Which other planets can you see humans on? - Within our solar system at one point

Palomar · 2003-12-30 13:31:34

*Shaun, you're putting me on. You are really a professional astronomer. C'mon, admit it. Opto--- my eye! (pardon the partial pun) :laugh:

you'll now be standing on the equator at midnight, wishing you'd brought thermal underwear with you!

*Tsk, tsk. Mentioning unmentionables in your post (shame on you).

If you stay put for another 88 days, you'll notice the Sun has now returned to its original position directly overhead, a total of 176 days after you began your lonely and uncomfortable vigil.

So noon to noon (or dawn to dawn, or dusk to dusk) on Mercury is a period of 176 days, which is exactly 2 Mercurian years.
A very peculiar situation, but there it is!

[And there are other anomalies to the Sun's apparent movement on Mercury, too, which relate to its marked orbital eccentricity. This eccentricity causes Mercury to move much faster at certain times in its orbit and leads to 'double dawns' and 'double sunsets' on occasions. In other words, the Sun can set, then appear to rise above the horizon again before finally sinking out of sight. And it can do the opposite at dawn; appearing, dropping back, then rising once more above the horizon.
But that's a whole different ball game and I'm not even going to try to explain that one!!]

*Yipes. I am like totally disoriented. I wonder why Arthur C. Clarke never went into detail about the orbit, sun, etc., with his Mercury mining colony in that one "2001" sequel (forget which)...perhaps he doesn't have the patience you possess regarding explanations!

Really cool, Shaun...thank you. A day without something new learned is, IMO, a wasted day.

(the room is starting to spin...I bump into things, {{CRASH!}})

--Cindy

Mad Grad Student · 2003-12-30 17:15:40

Another interesting phenomenon on Mercury I've heard of is that because of its highly eliptical orbit the sun sometimes appears to ballon in size as it rises then shrink as it sets. The apparent size change is caused by the fact that it is only 29 million miles away from the sun at its perigee and 43 million miles away at its apogee.

Its unfortunate that only one probe, Mariner 10, ever visited Mercury. In many respects its even harder to examine from Earth than planets like Neptune and Pluto. At its highest the planet only appears 17 degrees above the horizon, and at that angle Earthbound telescopes have to look through a lot of crudded-up polluted atmosphere to see it. Even the Hubble can't help, Mercury is too close to the sun to observe without damaging its sensative eyes. Hopefuly a new probe, Messenger, will give us some more shots of this extreme planet.

I wonder if there have ever been any plans to land people on Mercury circulating around anywhere. It actually shouldn't be too hard to reach, you can use Venus to brake and accelerate on the way to and from the planet. The only real problem is dealing with the intense heat on the sunny side. Jou could land at one of the poles and from there you could soak up all the sunshine you wanted to and still duck down in a valley to cool off. Mercury could be the third planet visited after Mars, after all, we'll need somewhere to go after the Red Planet.

Mark · 2003-12-30 17:28:59

I guess if humans were to constantly stick to the cooler side, they could walk around with protection. What is the gravity, pressure and radiation like on Mercury?

Honestly, I think my number 1 and 2 candidates are Mars and Titan. I say Mars because it's quite closer(compared to other planets, bar Venus, but it's impossible to land on Venus).

Titan, is very, very far, but in some respects it'd be easier to get humans on Titan because we wouldn't have to combat major(if any) pressure problems, since Titan's surface pressure is 1.5/1.6 bars, which is the equivalent of the pressure you'd feel at the bottom of a 10ft swimming pool, where as Mars, the pressure is a BIG issue, also, it seems there are some radiation problems with Mars, Titan doesn't seem to have any.

Beyond Mars and Titan, it's hard to say, possibly the dark side of Mercury or perhaps one of the Jovian moons like Callisto which doesn't have the major radiation problems of Europa for instance.

Rxke · 2003-12-30 18:30:30

Still think Mars has the advantage of being relatively warm, compared to Titan. It'd be a huge engineering problem to get reliable hardware in these temperatures. Or am i overly pessimistic?

It's bound to happen anyway, eventually, once Mars has a stable colony. Knowing human nature, we'll will be looking for an other 'elsewhere' before you know it.

Shaun Barrett · 2004-01-01 20:08:12

Hi Mark!
The gravity on Mercury is practically identical to that on Mars; you wouldn't notice any difference. The atmospheric pressure is much lower than on Mars, though, and can be effectively discounted all together as far as human survival is concerned; it's essentially a hard vacuum.
I'm not sure of the radiation environment. Mercury has a significant magnetic field, which is something of a mystery to scientists because of the planet's small size and what should consequently be an interior too cool for a liquid core. From memory I think Mercury's magnetic field is about 1% of Earth's but that's probably still enough to fend off most of the solar wind, even that close to the Sun. The lack of any atmospheric shielding, though, would leave the surface exposed to cosmic radiation.

