It would be quicker and easier to sample the vapor plumes coming from cracks in the ice shell of Europa. That would have organic compounds and possibly even detectable bacteria. I'm hoping Europa Clipper has this capability.

On a different note, I did once write a short fiction story attempting to view the world from the perspective of a ocean-dweller in Europa. Soft sci-fi (universal translator) and all in good fun, but maybe someone will find it interesting.

https://www.reddit.com/r/HFY/comments/81jgky/oc_the_icy_heig...

> It would be quicker and easier to sample the vapor plumes

I feel like the question of whether there's life out there or not is such a big and loaded one that nothing short of a video of Europa's equivalent of a kelp forest will do.

Look at how Mars research is going. It's all circumstantial evidence this, organic compound that. This feature looks like something made by bacteria. No, here's a plausible geological process that can do that. There must be methane-producing life. Actually, here's some simple chemistry that does the same. Maybe. This sample reacts to marked nutrients. Well, you see, there might be this oxidizing thing with the rocks...

I mean, it's great that scientific research is done and all. But following this search for biomarkers is so frustrating. Until someone puts a damn thing into a Petri dish and sees it divide under a microscope, it's all just peer-reviewed guesswork.

How can we be so certain the chemistry for life will be the same on these distant worlds?

Chemistry places limits on what is possible. Water is a common and powerful catalyst, it is unlike any life can exits without it just because so many useful reactions happen only in water. (this discounts other catalysts mostly because they are not as common as water). Carbon forms long chains with single or double bonds (also triple bonds but they tend to be unstable) in ways that no other atom will. Note too that water and carbon are extremely common, so even if something else is possible you are then playing the odds that it is common enough.

I'm sure a real chemists can place other limits on what is possible.

Not a real chemist but my understanding is that there is no other solvent with all of water's properties - cohesion, adhesion, high specific heat, pH neutrality, polarity, density (in solid and liquid form), and reactivity - no matter how rare. It is the only "universal solvent" (for polar molecules). In order to imagine other forms of life, you'd have to make the jump from carbon to silicon based life forms. Unfortunately, the energies involved in the chemical bonds would mean that the reactions leading to self replicating molecules would have to happen at very high temperatures or densities which seem to make any life form extremely unlikely. Theoretically catalysts could lower the reaction thresholds enough for life to take hold, but it's an open question how such complex catalysts (enzymes) would emerge while bootstrapping replication. Earth went through just the right series of steps and until the planet cooled down, "stuff" just didn't stay in one place long enough to react and form big molecules.

The Miller–Urey experiment applied an energy gradient to a soup of water, methane, ammonia, and hydrogen.

This produced a smorgasbord of organic compounds, nearly all of which were the building blocks of life on Earth.

It's possible that applying energy to a different soup would produce different results - but all of the chemicals I listed are incredibly common across the universe.

Given that, if life exists somewhere else in the universe, it's incredibly likely that it will be quite similar, in chemical composition, to life on Earth.

I think there will certainly be differences in their DNA or RNA equivalents, but water will still be a nice solvent at room temperature and carbon still likes to form complex bonds and complex molecules at those same temperatures.

Thus at those temperatures and pressures as are found on earth, we can most likely expect to find water and carbon based life.

Will they have a carbon cycle? Certainly. Will it be exactly the same Krebs cycle, down to the exact same molecules? Maybe not.

Another critical property of water is that its solid form (ice) is less dense than its liquid form. This means that large bodies of water freeze on top and seal in a warmer liquid layer below. If not for this, then all lakes and even oceans would freeze solid. Most of the planet's water would be frozen solid year-round. Even during the "Snowball Earth" eras in our ancient past, only the surface of the Earth was frozen; there was still liquid ocean below. Very few compounds have this property of lower density when frozen.

That was a nice story, I would love to know what happened in Enceladus.

Actually reaching Europa’s ocean and returning data is extremely difficult. At the equator temperatures of −160 °C; −260 °F keep the 6–19 mile thick ice roughly has hard as granite.

Instead of trying to pierce that, would it be a good strategy to send a radioactive weigh that will melt the ice over a decade?

Ok, that's how to get in, but not really how to get a data out :)

I like this idea! As it would take quite a while to melt its way down, you'd basically have to sink the entire rover or a submodule down with the radioactive heat source (not melting a hole then exploring it). If it's a one-way, single-purpose trip then it's not clear to me that the ice would necessarily pose any sort of issue with non-line-of-sight (aka radio) communications.

