Sulfur seas, lakes or rivers in Venus.

In a topic in extraterrestrial forum, I talked about the possibility of life on Venus. This time, I'll discuss the possibility of having liquid sulfur (in order to have life there, if possible on a sulfur solution).

Venus has an atmosphere rich in sulfur gases and CO2. If there's so many sulfur in the air (clouds of sulfur compounds), then I guess it would be possible to have at least small lakes of sulfur in some areas. I'm guessing that because we only have radar images and such images are not so clear and only in black and white. Here in Earth, we have clouds of water and liquid water too. Maybe in Venus, such compounds in clouds may be liquid on the surface! The high pressure would allow these compounds to be liquid at high temperatures. Maybe such "liquid" is in a critical form.

But we don't know what is this liquid (if there's any liquid there). Could be liquid made of pure sulfur (S8 rings)? Or even more plausible, lakes of sulfuric acid? Because I've read that would be possible to rain sulfuric acid. But such rain is enough to allow lakes or rivers? Or even with the high pressure, it's too hot to have any liquid there? It's only not liquid SO2 because even at such pressure the boiling point would be 105°C, too low for Venus.

In the case of H2SO4, the boiling point at 1 atm is 327 ºC. But at 90 atm (Venus air pressure), it would boil at 739°C (more than the average temperature on Venus). So to me H2SO4 liquid on the surface is very possible. In the case of S8 (pure sulfur), the boiling point in Earth is 444.6 °C, but on Venus it would be about 1495°C (more than the critical point), also being plausible on Venus. So with this in mind, Venus may not be so dry, but "wetter". And to me it's only a matter of time to discover H2SO4 or S8 liquids! And maybe life as we don't know it"

Due to the high pressure, could life develop only in a very pressurized air? Or all life in the universe depend on liquids? Why not pressurized air, serving as solvent? We only know the life forms on our planet, but I'm not convinced that every life will need liquid the way we need.

You might want to check out this thread at BAUT regarding this issue. For a start, your value for the boiling point of sulphuric acid is above the critical point for this substance, which is unphysical (same goes for the value you quote for sulphur) - what is your source for the values you give? Furthermore, at these temperatures the sulphuric acid breaks down to give sulphur trioxide and water vapour.

Your speculations also have to take into account the Magellan results - no evidence for seas or lakes in the radar data.

I had read that the brilliance of the mountains of Venus could be owed to snows of lead and bismuth sulphides.

As regards the sulphuric acid, it is raining, but drops evaporate long before to touch the surface.

But that's strange, because at such pressure, sulfuric acid should be liquid, or in a critical point. The known Venus temperature is the surface temperature or it's the air temperature in a specific altitude? Or this fact is maybe due to the composition of H2SO4, that may desintegrate at high pressure and temperature? Or even something related to the atmosphere? Or Venus surface is too hot for even H2SO4 in a critical point, despite the high pressures?

Too much rain for a dry surface to me says that the surface is too hot for liquid H2SO4 even at 90 atm. Venus is a strange world. I have read that part of Venus air composition is oxygen, I think it's 4%. The presence of oxygen and too much CO2 says to me that maybe Venus had life in the past, but the core may have "died", loss of magnetic field, temperatures raised, the radiation destroyed the possible oceans and life in it's inicial stage... and now we have the hellish world.

Maybe life on Venus was in a advanced stage, like the epoch of our dinossaurs, and the core died. Or maybe it was caused by violent asteroid collision that was strong and big enough to cause the collapse of the entire alien ecossystem (much worse than what happened on Earth), and that caused the "death" of the core, extreme raise in temperature and evaporation of oceans and liberation of CO2, that was trapped in the oceans. The process may have happened fast, if it was caused by huge impact.

I don't think that Venus died just in it's inicial stages. That's because Venus is almost as big as Earth and have similar density, so the core is hot enough to allow magnetic field for at least many billions of years, like on Earth. To me, it was caused by impact (that also caused the slow and inverse rotation), that caused a huge effect on that planet. Maybe an impact with a small planet? Even with such impact, the raise of temperature caused a complete transformation of the surface, so any craters may have disappeared, also caused by volcanism, if it has any now.

If Uranus suffered huge impact to cause it's almost 90° tilt, maybe Venus suffered in a similar way (but in case of Venus didn't cause huge tilt, but slow rotation in a inverse way). If it was only the loss of magnetic field, maybe the process would be slow and take some billion of years and maybe Venus would not be so extreme and violent as it now.

