Jupiter’s moon Europa was captured by the JunoCam instrument aboard NASA’s Juno spacecraft during the mission’s short flight on September 29, 2022. The images show the fractures, ridges and bands that criss-cross the moon’s surface. Credit: NASA/JPL-Caltech/SwRI /MSSS, Björn Jónsson (CC BY 3.0)
NASA‘s Juno has provided images supporting the theory of true polar wandering on Europa, showing that the moon’s ice shell has shifted. Images from the solar-powered spacecraft revealed intriguing features of Jupiter’s ice-clad moon, including geological disturbances and potential plume activity, suggesting liquid water and brine are reaching the surface.
Images captured by the JunoCam visible light camera aboard NASA’s Juno spacecraft support the theory that the ice crust at the north and south poles of JupiterThe moon Europa is no longer where it was. In addition, a high-resolution image from the spacecraft’s Stellar Reference Unit (SRU) shows evidence of possible plume activity and disturbances in the ice shell, indicating that brine has recently bubbled to the surface.
The JunoCam results were recently published in the Planetary Science Journal and the SRU results were published in the journal JGR planets.
On September 29, 2022, Juno made its closest flyby of Europa, coming within 220 miles (355 kilometers) of the moon’s frozen surface. The four photos taken by JunoCam and one by the SRU are the first high-resolution images of Europe since Galileo’s last flight in 2000.
Real polar walk
Juno’s ground track over Europa allowed imaging near the moon’s equator. Analyzing the data, the JunoCam team found that in addition to the expected ice blocks, walls, steep slopes, ridges and troughs, the camera also captured irregularly distributed depressions with steep walls 20 to 50 kilometers wide. They resemble large egg-shaped pits previously found in images from other locations in Europe.
It is thought that beneath Europa’s icy exterior lies a giant ocean, and these surface features have been linked to “true polar wandering,” a theory that Europa’s outer ice layer is essentially free-floating and moving.
This black-and-white photo of Europa’s surface was taken by the Stellar Reference Unit (SRU) aboard NASA’s Juno spacecraft during the September 29, 2022 flyby. The chaos element nicknamed “the Platypus” can be seen in the bottom right corner. Credit: NASA/JPL-Caltech/SwRI
“True polar drift occurs when Europa’s icy shell becomes disconnected from its rocky interior, resulting in high stress levels on the shell, leading to predictable fracture patterns,” said Candy Hansen, a Juno co-investigator leading the planning for JunoCam at the Planetary Science Institute in Tucson, Arizona. “This is the first time these fault patterns have been mapped in the Southern Hemisphere, suggesting that the effect of true polar wandering on the surface geology of Europe is greater than previously identified.”
The high-resolution JunoCam images have also been used to reclassify a previously prominent surface feature of the Europa map.
“Crater Gwern no longer exists,” Hansen said. “What was once thought to be a 21-kilometer-wide impact crater – one of Europe’s few documented impact craters – JunoCam data revealed that Gwern was a series of intersecting ridges that created an oval shadow.”
This annotated image of Europa’s surface from Juno’s SRU shows the location of a double ridge running east to west (blue box) with possible plume patches and the chaos feature the team calls “the Platypus” (orange box). These features indicate current surface activity and the presence of subsurface liquid water on Jupiter’s icy moon. Credit: NASA/JPL-Caltech/SwRI
The platypus
While all five of Juno’s Europa images are high-resolution, the image of the spacecraft’s black-and-white SRU offers the most detail. The SRU is designed to detect faint stars for navigation purposes and is sensitive to low light conditions. To avoid overexposure in the image, the team used the camera to capture the night side of Europa while it was illuminated only by sunlight scattered by Jupiter (a phenomenon called ‘Jupiter glare’).
This innovative imaging approach allowed complex surface features to stand out, revealing intricate networks of cross-cutting edges and dark spots of potential water vapor plumes. One intriguing feature, covering an area of 37 by 67 kilometers, was nicknamed ‘the Platypus’ because of its shape.
Characterized by chaotic terrain with hummocks, prominent ridges and dark reddish-brown material, the Platypus is the youngest feature in its neighborhood. The northern ‘torso’ and southern ‘beak’ – connected by a fractured ‘neck’ formation – interrupt the surrounding terrain with a lumpy matrix material containing numerous ice blocks 1 to 7 kilometers wide. Ridge formations collapse into the feature at the edges of the Platypus.
For the Juno team, these formations support the idea that the European ice shell could collapse in locations where there is salt water from the subsurface ocean below the surface.
About 50 kilometers north of the Platypus is a series of double ridges flanked by dark spots that resemble features found elsewhere in Europe and that scientists have believed to be cryovolcanic plume deposits.
“These features indicate current surface activity and the presence of subsurface liquid water on Europa,” said Heidi Becker, principal investigator for the SRU at NASA’s Jet Propulsion Laboratory in Southern California, which also manages the mission. “The SRU image provides a high-quality baseline for specific sites on NASA’s Europa Clipper mission and ESA’s (European Space Agency‘s) Juice missions can focus on looking for signs of change and brine.”
Europa Clipper’s focus is on Europa – including investigating whether the icy moon could have conditions suitable for life. Launch is scheduled for fall 2024 and arrival at Jupiter in 2030. Juice (Jupiter Icy Moons Explorer) was launched on April 14, 2023. The ESA mission will reach Jupiter in July 2031 to study many targets (the three major icy moons of Jupiter). , as well as the fiery Io and smaller moons, along with the planet’s atmosphere, magnetosphere and rings) with special attention to Ganymede.
Juno made its 61st close flyby of Jupiter on May 12. The 62nd flight past the gas giant, scheduled for June 13, will include an Io flight at an altitude of about 18,300 miles.
References:
“Juno’s JunoCam Images of Europa” by CJ Hansen, MA Ravine, PM Schenk, GC Collins, EJ Leonard, CB Phillips, MA Caplinger, F. Tosi, SJ Bolton and Björn Jónsson, March 21, 2024, The Planetary Science Journal.
DOI: 10.3847/PSJ/ad24f4
Reference: “A complex region of Europa’s surface with hints of recent activity revealed by Juno’s Stellar Reference Unit” by Heidi N. Becker, Jonathan I. Lunine, Paul M. Schenk, Meghan M. Florence, Martin J. Brennan, Candice J. Hansen, Yasmina M. Martos, Scott J. Bolton and James W. Alexander, December 22, 2023, Journal of Geophysical Research: Planets.
DOI: 10.1029/2023JE008105
JPL, a division of Caltech in Pasadena, California, manages the Juno mission for its principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency (ASI) funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft.