New Evidence Points To Icy Plate Tectonics On Europa (gizmodo.com)

According to new research published today in Journal of Geophysical Research: Planets, Europa has what it takes to support plate tectonics. "Using computer models, a team lead by Brown University planetary scientist Brandon Johnson was able to demonstrate the physical feasibility of icy plates driving deep into the icy interior in a processes similar to what's seen on Earth," reports Gizmodo. "Excitingly, this same process could be delivering important minerals to the ocean below, heightening the moon's status a potentially habitable world." From the report: Europa has surface features reminiscent of Earth's mid-ocean ridges. For astronomers, this hinted at geological processes akin to subduction zones, where, on Earth, tectonic plates slide underneath another, sinking deep into the planet's interior. Several years ago, researchers Simon Kattenhorn and Louise Prockter posited this explanation when they noticed that a 20,000 square-kilometer (7,722 square-mile) chunk of ice had mysteriously disappeared from Europa's surface. Their explanation was that Europa's surface, like a gigantic jigsaw puzzle, is composed of tectonic plates, and that occasionally a plate of ice will sink beneath the other into warmer layers below. But this observational evidence of extension and spreading needed to be supported by geophysical reality. To that end, Johnson's team ran a computer simulation to see if it was possible for ice to sink in this way.

On our planet, subduction is primarily driven by differences in temperature between a descending slab and the surrounding mantle. Dense crustal material features a negative buoyancy that drives it down into the mantle. The Brown University scientists figured a similar thing happens on Europa, but with ice. In the case of Europa, the researchers surmised that the moon has two frozen layers -- an outer lid of very cold ice that sits above a layer of slightly warmer convecting ice. Their models showed that subduction is indeed possible in this alien environment, but only if the outer shell contains varying amounts of salt. This added ingredient provides the necessary density differences for a slab to conduct.

Comments

Life we know it.

[dohzer]

this same process could be delivering important minerals to the ocean below, heightening the moon's status a potentially habitable world

*Habitable worlds for life as we know it.

Re:Life we know it.

[Baron_Yam]

Most people who feel the need to add, 'for life as we know it' when the subject comes up seem to be ignorant of the reasons we have for believing it is probably very safe to say 'life' instead of 'life as we know it'.

No, Si can't replace C as a backbone for complex molecules. Yes, you need a liquid in which chemistry can happen. And a (fairly gentle) energy gradient - enough to help chemistry along without breaking molecules apart before anything interesting happens with them.

There aren't any plasma beings living in a star's corona, or balloon animals floating in the atmosphere of a gas giant. No living rocks. These are INCREDIBLY safe assumptions.

What we don't have a firm grasp on is how abiogenesis happens, or how long it takes on average to develop from a chemical soup into an intelligent animal (and what factors might reasonably be used to predict variations from the average). We don't have a great understanding of where life might successfully start and take root, other than something identical to Earth... but at least we understand it is theoretically possible to be under the crust of an icy moon, in a rogue planet with enough core heat, etc.

Re:Life we know it.

[Maritz]

Hello fellow carbon chauvinist. You're right, Silicon doesn't work as a replacement for carbon. Carbon is the fucking daddy.

Re:Life we know it.

[Baron_Yam]

Unfortunately, the math says otherwise.

The Earth - the one example of intelligent life in the Milky Way known to humanity - is ~4.5 billion years old, and it's taken ~4 billion years of that time to have us evolve on it to the point we can post about it on Slashdot. We don't know, however, if that's an unusually long time, or an unusually short time.

Hopefully it's long or average, because our star is near the end of it's current Earth-supporting phase. If you assume you need a Sun-like star (smaller gets you a longer-lasting star, but the habitable zone gets closer to requiring planets to be tidally locked, and stellar temperament becomes a problem, too), then you pretty much want to know people can pop up on an orbiting rock in less than 4 billion years.

Anyway, at speeds we can reach with our technology, it would take around 5 million years to cross the galaxy. 5 million years is peanuts compared to the 4 billion years life has been on Earth so far. Now consider there are probably ~10 billion potentially habitable worlds in the Milky Way based on our current models.

Only ONE of those 10 billion worlds has to have intelligent life begin to colonize the galaxy a mere 5 million years before we started talking about it to arrive by tea time tomorrow.

And the Sun wasn't the first star of its class to be born. There's at least one similar star we know of that's over 11 billion years old, which potentially means there's an extra 7 billion years of leeway for aliens to set up shop everywhere. Well, not everywhere - obviously if they were zipping around the Milky Way more than 4 billion years ago, Earth would just have been a hot damp rock. On the other hand, you'd expect that with the extra lead time, they'd be around pretty much every star in the sky and we'd have seen SOMETHING by now.

Re: Life we know it.

[Baron_Yam]

Of course we do - anything we can't explain as a natural phenomenon.

The real (and immense) difficulty is in getting enough photons into our detectors, because the distances are vast and unless you have some silly dream of planet-sized megastructures... anything we'd look for would be tiny.

Minerals?

[Viol8]

Where from? The amounts of rock minerals from space dust and organics from reactions on the surface are probably minute. I suspect any significant minerals come from the moons core which AFAIK is thought to be made of rock.

Anyway, we have no idea what conditions are required for life to start. There may well be a minimum energy requirement which europa doesn't even get close to. Also you need some kind of energy gradiant. In an ocean sealed off dozens or even hundreds of km below the surface I suspect that gradient is shallow in the extreme.

Re:Minerals?

[Rei]

Well, then, since you feel qualified to weigh in on the amount of rocky mass recycled from the icy crust, off the top of your head you should be able to tell us the mass flux from impactors and space dust at Europa. What is it?

Because I guarantee you, people who study these things don't need to google it.

Re:Minerals?

[Dorianny]

The earliest claimed fossilized lifeforms on earth are as old as old as 4.28 billion years old. it suggests an almost instantaneous emergence of life after oceans formed 4.4 billion years ago. Obviously Europa doesn't have the same conditions as early earth but perhaps the Abiogenesis is simply slower instead of impossible under those conditions and Europa has had plenty of time. We just don't know

Re:Minerals?

[necro81]

Where from? The amounts of rock minerals from space dust and organics from reactions on the surface are probably minute.

Io is right next door (so to speak), and spews forth a lot of material from its volcanoes. Some of that material makes it into the Jovian space between the moons. Jupiter's magnetic field is a transport mechanism.

Also: we know that tons - literally, tons - of extraplanetary material rains down on the Earth each day. Jupiter, being as massive as it is, probably sucks up a lot more. Europa is a small target, but is traveling through this inward flux of material and is sure to pick some up.

Re:Minerals?

[Anonymous Coward]

Anyway, we have no idea what conditions are required for life to start. There may well be a minimum energy requirement which europa doesn't even get close to. Also you need some kind of energy gradiant. In an ocean sealed off dozens or even hundreds of km below the surface I suspect that gradient is shallow in the extreme.

Features such as Conamara chaos show extensive melt-through and rafting. That does not happen with an icy crust hundreds of kilometres thick.

The ice shell is probably less than 10km thick in most places and occasionally much thinner. Gives ample opportunity for surface materials (irradiated by the sun and radiation from jupiter) to be recycled into the subsurface ocean.

Re: Minerals?

[Anonymous Coward]

Except the surface of Europa is red-brown specifically because something is accumulating. The two competing ideas are either it is organic compounds due to UV interacting with carbon and nitrogen coming from below the ice, or a combination of sulfur and magnesium coming from off the moon. Results of Galileo lean toward the latter. Depending on the geology of the rock below the ice and ocean, sulfur from rock may be very small compared to what hits the surface.

You can't just say the amount hitting the surface is insignificant because it isn't black. The amount is enough to visually change the surface, but that also doesn't tell you whether it is significant enough to impact life or not. You need to compare the amount from other sources, e.g. from the rocks and vulcanology below the surface. That takes actual numeric estimates to compare, not just shooting from the hip. Unfortunately the papers I am familiar with enough are behind a paywall.

Re:Minerals?

[wbr1]

As you stated above with "I should think" indicates you have no practical knowledge of the subject at hand either. You just want to be 'internet correct' the best kind of correct.

I have no specific knowledge either, but I know Rei is highly intelligent and from past posts probably works in the field, even if this subject is not his direct area of study.

All that bitching aside, here is a paper with some numbers for you: http://people.virginia.edu/~re...

If Io were the only source of non-ice material to Europa’s surface and no loss occurred, then using the flux values from Table 1, sulfur compounds could be present on the surface at ~7% (molar abundance) relative to H2O, while Na and Cl could reach 0.3%. Silicon and magnesium could be comparable or slightly less than Na and Cl. These estimates assume uniform mixing and ignore hemispherical flux and gardening rate differences, which can produce surface concentrations that are a factor of 10 or more different between the leading and trailing sides (see Fig. 2 and caption).

Seems to me that there could be quite a bit of material present. Much from Io outgassing and 'splash' from impactors to IO settling on Europa, not even counting direct impacts to Europa.

Science.. try it sometime.

Silly idea to name a moon like a continent

[gotan]

The first picture that came to my mind were some giant ice sheets covering Europe doing some strange kind of tectonics.

Btw. I'm German, in which both items are spelled "Europa", and it took a few seconds to remember the moon and that the continent would be spelled "Europe" in English.

Of course in terms of Greek mythology it all makes perfect sense ...

Re:I *just* commented on that.

[Anonymous Coward]

I vote for Iapetus being called America.

- A mix of black and white on the surface, but due to its history, they're mostly separated.
- The distribution of its "assets" (mass) is far from equilibrium.
- A violent history
- A bulging waistline (with a belt)
- Elected a mentally-challenged racist as its president (I assume based on no evidence)

Tidal Forces

[Ayano]

I always anticipated this. Tidal forces affect liquids far more than rock or hot pressurized rock (mantle). I mean IO doesn't have anywhere near the amount of water that Europa does and it's being torn and scewed by these immense forces.

I don't see how this makes it more habitable however as large glacial tectonic forces, while similar is appearance to regulr tectonics don't seem to make life any easier on the surface. If anything it makes it more difficult to establish any kind of surface base given how quickly the ice can shift compared to normal mantle based tectonics.