Habitability of Neptune

[Rhadamantus]

I was reading this http://planetfuraha.blogspot.com/2013/0 ... nts-v.html, and I was wondering about the habitability of ice giants. Floating creatures of moderate size should be possible, there should be energy from up above, and there are (probably) great water-ammonia oceans. Earthlike life might not be possible, but carbon-water should. The question of what they'd breath is more difficult (methane is possible, I think), but it seems like ice giants should be quite habitable.

[Alyrium Denryle]

I was reading this http://planetfuraha.blogspot.com/2013/0 ... nts-v.html, and I was wondering about the habitability of ice giants. Floating creatures of moderate size should be possible, there should be energy from up above, and there are (probably) great water-ammonia oceans. Earthlike life might not be possible, but carbon-water should. The question of what they'd breath is more difficult (methane is possible, I think), but it seems like ice giants should be quite habitable.

You're not going to get much more than single celled organisms on a planet like Neptune, because energy inputs would be... low. Save for maybe around hydrothermal vents. Not enough sunlight for much else.

[SpottedKitty]

Not just energy inputs; by the time you get low enough in the atmosphere that the temperature's comfortably above brass-monkey level, the pressure is high enough to make any sort of complex critters unlikely.

Jupiter, though might be a bit better; I remember reading speculation recently that there might be zones in the atmosphere that would be moderately comfortable. Especially when you consider some of the places here on Earth where extremophiles have been living happily for a very, very long time.

[Esquire]

The habitability of Neptune is: zero, or effectively so. It is an uninhabitable planet. No complex organism - without absolutely ludicrous levels of bioengineering - could survive in such a hostile environment.

[Rhadamantus]

Not just energy inputs; by the time you get low enough in the atmosphere that the temperature's comfortably above brass-monkey level, the pressure is high enough to make any sort of complex critters unlikely.

Jupiter, though might be a bit better; I remember reading speculation recently that there might be zones in the atmosphere that would be moderately comfortable. Especially when you consider some of the places here on Earth where extremophiles have been living happily for a very, very long time.

Why? At 300 km down, it's 100 bars of pressure and 320 K. There's plenty of earth life at similiar pressures and temperatures.

[Guardsman Bass]

Stability would be a big issue. For there to even be micro-organisms, you'd need those parts of the ice giant to be relatively stable for long periods of time (or unstable but with the micro-organisms able to spread into new ones as the prior areas collapse). IIRC That rules out Jupiter because they believe the planet has some strong vertical circulation of air from higher levels of the atmosphere down to hotter, high pressure lower ones (and vice versa).

Why? At 300 km down, it's 100 bars of pressure and 320 K. There's plenty of earth life at similiar pressures and temperatures.

I bet we could design a buoyant probe powered by a RTG that could survive that pressure and temperature while doing radar scans and other measurements of Neptune or Uranus at that depth. The trick would be getting it down to that part of the planet's atmosphere intact - Neptune has some intense storm systems and high winds.

[Elheru Aran]

Jupiter, though might be a bit better; I remember reading speculation recently that there might be zones in the atmosphere that would be moderately comfortable. Especially when you consider some of the places here on Earth where extremophiles have been living happily for a very, very long time.

Not the first time that's been speculated. The most optimistic, IIRC, is Arthur C Clarke talking about giant air-jellyfish and manta-ray type critters floating in the atmosphere, using electricity as a weapon... some funky stuff.

[Sea Skimmer]

I bet we could design a buoyant probe powered by a RTG that could survive that pressure and temperature while doing radar scans and other measurements of Neptune or Uranus at that depth. The trick would be getting it down to that part of the planet's atmosphere intact - Neptune has some intense storm systems and high winds.

Maybe. Devising some kind of probe that can drop through the upper supersonic winds and then deploy is certainly not out of the question. But since the atmosphere is 80% hydrogen you've got a new problem if you go down any great depth which is getting any data back out, its going to start to attenuate radio waves rather strongly. Since photos aren't important data rates don't have to be that high to be useful, but they still gotta exist.