I find Mercury's magnetic field interesting because it ought not to be there according to current theories of planetary magnetism. As we've discussed in other threads here at New Mars, Dr. J. Marvin Herndon has come up with a hypothesis involving large, natural, uranium fission reactors in the centres of rocky planets. He thinks such reactors can explain the internal heat (volcanism) and magnetism of planetary interiors but his ideas have yet to gain general acceptance.
The old established theory is that a planet's internal heat is a combination of remnant heat from the body's accretion and meteoritic bombardment billions of years ago, together with the nuclear decay of a scattering of radioactive elements and their various isotopes throughout the mass of the planet. The magnetism is believed to arise from the combination of liquid metal in the core and its movement associated with the planet's rotation.
Mars is thought to be too small to have retained much internal heat over the 4.6 billion years of its existence and this seems to fit well with the observed lack of a global magnetic field. Yet there is good evidence that significant volcanism has continued throughout Mars' history and well into very recent times. If there's a liquid core and a 24 hour rotation period, where's the magnetic field? Mercury should also have little remaining internal heat due to its small size, and its rate of rotation is very much slower than that of Mars. Therefore it has theoretically even less likelihood of maintaining a global magnetic field than Mars, at least according to current wisdom. Yet it has quite a strong one!

It's always interesting when old established ideas about things no longer fully explain the facts. I sense that Mars and Mercury are going to force a re-think of what makes planets tick and I'm very much looking forward to the results of that.
Maybe Dr. Herndon is onto something!

Incidentally, I've only just realised something about the Bepi Columbo mission to Mercury, due for launch in 2011. Apparently it's supposed to include a lander (presumably solar-powered?) which will follow the terminator around the planet, just like that fictional settlement we've mentioned but without the rails!
It will advance at 3.6 km/h for a total of 4224 hours, completing one full circumnavigation of the planet.
How incredible!!
But what happens if it comes to a sheer-sided rift barring its forward progress and it has to detour sideways for a hundred kilometres or more?
???

GCNRevenger · 2004-01-01 21:03:23

Too bad I can't put headlines on posts... "nuclear saves the day."

The way to get to the outter planets will unquestionably be by a high-ISP engine with reasonably high thrust. This rules out chemical, solar sail, electric-ion, and solid-core nuclear rockets... so, there are only a few options: Gas-core nuclear rockets, the Vasimr plasma rocket, the Orion nuclear pulse rocket, or maybe the nuclear salt-water rocket. The salt-water rocket poses control and temperature resistance concerns, the Orion pulse rocket has proliferation and control concerns, which will make them hard to build. Gas Core nuclear has much higher thrust than Vasimr, so your Discovery-style ship spends less time accelerating and decelerating, and you don't have to rely on the engine for long periods of firing time or lug along a multi-megawatt power reactor.

As for the Mercury rover, why not put RTGs and a solar shade on it? When the advanced dynamic ones become available, they will produce much more power per pound of plutonium fuel, so you don't have to worry about getting stuck in the dark.

RobertDyck · 2004-01-02 12:09:31

Mercury has a significant magnetic field, which is something of a mystery to scientists because of the planet's small size and what should consequently be an interior too cool for a liquid core. From memory I think Mercury's magnetic field is about 1% of Earth's but that's probably still enough to fend off most of the solar wind, even that close to the Sun.

My understanding is that the thermal convection currents will cause convection cells in the mantle, not rotation of the core. I believe tides cause the crust to slow relative to rotation of the core, and that effect is amplified by convection currents. The friction of moving liquid metal of the core causes electric currents, and the rotational movement organizes that into a giant electromagnet. It's my belief that even if Mars has a liquid core, the movement will be continent size convection cells. Without rotation of the core itself relative to the rest of the planet, a dynamo can't form so no strong magnetic field. Mars has very small moons, so they don't exert tides. Earth does, so that started the dynamo by slowing the rotation of the crust more than the core. Mercury is so close to the Sun that gravity from the Sun itself causes tides. That's why Mercury's planetary rotation is a harmonic of its orbit. (Thanks Shaun, I didn't know that before.) The strength of tides is weaker than Earth, which probably resulted in a lesser differential between core and crust movement, which is why the magnetic field is weaker than Earth. Considering the rotation period of 58.6462 Earth days vs. Earth's rotation of 23 hours 56.07 minutes, a lesser differential makes sense.

RobS · 2004-01-03 04:29:57

After Mars, we should set up a Venus orbital station; it's much easier to accomplish than a trip to Mars, in fact. A Venus orbital station could be easy to set up if the hardware to stay in Venus orbit about 19 months is available.

After that, I'd set up a staffed outpost at one of the poles of Mercury. There's ample ice, according to existing data. The crew could explore the polar areas directly and the rest of the planet telerobotically. The equipment developed to send humans to Mars would give a good start on a system for Mercury. I've been revising my "Mars 24" proposal lately and added a Mercury appendix; I'll post it in a few days.

