-day precession cycle, averaging out the tide. After removing that and six smaller tidal components, they found a clean drift of 61.3 milliarcseconds per year - the signature of spacetime twisting. The value matched Einstein's predictions with a margin of error of one to two parts per thousand.

The measurement also tested Chern-Simons theory, a quantum gravity alternative that predicts different frame dragging. It didn't rule it out but severely narrowed its scope. Bonus: the experiment precisely measured the K1 tide's strength, which could help earthquake studies. And LARES-2 will keep giving data for centuries - because nothing says 'long-term commitment' like a disco ball in space.