Images of Jupiter's icy moon Europa captured by NASA's Juno spacecraft reveal some incredible features, including 'Jupiter shine', a platypus-shaped region and evidence that its frozen crust is 'wandering'.
The images of Europa were captured by Juno during a close flyby of the moon on 29 September 2022.
The spacecraft came within 220 miles (355 kilometres) of the surface and captured four pictures that are the first high-res pics of Europa since the Galileo mission’s final flyby in 2000.
Europa is of great interest to planetary scientists because it is thought to host a liquid ocean beneath its icy surface, making it a potentially habitable world.
Any information gleaned by Juno could inform the upcoming JUICE and Europa Clipper missions, which will explore the moon in greater detail.
Europa's wandering ice
Images captured by the probe's JunoCam visible-light camera and its Stellar Reference Unit (SRU) suggest the icy crust at Europa's north and south poles has 'wandered'.
Images near the moon’s equator show ice blocks, walls, scarps, ridges and troughs, as well as 12 to 31 mile (20 to 50 kilometres) wide steep-walled depressions.
One pic captured by the SRU shows a double ridge running east-west (blue box in the annotated image below) and a feature known as the 'Platypus' by the Juno team (orange).
These surface features have been associated with 'true polar wander,' a theory that Europa’s ice shell is free-floating and moves over time.
"True polar wander occurs if Europa’s icy shell is decoupled from its rocky interior, resulting in high stress levels on the shell, which lead to predictable fracture patterns," says Candy Hansen, a Juno co-investigator who leads planning for JunoCam at the Planetary Science Institute in Tucson, Arizona.
"This is the first time that these fracture patterns have been mapped in the southern hemisphere, suggesting that true polar wander’s effect on Europa’s surface geology is more extensive than previously identified."
Plumes on Europa?
Possible plume stains appear in the Juno images suggesting that, like Saturn's moon Enceladus, Europa's subsurface ocean regularly ruptures and sprays material out into space.
The Cassini spacecraft at Saturn famously dove through Enceladus's plumes, and analysis of Cassini data revealed complex molecules present within the liquid ocean lurking below.
If there are plumes spraying out from beneath the surface of Europa, could these be a target for the upcoming missions at Jupiter's icy moons?
The disappearing crater
"Crater Gwern is no more," says Hansen.
"What was once thought to be a 13-mile-wide impact crater — one of Europa’s few documented impact craters — Gwern was revealed in JunoCam data to be a set of intersecting ridges that created an oval shadow."
This means JunoCam imagery has been used to reclassify what was a formerly prominent surface feature, showing just how important close flybys of these moons can be.
New high res images can completely change the current understanding of a Solar System world's features and topography.
Jupitershine
Juno's SRU instrument is designed to detect dim stars for navigation purposes, so that orientation of images is possible.
As a result, the SRU is sensitive to low light and, to avoid over-illumination of the image, the Juno team got the camera to capture the unlit side of Europa while it was illuminated only by sunlight bouncing off Jupiter and onto the moon.
This phenomenon is known as Jupitershine, much like Earthshine, which involves sunlight bouncing off Earth and onto our Moon, illuminating the Moon's unlit side.
Platypus
One feature on Europa, covering an area 23 miles by 42 miles (37 kilometers by 67 kilometers), has been nicknamed 'the Platypus' because of its shape.
This area contains hummocks, prominent ridges and dark reddish-brown material, and consists of a northern 'torso' and southern 'bill' connected by a fractured 'neck' formation.
The Platypus contains lumpy material featuring ice blocks 0.6 to 4.3 miles (1 to 7 kilometres) wide.
Ridge formations collapse into the feature at the edges of the Platypus.
This suggests Europa’s ice shell could give way at points where there are pockets of briny water present from the subsurface ocean.
And roughly 31 miles (50 kilometres) north of the Platypus can be seen double ridges with dark stains that could be the aforementioned plume deposits.
"These features hint at present-day surface activity and the presence of subsurface liquid water on Europa," says Heidi Becker, lead co-investigator for the SRU at NASA’s Jet Propulsion Laboratory.
"The SRU’s image is a high-quality baseline for specific places NASA’s Europa Clipper mission and ESA’s (European Space Agency’s) JUICE missions can target to search for signs of change and brine."
Europa Clipper is scheduled to launch in autumn 2024 and arrive at Jupiter in 2030.
JUICE launched on 14 April 2023 and will reach Jupiter in July 2031.
It seems the coming decade could be a turning point in our understanding of Jupiter's icy moon Europa, and its potential to host life.
