So now we know what the news is, as expected, Hubble has found new evidence of possible plume activity on Europa. In a series of ten observations, they saw them on three occasions. Here are the images they created.

The possible plumes are in the seven o'clock position, not far from the South pole - though the central image here has another possible plume that's close to the equator.

Interestingly, they spotted them in the same position as the previous plume detection in 2012:

Hubble Sees Evidence of Water Vapor at Jupiter Moon

Note that in all these images, the photograph of Europa was not taken by Hubble. It just made the observation of the water plume - those large blue pixels in this last image. 

Europa is tidally locked to Jupiter, so every time Europa does a transit of Jupiter, we see the same face of it in the same orientation. This shows how it works:

So this could well be a recurring plume in the same place as for the 2012 observations.

This is potentially exciting news because the last time it spotted a plume of water, it seemed to be a once off observation and didn’t get repeated. After the initial excitement many astronomers concluded it was probably just a rare asteroid impact on Europa sending water up into space. Europa's Elusive Water Plume Paints Grim Picture For Life - Astrobiology Magazine

Now that Hubble has spotted it again, this makes asteroid impact a very unlikely explanation, especially as it's been observed in the same position approximately, multiple times. This suggests that it is probably a huge geyser. This is  very exciting news for astrobiologists, because such a huge geyser would suggest the water is coming from deep below the surface, maybe even indirectly or directly from the subsurface ocean 100 km below the surface. This image shows some of the possibilities.

In the case of Enceladus we have evidence that suggests that the material that Cassini observed was perhaps even in contact with hot rocks only a few months before the observations. However the ice cover for Europa is 100 kilometers which makes it rather difficult for tidal effects to keep a channel open all the way down to the subsurface ocean against the immense pressures of the ice closing the channel.

This seems a more likely scenario

There a hot plume of water from the ocean rises very slowly through the ice. We have evidence on the surface of chaotic terrain, which may be the result of one of these plumes reaching the surface. The water, denser than ice, would cause the surface of Europa to dip as it approached it, and then once it reached the surface, the water would freeze and break up into giant icebergs that would turn over and form the chaotic terrain. At least that's one explanation of how it might work. If so, these geysers could come from one of these giant rising hot plumes of liquid water.

This in turn is very interesting because this could make it one of our best chances in the solar system for finding extraterrestrial life and even possibly, complex multicellular life such as we have on Earth. There is almost no chance of life getting transferred from Earth to Europa or vice versa over the entire history of the solar system as models suggest that only a few meteorites have ever made that transition in the entire history of the solar system. And if the ocean material is indeed sent into space in a geyser, one of our spacecraft could sample it just by flying through it with no need for a lander.


They used a new approach. The previous images were done using near ultraviolet and imaging plumes against the dark background of the night sky. 

This time they observed Europa as it passed in front of Jupiter. Here is a Europa transit movie made with Hubble. This is something astronomers observe frequently - but Hubble can observe it with very high resolution.

Europa transit movie in near ultraviolet

This time, however, they imaged Europa in the far ultraviolet, with Jupiter behind as a light source. It's a similar technique to the one used for examining the atmospheres of exoplanets around other stars. Jupiter is very uniform in brightness in the far ultraviolet - and Europa's ice is also dark at this wavelength ,so letting them make especially sensitive measurements.

This shows a comparison of the 2012 observations on the right, and the 2014 observations on the left. Notice that the plumes in the 2014 observations show up as dark patches against the light background of Jupiter - and that Europa is dark in this wavelength. While the 2012 observations detected bright "water aurora" against a dark background of the night sky.

It was a difficult observation all the same. They recorded all the photons as individual events, building up a data set of millions of photons. Although the observations were made in 2014, they have spent the time since then analysing them, including writing the software to do the analysis. It was a lot of work. They are now confident in the results. It looks like plumes, and there is no other natural cause they can think of. They are being professionally cautious, but the only remaining hypothesis is some instrumental or observational error and they don't have any likely ways that that could happen either. Although we can't call it a detection yet, the case does seem a strong one.

The amount of water involved is quite substantial, of the order of a thousand metric tons, up to a few thousand metric tons of water. They can't say for sure that it is water though. They said that amongst other possibilities, it could be:

  • Water vapour
  • Ice particles as for Europa, or
  • Oxygen (from dissociated water) 
They don't have spectroscopy available, because of the technique they used, so they can't distinguish between these possibilities (unlike the 2012 observations).

This animation shows what they think may be going on:

And this is a composite image of all their observations:

We already have many observations of the geysers of Saturn's tiny moon Enceladus, by the Cassini spacecraft. Here is one of the images:

They vent into space (as ice of course, once they hit the vacuum of space) and escape its gravity, feeding one of the minor rings of Saturn.

Europa however is much larger, nearly as large as the Moon, 3,160 km in diameter (our Moon is 3,474 km in diameter), while Enceladus at 504 km in diameter is much smaller. As a result, Europa has much more gravity than Enceladus. Enceladus's gravity is 0.113 m/s² or 7% of lunar gravity, while Europa's gravity is 1.315 m/s², 81% of the lunar gravity of 1.622  m/s².