To me, Venus already had complex life when a huge body hit it, transforming it in a hellish world, even hotter than Mercury. Who knows if alien life on Venus came to Earth and created the oldest civilisations, like Lemuria or Atlantis? But that's just a speculation.

If such impact did not happened in Venus and even on Mars (to me Mars also suffered huge impact that caused fast loss of atmosphere and death of its core), maybe our solar system would have 3 habitable planets, 3 "Earths". Mars, being a small delicate low density world, with a huge impact died very fast.

I've read it suspected that Earth is just barely massive enough for plate tectonics. This allows Earth to get rid of energy. Venus, at 0.9 Earth-masses, lacked enough mass for plate tectonics, so energy built up. It is suspected that the crust underwent an resurfacing event in which the entire surface of Venus was covered in magma. This could perhaps have also outgassed what is now Venus' atmosphere.

Diakonov wrote:

If Uranus suffered huge impact to cause it's almost 90° tilt, maybe Venus suffered in a similar way (but in case of Venus didn't cause huge tilt, but slow rotation in a inverse way).

Can't the rotation rate of Venus be explained by tidal synchronisation with the sun?

The loss of the magnetic field, like with Mars, was a result of the interiors being insufficiently hot to faciltiate convection. The more massive a planet, the hotter the interior (in general). Mars and Venus simply weren't massive enough to keep up the internal activity.

Diakonov wrote:

If such impact did not happened in Venus and even on Mars (to me Mars also suffered huge impact that caused fast loss of atmosphere and death of its core), maybe our solar system would have 3 habitable planets, 3 "Earths". Mars, being a small delicate low density world, with a huge impact died very fast.

Recall that Earth, too, is suspected of being hit pretty hard. In this event, we gained the moon. This event would have devastated all life on Earth if any existed. Without a doubt, Earth was a different planet then, if Earth hadn't been hit, perhaps it would not be habitable today.

In the case of Mars, if I recall correctly (and I could be wrong), the loss of the Martian atmosphere was a result of a slow process in which solar wind excites atmospheric molecules, allowing them to attain escape velocity and leave the planet. This atmospheric escape has been detected for Mars, and Venus if I recall correctly, the atmospheric escape exists on Earth, but is less detectable because Earth is more massive and thus has a higher escape velocity.

With the Martian atmosphere escaping into space over the eons, the surface atmospheric pressure dropped. The boiling point of water approached (and surpassed) the temperature of the surface and then there was no more surface water.

Diakonov wrote:

Who knows if alien life on Venus came to Earth and created the oldest civilisations, like Lemuria or Atlantis? But that's just a speculation.

I don't really know if that counts as speculation. Imaginative though.

So if Earth was a bit smaller, it would not have life as we know?

Maybe if Venus was a moon of a gas giant in the habitable zone, maybe the tidal stress would cause it's interior to provoke plate tectonics. The same with Mars.

Yes, in the case of Mars it's too small to have plate tectonics for billion years, and due to its small mass, it lost heat easily. If there was life in Mars past on the surface, it was a question of time to be frozen. But there are also so many craters and the Hellas Basin and other huge craters... Maybe before the huge impact that created that basin, Mars may have had more air, certainly (to allow any life on the surface and liquid). Because huge impact on a planet with low escape velocity make it to lose its air fast.

But to me, in Venus, something that caused magma to go to the entire surface to melt in a fast event only could be a huge impact, something like Mars suffered. And that the melting process make any craters to disappear. We may not see craters in Venus due to the ressurfacing, but who knows it suffered a huge impact in the past that may have caused the actual environment of that world?

Or Venus had oceans but due to it's distance to Sun, it started to rotate even more slowly in a fast way and that caused the loss of magnetic field and plate tectonics, so that oceans boiled away and all the CO2 trapped gone to the air with sulfur compounds due to volcanism.

To me, if Venus was the same distance of Earth to Sun, it would have fast rotation, and the fast rotation causing plate tectonics and the keeping of life and magnetic field.

Maybe the problem on Venus is not it's mass, but it's distance to the sun. If was not so close, it may have had fast rotation, plate tectonic and magnetic field, much like Earth.

Earth is very lucky!

