Space

Europa's plumes may not originate from subsurface ocean

Europa's plumes may not origin...
An artist's representation of a plume erupting from a shallow pocket of briny water below the icy surface of Europa
An artist's representation of a plume erupting from a shallow pocket of briny water below the icy surface of Europa
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An artist's representation of a plume erupting from a shallow pocket of briny water below the icy surface of Europa
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An artist's representation of a plume erupting from a shallow pocket of briny water below the icy surface of Europa
Europa is regarded as one of the most likely places to find life off the Earth
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Europa is regarded as one of the most likely places to find life off the Earth

Jupiter’s moon Europa is a fascinating world, with a global subsurface ocean encased in an icy shell and plumes of water vapor that vent into space. A new study has simulated how these plumes might originate, revealing a surprisingly dynamic ice ball.

With an abundance of water and energy sources, Europa has long been considered one of the most promising places in the solar system to search for extraterrestrial life. The problem is, any signs of life would most likely be hiding in that subsurface ocean, buried beneath some 10 to 15 miles (16 to 24 km) of solid ice.

But in recent years a shortcut seemed to present itself. In 2012 Hubble spotted what looked like plumes of water vapor erupting from the south pole, and further evidence for them was gathered in follow-up studies in 2016 and 2018. The belief was that these plumes were gushing up from the ocean below, potentially carrying vital minerals and other clues to life and scattering them into space and across Europa’s icy surface, where we could study them more easily.

But do these plumes really originate in the ocean? That was the question tackled in the new study, by researchers at NASA and the Universities of Arizona, Texas and Stanford. And the answer might, unfortunately, be “no” – some of the plumes could be coming from much shallower lakes.

Europa is regarded as one of the most likely places to find life off the Earth
Europa is regarded as one of the most likely places to find life off the Earth

Starting with images from the Galileo probe, which observed Europa in the late 1990s and early 2000s, the team developed a model that could explain what may be causing the plumes. They focused on an 18-mile-wide (29-km) crater called Manannán, which has a spider-shaped feature that could be a smoking gun for a past plume.

According to the model, the impact that created the crater would have melted much of the ice in its path, and the center of Manannán would have been relatively warm for a while, before cooling back down.

Briny water would have persisted under the surface in scattered pockets, and the team showed that these little lakes could move sideways through the ice from colder to warmer areas. As a result, eventually all the water would have gathered at the center of the crater.

“We developed a way that a water pocket can move laterally – and that’s very important,” says Gregor Steinbrügge, lead author of the study. “It can move along thermal gradients, from cold to warm, and not only in the down direction as pulled by gravity.”

Over time, that central lake would begin to freeze too, pressurizing the remaining water until it burst forth into a plume more than a mile high. That model has a few implications for Europa as a whole.

“Even though plumes generated by brine pocket migration would not provide direct insight into Europa’s ocean, our findings suggest that Europa’s ice shell itself is very dynamic,” says Joana Voigt, co-lead author of the study.

That said, the team acknowledges that this mechanism can’t explain all Europan plumes, so we might still have some hope of getting a handy glimpse into the inner workings of this water world.

The researchers were also able to estimate how salty the ocean and the ice were. According to their calculations, Europa’s ocean may only have about a fifth of the salt content as Earthly oceans.

The study presents a bit of a mixed bag for future exploration of this icy moon, including NASA’s proposed Europa Clipper mission currently penciled in for 2025. On the one hand, the plumes may not necessarily be scattering minerals and life signs within reach. But on the other, the lower-than-expected saltiness could make it easier for spacecraft radar to penetrate the ice.

The research was published in the journal Geophysical Research Letters.

Source: Stanford

5 comments
Chris Coles
Here we see another conundrum, that gravity emanates from the centre of an object, and pulls everything towards it. (Scientific American, February 2002, Ask the experts; Why are planets round?). When in proven fact, clearly demonstrated; when two forces in opposition, along the same line, (as are the two lines of gravity from both sides of our planet), are, at the surface, yes; towards the centre; but at the centre, they create a single point of equilibrium, where the two forces meet and, under Newton's 3rd law, must create an equal and opposite action . . . back towards the surface. Thus gravity is towards the centre at the surface and towards the surface at the centre, with, again, a shell of balanced forces between the centre and the surface within the structure of the object. Now that adds another question to the debate regarding the plumes from Europa; are the plumes emanating from the balanced gravity shell, between the centre and the surface?
Cryptonoetic
Chris' observation is valid only if gravity is viewed as a matter-matter force (in three dimensions), which Einstein showed is not the case. Rather, gravity is an apparent force between mass objects which in reality are responding (inertially) to the curvature of space-time caused by their very presence. In this scenario, when in the presence of a mass object of Earth magnitude, other mass objects are attracted to a gravitational point minima in space-time, the geometry of which is determined by the distribution of Earth's mass density. So, gravity appears to "emanate" from the center of a (large) mass object to affect (i.e., "pull") nearby (small) mass objects when in fact the mass objects are actually free-falling towards the center of what is essentially a parabolic fold in space-time.
Cryptonoetic
Chris' observation is valid only if gravity is viewed as a matter-matter force (in three dimensions), which Einstein showed is not the case. Rather, gravity is an apparent force between mass objects which in reality are responding (inertially) to the curvature of space-time caused by their very presence. In this scenario, when in the presence of a mass object of Earth magnitude, other mass objects are attracted to a gravitational point minima in space-time, the geometry of which is determined by the distribution of Earth's mass density. So, gravity appears to "emanate" from the center of a (large) mass object to affect (i.e., "pull") nearby (small) mass objects when in fact the mass objects are actually free-falling towards the center of what is essentially a parabolic fold in space-time.
drBill
Thanks for the article. I'm glad it was done, but a model is not sufficient for me, and I look forward to the robot visit to pick up scrapings from the area modeled, as well as jumps to other loci, perhaps even catching a geyser at work.
Chris Coles
Cryptonoetic. Your repeated comment describes what one might describe as a theoretical concept; space-time, which Richard P. Feynman also once described as an answer to cover up confusion. Einstein may have described a concept called space-time, but he did not demonstrate it as a force, indeed, he could not do so. Yes, he and many others have followed with mathematical demonstrations that do indeed seem to support the concept. But none of you have actually demonstrated two forces in opposition along the same line; if you had, you would have discovered, as I had some time ago; that they cannot pass the central point of equilibrium, and thus the two forces have to return back towards the origin of the two forces, each side of the point of equilibrium. As gravity is a force towards the centre of an object at the surface, from both sides of the object, perpendicular to the tangent, and thus normal to the central point of the mass; then they must meet at that central point of equilibrium. Gravity is a demonstrable force towards the centre at the surface, but has to return back towards the surface from the centre of the mass; and in addition, as there are forces in each direction within the mass, then there also has to be a point along the line of the forces where they meet within the mass and form a shell of balanced gravity within the mass between the surface and the centre. SN1987A provides an excellent example, where the original supernova can be seen with a ring of objects surrounding the inner mass, where the outer ring has not moved since 1987. The two masses, the inner supernova mass and the outer ring are of equal mass and are locked together. Demonstrating balanced gravity. QED