Icy moon🌕

EXPLORING ICY MOONS New technology will study above and below surface ice. Skating on a frozen lake—with its ridges, stones, and cracks—can present challenges that skating on an indoor ice rink doesn’t. It’s possible to see and avoid most of those obstacles, no matter how large the lake; but imagine the difficulty and tools required to maneuver around slabs of ice as tall as mountains, cracks that are miles deep, and explosions of water from beneath your feet. Compared to ice on Earth, exploring ice-covered moons won’t be a skate in the park. NASA has learned a lot about the subzero-temperature moons Enceladus and Europa, where the agency wants to search for signs of life, among other observations. But a mission to either moon (they orbit Saturn and Jupiter, respectively) will take more preparation than tossing skates and a thermos of hot chocolate into the car. Just getting there is complicated (See Cosmic Neighborhood). Observations by robotic spacecraft have provided information about what’s occurring on the surface, revealing important details about the topography and environmental conditions. Slightly smaller than Earth's Moon, Europa is covered with a water-ice shell that’s probably 10 to 15 miles thick, while substantially thinner in some spots. Midday temperatures at the equator reach about -225°F. The surface is even colder toward the poles and at other times during the day. Beneath the surface is an ocean estimated to be 40 to 100 miles deep. To design and build technology that can withstand those conditions, engineers are using all of NASA’s experience in space. The Europa Clipper spacecraft will leverage all the data collected by the Voyager, Galileo, and Cassini missions in order to observe Jupiter’s sixth-closest moon and smallest of the four large Galilean bodies.

Europa is covered with a water-ice shell. “Jupiter’s very strong magnetic field accelerates charged particles to extremely high velocities. And that gives you an extremely large source of radiation,” explains Cynthia Phillips, Europa project staff scientist, who works at the SETI institute. “If a spacecraft were in orbit around Europa, it could only survive for about a month or two before the radiation would start to fry the electronics.” That’s because Europa is in one of Jupiter’s two powerful radiation rings. To maximize the observation time, the spacecraft will orbit Jupiter farther away from the dangerous radiation and execute multiple, close flybys of Europa. When Europa Clipper dives in for a closer look, it will be like “holding your breath, getting as close to Europa as you can to make all your observations, and then swinging back out as fast as you can,” says Phillips. The quick passes, lasting a matter of hours, ensure that the spacecraft spends most of its time in the less volatile regions of space. It will receive commands and send data back to Earth during that period. And that data will include maps of the surface and test results of material collected in space. “All of those charged particles from Jupiter are impacting the surface of Europa and modifying the surface chemically and physically,” says Phillips. “That can throw some of the surface materials off into space, where Europa Clipper can measure them. In addition, we’ll also have much better spectroscopic instruments to help us figure out what the composition of the surface is with remote observations.” These images of Jupiter's icy satellite Europa show surface features such as domes and ridges, as well as a region of disrupted terrain including crustal plates. Blue-white terrain indicates relatively pure water ice. The reddish areas contain water ice mixed with hydrated salts, potentially magnesium sulfate, or sulfuric acid. (Image Credit: NASA/JPL/University of Arizona) Remote sensing instruments include a near-infrared spectrometer for measuring the material composition. Radar instrumentation will sound below the surface of the ice, and a camera will do the mapping. But what Phillips and other scientists are hoping for is an opportunity to fly through plumes of frozen water-ice crystals. The relatively low resolution of the cameras and the low number of images that could be returned to Earth by earlier missions made it difficult to determine if any observations represented actual plumes. But subsequent pictures taken by the Hubble Space Telescope and measurements from a powerful Earth-based telescope support the possibility of plumes being ejected into space. Another piece of circumstantial evidence for plumes at Europa is the plume activity at Enceladus, says Phillips. “The Cassini mission discovered that Saturn’s tiny moon Enceladus was venting huge volumes of material into space.” The similarities between the moons reinforce the theory that plumes could be possible. However, only tests by in situ instruments will serve as definitive proof (See Dragon Flying). The conclusion that subsurface water exists on these moons is a hypothesis based on models. Scientists combine what they know about the laws of physics, chemistry, and other natural sciences with the data provided by multiple spacecraft missions to explain what they observe. The existence of that much water in an environment with such frigid temperatures is explained by another model—tidal heating—that could melt subsurface ice. In a laboratory simulating conditions on Europa at NASA's Jet Propulsion Laboratory, plain white table salt turned yellow (visible in a small well at the center of this photograph). The color is significant because scientists can now deduce that the yellow color previously observed on portions of the surface of Europa is actually salt. (Image Credit: NASA/JPL-Caltech) PreviousNext “Three moons of Jupiter—Io, Europa, and Ganymede—are in a tidally-locked resonance. That means every time Ganymede goes around once, Europa goes around twice, and Io goes around four times,” explains Phillips. “Normally, over time, orbits would tend to become circular. But the resonance of these moons causes Europa and Ganymede, and Europa and Io, to always line up in the same place. They tug on each other, and that makes the orbits noncircular.”😆 Called “forced eccentricity,” this gravitational tug-of-war constantly changes the distance between Europa and Jupiter. That means Jupiter pulls the moon toward itself, thereby increasing the tidal pull when the moon is close. When farther away from the planet, the tidal pull diminishes. The stretching and pulling creates energy that can, in theory, heat and melt the subsurface ice. In the case of Io, a moon very close to Jupiter, these tides are incredibly strong. That moon was predicted to have intense volcanic activity. When the Voyager spacecraft flew past Io for the first time, the prediction proved accurate. “We saw these huge volcanoes, lava flows, and volcanic plumes,” says Phillips.

This observation reinforces the likelihood that a portion of ice on Europa has melted into a liquid ocean. In turn, the motion of that water could explain some of Europa’s curious surface features. The cracks and ridges—and others that appear to be iceberg-like features—could be caused by subsurface water heaving blocks of ice, causing them to break and rotate before freezing into new positions. 🌏 Could a liquid water ocean beneath the surface of Jupiter’s moon Europa have the ingredients to support life? Here's how NASA's mission to Europa would find out. (Video Credit: NASA/JPL) Remote sensing spectroscopic observations indicate that the composition of all that ice is predominantly pure water ice with a low percentage of other materials, mostly salts. The same models suggest it likely comes from an interconnected ocean below the ice. “The Europa Clipper is going to be the first spacecraft that will just observe Europa,” says Phillips. “This is a modern mission. It has much higher sensitivity and much better detection limits in the instrumentation, built with the knowledge that we gained from Cassini. We’ll orbit Jupiter and have multiple flybys of Europa, probably about 40 or 50 flybys, maybe even more depending on how long the spacecraft lasts.” That data will help engineers develop a future lander. Phillips believes such a lander is essential to getting definitive confirmation about another very important Europa theory—the theory that it might harbor life...... thanks 😊