Ice-penetrating radar will hunt for water below and within Europa’s icy shell.

The latest from the clean room

REASON HF Radar Antenna

Engineers test one of two high frequency radar antennas for Europa Clipper’s REASON instrument on a hilltop at NASA’s Jet Propulsion Laboratory.



Step 1
Hardware Development

Europa Clipper’s instruments and other spacecraft hardware are developed at contractor facilities across the United States and Europe.


Europa Clipper will carry nine instruments with overlapping abilities and responsibilities. But only one can look directly into Europa’s icy shell. It’s called the Radar for Europa Assessment and Sounding: Ocean to Near-surface, or REASON.

Radar is a powerful and versatile science tool. It uses radio waves to detect objects from afar. An array of antennas transmits signals, which bounce off objects and return to the array with a time delay. A given radio wavelength will pass through certain kinds of matter but be reflected by other kinds of matter. When you know what matter you want to detect (water or salt, for example) and what you want to pass through (ice), you choose radio wavelengths or frequencies that pass through one but bounce off the other before the signal loses strength.

Interact with an isolated view of the instrument. download options ›
How It Works

How It Works

REASON transmits radio waves that bounce off features within the underlying ice. Some radio waves return to the spacecraft, but at a fraction of their original energy. By measuring the time difference between transmission and return, and knowing the speed radio waves travel through various materials, REASON learns how far the features are from the spacecraft.

By measuring the energy difference between transmitted signal and returning signal, combined with the measured distance, REASON can see differences in material properties. Scientists on Earth then use software to combine the radio waves to produce detailed images of the ice shell.

How We'll Use It

How We'll Use It

Different wavelengths of radio waves penetrate and bounce off different materials in distinct ways. REASON will use high frequency and very high frequency radio waves to penetrate Europa’s ice as much as 18 miles (30 kilometers) deep. It will search for the moon’s suspected ocean, measure ice thickness, and study the ice’s internal structure, including any internal water bodies that may connect the surface and the ocean. The instrument will also study the topography, composition, and roughness of Europa’s surface. And it can search Europa’s ionosphere for signs of plume activity.

“There are limits to what we can see with one frequency. But having two frequencies makes all of Europa accessible to us.”
- Don Blankenship, principal investigator for REASON
Meet the Team

Meet the Team

REASON Team Photo

Jupiter’s magnetic field hurls atomic particles at Europa’s surface nonstop, creating compounds that ocean microbes might use. Thinner ice, or water passing through the ice, would help the compounds reach the ocean, improving the odds that Europa can sustain life.

“We’ve used ice-penetrating radar for decades. That’s how we know how thick Earth’s ice sheets are.
- Don Blankenship, principal investigator for REASON

How thick is Europa’s ice? “Some people think it’s a few kilometers thick, and lots of people think it’s tens of kilometers thick,” said REASON principal investigator Don Blankenship. REASON applies proven technology to the question. “We’ve used ice-penetrating radar for decades,” Blankenship said. “That’s how we know Earth’s ice sheets’ thickness.” Europa’s ice thickness is so important that several of the mission’s science investigations will measure it. Only through collaboration will those investigations get a solid answer.

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