Scientists have made the most accurate measurement of the Earth’s spacetime twist, also known as the Lense-Thirring effect, to date. This phenomenon, predicted by Albert Einstein’s general theory of relativity, occurs when a rotating mass like the Earth pulls the fabric of space and time around with it in a perpetual swirl.
The measurement was made by a team of astronomers led by Ignazio Ciufolini, a physicist at the Wuhan Institute of Physics and Mathematics in China, using a satellite called LARES-2 (Laser Relativity Satellite 2). The satellite is a solid sphere of Inconel 718, a dense nickel-chromium alloy, covered with 303 corner-cube retroreflectors.
Measuring the Earth’s frame dragging has been challenging due to the planet’s relatively small mass and slow rotation. However, the LARES-2 satellite’s unique design, with a low area-to-mass ratio, allowed scientists to minimize the impact of other forces and make precise measurements.
Ciufolini said the idea is to measure gravitation. They have non-gravitational effects like photons impinging on the satellite and pushing it. So, the mass must be very large and the cross-section of the satellite very small, so the acceleration induced by photons is very, very small.
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The team used ground-based lasers to shoot at the LARES-2 satellite, which reflected the light back, allowing them to pinpoint its position down to roughly 1 millimeter. About 200,000 such observations formed the dataset used to measure the Earth’s frame dragging.
One of the main challenges in measuring frame dragging is the Earth’s irregular shape, which produces classical Newtonian forces on satellite orbits that are orders of magnitude larger than the frame dragging signal. To overcome this, Ciufolini proposed using two satellites in supplementary orbits, which would cancel out the Newtonian perturbations.
The LARES-2 satellite was placed in orbit at an altitude of roughly 12,265 kilometers by a Vega-C rocket in July 2022. The team used this satellite to make precise measurements of the Earth’s frame dragging.
After making precise measurements, the team was able to bring our uncertainty down from a few percentage points to just 0.2 percent.
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The experiment also yielded valuable data for theoretical physics. Ciufolini said the more you wait, the more data you accumulate, and the better the results of frame dragging measurements will be.
The LARES-2 satellite is expected to continue providing valuable data for theoretical physics, as it can last for hundreds of years.
It will keep working.