Water in and of itself isn't a great communications barrier, but the conductivity of sea/salt water causes it to act like a Faraday cage and kills/significantly dampens any radio waves attempting to pass through it.

Under the assumption that Europa's oceans are in fact salty, the frozen sea ice isn't actually all that salty. Ice in general isn't a good conductor as it's actually almost entirely the pure water that freezes leaving the salt behind (I'm not clear on whether it would precipitate but remain suspended between the the H2O molecules or if - given the lower density of Ice I - the water would freeze from the top down leaving the liquid seawater beneath it ever so slightly saltier while forming a layer of pure frozen ice on the top).

In all cases, keeping a base station while sinking a second module with the radioactive heat source then proxying all communication via the base station would be possible even if the ice did form some form of a Faraday cage that severely limited communication from beneath.

Maybe leaving a series of repeaters in a vertical line downwards would allow the information to make it to the surface where we could achieve LoS with an Earth satellite. I'm guessing taking 16 miles of some kind of cable is less realistic.

In any case it seems like there'd be astronomical expenses and many moving parts

That was my initial thought but my point is that it actually shouldn’t be necessary. 16 miles of non-conductive water should be fine for a single point-to-point em transmission at low bitrates.

> radioactive weigh that will melt the ice over a decade?

I've thought about this as well. I think there are "Prime Directive" type concerns with this approach though.

Wouldn't that have a huge impact on the ecosystem of the moon? (if it has an ecosystem)

Thinking that soon or later (after 1/10/100/1000) years the probe will for any reason release its radioactive payload into that environment, therefore contaminating it. (kind of similar as well if it keeps generating warmth at least partially for years and years and years => maybe in that case bacteria might start to increase/evolve because of that warmth, and any later observation would have to take that effect into account, which might be difficult to separate from all the local&natural causes - or it could be as well the opposite, with the probe "burning"/killing existing bacteria because they're not used to that warmth)

> −160 °C; −260 °F .. ice

something something Couple 'o Raptor rockets bolted onto a methane-harvesting sled for fuel, let 'er rip ..

/there I fixed it.

That’s a lot like hand waving a flame thrower to melt snow. https://what-if.xkcd.com/130/

Look, you take this gigantic tub(, i.e. Starship) of flammable material, you land it safely somewhere, you attach some kinda inflatable raft around the top/sides of it, you wire yourself up to the gas tanker on the surface, you light those rockets and let 'em rip!

It'll be the steam-cleanest Starship-converted-to-ice-submarine in the system ..

The mission study page for Europa Lander: https://www.jpl.nasa.gov/missions/europa-lander/

Europa Clipper, an orbiter, is an approved mission expected to launch in mid 2020s. https://www.jpl.nasa.gov/missions/europa-clipper/

I was thinking about this recently. It's kind of amazing to me that we've spent so much effort on Mars, deep space, and even Venus, but the whole time we've had this moon in the solar system that has an ocean waiting to be explored. Admittedly, I'm not that familiar with what exploration of Europa we may have already done, but I don't get the impression that it's gotten much priority. The potential benefit of learning about its ocean seems huge.

P.S. I'm not saying we shouldn't have sent Mars rovers or anything like that. :)

EDIT: Thanks for the kind replies.

Layperson here, but isn't the ocean covered with several kilometers of ice? It seems daunting to get a vessel all the way to Europa, drill through that much ice, get the vessel into the water, and subsequently send signals back to Earth. I'm not saying we shouldn't do that--in fact--the thought of what might be in those oceans makes me giddy with excitement, but it seems like an extremely challenging exercise to make a mission like that happen given our current technology.

Ex-NASA guy here. Not directly involved in Europa mission planning, but heard a lot through the grapevine back in the day. Europa is very challenging to get to mainly because it's located in an extremely harsh radiation environment.

https://www.astrobio.net/news-exclusive/hiding-from-jupiters...

The limiting factor is building electronics that won't fry.

This is a mission where I’d like to see a continuous stream of missions instead of One Big Mission. Let’s bring the assembly line to space exploration.

Assembly lines work if you have economies of scale, i.e. if the incremental cost of production can eventually be brought below the value of the product on the open market and you can start turning a profit. The economics of planetary exploration are fundamentally different because the product is not the thing you're mass-producing. The product is data, not spacecraft. Furthermore, the hardware required to produce the most valuable data, i.e. the data you don't already have, generally needs to be different from the hardware you've already built. That's the fundamental reason planetary exploration is unlikely to benefit much from mass production any time soon.