This means that you need a powerful geyser to send material into space far enough away for Hubble to spot it, so we always expected the Europan geysers to be harder to spot.


We do have a camera in orbit around Jupiter, JunoCam. So could it photograph these plumes? When asked this question during the NASA question and answer after the announcements, the team just said no, because Juno is in an orbit carefully designed to make sure it never comes close to Europa. That's to avoid any chance of contaminating it with Earth life at the end of its mission.

However, although Juno doesn’t go very close to Europa, it does occasionally get close enough so that it could image an active geyser as two pixels instead of less than one pixel. So if there is a visual element, such as dust, then perhaps, just maybe, it can spot that too? So then, I wonder if there is any chance of a follow up observation with Junocam on Juno - to see if there is anything visual such as particles, as for Enceladus. In particular if what they observed were ice particles, maybe it might be reasonably visible?

If so, it's probably not possible until March 2017, and September / October 2017 is the best configuration for Juno to observe Europa. It will still be at a distance but it would be a higher resolution image than we can achieve from Earth, even with Hubble, and a plume could span 2 pixels, enough for a chance of information about it, if it is more than just water vapour.

This is what Candice Hansen says about using JunoCam to image Europa:

"JunoCam or ASC can only detect plumes if they contain fine particles. The Hubble discovery (if real) only shows the presence of water vapor. We can predict by analogy to Enceladus that water vapor plumes will also contain particles. However, it is important to remember that the Hubble discovery was of gas, not particles. If the putative Europa plumes are Enceladus-like and do contain particles, they would not be as tall as Enceladus', because of Europa's higher gravity. Scaling for Europa’s gravity gives a maximum plume height of under 140 kilometers. To detect plumes, we need at least two pixels, so the image spatial scale would need to be better than 70 kilometers, at a relatively high phase angle where the particles would forward-scatter light to JunoCam and ASC.

"To achieve resolutions better than 70 kilometers per pixel, UVS needs to be within 40,000 kilometers of Europa; JunoCam, 100,000 kilometers; and ASC, 170,000 kilometers. For the cameras, given the low expected height of the plumes, there is not much flexibility.

"There are just four orbits that have Europa flybys that are closer than 300,000 km. Juno reaches the best available geometry in September 2017 as the rotation of the line of apsides brings Juno’s orbit close to Europa’s orbit:

"2017-03-08 253,118 km

2017-09-19 264,043 km

2017-10-03 92,267 km

2017-10-17 204,654 km"
Will Juno’s Instruments Observe the Moons of Jupiter?


NASA has plans for a Europa multiple flyby mission to be launched in 2022 on the SLS to get there in just 3 years. If you do a type II Hohmann transfer, spanning less than 180 degrees around the sun, then you can get from Earth to Jupiter in under two years as Voyager 2 did, taking one and a half years to reach Jupiter from Earth. So it is not a particularly long journey time from Earth.

Because of the strong radiation around Jupiter close to Europa, it actually makes most sense to do flybys of Europa rather than to orbit it. After each flyby, they will have plenty of time to send back the vast amounts of data they can collect with each close approach. The end result is much more data sent back and a mission that can last for years instead of just a month or two.


I think the best solution here is to focus on sampling any geysers as our main priority. We can definitely do that with a mission to Enceladus, and now it seems we may be able to do it for Europa as well. Enceladus is less known amongst the general public, but it also may have life.

Geysers on Enceladus (moon of Saturn). A spacecraft could fly through these geysers (Cassini has done so many times now). It could do a detailed analysis and even a life search as according to some theories, the water in these geysers was in Enceladus’ ocean as recently as a few months before they are ejected into space. Europa may have geysers also but with its larger gravity they may not go so high into space, so may be harder to spot.

With these new observations this now becomes a top priority. As with Cassini for Enceladus, a Europa flyby mission should be able to do multiple flybys of Europa. Cassini found out a lot about Enceladus's subsurface ocean from analysing the plumes, and that is with scientific instruments built 20 years ago (it was launched in 1997) and a mission that was planned at a time that we didn't know that geysers were even a possibility. 

A flyby mission can go through the plumes at different heights, and at different times in the orbit and gradually build up a picture of what is in the material. It can actually sample the material directly and analyse it on board the spacecraft. The Europa flyby will do around 45 flybys of Europa so will have plenty of opportunities to fly through the plumes.


It’s actually quite a challenge to land on Europa. I’m not at all sure we should be doing it now even. Rather controversially, NASA have a mandate to include a lander on this mission. This is a possible version of it, see A Lander for NASA’s Europa Mission

It's controversial because this is an idea put forward by Congress. This is not usually how you plan science missions, that a politician tells you that you have to do it in a particular way. That's more like the way that human missions are done, where the objectives are often to a large part political. Normally it's a case of asking the scientific community for suggestions, then detailed proposals, fully worked out with costings, and then they are compared with each other based on their scientific merits rather than their political merits. It seems odd to do it the other way around, for a pure science mission. 

The original plan was to have both lander and orbiter on the same mission. Now Congress have mandated NASA to do them as separate missions, and have also said that both missions have to use the Space Launch System (SLS) - a heavy booster being developed in the States, which itself is rather controversial, since it is going to be high cost, it's going to fly infrequently, and each launch is going to be extremely expensive. It will be a remarkable vehicle able to send large masses into space and send human crew on deep space missions. However some think it will be overtaken by the private sector who have their own independent ideas for ways to achieve heavy lift such as the Falcon Heavy. The Europa mission could cost upwards of 2-3 billion dollars not including the launch, possibly as much as 3-4 billion dollars. The SLS launches themselves will add $500 million to $1 billion apiece just for the launch. The whole thing is quite controversial. See Two SLS to Jupiter in the Space Review.

Anyway this is now a very unique mission, one of the few to have a launch vehicle selected by congressional mandate. All this does have its advantages though for a Europa mission.

First, the spacecraft can be far more massive. It can have more instruments, a much shorter transit time to Jupiter of only three years, and it can have more radiation shielding to protect it from Jupiter's ionizing radiation. It can get there so quickly because with such a capable launcher, there is no need for a gravity assist.

For the orbiter, the main controversy would be about the cost. The mission itself will be much more capable than it could be without the SLS. 

However for the lander, then in the case of Europa, there are additional reasons why a lander makes it more tricky. The first issue is that the surface of Europa has not yet been imaged in the detail needed to choose a landing site, and is thought to be very rugged in detail. Landing on Europa might be as risky and fraught with unknown quantities as landing Philae on comet 67p, though for different reasons. There is no risk of it bouncing off the surface, but it could crash on rugged terrain.

Another issue is that you have to sterilize the lander sufficiently for planetary protection, because the very last thing we want for Europa is to go there just to discover life that we brought ourselves. Is that something we can actually do at this stage? It's a huge challenge when the target is icy. A hard landing (crash) on the Europan surface could heat the ice to melting point, or even potentially contact liquid water beneath thin ice and the ice could then shield microbes from the ionizing radiation of Jupiter.

The strange thing here is that congress actually have mandated a launch date for the lander too. NASA has to launch it in 2024. That means they have to send it to Europa a year before the orbiter gets there, and so before they have any new data on the Europan surface conditions.

So let's look in detail at some of the issues with sending a lander to Europa based only on the knowledge we have about it so far. Is it something that we can actually do, realistically, in this time frame - with a launch in 2024, and do we know enough to design it before detailed observations of Europa from the orbiter?

First, the surface is unknown at the scale of meters, most of it. As an example of how little we know, one theory that has not yet been disproved is that parts of the surface might be covered in closely spaced vertical “ice blades” or “ice knives” which would make a landing there hard to achieve. On Earth these blades form quickly, in special conditions On Europa they would take millions of years to form, but it’s the same basic process. As Daniel Hobley said: "Light coming in at a high angle will illuminate the sides of the blades, causing them to retreat away,"

These are called Penitentes. See Penitentes: Peculiar Spikey Snow Formation in the Andes

This video shows how they form on Earth and decline, time lapse:

Here is a photo from the European Southern Observatory site high in the Atacama desert:

Planetary Analogue, see also their Icy Penitents by Moonlight on Chajnantor, and Iconic, Conical Licancabur Watches Over Chajnantor


On Europa, if they exist, these structures can potentially be meter scale or higher. With no atmosphere, the conditions on Europa might well be ideal for their formation. Our missions to Europa so far haven’t taken high enough resolution photos to see them. Ice blades threaten Europa landing - BBC News

They wouldn’t be the result of ice or snow subliming into an atmosphere, obviously. It’s a slightly different process. Instead they’d be the result of the sunlight causing the ice to sublime to water vapour in a vacuum at very low temperatures well below 0 °C. Also they would form slowly over much longer timescales, of millions of years.

The surface of Europa is about 50 million years old, so when we ask if penitentes can form on Europa, one of the main questions is, how much can the ice there erode under the influence of sunlight in 50 million years? The answer to this question is extremely sensitive to the peak temperatures on Europa, to the extent that twenty degrees can make a difference between formations that are meter scale and ones that are on the scale of millimeters.

In the paper: HOW ROUGH IS THE SURFACE OF EUROPA AT LANDER SCALE? Hobley et al produce this table

So, for a surface temperature of 132 °K (about -150 °C) it loses about 5.66 meters over the average age of the surface of 50 million years. For a temperature of 128 °K (-154 °C) it loses 1.28 meters in 50 million years, tailing off to 1 cm at 116 °K (-166 °C), and only millimeters at 114 °K

So this is very sensitive to the peak surface temperatures of Europa. Also, the surface is eroded by sputtering from the Jupiter radiation and from bolide (meteorite) impacts. That would counteract the effects of the ice blade formation at temperatures of 126 °C downwards. They conclude in the paper that the knives could be from one meter to 10 centimeters in height, probably restricted to within 15 or 20 degrees of the equator.

However Europa also has “true polar wander” by which the entire crust moves over the subsurface ocean. This could reduce the size of the blades but also move the ice blades away from the equatorial regions.


Other issues could include a frozen landscape consisting mainly of upturned icebergs. According to some ideas, then hot plumes of melted water rise from the deep subsurface sea and eventually reach the surface and produce these irregular landscapes, as icebergs form on the freezing surface, and then turn over.

One of the most interesting regions, thought to be most likely to have thin ice over liquid water by the “thin icers” is the Thera Macula

This might be a region of overturned icebergs with, perhaps, liquid water still present only a short distance below the surface. Most of these chaos regions are raised, which suggests the ice below them that lead to their formation has frozen. But Therea Macula is actually a dip in the surface of Europa which may be a sign that it has the denser melted water still beneath it. See Is Europa's ice thin or thick? At chaos terrain, it's both!


So there could also be liquid water close to the surface. Geysers are another possibility. So again there may be a small chance of our lander crashing through thin ice or a soft surface, especially if we land it on the most interesting regions such as Thera Macula. Or it could fall into a crevasse and be unable to communicate.

I know the plan is to orbit Europa for a while before the lander gets there, but what if the orbiter doesn’t find any suitable spot for the design of lander, and decides a different design of lander is needed, or no lander at all? Maybe the lander has to land somewhere uninteresting, or they have to hold back from landing at all for planetary protection reasons?


Then the other problem is that we don’t know how to sterilize a spacecraft 100%. Or more accurately, we can sterilize a spacecraft completely, but the methods that do this, such as prolonged heat, or ionizing radiation, also destroy the electronics so it won’t work any more. That includes of course the ionizing effect of Jupiter’s radiation - although the surface of Europa is riddled with ionizing radiation that would quickly kill any human, any spacecraft there has to survive this, at least up to the landing, which would mean that it is protected sufficiently that microbes could survive also.

If there are some microbes on the lander, and they survive to the landing, then it might impact into liquid, or create a liquid area due to a crash on Europa which might be deep enough to shield microbes so they can reproduce there. Or microbial spores brought to Europa with the lander could eventually in the future over thousands or years find their way into the ocean.


They plan to send the mission to Europa possibly as soon as 2022 to get there by 2025, using the SLS, which lets gets there, then our technology may be so advanced we can send a follow up orbiter or lander within months or a year or two. In any case I think we simply should not risk a lander at this stage due to planetary protection issues unless we can sterilize it 100%, or somehow can prove that there is no significant possibility of it irreversibly introducing Earth microbes to Europa. Even a 1 in 10,000 chance of contaminating Europa with Earth life, I think would be too high, given what we may be risking there, some unique discoveries that we could never do anywhere else. E.g. it could be some early form of life, not as far evolved as DNA or evolved in a different direction, which might be very vulnerable to DNA based life. And it’s probably impossible to do an accurate assessment of how likely it is that we could irreversibly introduce Earth life to Europa by mistake, we just don’t know enough yet about Europa or about exobiology with no examples yet of any known exobiology to base our decisions on.

Again by the 2030s we may have the technology to sterilize a spacecraft 100% without destroying the electronics. I hope so!


Meanwhile one thing we can do right away is to send a mission to Enceladus to analyse its geysers close up, and it would be reasonable I think to send life detection instruments on that mission too. Instruments that would help with analysing whatever is in the particles, able to detect complex organics, and also able to find indications of life too if present.

If funding permitted, perhaps we could also send an identical orbiter geyser fly through mission to Europa “on spec” just in case we find geysers there, to save time. I think that would be less risky than a lander, no danger of crashing, and likely to add to our understanding of Europa even if it has no geysers, by examining the region around Europa just as Cassini did for Rhea etc.

There’s some evidence already of possible water plumes from Europa - though it’s a one off observation by Hubble which hasn’t been repeated. It might have just been a meteorite impact. If it is evidence of geysers, that could be very exciting for search for life on Europa. Water Plumes on Europa: What Lies Beneath?

In any case as I said, I think we should equip any Europa orbiter with similar instruments to Cassini which would help with analysing any dust or ice particles or gas around Europa with the capability of detecting complex organics, which may be in them whether or not Europa has life, and I think we should add chirality detection at a minimum. There’d surely be some dust or gas to analyse even if there are no plumes.


Later we may do a sample return to Earth. But I think we can do a lot in situ - even just plumes, the composition probably varies depending on where you fly through them, and also on the position in the orbit, may also depend on conditions in the deep ocean, maybe it has the equivalent of algae blooms down there from time to time.And we have many instruments now we can send to do in situ searches, miniaturized “lab on a chip” that just ten years ago would fill an entire laboratory which also have minimal power requirements too.

