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Hopes for life on Europa diminish as probe finds lower oxygen levels

March 6, 2024 · Comment icon 5 comments

Could there be life beneath the surface of Europa ? Image Credit: NASA/JPL-Caltech
NASA's Juno spacecraft has sampled Europa's atmosphere and discovered less oxygen than had been expected.
Jupiter's icy moon Europa has long been thought of as one of the most habitable worlds in the Solar System. Now the Juno mission to Jupiter has directly sampled its atmosphere in detail for the first time. The results, published in Nature Astronomy, show that Europa's icy surface produces less oxygen than we thought.

There are plenty of reasons to be excited about the possibility of finding microbial life on Europa. Evidence from the Galileo mission has shown that the moon has an ocean below its icy surface containing about twice the amount of water as Earth's oceans. Also, models derived from Europa data show that its ocean floor is in contact with rock, enabling chemical water-rock interactions that produce energy, making it the prime candidate for life.

Telescope observations, meanwhile, reveal a weak, oxygen-rich atmosphere. It also looks as though plumes of water erupt intermittently from the ocean. And there is some evidence of the presence of basic chemical elements on the surface - including carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur - used by life on Earth. Some of these could seep down into the water from the atmosphere and surface.

The heating of Europa and its ocean is partly thanks to the moon's orbit around Jupiter, which produces tidal forces to heat an otherwise frigid environment.

Although Europa boasts three basic ingredients for life - water, the right chemical elements and a source of heat - we don't yet know if there has been enough time for life to develop.

The other prime candidate in our solar system is Mars, the Rosalind Franklin rover's target in 2028. Life might have started on Mars at the same time as it did on Earth, but then probably stopped due to climate change.

A third candidate is Saturn's moon Enceladus where the Cassini-Huygens mission discovered plumes of water from a sub-surface salty ocean, also in contact with rock at the ocean's floor.

Titan is the closest runner up in fourth place, with its thick atmosphere of organic compounds including hydrocarbon and tholins, born in the high atmosphere. These then float down to the surface coating it with ingredients for life.

Losing oxygen

The Juno mission boasts the best charged particle instruments sent to Jupiter so far. It can measure the energy, direction and composition of charged particles on the surface. Similar instruments at Saturn and Titan found tholins (a type of organic substance) there. But they also measured particles that suggested atmospheres at Saturn's moons Rhea and Dione, in addition to those at Titan and Enceladus.

These particles are known as pickup ions. Planetary atmospheres consist of neutral particles, but the top of an atmosphere becomes "ionised" (meaning it loses electrons) in sunlight and via collisions with other particles, forming ions (charged atoms that have lost electrons) and free electrons.
When a plasma - a charged gas making up the fourth state of matter beyond solid, liquid and gas - flows past an atmosphere with newly formed ions, it disturbs the atmosphere with electric fields which can accelerate the new ions - the first part of an ion pickup process.

These pickup ions then spiral around the planet's magnetic field and are usually lost from the atmosphere, while some hit the surface and are absorbed. The pickup process has rid the Martian atmosphere of particles after the red planet's magnetic field was lost 3.8 billion years ago.

Europa also has a pickup process. The new measurements show the telltale signs of pickup molecular oxygen and hydrogen ions from the surface and atmosphere. Some of these escape from Europa, whereas some hit the icy surface enhancing the amount of oxygen at and under the surface.

This confirms that oxygen and hydrogen are indeed the main constituents of Europa's atmosphere - in agreement with remote observations. However, the measurements imply that the amount of oxygen being produced - released by the surface to the atmosphere - is only about 12kg per second, at the lower end of earlier estimates from about 5kg to 1,100 kg per second.

This would indicate that the surface suffers very little erosion. The measurements indicate that this may amount to only 1.5cm of Europa's surface per million years, which is less than we had thought. So Europa is constantly losing oxygen due to pickup processes, with only a small amount of additional oxygen being released from the surface to replenish it and ending up back on the surface.

So what does that mean for its chances of hosting life? Some of the oxygen trapped in the surface may find its way to the subsurface ocean to nourish any life there. But based on the study's estimate of the overall loss of oxygen, this should be less than the 0.3kg-300kg per second estimated earlier.

It remains to be seen whether this rate, recorded on 29, September 2022, is usual. Perhaps it is not representative of the overall oxygen on the moon. It may be that the eruption of plumes, orbital position and upstream conditions increase and decrease the rate at certain times, respectively.

Nasa's Europa Clipper mission, to be launched later this year, and the Juice mission which will make two flybys of Europa on its way to orbit Ganymede, will be able to follow up these measurements, and provide much more information on Europa's habitability.

Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCL

This article is republished from The Conversation under a Creative Commons license.

Read the original article. The Conversation

Source: The Conversation | Comments (5)

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Recent comments on this story
Comment icon #1 Posted by Nicolette 3 months ago
I thought europa was hypothesized to be habitable under the crust, not in the atmosphere. The article also still labelled the atmosphere "oxygen rich". Aside from atmosphere loss i find it hard to believe that a ball of H2O is too low on O for life . Not to mention that there is life here in mono lake that doesn't require oxygen, so it's a bit shortsighted and premature to decide all life elswhere requires it.
Comment icon #2 Posted by Waspie_Dwarf 3 months ago
I find myself asking this virtually every time you comment on a science story... have you actually read the article? From the front page story: From the NASA release I linked to:   And your point is? The atmosphere is extremely sparse. From the front page article:   Care to provide a source for this claim? In 2010 two NASA scientists proposed that some of the bacteria in Mono lake used arsenic instead of phosphorous (not oxygen). In 2012 these claims were shown to be untrue. Source: Source: [More]
Comment icon #3 Posted by Nicolette 3 months ago
Pretty much like every time i post, you were too focused on trying to prove me wrong to even realize that you flat out missed the point. Yes realizing that life doesnt have to have identicle processes to us is relevant to europa and the ridiculous conclusion that there isn't life because the atmosphere is thin and not all oxygen like people thought. Our atmosphere isnt all oxygen either. Not that it even matters when we are talking about an ocean planet hypothesized to be habitable in the ocean under a thick worldwide ice shell. Nobody thought any potantiel life down there was breathing the ai... [More]
Comment icon #4 Posted by Nicolette 3 months ago
Also I threw out a random incorrect example. If you were wise enough to get past in instead of trying to prove me wrong you would notice that we do have a species here on earth, henneguya salminicola, that doesn't require oxygen.  So the premise of the title is nonsense when referring to a ice-shelled watery moon. Life doesn't need oxygen in the atmosphere, everything it needs is there. Why is anyone trying to say otherwise for no apparent reason? That's sus.  
Comment icon #5 Posted by Waspie_Dwarf 2 months ago
Or, to put it more honestly, you were wrong.   Don't worth about that. proving you wrong generally takes no effort at all, you tend to enter a battle of knowledge unarmed. Besides all I asked for was a source for your claim at which point YOU proved yourself wrong.   Well done, you obviously used google when trying to prove ME wrong. Unfortunately, as is your habit, you either didn't read it properly or understand it fully. Henneguya salminicola is an endoparasite that lives within fish. Whilst it has lost the ability for aerobic respiration it requires a host fish to live in. Notice the use... [More]

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