Just as early mariners used simple compasses to chart courses across the sea, today’s ships, planes, satellites, and smartphones can rely on Earth’s magnetic field to find their bearings. The difference is that today’s rather more sophisticated compasses have the aid of complex models, like the commonly used World Magnetic Model (WMM), that try to capture the multifaceted processes that create Earth’s magnetosphere. A compass can rely on the WMM or similar models to convert a needle pointing to magnetic north to a heading with respect to true north. (The two norths differ by ever-changing angles.)

These models are not perfect: There are differences between the magnetosphere that they predict and the magnetosphere that satellites observe. Scientists have traditionally ascribed these differences to space currents that flow through the magnetic field high in Earth’s upper atmosphere. But new research complicates the picture, suggesting that the differences are the result of observational biases, incomplete models, or both.

For craft that require sensitive navigation, particularly around Earth’s poles, any of these complications pose a problem. And those problems stand to grow as polar ice melts around the North Pole, opening up potential new shipping routes.

Earth’s magnetic field is multifaceted and complex, but models like the WMM can project it out a few years at a time. The WMM’s current edition, released in December 2019, contains estimates of Earth’s magnetic field from the start of 2020 to the end of 2024. (The next version, covering 2025 through 2029, is scheduled for release in December of this year.)

“Compasses need to account for space currents already, but this adds more complication and sources of noise that have to be dealt with.” —Mark Moldwin, University of Michigan

These models do not always account for space currents, which are often pushed around by extraterrestrial forces like the solar wind. But if space currents are responsible for the discrepancies between models and observations, scientists could identify them by simply finding the differences, which they call “residuals.” Moreover, there would then be little reason for one of Earth’s hemispheres to display more residuals than the other—except that’s what existing models predict.

But the new study’s authors, space physicists Yining Shi and Mark Moldwin from the University of Michigan, had been among a number of researchers who had spotted an imbalance in residuals. More residuals seemed to emerge from the magnetic woodwork, so to speak, in the southern hemisphere than in the Northern Hemisphere. “We wanted to take a closer look at them,” Moldwin said.

Shi and Moldwin compared estimates between 2014 and 2020 from another Earth magnetic field model, IGRF-13, with observations from the European Space Agency’s Swarm mission, a trio of satellites that have continually measured Earth’s magnetic field since their 2014 launch.

When they focused on residuals over that time period, they did indeed find about 12 percent more major residuals in the Southern Hemisphere than in the Northern. All of these large residuals were found in the polar regions. Many were concentrated at latitudes of 70 degrees north and south, where scientists expect to find space currents.

But another spate of residuals were concentrated closer to Earth’s geographic poles, about 80 degrees north and south, where they have no obvious geophysical explanation. Moreover, the distributions of these poles differed—matching the fact that Earth’s geographic poles map to different magnetic coordinates.

This second peak in particular led the researchers to consider alternative explanations. It is possible, for instance, that IGRF-13 simply does not capture all of the factors driving Earth’s magnetosphere around the poles. But another cause could be the satellites themselves. Shi and Moldwin say that, because Swarm satellites reside in orbits that cross the poles, Earth’s northern and southern polar regions are overrepresented in their magnetic measurements.

“Compasses need to account for space currents already, but this adds more complication and sources of noise that have to be dealt with,” Moldwin said.

Now, Shi is examining these residuals more closely to pick apart the causes of the residuals—which ones have actual geophysical explanations and which are the result of statistical errors.

Shi and Moldwin published their work on 6 May in Journal of Geophysical Research: Space Physics.

A recent Bluetooth connection between a device on Earth and a satellite in orbit signals a potential new space race—this time, for global location-tracking networks.

Seattle-based startup Hubble Network announced today that it had a letter of understanding with San Francisco-based startup Life360 to develop a global, satellite-based Internet of Things (IoT) tracking system. The announcement follows on the heels of a 29 April announcement from Hubble Network that it had established the first Bluetooth connection between a device on Earth and a satellite. The pair of announcements sets the stage for an IoT tracking system that aims to rival Apple’s AirTags, Samsung’s Galaxy SmartTag2, and the Cube GPS Tracker.

