> Enceladus is far smaller than the Jovian ocean worlds, roughly the size of Ohio
Why not just say 'has a diameter of about 500 km'? The propensity of astronomers to compare diameters of a small spherical object to a surface patch of a much larger spherical object is intriguing. Similar things happen with 'the Great Red Spot is about two Earths wide'.
When trying to describe sizes and scale, having a reference that one of their readers would be able to go "oh, ... that size, huh?" is useful. There's a meme about "Americans will use anything but the metric system" when describing buildings as "100 school buses back to back" or "3 football fields"; but it's to make numbers real and relatable.
If the article said "500km", someone in the comments would go "that's about as wide as Germany!" or similar.
And, since it was km -> "state size", it was almost certainly for the American audience, since they would have used something like the size of Germany for a European, or "twice the size of South Korea" or something.
For science education, I am strongly for using the units directly to describe everything at first, with these looser comparisons in brackets, rather than inline prose. So I would've instead said, 'is 500 km in diameter (roughly the size of Ohio, or Germany from East to West)'. For extremely large or small values I would use scientific notation only, and expect my audience to understand it, because I'd expect their education to be up to mark.
You said these comparisons are made to make things real or relatable; I personally would expect more out of my audience and give them the magnitude and units directly. I'm not writing for a tabloid; having a strong grounding in units understanding without needing to relate to daily phenomena is in my view critical to not making apparently trivial mistakes that can potentially lead to horrible disasters.
I am realy excited for the Findings on these missions. Altough I am still missing an Enceladus mission because enceladus is among the most fascinating ocean worlds.
> This remarkable transformation in our understanding is the result of just three missions: Voyager, Galileo, and Cassini—along with some computer modeling and hard staring by the Hubble and Webb space telescopes.
Seems odd to neglect to mention New Horizons immediately after mentioning the probable existence of liquid oceans under Pluto's surface, a finding made possible thanks primarily to New Horizons.
No shade on New Horizons intended, but I was talking about the early 2000's revolution in understanding of ice moons/ocean worlds, and that preceded the Pluto flyby by a lot.
It was a valuable piece of corroborating evidence, but not shocking and unexpected in the way results from those three missions were. We had good reason to believe Pluto would look a lot like Triton, and it does.
Fair enough, though how common was that belief that Pluto would look like Triton? Before the first photos from New Horizons pretty much every artistic rendition of Pluto I'd seen was a solid ball of rock and/or ice, more like Ceres than Triton.
Both were known to be Kuiper Belt objects, so it was expected there would at least be a family resemblance. I don't think anyone expected Pluto to be more active than Triton; that was certainly a surprise.
If there are planetologists reading the thread, I'd love to hear a more authorative perspective than mine!
True for all the Galilean Moons more or less. Their orbits all lie within the Jovian equivalent of the Van Allen belts. And Jupiter's magnetic field is much stronger than earth's.
Not Callisto. Being within Jupiter's magnetosphere but out of reach of Io's shenanigans makes it one of the mildest radiation environments in the solar system.
Io is in orbital resonance with Europa and Ganymede, which causes its orbit to be slightly elliptical. Due to Jupiter's immense gravitational field strength, Io experiences a very high changing tidal force, which causes a changing stress and strain on the entire structure of Io, which causes tidal heating due to friction. This makes it by far the most volcanically active body in the Solar System. Its surface is regularly completely resurfaced, and is covered in sulfur compounds.
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
> What about rocks in the surface of the water?. Some volcanic rocks can float.
This is... not something you lay plans on. Even on Earth, these rocks are formed at surface pressure, just barely float, and don't float for long (I've tried). If they form in the deep ocean, I'm guessing the pressure isn't going to let the bubbles be big enough to create bouyancy at all. Either way they would be super rare.
1) If those hypothetical mineral resources are rare, organisms would be hard pressed by evolution to start collecting them from the bottom and make it float again.
Animals can synthesize "rocks", they make buoyant shells with hard materials that sink naturally. Some dress on pods made of collected pebbles. If the upper ice layer was created after the lower ice layer we may find aliens hiding inside a meteorites case. The Earth developed similar solutions that can be colonial, like Sabellaria worms, or individual, like caddisfly larvae.
