Swarm satellites reveal oceanic tidal magnetism

Swarm satellites reveal oceanic tidal magnetism
by Erica Marchand
Paris, France (SPX) Jan 23, 2025

A recent study utilizing data from ESA's Swarm satellite mission has uncovered subtle magnetic signatures generated by Earth's ocean tides. These findings not only offer new insights into how magma is distributed beneath the seafloor but also hold potential for assessing long-term trends in global ocean temperatures and salinity.

Swarm consists of three satellites dedicated to studying Earth's geomagnetic field. This protective magnetic field, which extends from the planet's core into space, is primarily driven by liquid iron in Earth's outer core, with additional contributions from magnetized rocks in the crust. Surprisingly, the salty water in Earth's oceans also plays a role, as it conducts electricity moderately well. As tides flow through the planet's magnetic field, they generate weak electric currents that induce small magnetic signals detectable from space.

Operating at altitudes between 462 km and 511 km, Swarm's satellites are capable of measuring Earth's magnetic field with unprecedented accuracy. This enables the detection of faint tidal signals and the separation of these from stronger magnetic sources within Earth's interior.

"This study shows that Swarm can provide data on properties of the entire water column of our oceans," said Anja Stromme, ESA's Swarm Mission Manager.

The research also highlights how Swarm's data could shed light on magma distribution, potentially enhancing the understanding of volcanic events like the Hunga-Tonga eruption in 2022. The findings were published in Philosophical Transactions of the Royal Society A, the world's oldest scientific journal, by researchers from the University of Cologne and the Technical University of Denmark.

Extended mission yields new insights

Launched in 2013 with a planned four-year mission, Swarm has exceeded expectations and remains operational in its 12th year. Anja Stromme noted, "This is one of the benefits of flying missions for longer than originally planned. By extending the mission, we can address scientific questions that weren't initially envisioned."

As the satellites' orbits gradually decay, bringing them closer to Earth, their advanced sensors - including high-precision magnetometers - have captured magnetic signals that were harder to detect during the mission's early, higher-altitude phase.

Solar cycle aids detection

Swarm's ability to detect these faint oceanic signals was aided by reduced solar activity during 2017. "These are among the smallest signals detected by the Swarm mission so far," explained lead author Alexander Grayver from the University of Cologne.

"The data are particularly good because they were gathered during a period of solar minimum, when there was less noise due to space weather."

During the quiet phase of the Sun's 11-year cycle, space weather phenomena like the Northern Lights become less frequent due to reduced solar electromagnetic emissions. This calmer solar environment made it easier for Swarm's instruments to detect geomagnetic signals originating from Earth.

Looking ahead, researchers hope that the Swarm mission may still be operational during the next solar minimum, expected after 2030. By then, the satellites will be at lower altitudes, potentially allowing for even more refined measurements of Earth's magnetic field and the signals linked to ocean temperatures and salinity.