Earth is full of mysteries, from its ferociously hot core to the magnetic field it generates that protects us from cosmic and solar radiation.

Thanks to a collaboration between the European Space Agency’s Swarm mission, and the Macau Science Satellite-1 (MSS-1), we have an unprecedented opportunity to drill deeper into them.

Both Swarm and MSS-1 are constellations of satellites that carry sophisticated magnetometers and other instruments to precisely measure Earth’s dynamic magnetic field, including even the most subtle of signals such as those generated by the tidal movement of seawater.

At the first joint Swarm-MSS-1 international science conference hosted by the Macau Institute of Space Technology and Application in May 2025, we learned why this is such a special collaboration.

Close encounters and complementary data

Swarm consists of three polar-orbiting satellites, two (Swarm A and C) orbiting slightly lower from an original altitude of 462 km with another (Swarm B) orbiting higher from an initial 511 km. MSS-1 consists of two low-inclination satellites, one of which carries similar absolute magnetometers as those flown on Swarm, following near-circular orbits at an initial 430 km altitude.

The different perspectives of Swarm and MSS-1 are already providing interesting insights thanks to the combination of polar and low inclination satellite data. Swarm’s polar orbit measures the whole planet, whilst MSS-1 is limited to latitudes up to 41ᵒ North and South. However, MSS-1 gets better local-time coverage within that band.

Since MSS-1A launched in May 2023 there have been around five “close encounters” – when two or more satellites pass within 100 km of each other – between Swarm and MSS-1A every three weeks. These encounters last between 4 and 30 seconds, with an average of 13 seconds per encounter.

“This is a great opportunity both to calibrate satellite data and to hone in on geophysical processes, such as in-situ ionospheric currents,” said Nils Olsen, head of the Swarm DISC, who presented these close encounters at the conference.

“The close encounters show Swarm and MSS-1 agree excellently, with some interesting differences – information that will help us to improve the magnetic field data from both missions even further.”

Some of those differences were exemplified by Xin Yi Rang of Wuhan University, whose analysis of vector magnetic field data showed excellent agreement between Swarm A and MSS-1A, but also that MSS-1A could pick up more equatorial plasma bubbles due to its low inclination.

Patrick Alken also noted that MSS-1’s low inclination opens new observations around the magnetic equator that cannot be captured with polar orbits.

Revealing the mysteries of Earth, together

During his wrap up in the closing stages of the conference, Keke Zhang, Director and Chair Professor, State Key Laboratory of Lunar and Planetary Sciences, of Macau Institute of Space Technology and Application, praised the Swarm community for their vital help calibrating and validating MSS-1 data, enabling the mission to thrive.

Within just two years of launch, a special issue was released in Earth and Planetary Physics marking the first findings of MSS-1, including collaborations with Swarm spanning the whole Earth system.

In Macau we heard how the two missions were being used to reconstruct core flow, understand the core-mantle boundary, Earth’s lithosphere and tidal magnetic signals, the South Atlantic anomaly, the equatorial electrojet, and perform in-depth analysis (along with platform magnetometer data from ESA’s CryoSat mission) of ionospheric and magnetic currents during the Mother’s Day geomagnetic superstorm of May 2024.

One particularly useful aspect of the collaboration is that the MSS-1 team has worked to make their data compatible with those of Swarm, making intercomparisons easier.

Though it is currently still in the planning stages, Ashley Smith of the University of Edinburgh has been working on ways to make the joint data usable within Swarm’s data visualisation workspace, VirES, when added by the user themselves currently.

“VirES is a home for geomagnetic data and a global infrastructure, not just for Swarm,” said Ashley. “Adding more satellite data, such as those of MSS-1, would strengthen the global geomagnetic observing system.”

An unprecedented constellation

“Swarm is doing excellently,” ESA’s Enkelejda Qamili said at the start of the conference. “All the instruments are performing well and are not degrading.”

This is great news, as it is hoped that both Swarm and MSS-1 can continue to fly into an era in which ESA’s future scout constellation, NanoMagSat, will also be in orbit.

NanoMagSat is designed as a follow-on to Swarm, featuring miniaturised but still highly precise instruments including an absolute magnetometer, a high-frequency magnetometer and a Langmuir probe and Science GNSS receivers, on each of three small satellites.

“The hope is, by the time we have NanoMagSat, we still have MSS-1 and we still have Swarm,” said Gauthier Hulot, Principal Investigator and CNRS Research Director at the Institut de Physique du Globe de Paris within Université Paris Cité, speaking at the event in Macau.

“We are targeting the data to be just as good as Swarm. Hopefully, even better.”

NanoMagSat’s first satellite is due to launch in 2027, with the full constellation in place by 2028. A minimum of three years of constellation operation is planned.

Thanks to two campaigns to raise the orbits of Swarm A and C in 2022 and 2023 to help them survive the current solar maximum, current predictions indicate all three satellites could fly into the 2030s.

“Having Swarm and MSS fly alongside NanoMagSat would be an incredible opportunity,” said Anja Strømme, Swarm mission manager.

“Together we can enhance our ability to monitor and protect against space weather hazards, and continue to support precise navigation and reference magnetic field models for the good of Europe and the rest of the world.”