I've just looked up, and the theory is that the ice is 15-25 km[1] thick.

The deepest hole on Earth is 12 km [2].

[1] - https://europa.nasa.gov/europa/faq/

[2] - https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

But to be fair, the limiting factor on earth was that it got much hotter much faster than scientists had expected. We aren't likely to have that issue on Europa.

Rather than having to keep the drill bit cool, to drill through ice you could use a heated drill bit. Perhaps using using radioactive material to heat the drill bit and cut through the ice like a hot knife.

(Of course, irradiating an alien ocean is perhaps not the greatest idea ever.)

It sounds to me like Elon Musk needs to combine efforts between SpaceX and The Boring Company.

Radium-knife: cooks the steak while you slice it!

It also means launching a large amount of radioactive material through the atmosphere which may end badly

The advantage on Earth is that you have dozens of machinists, operators, labourers, and tens of thousands of tonns of supplies necessary for digging these holes.

You can't do that with one robot, and a weight budget of a few tonns.

While I am radically milquetoast on engineering things, to me it doesn't seem nearly as impossible as mining the deep, deep oceans of Earth. Similar constraints, similar win/fail procedure. If we really wanted to drill into Europa, we'd have it up and running in a manner of years, imho.

Getting there, of course, is the other big challenge, but honestly .. a fleet of Starship's, maybe 100 or so .. sent to Europa with enough guts to build a base .. I could see it happening in 20 - 30 years, maybe .. if not sooner.

I don't think it isn't challenging. I think it's definitely possible; just expensive. And I think it's actually cheaper than a lot might think: the biggest expense until now has been getting there. But with SpaceX and reusable rockets that looks to be a helluva lot cheaper. It's still challenging on a technical level but tractable to the higher ends of science budgets, or even middle ends of, say, oil and mining budgets.

Once you are in an ocean covered with miles of ice, how do you send a signal?

Why would you dig deep into an ocean covered with miles of ice without a tether to a station?

Suppose it looks like this:

    ----- upper ice surface -----
     ice ice ice ice ice ice ice
    ~~~~~ lower ice surface ~~~~~

Then a tether station might look like this with a conduit/shaft between

         beep
         /|\
    ------|----------
          |
    ~~~~~~|~~~~~~~~~~
         \|/
        beep

Then you can have a swimmer-rover:

         hi!
         /|\
    ------|----------
          |
    ~~~~~~|~~~~~~~~~~
         \|/
        .
    <-> hi!

sorry I'm just a software dude :|

It would be my first instinct too, but I'm assuming miles of cable in frozen ice that probably move will not last for long.

But maybe setup a wireless relay? Not easy through that much ice.

This mission is starting to sound really expensive

Yup! It definitely would still be an expensive mission! But I think getting there is no longer the biggest expense :)

Ice carries radio waves a lot better than water. Once sunk through the ice, the entire probe, or a small buoy, could float up to the underside of the ice and transmit clearly to the surface.

leave sending station above ground. send down hot ice melting probe (no drilling) attached to long cable.

The meltwater would have to be removed, or the cable itself heated.

The Jupiter Icy Moons Explorer is scheduled to launch in 2022. It is scheduled to do 2 flybys of Europa, and several more of Callisto, before settling into orbit around Ganymede in 2032. [1]

The Europa Clipper is scheduled to launch in 2024. It will conduct many (wikipedia says 44) flybys of Europa before eventually being destroyed by radiation. The flybys should provide spectrometry and ground-penetrating radar images of the entire surface, and mass spectrometry of any dust it flies through at low altitudes. [2]

Finally, the Europa Lander is currently proposed to launch in 2025. Among other objectives, it would analyze the composition of the ice, looking for chemical signs of life. [3]

Unfortunately, neither of these Europa missions will provide spectacular, years-long presence like Spirit, Opportunity, Curiosity, or the various satellites in orbit around Mars. The radiation is too intense. Europa Clipper will do flybys to allow its instruments to capture brief deluges of data, then give the radios lots of time to transmit while the spacecraft isn't bathed in radiation. Europa Lander will not have solar panels or an RTG, instead being powered by non-rechargeable batteries. The battery duration roughly matches the estimated electronics lifespan in the high-rad environment: about 3 weeks.

[1] https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Explorer

[2] https://en.wikipedia.org/wiki/Europa_Clipper

[3] https://en.wikipedia.org/wiki/Europa_Lander_(NASA)