If one was crazy enough it might be possible to have a rocket launch a radio probe back up at the end of the mission though. It wouldn't need to get back into orbit, just back high enough to make transmission to something else in orbit.

[Rhadamantus]

I bet we could design a buoyant probe powered by a RTG that could survive that pressure and temperature while doing radar scans and other measurements of Neptune or Uranus at that depth. The trick would be getting it down to that part of the planet's atmosphere intact - Neptune has some intense storm systems and high winds.

Maybe. Devising some kind of probe that can drop through the upper supersonic winds and then deploy is certainly not out of the question. But since the atmosphere is 80% hydrogen you've got a new problem if you go down any great depth which is getting any data back out, its going to start to attenuate radio waves rather strongly. Since photos aren't important data rates don't have to be that high to be useful, but they still gotta exist.

If one was crazy enough it might be possible to have a rocket launch a radio probe back up at the end of the mission though. It wouldn't need to get back into orbit, just back high enough to make transmission to something else in orbit.

Gravity's pretty low, too (1g at that altitude on both, give or take.) It shouldn't take an inordinate amount of delta-v (though air drag would pose a problem. How much would there be?). And the hydrogen sulfide cloud decks could also be candidates for life.

[Guardsman Bass]

I bet we could design a buoyant probe powered by a RTG that could survive that pressure and temperature while doing radar scans and other measurements of Neptune or Uranus at that depth. The trick would be getting it down to that part of the planet's atmosphere intact - Neptune has some intense storm systems and high winds.

Maybe. Devising some kind of probe that can drop through the upper supersonic winds and then deploy is certainly not out of the question. But since the atmosphere is 80% hydrogen you've got a new problem if you go down any great depth which is getting any data back out, its going to start to attenuate radio waves rather strongly. Since photos aren't important data rates don't have to be that high to be useful, but they still gotta exist.

If one was crazy enough it might be possible to have a rocket launch a radio probe back up at the end of the mission though. It wouldn't need to get back into orbit, just back high enough to make transmission to something else in orbit.

You'd need to make the diving probe much larger to include a suborbital radio probe, but any mission sending a long-lasting diving probe to Neptune is going to be large, and in general a Neptune orbital mission will probably need to be large because it's going to need a formidable propulsion system just to slow down once it's there (unless the research team is willing to wait decades for the probe to get there). I'm thinking either a big RTG or a Project Prometheus successor system with output in the tens of KW.

The data rates from transmission wouldn't need to be high. The Galileo entry probe in Jupiter had a data rate of around 128 bytes per second, and sent about 3.5 MB of data before they lost contact with it.

[jwl]

I bet we could design a buoyant probe powered by a RTG that could survive that pressure and temperature while doing radar scans and other measurements of Neptune or Uranus at that depth. The trick would be getting it down to that part of the planet's atmosphere intact - Neptune has some intense storm systems and high winds.

Maybe. Devising some kind of probe that can drop through the upper supersonic winds and then deploy is certainly not out of the question. But since the atmosphere is 80% hydrogen you've got a new problem if you go down any great depth which is getting any data back out, its going to start to attenuate radio waves rather strongly. Since photos aren't important data rates don't have to be that high to be useful, but they still gotta exist.

If one was crazy enough it might be possible to have a rocket launch a radio probe back up at the end of the mission though. It wouldn't need to get back into orbit, just back high enough to make transmission to something else in orbit.

Put a second probe at a higher altitude, the first probe sends data to the second probe acoustically and the second probe beams the information back to earth.

[Sea Skimmer]

Put a second probe at a higher altitude, the first probe sends data to the second probe acoustically and the second probe beams the information back to earth.

Wind says that won't work I'm afraid, and people estimate 700-1300mph winds for the upper levels of Neptune.... speeds and vectors would be far different at different altitudes and the balloons would be hundreds of miles apart in no time.

