Juno has nine different research instruments, and as the spacecraft flew past Europa, they collected data on the moon’s magnetic field, gravitational field and almost nonexistent “atmosphere” of dilute gas. “The most likely material to create this magnetic signature,” Paganini says, “is a global ocean of salty water.”Ĭould Juno’s flyby of Europa lead to similarly groundbreaking findings about Jupiter’s moon? For now, it’s too early to say the data are still being analyzed. The probe found that the moon distorts Jupiter’s surrounding magnetic field in a telltale way that is indicative of some electrically conductive fluid lurking beneath the surface. For example, it was the Galileo flybys that supplied the best available evidence of Europa harboring a global liquid ocean. Astronomers can and do routinely observe the moon remotely, but getting up close and personal has undeniable perks. Galileo swung within 351 km of Europa in 2000 and, before that, flew by at a record-setting 200 km in 1997.īecause these flybys have been so infrequent, available data on Europa are sparse. Besides Juno, which swung past Europa at a distance of 352 km, the only other probe to get close to the moon was NASA’s Galileo-and that was more than two decades ago. The dark, cold depths of the outer solar system take years to reach and are a challenging environment for any spacecraft-but those venturing into the vicinity of Europa must also contend with the belt of harsh radiation that envelops the moon, produced by charged particles trapped in Jupiter’s powerful gravitational field. Still, in spite of the enthusiasm around Europa, there have only been a few flybys of the icy moon. The moon appears uniformly pale orange because the camera’s color balance is optimized for Jupiter. “So these missions and their detailed studies are key to shortening the gap between Europa being just a promising habitable world and having the data needed to confirm its habitability.” One of the four unprocessed images of Europa’s surface taken by the Juno probe. “Europa is one of the most promising worlds in our search for habitability and life,” says Lucas Paganini, program scientist of the Juno mission. But if we’ve found a potential liquid ocean just a couple of planets away, that certainly seems like a good place to start looking, Bolton suggests. “So if we find any, maybe they’re important to life all the time.” Of course, it might turn out that life can emerge without an ocean-or even a single drop of water. That fascination, Bolton says, comes from a perspective that’s “a little bit egotistical.” Jupiter has a grand total of 80 known satellites, but Europa’s vast ocean-thought to be more voluminous than Earth’s-makes the moon one of the most fascinating targets of research in the entire solar system. “Last year we flew by Ganymede,” says Scott Bolton, principal investigator of the Juno mission. After several years of focusing the spacecraft’s investigations almost exclusively on Jupiter, NASA officials gave Juno a new lease on life, extending the mission to study some of the planet’s moons. Juno launched in 2011 and has been swinging around Jupiter’s neighborhood since 2016, collecting data on the planet’s clouds, weather, atmospheric properties and overall composition-in large part to better illuminate how the gas giant was formed. This flyby is particularly thrilling because Juno was never meant to study Europa, let alone approach it so closely the probe was designed to research Jupiter itself. The resulting images-four of them in all-offer a detailed portrait of the distant world’s jumbled, chaotic surface, which is crisscrossed by jagged fractures and pocked with craterlike natural depressions-both likely products of the moon’s distinctly unearthly geologic activity. The Juno probe’s encounter with Europa was speedy, and brief: The spacecraft flew by Europa at 23 kilometers per second, rapidly rotating the entire time, so it had to perfectly time its photographs as it passed. But in many ways, this flyby was just a teaser for upcoming missions-especially Europa Clipper, which is scheduled to launch in 2024 for a series of close-up orbital encounters with the icy moon to search for signs of habitability and perhaps even life itself. And in addition to the images, Juno collected a trove of data that scientists will pore over in the months ahead to look for signs of watery plumes that might periodically erupt from an enormous briny ocean concealed beneath the crust. The flyby produced wonderfully detailed images of the frosty surface of Jupiter’s fourth-largest moon. Then, on September 29, NASA’s Juno probe swung past Jupiter’s icy moon Europa-the closest approach to that natural satellite by any probe since 2000. On September 26 the planet made its closest approach to Earth since 1963, delighting sky watchers around the globe. The last week of September was a big deal for Jupiter.
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