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Zitat von 20.01.2023 The JUICE spacecraft sets off for Europe's spaceport - From Europe to Jupiter via Kourou
The Jupiter Icy Moons Explorer (JUICE) spacecraft is in Toulouse being prepared for transport to Europe's spaceport in Kourou. The spacecraft is scheduled for launch in April on an Ariane 5 launcher. After arriving in the Jupiter system in July 2031, JUICE will study the planet and its icy moons from orbit, first around Jupiter and later around Ganymede. DLR is providing the Ganymede Laser Altimeter (GALA) and significant contributions to the JANUS camera. The German Space Agency at DLR provides funding to a total of seven instruments on JUICE. Focus: Jupiter, icy moons, exploration, search for life
JUICE must first be transported from Europe to South America. At present, the spacecraft, which has not yet been fuelled and weighs approximately 2400 kilograms empty, is located at the industrial prime contractor, Airbus Defence and Space, in Toulouse, southern France. There it was presented to the media on 20 January 2023 before being packed for transport to Kourou on an Antonov cargo aircraft. The transport across the Atlantic will take place in early February. In Kourou, the spacecraft will then be placed on the Ariane 5 ECA launcher and encased in a protective fairing. When fuelled, the JUICE spacecraft will weigh 6.1 tonnes. The launch window for the eight-year journey to Jupiter opens in April.
Three ice worlds and a volcanic hellscape
Io, the innermost of the four, is so violently deformed by the planet's tidal forces that magma is permanently formed in the rock mantle at temperatures of well over 1000 degrees Celsius. This molten rock is transported to the surface by enormous volcanoes. Sulphur-yellow Io is the most volcanically active body in the Solar System. From the innermost outwards, the three satellites Europa, Ganymede and Callisto follow. Ganymede, with a diameter of 5262 kilometres, is the largest moon in the Solar System; Europa and Io, with diameters of less than 4000 kilometres, are about as large as Earth's Moon; Callisto, with a diameter of 4821 kilometres, is the third largest moon in our planetary system.
It takes Europa twice as long as Io to orbit Jupiter; Ganymede four times as long. This means that these three moons repeatedly line up like a string of pearls. This creates resonance effects that, through interactions with the powerful gravitation and tidal forces emanating from Jupiter, generate heat in the interior of Europa and Ganymede. This causes enough heat to be present under their ice crusts, which are as cold as minus 160 degrees Celsius, which prevents water from freezing even at a distance of over 700 million kilometres from the Sun. This sustains deep layers of water, called subsurface oceans. Oceans (and life?) under kilometre-thick ice crusts
In the case of Europa, it could be that the ocean under the ice crust, which is only a few kilometres thick, is more than 100 kilometres deep. This would mean that there is more water under the moon's surface than in all the oceans on Earth combined. There could also be an ocean below the surface of Callisto; as with Ganymede, magnetic field measurements have provided clear indications here. Both Ganymede and Callisto could have several layers of water, but located at greater depths.
Water is a basic prerequisite for the emergence and development of life as we know it. It is therefore conceivable that, hidden from the view of observations made from space, life has developed in the subsurface oceans of Jupiter's icy moons. JUICE will not be able to determine this, but it will be able to characterise the icy moons in more detail than NASA's Voyager (flyby 1979) and Galileo (orbiter, 1995-2003) missions, as well as confirm the presence of the oceans, how deep they are, how much water they contain and which mineral substances could be dissolved in the water.
Tracking the oceans with lasers
The Ganymede Laser Altimeter (GALA) will measure the tidal deformation of Ganymede's ice crust to provide evidence for the existence of the global interior ocean. In addition, several million time-of-flight measurements will be used to produce a comprehensive map of the moon's regional and local topography, which will be assembled into a global elevation model of Ganymede. This will allow us to understand the processes that shaped the unique surface of this icy moon. The tidal deformation of the satellite's shape will also be determined using measurements taken at different times during Ganymede's seven-day orbit around Jupiter. From the strength of the deformation at the different orbital points, the existence of the inner ocean can be proven, and the mechanical properties of the overlying ice layer determined.
The altimeter will also be used to acquire measurements of Europa and Callisto. While researchers hope to find evidence of water just below Europa’s surface, in the case of Callisto it is likely to be found in deeper layers. GALA was developed under DLR's supervision, in collaboration with industrial partner HENSOLDT Optronics GmbH (Oberkochen) and research institutions from Germany, Japan, Switzerland and Spain. It will be the first time that such an instrument has been used in the outer Solar System.
JUICE will reach Jupiter in July 2031 and complete a total of 35 flybys of the moons by November 2035. In September 2034, the spacecraft will be steered into an elliptical, later circular, orbit around Ganymede. JUICE will be the first mission to orbit the moon of another planet. By the time the mission ends in September 2035, JUICE will have orbited Ganymede approximately 1250 times. Should fuel still be available, further orbits will take place at an altitude of just 200 kilometres, enabling measurements of a quality that would set the standard for decades to come. At the end of the mission, the spacecraft will be deliberately steered to crash into the surface of Ganymede and be completely destroyed in the collision with the rock-hard ice. As the suspected ocean inside Ganymede is estimated to be 100 kilometres deep and night temperatures below minus 160 degrees Celsius, there is no danger of contamination of Ganymede’s ocean by terrestrial microbes that might have travelled along on JUICE as 'stowaways'.
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