Home South pole ice NASA’s Juno probe will peer under the icy crust of Europe

NASA’s Juno probe will peer under the icy crust of Europe


On September 29, NASA’s Juno probe will make the closest flyby of Jupiter’s icy moon Europa in more than 20 years as the spacecraft embarks on a probe mission deep into the ice of Europa in search of pockets of liquid water.

Europe contains a global ocean under a solid crust of ice, making this moon one of the most intriguing places on Earth. solar system at search for extraterrestrial life and one of the priorities of astrobiologists. Although Juno can’t tell us if Europa is home to extraterrestrial life, it will tell us more about the moon’s icy crust, like its thickness and whether there are underground pockets of liquid water that could reach the surface.

Juno arrive at Jupiter in July 2016, and its mission focused on study the atmosphere of Jupiterfrom the heights of its ruddy-brown cloud tops to the depths of the lower cloud layers hundreds of kilometers deep, as well as learning about the gas giant’s powerful magnetic field and its inner structure down to its core.

In 2021, NASA granted Juno a mission extension and gave it a new purpose: to study some of the the moons of Jupiter. In June 2021, the spacecraft flew within 645 miles (1,038 kilometers) of Ganymede, which, at 3,273 miles (5,268 km) in diameter, is the largest moon in the solar system. Then it will be Europe’s turn, with Juno expected to pass in front of the moon just 355 km above Europa’s surface. Juno will not see the whole moon but rather a small fraction of the surface. Still, Juno’s cameras have a wide field of view — much like that of a smartphone camera — allowing the spacecraft to take in more scenery than a normal camera.

Related: Jupiter’s Ganymede, the largest moon in the solar system, looks stunning in these first photos of NASA’s epic Juno flyby

Look under the ice

Juno’s work at Europa is considered a “reconnaissance mission” for the next NASA mission European Clipper mission, Scott Bolton, associate vice president of the Southwest Research Institute’s space science and engineering division and principal investigator of the Juno mission, told Space.com. “But we are still going to do a lot of science at Europa.”

The key to this science will be Juno’s Microwave Radiometer (MWR). “It’s a new kind of instrument we’ve invented to see under Jupiter’s clouds,” Bolton said. “‘But we can apply the same instrument to an icy satellite and see a bit in the ice.’

The MWR operates at six wavelengths and can detect thermal emission below the icy surface. The depth at which it can detect such an emission depends on the level of impurities in the ice. The purer the ice, the deeper the MWR will be able to “see” into the ice.

Although the findings of Overview of Juno Ganymede are still being written, Bolton revealed that when Juno directed the MWR to Ganymede, the instrument confirmed that the giant moon’s icy crust was very thick.

Europa might be a different story, at least at certain points on the moon. Scientists hope to one day drill through the ice, into the moon’s dark subterranean ocean. The ice crust is expected to be 30 km deep, at least in most areas, but the crust may be thinner in some areas.

Related: Chaos reigns in detailed new views of Europa, Jupiter’s icy moon

A close-up of the terrain of Europa, as seen by the Galileo spacecraft in 1998. (Image credit: NASA/JPL-Caltech/SETI Institute)

Previous missions that imaged Europa – the Traveler 1 and Traveler 2 spaceship, and the Galileo orbiter – discovered that parts of the moon’s surface are stained with material that appears to have sprung up from below. Juno’s infrared camera and spectrometer will analyze the composition of this material to determine if it is composed of salts or organic molecules.

One theory is that water pockets can form in the basement, either by the liquid rising by convection through the ice shell, or by the melting of the ice in the shell, possibly due to the stresses exerted on it by Jupiter’s gravitational tides. The MWR should be able to tell if there are pockets of water near the surface.

“When we were developing Juno, we didn’t really think we were getting close to icy satellites; we were completely focused on Jupiter,” Bolton said. “Now that we are looking at the moons for our extended mission, it has become apparent that the microwave radiometer works incredibly well on icy bodies as well as on gas giantsso I believe it will become a common workhorse in future planetary exploration.”