Anyway this is a probably big problem if you want greater then say 100km depth, but its not like a higher altitude wouldn't be useful. But it's also worth considering just how much we can do with remote sensing now compared to even 1990s space probes, I think its safe to say that we would need to send an orbiter to Neptune just to get enough design data to design a balloon with a decent chance of success at all, and it might tell us an awful lot of what a probe would too. Something else to think on is an atmospheric skimming probe to collect gas samples, but then boosts back into orbit.

You'd need to make the diving probe much larger to include a suborbital radio probe, but any mission sending a long-lasting diving probe to Neptune is going to be large, and in general a Neptune orbital mission will probably need to be large because it's going to need a formidable propulsion system just to slow down once it's there (unless the research team is willing to wait decades for the probe to get there). I'm thinking either a big RTG or a Project Prometheus successor system with output in the tens of KW.

A mission like this would be so long the RTG power curve starts to be not so amazing looking if you want it providing propulsive power at the end. Nuclear reacto

The data rates from transmission wouldn't need to be high. The Galileo entry probe in Jupiter had a data rate of around 128 bytes per second, and sent about 3.5 MB of data before they lost contact with it.

That is high when were talking about radio propagation problems though. Remember radio systems on earth exist where the reliable data rate is like 3 bites per second, ELF for example. Of course we can't even think about ELF here, which would work through the whole planet in principle, because the required antennas are too big, but that's where things get in this kind of field. Galileo used a a 95 GHz transmitter as I recall, which can negate certain gases, but its strongly absorbed by water vapor. As I recall a lot of that is from an oxygen band it runs afoul, but some is the hydrogen.

The problem is what depth do we hit that at which the mass of hydrogen overhead exceeds that of a 20m depth of water?

[jwl]

Put a second probe at a higher altitude, the first probe sends data to the second probe acoustically and the second probe beams the information back to earth.

Wind says that won't work I'm afraid, and people estimate 700-1300mph winds for the upper levels of Neptune.... speeds and vectors would be far different at different altitudes and the balloons would be hundreds of miles apart in no time.

That assumes the probe just hangs there without doing anything to correct its position. Hot air ballooners on earth seem able to navigate to where they want to go.

[Simon_Jester]

Not in thousand mile an hour winds they don't.

[SpottedKitty]

Hot air ballooners on earth seem able to navigate to where they want to go.

Only in terms of moving to different altitudes to catch winds moving in different directions; that's not always easy, or even possible. And for the landing, you're still stuck with whichever way the surface winds are going.

[phred]

Would it be possible to have a large probe that sits up high in the atmosphere dropping sensors farther down in on tethers?

Also for a frame of reference on the hot air balloon idea, the balloon companies in Napa valley don't launch in 15MPH winds. Granted that's for safety concerns, but gives an idea of how hard that method of flight control is

[jwl]

Would it be possible to have a large probe that sits up high in the atmosphere dropping sensors farther down in on tethers?

Also for a frame of reference on the hot air balloon idea, the balloon companies in Napa valley don't launch in 15MPH winds. Granted that's for safety concerns, but gives an idea of how hard that method of flight control is

But that's because of the launch itself and the danger of the ground. That isn't a problem on Neptune.

[Guardsman Bass]

Wind says that won't work I'm afraid, and people estimate 700-1300mph winds for the upper levels of Neptune.... speeds and vectors would be far different at different altitudes and the balloons would be hundreds of miles apart in no time.

Anyway this is a probably big problem if you want greater then say 100km depth, but its not like a higher altitude wouldn't be useful. But it's also worth considering just how much we can do with remote sensing now compared to even 1990s space probes, I think its safe to say that we would need to send an orbiter to Neptune just to get enough design data to design a balloon with a decent chance of success at all, and it might tell us an awful lot of what a probe would too. Something else to think on is an atmospheric skimming probe to collect gas samples, but then boosts back into orbit.

That would go well with a large orbiter with plentiful on-board power. You could afford to give it the works in terms of instrumentation, so if it's easier to do measurements from orbit rather than with the Diver spacecraft, they'll do it.