Fill this pods with organisms able to extract the energy of chemical links in those rocks, and you have food and refuge in the same packet. Go a little further and you developed luminescence. We can't guarantee that this life evolved eyes, but bioluminescence is the most popular way to communicate among life beings on earth so if aliens didn't evolved eyes the alternative solutions will became very bizarre and unexpected really fast.
------------------------------------
2) Maybe we will not need to dig all the way down to find life. Biocenosis will fit every possible niche, so is 100% guaranteed that the transition "upper ice layer" -> "liquid surface" will be colonized by life.
First because it poses a topological advantage (halves the directions of possible attacks by predators, and allows predators to ambush and hide in irregular ice).
Evolution later would select organisms that burrow up in the ice layer. Burrows are a safer place to rest and nest than just a surface of ice, so the trait would be selected fast by evolutionary pressure. We can expect tunnels shaped as and 'A' populated by filterers also. They will create currents between an entry and an exit to use the energy more efficiently
So we may suspect the presence of life if we can detect indirectly a thin layer in the ice/water frontier that: a) is less dense than ice, but more dense than liquid or gas bubbles, and b) is structurally different than what physics would predict for the formation and extension of ice cracks.
And if there aren't any alterations in this boundary, it may be no life at all, or life may be very rare.
Lovely article. Although:
> Enceladus is far smaller than the Jovian ocean worlds, roughly the size of Ohio
Why not just say 'has a diameter of about 500 km'? The propensity of astronomers to compare diameters of a small spherical object to a surface patch of a much larger spherical object is intriguing. Similar things happen with 'the Great Red Spot is about two Earths wide'.
When trying to describe sizes and scale, having a reference that one of their readers would be able to go "oh, ... that size, huh?" is useful. There's a meme about "Americans will use anything but the metric system" when describing buildings as "100 school buses back to back" or "3 football fields"; but it's to make numbers real and relatable.
If the article said "500km", someone in the comments would go "that's about as wide as Germany!" or similar.
And, since it was km -> "state size", it was almost certainly for the American audience, since they would have used something like the size of Germany for a European, or "twice the size of South Korea" or something.
For science education, I am strongly for using the units directly to describe everything at first, with these looser comparisons in brackets, rather than inline prose. So I would've instead said, 'is 500 km in diameter (roughly the size of Ohio, or Germany from East to West)'. For extremely large or small values I would use scientific notation only, and expect my audience to understand it, because I'd expect their education to be up to mark.
You said these comparisons are made to make things real or relatable; I personally would expect more out of my audience and give them the magnitude and units directly. I'm not writing for a tabloid; having a strong grounding in units understanding without needing to relate to daily phenomena is in my view critical to not making apparently trivial mistakes that can potentially lead to horrible disasters.
When has there ever been a horrible disaster in space exploration because of units? ;)
Set your calendars:
Europa Clipper, launched 2024, starts Europa flybys on March 2031
Dragonfly, hopefully launching July 2028, arriving on Titan 2034
https://en.wikipedia.org/wiki/Europa_Clipper
https://en.wikipedia.org/wiki/Dragonfly_(Titan_space_probe)
I am realy excited for the Findings on these missions. Altough I am still missing an Enceladus mission because enceladus is among the most fascinating ocean worlds.
> This remarkable transformation in our understanding is the result of just three missions: Voyager, Galileo, and Cassini—along with some computer modeling and hard staring by the Hubble and Webb space telescopes.
Seems odd to neglect to mention New Horizons immediately after mentioning the probable existence of liquid oceans under Pluto's surface, a finding made possible thanks primarily to New Horizons.
No shade on New Horizons intended, but I was talking about the early 2000's revolution in understanding of ice moons/ocean worlds, and that preceded the Pluto flyby by a lot.
It was a valuable piece of corroborating evidence, but not shocking and unexpected in the way results from those three missions were. We had good reason to believe Pluto would look a lot like Triton, and it does.
Fair enough, though how common was that belief that Pluto would look like Triton? Before the first photos from New Horizons pretty much every artistic rendition of Pluto I'd seen was a solid ball of rock and/or ice, more like Ceres than Triton.