Diakonov wrote:

But that's strange, because at such pressure, sulfuric acid should be liquid, or in a critical point. The known Venus temperature is the surface temperature or it's the air temperature in a specific altitude? Or this fact is maybe due to the composition of H2SO4, that may desintegrate at high pressure and temperature? Or even something related to the atmosphere? Or Venus surface is too hot for even H2SO4 in a critical point, despite the high pressures?

That's the point I mentioned above. The critical point of sulphuric acid is 925 K, 6.4 MPa. The pressure at the surface of Venus is 9.3 MPa, which exceeds the critical pressure, so sulphuric acid would be supercritical at the Venusian surface (there is no melting point at that pressure). Furthermore the value you gave in your first post (1012 K) exceeds the critical temperature, so cannot correspond to the melting point of sulphuric acid at any pressure. In any case, before you get to the surface, the following reaction becomes favourable: H₂SO₄ → H₂O + SO₃. The sulphuric acid doesn't get to the surface.

Diakonov wrote:

To me, Venus already had complex life when a huge body hit it, transforming it in a hellish world, even hotter than Mercury. Who knows if alien life on Venus came to Earth and created the oldest civilisations, like Lemuria or Atlantis? But that's just a speculation.

There is absolutely no evidence that Atlantis or Lemuria ever existed. Such ideas were more popular before the theory of plate tectonics invalidated the need for sunken continents and landbridges to explain how species of prehistoric animals could exist on separate continents.

Sirius_Alpha wrote:

I've read it suspected that Earth is just barely massive enough for plate tectonics. This allows Earth to get rid of energy. Venus, at 0.9 Earth-masses, lacked enough mass for plate tectonics, so energy built up. It is suspected that the crust underwent an resurfacing event in which the entire surface of Venus was covered in magma. This could perhaps have also outgassed what is now Venus' atmosphere.

There are two issues that strongly disfavour "Earth-style tectonics" on Venus: the planet is extremely dry, and the absolute surface temperature is over twice the value on Earth. The dry nature of the Venusian surface means that the process of subduction cannot be lubricated in the same way as it can on Earth. The higher surface temperature results in a reduced thermal gradient through the crust, which reduces the amount of work that can be done by the heat being lost through the crust. These conditions both arise thanks to the runaway greenhouse effect, so maybe Venus was doing something more similar to Earth tectonics when it still had oceans (if indeed this was ever the case) - though maybe not, as it is not entirely clear that Earth was doing "Earth-style tectonics" for the early part of its history.

What a 4.54 billion-year-old, 0.9 Earth-mass planet in the water zone would be doing tectonically I don't know, but I don't think the case of Venus means that "Earth-style tectonics" would not occur on such a planet if it had oceans like Earth.

Venus may not have plate tectonics now, but certainly had in its past when it was more active. In the past, it certainly had faster rotation, so more heat on Venus core and magnetic field. In past, Venus was active, so it may had oceans and continents. But with time, due to the proximity of Venus related to Sun, Venus started to rotate more slowly, and the lower rotation caused the collapse of the alien ecossystem (if it had any). Caused disturbance in the atmosphere, the slow rotation made the sun-facing oceans to boil away, and that started to happen in the entire planet, slowly. But the question is how the magma came to surface to cause ressurface. Maybe a huge impact with big asteroid or small planet accelerated the process of greenhouse effect. The impact heated even more the planet, and it heated so much that the remaining oceans boiled away forever and the extreme heat melt the surface, turning Venus into a dead world. The impact stressed volcanoes that caused much magma to come to surface, helping the process of ressurfacion. And all that transformed Venus into what is today. That's my vision of Venus past.

In the case of Mars, Mars had advanced life when it was already loosing its heat due to death of its core due to low mass. Mars had more air, enough to any organism there to breathe. But huge impacts, like the formed Hellas Basin made Mars to lose more of its air and life on the surface, turning Mars into an almost airless world, also cold. But who knows if there's still heat beneath the surface, enough to allow at least microbes. Some people think that intelligent alien live under the surface. Some of NASA images are interesting and may suggest this fact (even if its not enough to prove). If there was intelligent life before any cataclism that destroyed surface ecossystem, its probable to have intelligent alien under the surface, living in caverns. But to me its more probable to have microbes only than intelligent life inside underground caves. But who knows? Mars still a mistery.

