20 years ago, during the flyby of Europa, the moon of Jupiter, the Galileo space probe witnessed a water plume.
A group of scientists have found new evidence for this event. Using computer simulations, they reproduced the data collected by the onboard particle detector. Europe has a crust of frozen water and an underground ocean, that is, favorable conditions for simple life forms. The plumes of water will give future missions to Jupiter the possibility of direct contact with the lunar body of water.
A layered internal structure with a liquid iron core, a thin oxygen-rich atmosphere induced by a magnetic field is Europa, Jupiter's fourth largest moon, which has more planetary resemblance than its moon. Another feature: the outer crust of frozen water up to 18 kilometers thick, hiding an underground ocean of water. Thanks to new calculations, there is more and more evidence that Europe is throwing plumes of water into space during cryovolcanic eruptions. Saturn's moon Enceladus exhibits similar behavior. During the Cassini mission, onboard cameras took impressive pictures of its plumes.
There is still no overwhelming evidence that Europe is also throwing water into space.
“However, various theories, models and anecdotal evidence suggest that Europe is also showing plumes,” says Elias Roussos. In recent years, researchers from several institutions in Europe and the United States have independently found evidence of a specific plume. Several of these teams evaluated data from a magnetometer aboard the Galileo spacecraft, which has spent 8 years since 1995 exploring the Jupiter system. During Europa's 2000 flyby, data showed deviations in Jupiter's magnetic field near the moon. This could be due to a plume that occurred at the same time.
ESA scientist Dr. Hans Heybris and his colleagues also revised the flyby data in 2000, focusing on measurements made by the Energy Particle Detector (EPD). Among other things, the EPD recorded the distribution of high-energy protons trapped in Jupiter's magnetic field.
Jupiter's magnetic field is 20 times stronger than Earth's and extends several million kilometers into space. Europa revolves around Jupiter in this huge magnetic shield. During the flyby, the EPD recorded significantly fewer protons near the moon than expected. Previously, researchers assumed that the moon itself was obstructing the detector's view.
But current results point to a different cause. In sophisticated computer simulations, scientists have modeled the movements of high-energy protons during flight in an attempt to replicate EPD measurements. This was only possible if the plume affected the European environment. When high-energy protons collide with uncharged particles from the atmosphere or the moon's plume, they include electrons from them, thus becoming uncharged particles. “This means they no longer enter Jupiter's magnetic field and can leave the system at high speed,” explains ESA's Dr. Hans Heybris.
Future missions to the Jupiter system will be able to come into direct contact with the moon's underground water reservoir and characterize it. In 2022, the ESA mission JUICE (Jupiter Icy Moon Explorer) starts. NASA is also preparing the Europa-Clipper mission, due to launch in 2023.