As for returning it to Earth, if we return a sample likely to contain life or with some chance of life, I think we should return to above GEO, furthest in delta v away from both the Earth or Moon and study it telerobotically from Earth until we are sure what is in it and what precautions are needed if any. I don't think it makes much sense economically, legally, or that we can even do it safely, to try to build a facility to study all conceivable forms of exobiology on the surface of Earth quite yet when we don't yet know of a single example of exobiology outside of Earth.,

Quarantine just doesn't work, see my Case For Moon First - why quarantine doesn’t work - this is for Mars, but the same would apply for life returned from anywhere. There is no way we'd abandon an astronaut permanently in the ISS if they were exposed to Europa samples, I don't think it is ethically or legally possible to do that even if they consented.

A quarantine period only works if you know what you are quarantining against and how long you need to do the quarantine for. And the risks are not just the effects on humans but effects on many other creatures, plants etc as well as long term effects on ecosystems. We can't test that in space just by exposing lifeforms to it. I think there is no alternative to really knowing what is in the sample before you decide whether you can expose humans and other lifeforms to it and what precautions to take. Which means you have to study it somewhere isolated from Earth's lifeforms first and I think you'd need stupendously reliable methods to do that on Earth, far better to do it telerobotically in orbit.

So, I think that’s the way ahead myself, sample the plumes in situ. Return samples eventually but to above GEO. And if we do a lander, it needs to be sterilized sufficiently for biologically reversible exploration. We must not introduce Earth life irreversibly to Europa or Enceladus, in my view. If it’s likely to encounter liquid water, or create a liquid water habitat through impact, hard to see how anything short of 100% sterilization would be sufficient. We need some way to sterilize all the life from a lander while keeping the electronics intact. One promising approach may be to use supercritical CO2 snow in combination with other methods .I think that may be possible in the future but we can’t do it quite yet.


You might wonder - what about Titan? We have already landed a spacecraft there, so what makes it so different? Can we apply the same methods or similar for a lander on Europa?

Well, Huygens was a comparatively easy experiment since Cassini was going to Saturn's system anyway. With Titan’s thick atmosphere they could use aerobraking. Also the Titan’s surface is so cold Earth life can’t survive there so there were almost no planetary protection issues. (Titan may have a deep subsurface liquid water ocean but if so, then there doesn’t seem to be much communication with the surface).

And actually there is a remote possibility of life in Titan’s oceans though it would be very exotic for us. First, because of the extreme cold, it would surely rely on chemical reactions that run much faster at those temperatures than the ones in our cells would do - otherwise the life there would be very sluggish. There’d be evolutionary pressure to use faster chemical reactions.

Also it would have the cells kind of “inside out” with non polar molecules facing the methane / ethane oceans, because those are non polar liquids, instead of the usual arrangement. Indeed it might be made of a small polar molecule like acrylonitrile sticking together to form a non polar membrane in the non polar solvent of methane

Normal cell walls are arranged to be polar (having regions of positive and negative charge both inside and outside to attract the water) like this:

The tail repels water (hydrophobic) so naturally meets together in the middle of the cell wall. For details of this idea that life on Titan would need to use a non polar membrane, see Is There a Kraken in Kraken Mare? What Kind of Life Would We Find on Titan? - Universe Today, and Possible oxygen free cell structure made of organic nitrogen compounds that could function at the low temperatures of Titan's ocean.

Glint of sunlight on the lake region around the northern pole of Titan.

Cassini did make some measurements that Chris McKay interpreted as possibly a sign of life processes on Titan, though he listed several other possibilities that may be more likely: Alien Life on Titan? Hang on Just a Minute… - Universe Today

However Huygens was not designed to search for life. Maybe some future spacecraft to Titan’s oceans will take off from where it began?

See also Prebiotic Chemistry on Titan?


Huygens was an easy experiment yes, for Titan. We can’t do aerobraking on Europa.

However you could do equally easy experiments for Europa - one idea is a penetrator, using what we could call "ice breaking" to slow it down. I'm not a fan of that myself for planetary protection reasons unless the penetrator can be sterilized 100%.


However there’s a planetary protection friendly version of it. You could use two spacecraft - a dumb penetrator consisting of just a metal slug, easily sterilized. This sends a plume of ice into space. You could use two “dumb penetrators” with the second one closely following the first for more effect.

In effect, you are creating an artificial geyser here. This would be followed by a low flying orbiter to capture the sample for analysis.

That would have minimal planetary protection issues if the dumb penetrators can be 100% sterile - e.g. just lumps of metal heated beforehand to temperatures where no Earth microbes could survive or otherwise 100% sterilized before impact. This is an idea Bernd Dachwald (head of the German IceMole project) once suggested to me in conversation, which I think is an interesting one.

However if Europa is indeed producing geysers naturally, we don't need to do this, we can just observe the plumes "as is".


Another interesting idea, here is an old mission idea to send “chipsats” to Europa’s surface, each one rather “dumb” but lots of them, each one consists of just a few sensors on a flat chip. Some would fail but enough would get through, and they would be able to survive impacts that a larger more complex lander couldn’t.

That sounds like a kind of a lander that is so minimal, perhaps it could be 100% sterilized by supercritical CO2 snow or something similar? That’s a technique that can remove all the organics from the surface of an electronics chip without damaging the chip. It’s been shown to work with USB drives. So though it might be tricky to scale up to a complete spacecraft, I wonder if it is good enough to 100% sterilize chipsats? It would have to be 100% reliable.

