On September 29, NASA’s Juno probe will make its closest flyby of Jupiter’s icy moon Europa in over 20 years as the spacecraft embarks on a mission to penetrate deep into Europa’s ice in search of pockets of liquid water.
Europe contains a global ocean beneath a solid crust of ice, making this moon one of the most fascinating places on earth solar system to Search for extraterrestrial life and one of The top priorities of astrobiologists. Although Juno can’t tell us if Europa harbors extraterrestrial life, it will teach us more about the moon’s icy crust, such as how thick it is and if there are any underground pockets of liquid water that could reach the surface.
Juno arrived at Jupiter in July 2016, and its mission has focused on that Studying the atmosphere of Jupiterfrom the heights of its reddish-brown cloud tops to the depths of the lower cloud layers hundreds of kilometers deep, as well as learning about the gas giant’s strong magnetic field and its internal structure down to its core.
In 2021, NASA granted Juno a mission extension and gave her a new goal: to study some of them Jupiter’s moons. In June 2021, the spacecraft flew within 645 miles (1,038 kilometers) of Ganymede, which is the largest moon in the solar system at 5,268 km (3,273 miles) in diameter. Europa will be next, with Juno hurtling past the Moon just 220 miles (355 km) above Europa’s surface. Juno will not see the entire moon, only a small fraction of the surface. However, Juno’s cameras have a wide field of view – a bit like that of a smartphone camera – allowing the spacecraft to capture more of the landscape than a regular camera could.
Related: Jupiter’s Ganymede, the largest moon in the solar system, looks amazing in these first photos of NASA’s epic Juno flyby
Look under the ice
Juno’s work at Europa is seen as a “scouting mission” for the upcoming NASA Europe clippers mission, Scott Bolton, associate vice president of the Southwest Research Institute’s division of space science and engineering and principal investigator on the Juno mission, told Space.com. “But we will still be doing quite a lot of science at Europa.”
The key to this science will be Juno’s microwave radiometer (MWR). “This is a new type of instrument that we invented to see under the clouds of Jupiter,” Bolton said. “‘But we can apply the same instrument to an ice satellite and look a little bit inside the ice.”
The MWR operates at six wavelengths and can detect thermal emission from below the ice surface. How deep it can detect such emissions depends on the level of contamination in the ice. The purer the ice, the deeper the MWR can “see” into the ice.
Although the findings from Juno’s flyby of Ganymede yet to be written, Bolton revealed that when Juno aimed the MWR at Ganymede, the instrument confirmed that the giant moon’s icy crust was very thick.
Europa could be a different story, at least in certain places on the moon. Scientists hope to one day drill through the ice into the moon’s dark, subsurface ocean. The ice crust is expected to be 30 km deep in at least most regions, but the crust may be thinner in some areas.
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Previous missions that have mapped Europe – the traveler 1 and traveler 2 spaceship and the Galileo orbiter – noticed that parts of the lunar surface are stained by material that appears to have swollen from below. Juno’s infrared camera and spectrometer will analyze the composition of this material to determine whether it consists of salts or organic molecules.
That’s a theory Water nests can form underground, either by fluid convectively rising through the ice shell, or by the melting of the ice in the shell, possibly as a result of stresses exerted on it by Jupiter’s gravitational tides. The MWR should be able to detect if there are water pockets near the surface.
“When we were developing Juno, we didn’t really think about going near the ice satellites; we were completely focused on Jupiter,” Bolton said. “Now that we’re looking at the moons for our expanded mission, it’s become apparent that the microwave radiometer works incredibly well on icy bodies, too gas giantsso I believe it will become a mainstream workhorse in future planetary exploration.”
The possibility of liquid water near the surface is controversial Evidence of erupting geysers of waters rising high above the surface and into space. In 2013 the Hubble Space Telescope discovered cloud-shaped clouds of hydrogen and oxygen (which together form water) and saw the possible silhouette of these clouds in 2016. Scientists sifting through archived data from the Galileo spacecraft found that it had measured subtle perturbations in Jupiter’s magnetosphere near Europa that could be the result of charged particles in the cloud deflecting the giant planet’s magnetic field.
In 2021, scientists enough water vapor detected released across Europe to fill an Olympic-size swimming pool in just minutes. How this water vapor got there remains uncertain, however, as scientists have not yet been able to confirm the existence of water geysers.
Could Juno make the first confirmed discovery of a geyser during its flyby? “It’s a long road,” Bolton said. “If the feathers exist, then we have to be lucky and let them fly off as we fly by, and they have to be in a place that we happen to be looking at.”
Yet even if Juno doesn’t spot a cloud in action, the spacecraft could see a geological feature on the surface emitting water vapor, analogous to the “tiger stripes” on Saturnicy moon Enceladus releasing their own water geysers. Alternatively, Juno’s navigation cameras will look for ice particles drifting back onto Europa’s surface, reflecting and scattering light.
Juno’s polar orbit around Jupiter, overflying North Pole and then the South Pole, means it will approach Europa from a high inclination, giving the spacecraft its first glimpse of the moon’s polar regions. In contrast, previous missions have embraced the plane of the moons and focused on their equatorial regions. Juno’s orbit also means it’s the only chance for the spacecraft to see Europa up close.
“What is happening is that Juno’s orbit is now being twisted by Jupiter’s gravitational field,” Bolton said. “We’ve always crossed the equator, but as we get closer to Jupiter, the point at which we cross the equator moves inward.”
Juno crossed Jupiter’s equator at the distance from Ganymede – 665,000 miles, 1.07 million km) in the summer of 2021. Now the spacecraft is crossing Jupiter’s equator at a distance of 383,000 miles (617,000 km) from Europa. And in December 2023 and February 2024, Juno will cross Jupiter’s equator at the distance of its volcanic moon yes – 262,000 miles (422,000 km) – and conduct two close flybys, both within 932 miles (1,500 km).
Juno’s extended mission will last until 2025, at which point mission scientists must make an assessment: whether the spacecraft has enough propellant to continue pointing its antenna at it Earth and is in good condition to continue or whether the mission needs to be completed.
“I imagine NASA would consider another extension if the spacecraft is healthy,” Bolton said.
The main problem is radiation. Juno’s orbit around the giant planet is elliptical, and every time it reaches the perijove – that is, its closest point to Jupiter – it receives a large dose of radiation from the charged particles trapped within Jupiter’s strong magnetosphere and routinely hammer the surface of the planet’s moons. To withstand that radiation, Juno is built “like an armored tank with shields,” Bolton said, “but eventually our shields won’t hold up anymore star trek language, and the radiation will damage Juno’s electronics.”
Juno’s encounter with Europa may be their only capture, but it won’t be the last spacecraft to visit Jupiter’s icy moons. NASA’s long-awaited Europa Clipper mission is here The launch is planned for October 2024 and arrive in orbit around Jupiter in April 2030. Europa Clipper will conduct nearly 50 close flybys of Europa to fully characterize the Moon and continue Juno’s search for pockets of liquid water underground that could potentially support life. Meanwhile, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) will launch in April 2023 and arrive at Jupiter in July 2031 to study Europa, Ganymede and Callisto.
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