Related to the possibility of liquid water near the surface is controversial evidence of geyser eruption of water rising high above the surface and into space. In 2013, the The Hubble Space Telescope detected plume-like clouds of hydrogen and oxygen (which when combined make water) and in 2016 saw the possible silhouette of these plumes. Scientists examining archived data from the Galileo spacecraft found it had measured subtle disturbances in Jupiter’s magnetosphere near Europa that may be the result of charged particles in the plume deflecting the giant planet’s magnetic field.

Artist’s impression of a plume of water vapor rising from the surface of Europa. (Image credit: NASA/ESA/K. Retherford/SWRI)

In 2021, scientists detected enough water vapor be launched on Europe to fill an Olympic size swimming pool in minutes. However, how this water vapor got there remains unclear, as scientists have so far failed to confirm the existence of water geysers.

Could Juno make the first confirmed detection of a geyser during its flyby? “It’s long,” Bolton said. “If the plumes exist, then we must be lucky and blow them up while we’re flying over, and they must be somewhere we’re looking.”

Yet even if Juno does not spot a plume in action, the spacecraft could see a geologic feature on the surface that emits water vapor, analogous to “tiger stripes” on Saturnis the icy moon Enceladus which release their own water geysers. Alternatively, Juno’s navigation cameras will chase icy particles drifting toward Europa’s surface, reflecting and scattering light.

Juno’s polar orbit around Jupiter, flying over the North Pole then the south pole, means it will approach Europa from a steep inclination, giving the spacecraft views of the moon’s polar regions for the first time. In contrast, previous missions hugged the plane of the moons and focused on their equatorial regions. Juno’s orbit also means it’s the spacecraft’s only chance to observe Europa up close.

Did the Hubble Space Telescope see a plume of water gushing out of Europa? (Image credit: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center)

“What’s happening is Juno’s orbit is now being twisted by Jupiter’s gravitational field,” Bolton said. “We have always crossed the equator, but as we get closer to Jupiter, the point at which we cross the equator moves inward.”

Juno crossed the equator of Jupiter at the distance of Ganymede – 665,000 miles, 1.07 million km) in the summer of 2021. Now the spacecraft crosses the equator of Jupiter at the distance of Europa – 383 000 miles (617,000 km). And in December 2023 and February 2024, Juno will cross Jupiter’s equator at the distance of its volcanic moon. Io – 262,000 miles (422,000 km) – and make two close overflights, both within 932 miles (1,500 km).

Juno’s extended mission will last until 2025, when mission scientists will have to make an assessment: whether the spacecraft has enough thruster to continue pointing its antenna toward Earth and is in good enough condition to continue, or if the mission will have to end.

“I imagine NASA would consider another expansion if the spacecraft is healthy,” Bolton said.

The main problem is radiation. Juno’s orbit around the giant planet is elliptical, and each time it reaches the perijove – that is, its closest point to Jupiter – it receives a large dose of radiation from charged particles that are trapped in Jupiter’s mighty magnetosphere and regularly hammer the surface of the planet’s moons. To withstand this radiation, Juno is built “like an armored tank with shields,” Bolton said, “but eventually our shields won’t hold up, to use star trek tongue, and the radiation will begin to damage Juno’s electronics.”

Juno’s encounter with Europa may be its only chance, but it won’t be the last spacecraft to visit Jupiter’s icy moons. NASA’s long-awaited Europa Clipper mission is launch scheduled 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 follow Juno’s search for pockets of liquid water underground that could potentially support life. . Meanwhile, European Space Agency explorer Jupiter Icy Moons (JUICE) will be launched in April 2023, for an arrival at Jupiter in July 2031, on a mission to study Europe, Ganymede and Callisto.

Follow Keith Cooper on Twitter @21stCenturySETI. Follow us on Twitter @Spacedotcom and on Facebook.