A mysterious spider-like structure lurking on Jupiter’s fourth largest moon Europa may finally have a good explanation, nearly 30 years after its discovery. The arachnid impostor has also been given a devilish new name.
In March 1998, NASA’s Galileo spacecraft (which studied Jupiter and its major moons from 1995 to 2003) approached the frozen ocean moon Europa, considered one of the most likely locations in the solar system for extraterrestrial life. During the flight, the spacecraft mapped a 22-kilometre-wide impact structure called Manannan Crater on the moon’s icy surface, and discovered that something strange was lurking inside.
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But in a new study published in The Planetary Science Journal on December 2, researchers proposed an alternative explanation. The idea is that Jupiter’s spiders formed in a way similar to how Earth’s dark dendritic patterns, known as “lake stars,” typically form. These features are formed when snow falls on a frozen lake and water seeps through small holes in the ice.
With this in mind, researchers used a similar technique to partially recreate Manannan Crater’s mysterious shape in the lab. The researchers ultimately named Europa’s arachnid-like asterisk Damhan Alla, which means “spider” or “wall devil” in Irish. (Manannan is a Celtic god in Irish mythology, which is part of the inspiration for the new name.)
“Lake stars are truly beautiful and are common in frozen lakes and ponds that are covered in snow or slush,” study lead author Laura McCune, a planetary scientist at the University of Central Florida, said in a statement. “It’s great to think that they might provide a glimpse into the processes occurring on Europa, and even on other icy oceanic worlds in the solar system.”
But rather than water rising through a small hole, as happens when lake stars form on Earth, Damhan Alla likely formed from an asteroid impact. The asteroid’s impact caused small cracks in Europa’s icy shell, allowing salt water to seep upwards and creating spider-like patterns on the surface. (This asteroid impact likely occurred after the Manannan crater had already formed.)
The researchers also noted similarities between Damhan Alla and the infamous “Martian spider.” Spiders are dust deposits on the surface of Mars that look like swarming spiders when viewed from above. These pseudoarachnids, known as arachnids, form when carbon dioxide ice submerged in water sublimates or directly turns into gas. McCune’s team has recreated these features on Earth before.
The similarity in shape between Damhan Alla and Mars spiders is due to the way “fluids flow across porous surfaces,” McCune said. In theory, similar spider features could form on other frozen oceanic worlds, including Saturn’s moon Enceladus, Jupiter’s other moon Ganymede, and the dwarf planet Ceres in the asteroid belt beyond Mars.
Dr. McCune is currently establishing a new lab focused on studying how these different spider-like features form on different moons of the solar system. She hopes to provide valuable insights that will help inform NASA’s European Clipper mission, which will launch in October 2024 and arrive in 2030 to extensively study Jupiter’s water moons.
“The significance of our research is truly exciting,” McCune said. “Surface features like this can tell us a lot about what’s going on beneath the ice. If we can observe more features with European Clipper, it could indicate a local brine pool beneath the surface,” she added.
And these pools could be a good place to start looking for signs of extraterrestrial life.
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