"ATTEMPT NO LANDING THERE" --New NASA Mission to Europa will Ignore Arthur C Clarke's Warning (2014 Most Popular)


There’s no in principle reason to prevent 100% sterile electronics. You just have to find some process that electronics can withstand and life can’t. If you heat metal to hundreds of degrees C for instance, no life will survive and the result will be 100% sterile. The problem is that this will destroy the spacecraft electronics too. So can we find a way to sterilize it of Earth microbes without destroying the delicate equipment? That’s the big question here.

Also all this might be far easier to do with a chipsat than with a large conventional spacecraft.

First one method being explored by the European Space Agency is Deep cleaning with carbon dioxide. and Science Daily article about it.

  • CO2 a liquid at 100 atmospheres and 50 C.
  • And then on release of pressure turns to snow and takes the dirt, organics, everything away leaving the surface dry.
  • Mixed with Hydrogen peroxide and other chemical to increase effectiveness.
  • Can be used even with sensitive electronics. Was used to clean usb drives in testing and they functioned afterwards.
  • Surface is left with no trace of organics, not just with dead micro-organisms. Major plus!

Could you remove all traces of organics from the exterior in this way? And - can you also keep exterior and interior separate so there is no chance of leaking contamination from inside the mole?


Then also, if you can make the whole thing able to withstand high temperatures, you can just heat it up to a high enough temperature to sterilize all life.

The main issue with sterilizing modern spacecraft is that many instruments are quite delicate, also they can go out of alignment,so even the sterilization temperatures used for Viking of 111 °C for 40 hours is too much for them.

But there are electronic circuits now designed to operate at up to 200°C . High-Temperature Electronics

And there are other developments that should permit temperatures of 200°C upwards :).High-Temperature Electronics Operate at 300 degrees C | EE Times and Designing for extreme temperatures

There’s an economic incentive for developing these electronics, as they are useful in oil wells and motor cars.

I’ve never seen this suggested for a way to keep Europa landers sterile, but it sounds as if it should work!

Back to the drawing board probably for a lot of the designs to make the whole thing uses chips and solders etc that work up to high enough temperatures for 100% sterilization. But it seems like it may be possible! Thanks to Adeel Khan for the suggestion

Is this right? Is it possible to achieve 100% sterilization by heating electronics that’s capable of resisting temperatures of up to 300 C. I wonder if anyone working in the field of spacecraft sterilization has investigated this, either experimentally or in theory. Or is there some other way to achieve 100% sterile electronics such as the CO2 snow approach?

I think we need to look into that myself before we consider sending any probes to habitats that may include liquid water habitable to Earth life. Except of course for the plume flybys. They are safe so long as the ice particles they collect can’t dislodge microbe spores and return them to the liquid water in the subsurface oceans. That sounds likely to be for all practical purposes, zero risk though you’d need to examine it carefully of course.


Perhaps for the best results both can be used one after the other. High temperature to make sure there is nothing viable. Then CO2 snow to remove the organics as far as possible. Heat it up again before it is released from the orbiter for a final precaution to make sure.

Especially for electronics in an impactor / penetrator as that would have to withstand high g force and perhaps high temperatures too, so it would need to use specially hardened electronics. And it needs to be hardened for the ionizing radiation for Europa as well so you are hardly talking about “off the shelf” electronics here.


Another idea, just for fun for now - but: land a sterile 3D printer + some raw material feedstock for it, also sterile. The surface would be high vacuum, ideal for electronics. First thing it does is to 3D print a shelter for itself or dig below the surface for protection from the cosmic radiation. Then it sets about printing out whatever you need, including a Europa submarine from the sterile components you supplied it with. If it is a nanoscale printer it can do circuit boards as well. So all you need to do is to send it some sterile chips to attach to those circuit boards, and other hard to print out components pre-sterilized. Most of the rest it does itself.

This is a bit far future perhaps.But perhaps some element of 3D printing could help for an idea of partial in situ construction of devices for helping to study Europa in a sterile way? Especially small chipsat type devices. Sterile electronics plus 3D printing of some extra components to help with mobility or sampling or some such.


If we can’t do it, I think we simply should not send a lander or submarine to Europa until we can, and should not risk introducing Earth microbes to a habitable environment on Europa.

It is just risking too much to do that. Not just for us, not just for the mission that goes to Europa right now, but for our descendants and indeed all future civilizations on Earth also. It would be just tragic to find some interesting form of exobiology on Europa only to know that we have seeded Europa with microbes that will eventually make it extinct.

It could be very vulnerable to Earth life. The example I like best there is the idea of some primitive early life, for instance RNA based, or even an RNA ocean or autopoetic cells. If Europa was like that, then introduced Earth microbes in a globally connected ocean through exponential growth would surely do short work of converting it all to DNA based life.