Earth also had huge impacts, but due to its mass and right distance to Sun, these factors kept a balanced atmosphere and ecossystem, plus the presence of magnetic field and plate tectonics, due to fast rotation and enough mass for that. So with all this, yes, Earth is lucky! It has all factors to keep it balanced. Because life need a balanced environment. But until when Earth will continue to be lucky? Maybe before a really huge impact or the increasing size of Sun in some billion years.

Diakonov wrote:

Some people think that intelligent alien live under the surface.

Probably not anyone here, and I dare say probably not anyone who is worth taking seriously in the matters of science.

Diakonov wrote:

Some of NASA images are interesting and may suggest this fact

I have seen no images from any spacecraft at Mars suggesting life. Especially advanced life.

Is there any reason in-particular you believe advanced life existed on Mars?

Again, the loss of the atmosphere can be more easily explained by atmospheric escape, not by a large scale impact. If the impact was the leading hypothesis as to why the atmosphere was gone, we would expect Earth to be rather lacking in atmosphere too. Venus has much more of an atmosphere than Earth, and you are claiming Venus to have been hit rather hard in the past.

I'm saying that huge impact caused loss of air on Mars due to its low escape velocity. Low gravity planets are more fragile and lose more air than higher gravity worlds. Maybe Venus and Earth have enough escape velocity to avoid the loss of most part of atmosphere. Also, the amount of air loss depend on the angle of impact and the size of the body. In case of Venus, it may have lost part of its air, but later replanished by volcanism and freedom of CO2 in its remaining oceans caused by huge impact, that may have caused the ressurfacing process and filled the air of CO2 excess.

Earth, in its past may have had thick atmosphere, but with the huge impact that formed the Moon it lost most of its air, if the atmosphere was thicker. So that may happened on Earth. In the case of Venus, a huge impact may have caused the melt of the entire surface. The heat caused by the hitting impact provoked volcanism and excess production of gases. Also, the remaining oceans boiled away and all the CO2 trapped gone to the air, while that not happened on Earth. If it happened on Earth, our atmosphere would be like Venus.

If the oceans boiled away on Earth, its atmosphere would be much like Venus. And it would be worse, because Earth mass is higher than Venus, so Earth in fact could have air thicker than Venus. And with magnetic field, it could trap even more air, becoming hotter than Venus due to higher air pressure.

But there's a problem. We don't know if Earth already had oceans when the Moon formed. Maybe not. Maybe the formation of Moon was important to remove the excess of air and CO2 gas, that could be toxic for life.

Maybe the impact on Earth was huge enough to cause it to lose most of its primordial air. But the impact on Venus was not enough to make it lose most of its air, causing it to have even more air. What I'm saying is the process to remove the excess of air on Venus was not well enough (only if it suffered huge impact). But even if Venus had air more like Earth, because of its slow rotation it would not be possible to have life, at least on the surface. If Venus had lost most of its air, due to slow rotation, the temperatures would be extreme variable between day and night. Or it could have a system to transport the excess of heat to night, and the excess of cold to the day side, causing it to have a stable environment. But its just a hypothesis.

Diakonov wrote:

Maybe the impact on Earth was huge enough to cause it to lose most of its primordial air. But the impact on Venus was not enough to make it lose most of its air, causing it to have even more air. What I'm saying is the process to remove the excess of air on Venus was not well enough (only if it suffered huge impact). But even if Venus had air more like Earth, because of its slow rotation it would not be possible to have life, at least on the surface. If Venus had lost most of its air, due to slow rotation, the temperatures would be extreme variable between day and night. Or it could have a system to transport the excess of heat to night, and the excess of cold to the day side, causing it to have a stable environment. But its just a hypothesis.

Actually, Earth has a lot more atmosphere than you'd think, but a lot of the carbon dioxide is locked up in clathrates on the ocean floor and in carbonate rocks in the crust. If you take these reservoirs into account, Earth and Venus have similar amounts of carbon dioxide.

On Venus, the temperature is too high for the crustal reservoir to be stable, and the CO₂ is in the atmosphere. Trigger a runaway greenhouse on Earth and pretty soon the atmosphere would bulk up. Evaporate the oceans, the subduction zones would start to seize up, and pretty soon you've a planet that looks quite Venus-like.

Diakonov wrote:

But there's a problem. We don't know if Earth already had oceans when the Moon formed. Maybe not. Maybe the formation of Moon was important to remove the excess of air and CO2 gas, that could be toxic for life.

If I recall, CO₂ is fine for life. Free oxygen was quite toxic for primordial life, however, since it's very reactive.