Bluetooth, the wireless technology that connects home speakers and earbuds to phones, typically traverses meters, not hundreds of kilometers (520 km, in the case of Hubble Network’s two orbiting satellites). The trick to extending the tech’s range, Hubble Network says, lies in the startup’s patented, high-sensitivity signal detection system on a LEO satellite.

“We believe this is comparable to when GPS was first made available for public use.” —Alex Haro, Hubble Network

The caveat, however, is that the connection is device-to-satellite only. The satellite can’t ping devices back on Earth to say “signal received,” for example. This is because location-tracking tags operate on tiny energy budgets—often powered by button-sized batteries and running on a single charge for months or even years at a stretch. Tags are also able to perform only minimal signal processing. That means that tracking devices cannot include the sensitive phased-array antennas and digital beamforming needed to tease out a vanishingly tiny Bluetooth signal racing through the stratosphere.

“There is a massive enterprise and industrial market for ‘send only’ applications,” says Alex Haro, CEO of Hubble Network. “Once deployed, these sensors and devices don’t need Internet connectivity except to send out their location and telemetry data, such as temperature, humidity, shock, and moisture. Hubble enables sensors and asset trackers to be deployed globally in a very battery- and cost-efficient manner.”

Other applications for the company’s technologies, Haro says, include asset tracking, environmental monitoring, container and pallet tracking, predictive maintenance, smart agriculture applications, fleet management, smart buildings, and electrical grid monitoring.

“To give you a sense of how much better Hubble Network is compared to existing satellite providers like Globalstar,” Haro says, “We are 50 times cheaper and have 20 times longer battery life. For example, we can build a Tile device that is locatable anywhere in the world without any cellular reception and lasts for years on a single coin cell battery. This will be a game-changer in the AirTag market for consumers.”

Hubble Network chief space officer John Kim (left) and two company engineers perform tests on the company’s signal-sensing satellite technology. Hubble Network

The Hubble Network system—and presumably the enhanced Life360 Tags that should follow today’s announcement—use a lower energy iteration of the familiar Bluetooth wireless protocol.

Like its more famous cousin, Bluetooth Low-Energy (BLE) uses the 2.4 gigahertz band—a globally unlicensed spectrum band that many Wi-Fi routers, microwave ovens, baby monitors, wireless microphones, and other consumer devices also use.

Haro says BLE offered the most compelling, supposedly “short-range” wireless standard for Hubble Network’s purposes. By contrast, he says, the long-range, wide-area network LoRaWAN operates on a communications band, 900 megahertz, that some countries and regions regulate differently from others—making a potentially global standard around it that much more difficult to establish and maintain. Plus, he says, 2.4 GHz antennas can be roughly one-third the size of a standard LoRaWAN antenna, which makes a difference when launching material into space, when every gram matters.

Haro says that Hubble Network’s technology does require changing the sending device’s software in order to communicate with a BLE receiver satellite in orbit. And it doesn’t require any hardware modifications of the device, save one—adding a standard BLE antenna. “This is the first time that a Bluetooth chip can send data from the ground to a satellite in orbit,” Haro says. “We require the Hubble software stack loaded onto the chip to make this possible, but no physical modifications are needed. Off-the-shelf BLE chips are now capable of communicating directly with LEO satellites.”

“We believe this is comparable to when GPS was first made available for public use,” Haro adds. “It was a groundbreaking moment in technology history that significantly impacted everyday users in ways previously unavailable.”

What remains, of course, is the next hardest part: Launching all of the satellites needed to create a globally available tracking network. As to whether other companies or countries will be developing their own competitor technologies, now that Bluetooth has been revealed to have long-range communication capabilities, Haro did not speculate beyond what he envisions for his own company’s LEO ambitions.

“We currently have our first two satellites in orbit as of 4 March,” Haro says. “We plan to continue launching more satellites, aiming to have 32 in orbit by early 2026. Our pilot customers are already updating and testing their devices on our network, and we will continue to scale our constellation over the next 3 to 5 years.”