Both were known to be Kuiper Belt objects, so it was expected there would at least be a family resemblance. I don't think anyone expected Pluto to be more active than Triton; that was certainly a surprise.
If there are planetologists reading the thread, I'd love to hear a more authorative perspective than mine!
Great read, other than Europa I wasn't aware of these other candidate ocean moons.
All these worlds are yours, except for Europa, attempt no landings there.
TIL
> The radiation environment around Europa is punishing; an astronaut standing on the surface would get a fatal dose in about a day
True for all the Galilean Moons more or less. Their orbits all lie within the Jovian equivalent of the Van Allen belts. And Jupiter's magnetic field is much stronger than earth's.
Not Callisto. Being within Jupiter's magnetosphere but out of reach of Io's shenanigans makes it one of the mildest radiation environments in the solar system.
I'm interested in learning more about "Io's shenanigans". What are you referring to?
Io is in orbital resonance with Europa and Ganymede, which causes its orbit to be slightly elliptical. Due to Jupiter's immense gravitational field strength, Io experiences a very high changing tidal force, which causes a changing stress and strain on the entire structure of Io, which causes tidal heating due to friction. This makes it by far the most volcanically active body in the Solar System. Its surface is regularly completely resurfaced, and is covered in sulfur compounds.
https://science.nasa.gov/jupiter/jupiter-moons/io/facts/#h-m...
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
Not true at all, the daily dose on Ganymede (which has a magnetic field of its own) is ~70 mSv/day, and Callisto is 0.1 mSv/day.
Io, meanwhile, is 35 Sv/day. Location really matters among the four Galilean moons.
I was born in a water moon.
Beautifully designed article. Very cool images and diagrams.
> We want rocks in contact with water,
But there is ice compressed between the water column and the xenoceanic bottom, ok. I see the problem.
What about rocks in the surface of the water?. Some volcanic rocks can float.
> What about rocks in the surface of the water?. Some volcanic rocks can float.
This is... not something you lay plans on. Even on Earth, these rocks are formed at surface pressure, just barely float, and don't float for long (I've tried). If they form in the deep ocean, I'm guessing the pressure isn't going to let the bubbles be big enough to create bouyancy at all. Either way they would be super rare.
1) If those hypothetical mineral resources are rare, organisms would be hard pressed by evolution to start collecting them from the bottom and make it float again.
Animals can synthesize "rocks", they make buoyant shells with hard materials that sink naturally. Some dress on pods made of collected pebbles. If the upper ice layer was created after the lower ice layer we may find aliens hiding inside a meteorites case. The Earth developed similar solutions that can be colonial, like Sabellaria worms, or individual, like caddisfly larvae.
Fill this pods with organisms able to extract the energy of chemical links in those rocks, and you have food and refuge in the same packet. Go a little further and you developed luminescence. We can't guarantee that this life evolved eyes, but bioluminescence is the most popular way to communicate among life beings on earth so if aliens didn't evolved eyes the alternative solutions will became very bizarre and unexpected really fast.
------------------------------------
2) Maybe we will not need to dig all the way down to find life. Biocenosis will fit every possible niche, so is 100% guaranteed that the transition "upper ice layer" -> "liquid surface" will be colonized by life.
First because it poses a topological advantage (halves the directions of possible attacks by predators, and allows predators to ambush and hide in irregular ice).
Evolution later would select organisms that burrow up in the ice layer. Burrows are a safer place to rest and nest than just a surface of ice, so the trait would be selected fast by evolutionary pressure. We can expect tunnels shaped as and 'A' populated by filterers also. They will create currents between an entry and an exit to use the energy more efficiently
So we may suspect the presence of life if we can detect indirectly a thin layer in the ice/water frontier that: a) is less dense than ice, but more dense than liquid or gas bubbles, and b) is structurally different than what physics would predict for the formation and extension of ice cracks.
And if there aren't any alterations in this boundary, it may be no life at all, or life may be very rare.
I guess I'm now officially old and cranky, as planetoids receiving glow-ups was just a bit much as a term.