Satellites detect hidden magnetic signals in Earth's oceans

Data from the European Space Agency’s Swarm mission has revealed a fascinating discovery. Researchers have found that faint magnetic signals created by ocean tides can help map magma distribution beneath the seabed.

These signals could also provide insights into long-term changes in global ocean temperatures and salinity.

Swarm’s ability to detect these subtle magnetic variations is a significant step forward in geophysical research. By studying these weak signals, scientists can better understand the complex interactions between Earth’s magnetic field, ocean currents, and even volcanic activity beneath the sea.

Swarm’s unique capabilities

Swarm is a constellation of three satellites that orbit the Earth between 462 km (287 miles) and 511 km (318 miles) above the surface. 

Launched in 2013, these satellites were designed to study Earth’s geomagnetic field with unprecedented accuracy.

Earth’s magnetic field extends into space and acts as a protective shield against solar radiation. The primary source of this field is believed to be the movement of liquid iron in the outer core.

However, other factors contribute to the planet’s overall magnetism, including magnetized rocks in the crust.

While the oceans are not typically considered a source of magnetism, salty seawater is a moderate conductor of electricity.

As ocean tides move across Earth’s magnetic field, they generate weak electric currents, which, in turn, produce faint magnetic signals.

These signals are extremely weak compared to those generated by the planet’s core, but Swarm’s highly sensitive instruments can detect them from space.

Ocean’s hidden magnetic signature

Swarm’s advanced sensors, including state-of-the-art magnetometers, can distinguish the faint tidal magnetic signals from other, stronger sources. This ability allows researchers to study the entire water column of the ocean in ways never before possible.

“This study shows that Swarm can provide data on properties of the entire water column of our oceans,” noted Anja Strømme, ESA’s Swarm Mission Manager.

This capability is a game-changer for oceanography and climate science. By analyzing these magnetic signatures, scientists can gain new insights into ocean dynamics, including variations in temperature and salinity over time.

These factors play a crucial role in understanding climate change and predicting future environmental shifts.

Distribution of magma beneath the ocean

Beyond its contributions to ocean science, Swarm is also helping researchers study the distribution of magma beneath the ocean floor. This information is essential for understanding volcanic activity, particularly in seismically active regions.

One of the most significant volcanic events in recent history, the 2022 Hunga-Tonga eruption, demonstrated the destructive power of underwater volcanoes.

Understanding how magma moves and accumulates beneath the seabed could improve early warning systems for such eruptions in the future.

Swarm’s unexpected longevity

Swarm was originally designed as a four-year mission, yet it has been operational for over a decade. The extended mission duration has provided scientists with the opportunity to explore new research questions that were not initially considered.

“This is one of the benefits of flying missions for longer than originally planned. So, by flying as long as the scientific output is of excellent quality and resources allow, you can tackle scientific questions that weren’t originally envisaged,” said Anja Strømme.

As the satellites gradually descend due to atmospheric drag, they are now positioned to capture even weaker magnetic signals from the ocean that were previously beyond the reach of their instruments.

This unintended benefit has opened new avenues of research, allowing Swarm to contribute even more valuable data in its later years.

Solar activity and faint signals

One of the key factors that allowed Swarm to detect these weak oceanic magnetic signatures was the Sun’s period of low activity around 2017.

During this time, known as a solar minimum, there was less interference from space weather, allowing the satellites to collect cleaner data.

“These are among the smallest signals detected by the Swarm mission so far,” explained study 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.”

The solar minimum is a phase in the Sun’s 11-year cycle when its surface activity is at its lowest. During this time, the Sun emits fewer charged particles and less electromagnetic radiation.

This reduction in solar interference makes it easier for Swarm’s instruments to detect weak geomagnetic signals that would otherwise be obscured.

Future studies of subtle magnetic signals

Scientists are hopeful that Swarm will continue to operate beyond 2030, despite its gradual descent. If the mission remains active during the next solar minimum, it will have another opportunity to detect these subtle magnetic signals with even greater clarity.

With each new discovery, Swarm reinforces the value of long-term space missions. What began as a project to study Earth’s magnetism has evolved into a powerful tool for understanding the planet’s oceans, climate, and even volcanic activity.

As Swarm continues its journey, its data will remain a critical resource for researchers seeking to unravel the hidden forces shaping our planet.

Whether through tracking ocean currents, mapping magma flows, or detecting the smallest fluctuations in Earth’s magnetic field, Swarm is proving that even the faintest signals can reveal profound scientific insights.

The study is published in the journal Philosophical Transactions of the Royal Society A.

Image Credit: European Space Agency

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