Visualizing Electric Currents in Space

The Electrojet Zeeman Imaging Explorer (EZIE) mission, led by APL Principal Investigator Sam Yee, will determine the structure and evolution of Earth’s electrojets — electric currents flowing in Earth’s ionosphere that are central to the electrical circuit that couples the planet’s magnetosphere to its atmosphere.


Earth’s intense electric currents called electrojets are located around 60-90 miles above the planet’s poles and Sun-facing equator and extend into Earth’s magnetosphere. At the poles, these currents form as Earth’s magnetosphere recoils after being dragged behind the planet by the Sun’s solar wind. The process explosively releases energy into the ionosphere — the high-altitude part of the atmosphere where ionized gas allows electrical currents to flow — and generates the dancing auroras. As such, these intense electric currents are central to the complex space weather system that is increasingly affecting our technological society.

Selected in December 2020 to be one of NASA’s next space physics missions, the Electrojet Zeeman Imaging Explorer (EZIE) mission will uncover new and unprecedented details about the electrojets over its 18-month duration, testing the last 50 years’ worth of various — and conflicting — hypotheses of how the electrojets form and evolve.

Using a trio of small satellites spaced 2-10 minutes apart at some 260-390 miles above Earth’s surface, the mission will characterize the electrojets’ structure over time and space. It will fill gaps in our understanding of this phenomenon and provide findings that scientists can apply to other magnetized planets, whether in our solar system or elsewhere, that are also linked to the surrounding space through electrical currents.

Spacecraft and Instruments 

Each of EZIE’s three SmallSats will be equipped with a microwave electrojet magnetogram instrument capable of imaging Earth’s magnetic field and the electrojets. It does this by exploiting the so-called Zeeman effect -- a splitting of spectral lines, which in EZIE’s case is from thermal radiation emitted by oxygen in the ionosphere.

Each satellite carries an instrument to produce unprecedented 2D maps of the electrojets’ distribution across some 90-300 miles from 50 miles above Earth’s surface. That altitude, to date, has been challenging to directly measure because it’s too high for weather balloons and too low for satellites.

Mission Facts


June 2024

Principal Investigator 

Sam Yee, Johns Hopkins APL

Project Manager 

Nelofar Mosavi, Johns Hopkins APL

Project Scientist 

Jesper Gjerloev, Johns Hopkins APL

Artist rendering of the EZIE spacecraft.
An interactive, 3D rendering of the EZIE spacecraft. Click on the image and drag to see all angles of the spacecraft.
Source: Johns Hopkins APL