Some enthusiasts suggest we just send life to Europa to seed it with Earth life. The problem with this idea is that then we won't be able to find out about the life that is already there, if there is any - or pre-biotic or non biotic chemistry - or whatever there is there right now. Especially since our life could make it extinct. About half of Earth's biological history in terms of gene complexity is unknown to us. We just have no idea how the early organic chemicals developed into lifeforms as complex as the simplest microbes. Lot's of sketched out suggestions but no answers and it is way beyond any attempt to simulate in a laboratory.

Well one likely thing to find in the Europa ocean, if life is common, is some early form of life. Maybe RNA based life. Maybe just an RNA ocean. Or maybe autopoetic cells. Or some primitive lifeform that reproduces, sort of, but not nearly as accurately as DNA life does. Or perhaps it's RNA based using ribozymes in the place of ribosomes, everything done in RNA. And that's just a few examples based on what might have happened in our own planet's past. Europa life may well not be related to Earth life at all. In the entire history of the solar system, at most a handful of rocks may have made it from Earth to Europa. So it could be something else as well.

As those examples show, it could be very vulnerable. An RNA ocean say, or RNA only lifeform could perhaps become extinct after just a few years of exponential growth after the first contamination by Earth life throughout the entire ocean, especially if it is all connected and its ocean has food sources for the life to use. And however quickly or slowly it happens, there is no way we could reverse something like that once it got started. It would be the worst possible anticlimax to all our searches for life in our solar system, to know that Europa was such a biologically fascinating place, until the first probes from Earth landed there, and is no longer like that.

Until we know what's there, I think we have to treat every potentially habitable planet or moon or other habitat in our solar system as if it was the only one of its type in the solar system. Because a lifeform that evolves in Europa's ocean may well not evolve in Enceladus, or Ceres or on Mars or whatever place you study next. It could be our only opportunity for light years in every direction, to study such a lifeform.

  • Perhaps they all have different unique lifeforms or types of pre-biotic life.
  • Perhaps they all have almost identical independently evolved life (very surprising I think).
  • Perhaps life from a previous star seeded them all or most of them.
  • Perhaps only one of them has life, or none of them do.
  • They are sure to have complex chemistry and we can learn from that also, maybe learn that life evolves only with great difficulty and find out what happens when it doesn't evolve too. We won't know until we find out.

As for experiments in Earth based life in space - we can do closed system habitats to try that out anywhere. For instance the Moon may have vast caves kilometers in diameter, so maybe we do it there. Or in free flying space habitats. There's enough material in the asteroid belt alone to create habitats with a total land area a thousand times that of Earth. There may be many opportunities to do that. We don't need to have as our first priority to turn everything into the closest possible approximation to Earth we can imagine, especially a very poor imitation of it, an ocean covered in kilometers of ice with the harsh environment of Jupiter's radiation on the surface, and too far from the sun for most photosynthetic life to be practical and not at all in its oceans (except for life that uses the heat radiation from hydrothermal vents for photosynthesis).

And meanwhile constructed habitats from asteroid materials can be designed with whatever environment you like, tropical gardens if you like, depending how much sunlight you reflect into it using space mirrors or solar collectors, or simulate conditions on Europa or Mars or other places in our solar system if that's your aim. Or you could simulate some the conditions on an interesting exoplanet. You can use spinning habitats with artificial gravity for whatever level of gravity you want, too.

That's looking forward a bit there - but only decades, centuries at most. You could build a Stanford Torus habitat within a decade or two with the funding and political will to do so even with present day technology. If we want to explore setting up habitats with Earth life in it outside of Earth, I think things like that would be the way to go - starting on a much smaller scale first probably. You could start with small exovivaria in LEO or on the Moon, and experiments with closed system recycling.

While there’s no way we can duplicate the billions of years of Europa’s history and the vast oceans larger than Earth’s oceans. If we mess it up, then the nearest “Europa” analogue may be light years away. And even then, chances are that if Europa and some Europa analogue both have life, even then most likely it has its own unique lifeforms, probably not even the same informational polymer in the place of whatever Europa has - not at all likely that it has the same lifeforms or proto life that evolved on Europa.


I think it might be partly that they were sending a spacecraft to the Saturn system anyway. In the case of the Jupiter system, then it’s much harder to visit Europa for more than a short time because of the ionizing radiation. Still you could do a penetrator with a fast flyby and that would work much like Huygens. It could communicate back to Earth during the flight to Europa and if it survived the landing, do some experiments and report back during its design life whatever it is.

But it would have many more planetary protection issues to work through than a Titan mission. I think myself it is best to wait for the orbiter mission first before we decide what to do next. We might well confirm the plumes on Europa and that would make it really easy to sample it’s ocean with a low flyby or orbiter and then we might not need a lander at all for the first missions there.


During the Q / A, the team mention the idea of sending in situ life detection instruments to Europa in the future. We could use these on a flyby or a lander. So what instruments could we send? Actually there are many such already developed. Some of them have exquisite sensitivity, and could find life based on the minutest of traces, even able to detect a single molecule in the sample of biochemical interest.

