Plasma sensors will help study Europa’s ice thickness, ocean depth, and conductivity.

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PIMS Faraday Cup Sensors

216 pims faraday cup sensors

Recently assembled Faraday cup sensors and instrument housings in two configurations.


NASA/Johns Hopkins APL/Ed Whitman


Jupiter’s magnetic field induces a magnetic field at Europa. The mission’s magnetometer investigation will study the moon’s magnetic field. The goal is to reveal Europa’s ocean depth and conductivity, and ice shell thickness.

Jupiter’s magnetic field also carries charged particles called plasma from the volcanic moon Io, Jupiter’s ionosphere, and Europa itself. The plasma distorts Europa’s induced magnetic field and distorts the magnetic signal. The Plasma Instrument for Magnetic Sounding, or PIMS, will study the density, temperature and flow of plasma near Europa. PIMS will help correct the magnetic induction signal for plasma distortions around Europa. It's the key to precisely determining Europa's ice shell thickness, ocean depth, and conductivity.

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How It Works

How It Works

PIMS has four sensors called Faraday cups to study plasma’s density, temperature, and velocity. Each cup is about three inches (eight centimeters) deep and eight inches (20 centimeters) wide. A grid near the top of each cup produces an electric field to block unwanted particles. In the bottom of each cup is a flat, circular detector plate with three 120-degree segments, like a pie with three equal slices. Plasma creates an electrical current when it strikes the plate, revealing the plasma’s speed and density.

If plasma enters the Faraday cup head-on, it strikes the center of the plate and generates equal currents on all three segments. When plasma enters the cup at an angle, it strikes one segment more than the other two. That tells the instrument what direction the plasma was coming from.

How We'll Use It

How We'll Use It

Jupiter rotates once every 10 hours, carrying with it a donut-shaped ring of plasma (ions and electrons). “It’s like a river of particles flowing at 100 kilometers per second,” said Joseph Westlake, principal investigator for PIMS and chief scientist for space physics at the Johns Hopkins University Applied Physics Laboratory. That’s more than 200,000 miles per hour, or about 100 times the speed of a bullet.

“Plasma distorts magnetic fields around Europa and obscures the induction signal from the magnetometer,” said Corey Cochrane, a JPL engineer and scientist on the ECM and PIMS teams. “PIMS will allow us to model the plasma and subtract its contribution from magnetometer data.” It will let scientists study Europa’s ocean depth and conductivity, and ice shell thickness.

Meet the Team

Meet the Team

PIMS Team Photo

“PIMS and the magnetometer are so coupled to make one, combined measurement,” said Abi Rymer, a space physicist at the Johns Hopkins University Applied Physics lab, and a co-investigator and investigation scientist for PIMS. The two investigations are so connected that early on the scientists considered combining the two into one investigation.

“It’s totally fun to be a part of this thing. It’s definitely a dream job.”
- Corey Cochrane, a JPL engineer and scientist, and member of Europa Clipper’s PIMS and ECM teams

Westlake said the collaboration between the mission’s science and engineering teams is impressive. “I work multiple programs, and this is really a breath of fresh air,” Westlake said. “Huge kudos to the folks at JPL and to project scientist Bob Pappalardo. He’s gone to great lengths to keep the team collaborating. It’s such a big team, I don’t know how he manages it. I still haven’t figured out how to push Bob’s buttons. He might not have buttons.”

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