What I'm talking about excess of CO2 is its excess would turn Earth into Venus-like world. Too much CO2 heat too much a planet, so it was important for Earth to lose part of its primordial air. Or maybe it wouldn't be suitable for life (it would be too hot today).

Life on Earth started before or after the impact that formed the Moon?

But Earth does have as much (more?) CO₂ as Venus, just stored away in the oceans. If Venus had oceans, not only would it perhaps have less CO₂ in the atmosphere, it would also likely have had plate tectonics.

Diakonov wrote:

Life on Earth started before or after the impact that formed the Moon?

Perhaps both, definitely after. If any life was on Earth before the impact, it was obliterated. The life that is on Earth now evolved from life that formed after the moon-forming impact.

But in the case of CO2, I'm talking about the excess of CO2 in the atmosphere, not the stored. Maybe Earth in its past had air rich in CO2 and the impact or any other impact caused the excess of air to go to space. In that case, the excess of CO2 already in the air. There's much CO2 stored, of course, but maybe Earth lost the excess (in the air) that would turn our world unhabitable. If Earth already had oceans when the impact happened, we don't know, but if oceans only existed after the impact, their formation captured the excess of CO2 and stored it, allowing our world to have temperature suitable for life as we know it. Maybe such impact caused the water in the interior of Earth to go to the surface, forming our oceans.

But Venus was unlucky and if it suffered such impact, it not happened (formation of ocean) and with slow rotation it turned in what is now.

Diakonov wrote:

But in the case of CO2, I'm talking about the excess of CO2 in the atmosphere, not the stored. Maybe Earth in its past had air rich in CO2 and the impact or any other impact caused the excess of air to go to space.

You don't need to invoke an impact removing most of Earth's atmosphere to explain the difference between the amounts of atmosphere on Earth and Venus: you just have to heat one of the planets up sufficiently that it releases all of the potential atmosphere stored in its crust.

Basically, Earth hasn't managed to outgas the vast majority of its carbon dioxide, which is instead still stored in crustal rocks. We know the crust contains reservoirs of material that can release carbon dioxide because the gas is released in volcanic eruptions. Fortunately for us, most of it stays in the crust. Venus got too hot because it is closer to the Sun: it underwent a runaway greenhouse, causing the temperatures to rise sufficiently high that the carbonate rocks broke down and released their carbon dioxide into the atmosphere. Earth is too cold for enough water vapour to get into the atmosphere to trigger such a runaway, at least for the next billion years or so.

I have to agree with you, because temperature is a factor to cause the liberation of CO2 in the air, from both crust and oceans. But it will also depend on the air pressure. Higher air pressure allow water to be liquid at higher temperatures, so if Earth had higher air pressure and if it was a bit hotter it wouldn't be a problem. Escape velocity and magnetic field also counts. Each factor is a variant to determine the balance of a living environment.

But I still think of impact because in the past, as I know, there were much more asteroids, there was a period in the history of the solar system in which asteroids were larger in quantity. So to me is still plausible that, in Venus, some impact or more impacts may have had not caused, but increased the speed of runaway greenhouse effect. The same would occur in Earth if the impact was strong enough, depending on the mass of the body.

Earth, Moon, Mars, Mercury and moons of outer planets suffered many impacts. Why not Venus? Yes, slow rotation and higher temperature are the main explanation and I agree with that, but I also count for impacts. Impacts, if huge, can transform the environment of a planet forever. And this, on Earth, caused the extinction of dinossaurs and transformed the climate of Earth. And all that was caused by only one asteroid. Imagine now bigger asteroids or even planetoids?

Both Earth and Venus are suspected of accumulating out of a handful of oligarchs (maybe ~10?), whereas Mercury and Mars may be oligarchs that were never merged into the others (there is a significant mass difference between Earth+Venus and Mercury+Mars).

So I don't think anyone here is disputing that Venus got hit, hard, in its past. I think what's disputed in this thread (and this is something I've been trying to figure out*, so correct me if I'm wrong) is the affect it had on the planet, and its prospects for habitability. It seems to me that on each of the four terrestrial planets, all their massive impacts occurred at a time where they were too young to be habitable anyway.

* but I'm definitely finding this thread very interesting to read.