An atmospheric skimmer would have to dip pretty low to get anything useful that the orbiter couldn't get. I don't think they'd risk having an automated rendezvous go wrong and damage the main spacecraft, either, so the measurements of the sample would have to be done on board the skimmer and transmitted.

A mission like this would be so long the RTG power curve starts to be not so amazing looking if you want it providing propulsive power at the end. Nuclear reacto

Project Prometheus's successor it is, then (assuming they ever find any money for it that doesn't immediately then get eaten by SLS and the crewed program). We'd need something that could be reliable for 30-40 years, which I don't think is impossible. The cancelled Jupiter Icy Moons Orbiter mission had a projected mission life-time of 20 years, with an on-board power source of 200 KW. For the outbound acceleration phase, they might be able to supplement that with solar panels the ship could then jettison along the way.

They might be able to even make the trip in less than 10 years. There was a proposed Neptune Orbiter mission more than a decade ago that was expected to make the trip from launch to Neptune in ~10 years with gravity assists, and would have used either RTGs or a small nuclear reactor.

The problem is what depth do we hit that at which the mass of hydrogen overhead exceeds that of a 20m depth of water?

I don't know. The figure up-thread was around 100 times Earth's atmospheric pressure, maybe a bit less (we'd want to aim for a temperature band in the 273-373 K range). That would certainly be a lot higher in pressure than 20 meters of water - Venus's atmosphere is around 93 times Earth's pressure at the surface and the equivalent of 900 meters deep in the ocean.

[Rhadamantus]

Wind says that won't work I'm afraid, and people estimate 700-1300mph winds for the upper levels of Neptune.... speeds and vectors would be far different at different altitudes and the balloons would be hundreds of miles apart in no time.

Anyway this is a probably big problem if you want greater then say 100km depth, but its not like a higher altitude wouldn't be useful. But it's also worth considering just how much we can do with remote sensing now compared to even 1990s space probes, I think its safe to say that we would need to send an orbiter to Neptune just to get enough design data to design a balloon with a decent chance of success at all, and it might tell us an awful lot of what a probe would too. Something else to think on is an atmospheric skimming probe to collect gas samples, but then boosts back into orbit.

That would go well with a large orbiter with plentiful on-board power. You could afford to give it the works in terms of instrumentation, so if it's easier to do measurements from orbit rather than with the Diver spacecraft, they'll do it.

An atmospheric skimmer would have to dip pretty low to get anything useful that the orbiter couldn't get. I don't think they'd risk having an automated rendezvous go wrong and damage the main spacecraft, either, so the measurements of the sample would have to be done on board the skimmer and transmitted.

A mission like this would be so long the RTG power curve starts to be not so amazing looking if you want it providing propulsive power at the end. Nuclear reacto

Project Prometheus's successor it is, then (assuming they ever find any money for it that doesn't immediately then get eaten by SLS and the crewed program). We'd need something that could be reliable for 30-40 years, which I don't think is impossible. The cancelled Jupiter Icy Moons Orbiter mission had a projected mission life-time of 20 years, with an on-board power source of 200 KW. For the outbound acceleration phase, they might be able to supplement that with solar panels the ship could then jettison along the way.

They might be able to even make the trip in less than 10 years. There was a proposed Neptune Orbiter mission more than a decade ago that was expected to make the trip from launch to Neptune in ~10 years with gravity assists, and would have used either RTGs or a small nuclear reactor.

The problem is what depth do we hit that at which the mass of hydrogen overhead exceeds that of a 20m depth of water?

I don't know. The figure up-thread was around 100 times Earth's atmospheric pressure, maybe a bit less (we'd want to aim for a temperature band in the 273-373 K range). That would certainly be a lot higher in pressure than 20 meters of water - Venus's atmosphere is around 93 times Earth's pressure at the surface and the equivalent of 900 meters deep in the ocean.

20 meters of water is, in pressure, two bars. In mass of hydrogen, maybe a hundred kilometers from the top of the atmosphere. Either way, probably not enough.