Everything in the universe whose temperature is above absolute zero emits light. Trees, bagels, birds, and even you emit light at radio and infrared wavelengths. You're making photons from scratch in this very moment, as is Europa. The icy moon is a few times farther from the Sun than Earth is, so its surface is incredibly cold. But it still emits infrared light. And that’s what Europa Clipper’s thermal imager will study in detail.
The Europa Thermal Emission Imaging System, or E-THEMIS, will map Europa’s temperatures. It will seek clues about activity such as cryovolcanos, and regions where the moon’s suspected ocean may be near the surface.
How It Works
Objects emit different wavelengths of light depending on their temperatures. E-THEMIS will analyze infrared light from Europa to map the moon’s surface temperature.
Like visible light, infrared is photons. But infrared is outside humans' visual range. E-THEMIS directs infrared light through three filters. Each allows only certain wavelengths to pass through. The light then strikes a detector with three segments, each sensitive to one “color,” or wavelength range, of light.
E-THEMIS will use the spacecraft’s motion to scan strips of Europa’s surface. “It’s like the panorama feature on a smart phone,” said Sylvain Piqueux, a JPL planetary scientist on the E-THEMIS science team. “But instead you have three phones next to each other, each observing a different color.”
How We’ll Use It“One of the things I love about space exploration is that nothing ever looks the way the smartest people think it’s going to look.”
How We’ll Use It
E-THEMIS will scan Europa's surface for relatively warm ice, which may be a sign of recent resurfacing. Other instruments can then target those areas to learn about the moon’s subsurface chemistry. Warmer ice could also mean Europa's suspected ocean is closer to the surface in that location.
Also, when part of Europa rotates out of sunlight, thermal inertia causes granular material to cool faster than large blocks. E-THEMIS will record surface cooling rates to learn about the texture of Europa’s surface. Mapping surface temperature and water near the surface will help to understand Europa’s small-scale properties and might even help to find sites for a possible future lander. “You don’t want the lander to sink into snow-like fluff, or land on a surface so hard that it can’t scrape or drill anything,” Piqueux said.Meet the Team
Meet the Team
E-THEMIS principal investigator Phil Christensen is a planetary geologist at Arizona State University. “I’m most excited for E-THEMIS to detect warmer locations where liquid water is near the surface. We might someday land in one of those spots and send a probe into Europa’s water.”
Julie Rathbun is a planetary scientist at the Planetary Science Institute and a member of the E-THEMIS team. “One of E-THEMIS’s strenghts is it looks in different wavelengths,” she said. Shorter wavelengths are more sensitive to warmer material, while longer wavelengths are more sensitive to cooler material. “Because there are different temperatures on the surface, we can figure out what percent of the surface is solid ice versus something more granulated.”