Ah, there's also other thing I have in mind. In fact, there are many asteroids that orbit near the orbit of Earth. And maybe on Venus too. If asteroids hit the inner planets on the past, it means that there were more asteroids in the inner system. So certainly some of them hit Venus too, because Venus orbit is close to Earth, even more than Mars! Maybe that most asteroids that hit Mars were from the asteroids belt, and that hit Earth, Venus and Mercury were that near-Earth asteroids.

I still think that a planet as massive as Venus or Mars could sustain life and volcanism. To me life and volcanism depend not only in mass of a planet, but also they way it formed, internal temperature and chemicals involved. Venus was simply unlucky due to the slow rotation caused by the distance from the Sun.

In the case of Mars, Mars itself is not enough to sustain life and volcanism for long periods, but if a world as massive, little more or little less than Mars orbit a gas giant, and if it's near enough to keep volcanism, it would be possible to keep a stable environment. Think of a bigger and more stable Io with enough gravity to keep a thick enough atmosphere and adequate temperature for liquid water. That's exactly the kind of environment what I'm talking about. Ok, life may be poor in such world, but still would have life and water.

The tidal stress would create at least a small magnetic field (depending also of the composition of the core) to protect such world from the particles of the star and of the planet it orbit. A thick enough atmosphere would help to avoid the radiation particles going to the surface of the moon.

Even if the moon lack magnetic field, if it has at least a thick enough atmosphere, the magnetic field of the planet would protect the moon from the star. But in this case, the gas giant can't be too massive, or its radiation belt will make life impossible on the surface of such moon. But if it's like Europa, but bigger, it won't be a problem at all.

Diakonov wrote:

I still think that a planet as massive as Venus or Mars could sustain life and volcanism. To me life and volcanism depend not only in mass of a planet, but also they way it formed, internal temperature and chemicals involved. Venus was simply unlucky due to the slow rotation caused by the distance from the Sun.

Well yeah Mars and Venus were certainly active in the past. But as you stated, these are initial conditions. Recall that those planets are something like 4.5 Gyr old. They have had plenty of time for volcanism to stop. Same goes for Mercury. So perhaps "not anymore" is a better response to "Is the planet active?" I don't see why we shouldn't expect exoplanets of similar mass to have their internal activity stop by a Gyr or so after their formation (all else aside).

Diakonov wrote:

Think of a bigger and more stable Io with enough gravity to keep a thick enough atmosphere and adequate temperature for liquid water. That's exactly the kind of environment what I'm talking about. Ok, life may be poor in such world, but still would have life and water.

That's a great way to keep the body active, as Io and Enceladus (and Titan?) show. The major problem with the idea is that tidal forces work more efficiently the closer the body is to the planet. Giant planets have a high-radiation circumplanetary environment. So to keep tides active, you may have to bathe the planet in lethal radiation.

However you could probably keep the tidal heat flowing but at a great distance by having additional moons to interact with.

Yet another problem with the "Habitable moon" idea is the difficulty in forming such a moon in the first place. The total mass of the non-captured moons of the gas planet in our solar system seem to be extremely low, relative to the mass of the planet. It's perhaps reasonable to expect that moon mass scales with planet mass, as suggested by the planets in our solar system. Jupiter, for all its glory, was able to scrounge up a moon system weighing only 5.3 lunar masses. Mars is something like ~10 Lunar masses. So perhaps a 2 Jupiter-mass planet can host a Mars-mass moon, assuming all (or the vast majority) of its circumplanetary disk collected together into a single moon. However the moon systems of Jovian planets greater than 1 Jupiter-mass are poorly known. There's no certainty that super-Jovians can crank out high-mass moons. So while it may be possible, it may not be likely.

Diakonov wrote:

The tidal stress would create at least a small magnetic field (depending also of the composition of the core) to protect such world from the particles of the star and of the planet it orbit. A thick enough atmosphere would help to avoid the radiation particles going to the surface of the moon.

For a significant magnetic field, if I recall, one would need a significant amount of metals in the interior. The moons of the gas giants seem to be mostly ice. Those moons of Jupiter that do have a magnetic field only barely do, and it doesn't protect them much.

Diakonov wrote:

or its radiation belt will make life impossible on the surface of such moon. But if it's like Europa, but bigger, it won't be a problem at all.

Europa is also too close to the planet for life as we know it on the surface. Life may be hiding underneath the ice.


With the possibilities you've outlined for a habitable moon (Thick atmosphere, strong magnetic field, high mass), based on what we see in our solar system, none of these are very common. But so far, exoplanetary systems have a habit of surprising us!