Most of these instruments were developed for Mars. Whether they can be used as is for Europa, or need more modification, this shows the range of instruments we can send. I've no idea about the engineering challenge, to examine materials captured in an aerogel "in situ". One issue is to ensure that the readings are not confused by the material that makes up the aerogel so the composition of the aerogel is important. It also helps if you can do a slow flyby, so that there is less damage during impact into the aerogel. Anyway here are some of the instruments we can send, and some are exquisitely sensitive and would surely detect life if it is there.

I think if astrobiologists were asked, maybe in a competition to devise astrobiological instruments to send to Europa, they would rise to the challenge to devise instruments for a Europa flyby and you might get some surprises, neat ideas that you didn't expect. With the huge mass of the Europa missions on SLS, you could fly many of them - a lot of them are "labs on a chip" that weigh hardly anything.

Here are some ones that are already at quite a developed state, with an eye to eventually fly to Mars:

Rapid non destructive preliminary sampling

  • Raman spectrometry - analyses scattered light emitted by a laser on the sample. Non destructive sampling able to identify organics and signatures for life. It's sensitive, can measure the distribution of the organics and other compounds by pointing the laser at different points on the surface - and is non destructive so it can be applied first before any of the other tests.

Detection of trace levels of organics and of chirality

Direct search for DNA

These can detect life on Mars if it is DNA based so related to Earth life. As DNA sequencers, they can sequence the entire genome of any lifeform found.

  • Miniaturized DNA sequencer could work if we had a common ancestor right back to the very early solar system whenever DNA first evolved. This is in a reasonably advanced state. They say it could be ready to fly by 2018.

Electron microscope

Search for life directly by checking for metabolic reactions

These can detect life even if it doesn't use any recognized form of conventional life chemistry. But requires the life to be "cultivable" in vitro when it meets appropriate conditions for growth.

  • Microbial fuel cells, where you check for redox reactions directly by measuring the electrons and protons they liberate. This is sensitive to small numbers of microbes and has the advantage it could detect life even if not based on carbon or any form of conventional chemistry we know of.
  • Levin’s idea of chiral labeled release, where he has refined it so you feed the medium with a chiral solution with only one isomer of each amino acid. If the CO2 is given off when you feed it one isomer and not with the other, that would be a reasonably strong indication of life.This has the advantage that the life just needs to metabolize amino acids, and to produce a waste gas that contains carbon (such as methane).

There are many instruments like this we could send, and several of them are already space qualified but never flown.


I also wonder about an optical microscope. Why not send, not just a "geologist's hand lens" but a diffraction limited optical microscope? With resolution of 200 nm. It could tell us things about the behaviour and structure of micro-organisms or protocells we might not be able to find out by other methods. 

Ideally you want to see the structure of protocells if they exist, and other sub-optical limit structures, so I do wonder also about the microscopes that go beyond the diffraction limit, but I'd have thought they are probably too complex to send into space? Probably won't verify life or protolife unless it is actually still viable and active. But could give interesting data in combination with the other instruments.


Yes we might well get get ambiguous results. That's how science works. But if we are so scared of ambiguous results that we never fly anything unless we are sure it will give a clear cut result - surely that's going to slow down the pace of discovery? If you only search for things you know you can discover, with proven instruments you have already sent into space, you may be missing out on new discoveries that perhaps could be made easily with different instruments..

After the ambiguous Viking results, we should have done a follow up to resolve the ambiguity, e.g. using Levin's idea of a chiral labelled release to test uptake according to chirality of the organics. That's the scientific way to deal with it, not to give up, but to try to find out what happened. We have competing theories about what happened with Viking, but without further experiments, you can't resolve it just through theory.

Then also, negative results are mportant. If you send a DNA sequencer to test for DNA - well it is one hypothesis that Europan life could be related to Earth life through cells from before the origins of our solar system. If you find other indications that may indicate life, or strongly indicate it, but no DNA that's a significant null result. Based on that one can decide what to fly in the next mission for a follow up.

Europa is only two years travel time from Earth, and by the 2020s we may have more heavy lift capabilities that will make it easy to send follow up missions to resolve the questions that early missions raise. And as well as that - just sending the instruments at all gives exobiologist experience in sending their instruments in space, which then become space rated for future missions, so adding to exobiology experience. It also helps inspire a whole generation of astrobiologists, to see their instruments fly in space. At the moment only geological instruments have flown, apart from the very early Viking instrument. You have to start somewhere with the astrobiological in situ searches.


Part of this article originated as my answer toIf there is a possibility of life on Europa, then why did NASA land a craft on Titan and not Europa? on Quora

Get notifications of new blog posts

If you want to get alerts every time I do one of these posts, join my Robert Walker - Science20 Blog Alerts facebook page.

To get a red facebook alert every time I post a new science20 article, or post an idea for a new article, then select "all on" in the page's Liked drop menu above.

Or subscribe to the associated twitter feed.

For email alerts about once every month or so, subscribe to Robert Walker's Science 20 blog Monthly Alerts on Google Groups.


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon