After months of testing, an ASU-designed and -built instrument to measure the surface temperature of a moon of Jupiter has arrived at NASA's Jet Propulsion Laboratory in Southern California. There it will join eight other instruments and become an integral part of the agency's Europa Clipper spacecraft.

The instrument is the Europa Thermal Emission Imaging System (E-THEMIS) led by Regents Professor Philip Christensen of Arizona State University’s School of Earth and Space Exploration.

The Europa Clipper is a robotic spacecraft sent to investigate Jupiter's ice-shrouded moon Europa. It is planned to launch on a SpaceX Falcon Heavy rocket in October 2024 and arrive at Jupiter in April 2030 after making flybys of Mars in 2025 and Earth in 2026. These planetary flybys use the masses of Mars and Earth to boost the spacecraft's velocity so it can reach the Jupiter system.

After entering orbit at Jupiter, the spacecraft will make about 50 flybys of Europa to investigate whether the moon could harbor conditions suitable for life.

Video by Steve Filmer/ASU

E-THEMIS is an infrared camera designed to map temperatures across Europa’s surface. Its images, taken in three heat-sensitive bands, will help scientists find clues about Europa’s geological activity, including regions where the moon's presumed ocean may lie near the surface. Although Europa is slightly smaller than Earth's moon, scientists think its ocean may hold twice the volume of Earth's oceans.

“Europa's surface is an extremely cold shell of ice, but the ocean below is liquid water," Christensen says. "E-THEMIS can see warmer regions, whether caused by impacts, convection or liquid water lying much closer to the surface than the ocean."

Even if many years have passed, he says, "The ice will still be warm. From these temperature images, E-THEMIS will give us an excellent opportunity to study the geologic activity of Europa."

Besides identifying any warm areas on Europa's surface, E-THEMIS images will also help scientists determine the physical state of the icy surface. As parts of Europa's landscape cool after local sunset, areas of solid ice will stay warmer longer, while those with a granular texture will lose heat more rapidly. By mapping the rates of cooling across the surface, scientists will better understand Europa’s small-scale properties. This technique might even help to identify sites for a possible future lander. 

Measuring solar warmth

To check out the instrument's optics and sensors, in January 2022 the ASU team took test images with the E-THEMIS camera from the rooftop of the Interdisciplinary Science and Technology Building 4 (ISTB4) on ASU's Tempe campus. The images show Sun Devil Stadium and “A” Mountain, among other local landmarks.

The instrument worked perfectly, with E-THEMIS making temperature-sensing images at midday, in late afternoon and after sunset. As designed, these clearly revealed how the temperature of the buildings and landscape responded to changes in sunlight as the day progressed, and they show the features cooling after sunset.

Surviving a rough neighborhood

When Europa Clipper arrives at Jupiter, it will encounter an extremely harsh environment. The giant planet poses major difficulties for any spacecraft operating in its vicinity. First, it's cold out there because Jupiter orbits more than five times farther from the sun than Earth, and sunlight has less than 4% the strength it has at Earth. But the biggest problems come from Jupiter's severe radiation environment.

The most massive planet in the solar system, and rotating more than twice every 24 hours, Jupiter spins out a large and powerful magnetic field. This creates a zone of trapped radiation around the planet similar to the Van Allen radiation belts around Earth, but thousands of times stronger. Europa Clipper must fly through this radiation zone again and again over the course of its mission.