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Nasa’s Juno spacecraft approaches Jupiter moon to unlock its mysteries

Nasa’s Juno spacecraft will fly close to Jupiter’s moon Ganymede today, offering scientists their closest encounter with it in over 20 years.

Ganymede is the largest moon in the solar system and is actually larger than the planet Mercury by volume. It is thought to contain an internal ocean under its crust that could contain more water than all of the Earth’s oceans combined.

Later this evening, Juno will come within 1,038km of its surface - the closest a spacecraft has come to the satellite since Nasa’s Galileo spacecraft made its penultimate close approach back on May 20 2000.

Along with striking imagery, the solar-powered spacecraft’s flyby will yield insights into the moon’s composition, ionosphere, magnetosphere and ice shell. Juno’s measurements of the radiation environment near the moon will also benefit future missions to the Jovian system.

“Juno carries a suite of sensitive instruments capable of seeing Ganymede in ways never before possible,” said Scott Bolton, Juno’s principal investigator.

“By flying so close, we will bring the exploration of Ganymede into the 21st century, both complementing future missions with our unique sensors and helping prepare for the next generation of missions to the Jovian system – Nasa’s Europa Clipper and ESA’s [European Space Agency’s] JUpiter ICy moons Explorer [JUICE] mission.”

Juno’s science instruments will begin collecting data about three hours before the spacecraft’s closest approach and its microwave radiometer (MWR) will be used to peer into Ganymede’s water-ice crust, obtaining data on its composition and temperature.

“Ganymede’s ice shell has some light and dark regions, suggesting that some areas may be pure ice while other areas contain dirty ice,” said Bolton.

“MWR will provide the first in-depth investigation of how the composition and structure of the ice varies with depth, leading to a better understanding of how the ice shell forms and the ongoing processes that resurface the ice over time.”

The results will complement those from ESA’s forthcoming JUICE mission, which will look at the ice using radar at different wavelengths when it becomes the first spacecraft to orbit a moon other than Earth’s Moon in 2032.

As Juno passes behind Ganymede, radio signals will pass through its ionosphere, causing small changes in the frequency that should be picked up by two antennas at the Deep Space Network’s Canberra complex in Australia.

Dustin Buccino, a signal analysis engineer for the Juno mission, said: “If we can measure this change, we might be able to understand the connection between Ganymede’s ionosphere, its intrinsic magnetic field and Jupiter’s magnetosphere.”

Juno’s onboard imager will be used to snap some shots at resolutions equivalent to the best from Voyager and Galileo.

The Juno science team will scour the images, comparing them to those from previous missions, looking for changes in surface features that might have occurred over four-plus decades.

Any changes to crater distribution on the surface could help astronomers better understand the current population of objects that impact moons in the outer solar system.

Due to the speed of the flyby, Juno will only have about 25 minutes to take around five images.

In 2017, Juno became forced into making long orbits around Jupiter due to sticky valves. This meant that it took longer to gather the data required to complete its mission of surveying Jupiter and its moons. The extension of the mission cost Nasa ten millions of dollars.

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