After Mercury, I'd head for Callisto, from which the Galilean moons can be explored robotically, then the Saturnian system. I'm pessimistic we can develop equipment that allows humans to explore Titan directly; a thick, COLD atmosphere that's also flammable is pretty dangerous.

-- RobS

GCNRevenger · 2004-01-03 12:57:14

Another concern about solar storm events is the lack of warning you would have on/near Mercury. Since the solar storm effect's main lethal blow doesn't travel at the speed of light, its possible to warn astronauts that its coming... the trouble is though, at the distance Mercury is at, such warning would be awfully short, maybe down to the seconds. The only way around this hazard would be to not live on the surface and to only leave the "bunker" for very short periods.

RobertDyck · 2004-01-03 17:49:16

To address the primary issue of this thread, I see humans on Mars, the Moon (great for telescopes, mining, and vacuum industry), Mercury (it's high density and hot temperature should provide great mines), as well as Ganymede and Callisto (surface is dirty ice, could be terraformed), Io (great geothermal energy, and sulphur deposits), and sky colonies on Jupiter (gas mines, plastics manufacture). I also see humans on Venus. Mars could be terraformed, as could Venus, Ganymede, and Callisto. Luna (Earth's moon), Mercury, and Io should be left as airless bodies for industry. Planets farther from the Sun have a problem with very low solar energy; hard to heat and hard to power industry.

I have said before Venus could be terraformed with genetically engineered bacteria/archaea. Could humans stand on Venus without terraforming? That's actually an interesting question. The Newt Suit is a diving hard suit that maintains low pressure inside. The standard version is made from cast aluminum and can withstand pressure 1,000 feet. The U.S. Navy contracted the manufacturer to build one that can handle 2,000 feet. The pressure on Venus is 92 bars, equivalent to 3,000 feet. Could the suit be modified to handle it? Its joints use oil bearings, would the high temperature or corrosive atmosphere damage the joints? Could the inside be maintained at suitable temperature when the surface is 850?F? Could it be built to withstand the carbonyl sulphide without corroding? The standard Newt Suit masses 378kg (832 pounds), which only weighs 2-4kg (4-8 pounds) in water, but on the surface of Venus expect it to weigh 342.8kg (755 pounds). It would be hard to move in that, but some sort of vehicle might be possible.

Palomar · 2004-01-03 20:46:44

To address the primary issue of this thread, I see humans on ... Io (great geothermal energy, and sulphur deposits), ... and Io should be left as airless bodies for industry.

*Hi Robert: I'm surprised to read your comments with regards to Io. How do you figure humans will be able to even get close to Io, considering it is within Jupiter's lethal radiation field/belts/whatever?

Am I misunderstanding you somehow? If not, please explain?

--Cindy

Mad Grad Student · 2004-01-03 23:24:04

I don't see what the problem is with exploring Titan. The moon itself is a friendly, as far as space goes, target, the only problem is that you have to wait so long to get there. Following a wasteful Voyager trajectory it takes three years, and the parsimonious Cassini trajectory takes seven. Who's gonna wait that long? We're not going there untill we get some more advanced drive system.

That said, Titan would be relatively friendly place compared to others. It's pretty much the only place off of Earth that you can walk around on without a spacesuit, just very thick clothes! My ideal Titan suit would consist of two layers of Aerogel-padded clothes on every square inch of the body, seals to make sure no cryogenic methane gets in, an oxygen tank and mask, and a faceplate with an image intesifier built in. The image intensifer (aka night vision) would be useful because noon on Titan is like twilight here.

Since you don't have to worry about pressure, the only components necessary of the standard spacesuit are the oxygen and warmth. Aerogel can make -100 dgrees Farenheit feel like room temperatrue, and multiple layers would do the trick. I'd say that you could probably wear as little on Titan as people need to wear to reach the summit of Mount Everest. Just make sure you never touch the ambient atmosphere, that's instant frostbite for sure!

RobS · 2004-01-04 03:56:21

Your comments about aerogel's insulating properties give me more confidence that people could manage on Titan. If there is any wind, the cooling effect of the dense atmosphere would be magnified, but I suppose we could develop the technology to handle it. I don't think it is an easy solution, though. Antarctic and Mount Everest conditions are not similar; we're talking about crygenic conditions. People could train in a chamber containing liquid methane. And that stuff IS flammable if any of the humans' oxygen get to it; that's what I meant by flammable.

Even the Martian poles are not exactly comparable, though establishment of a base there would generate related experience.

I hope people can explore Titan; the geology will probably be wierd and fascinating.

As for Mercury, I wonder whether the poles are reasonably safe from solar storms. If there is a strong enough magnetic field to create Van Allen belts, maybe not; the radiation would be focused on the poles. I suspect any Mercury base has to be well buried to protect against radiation anyway, and ships traveling there would need special shielding. The main value of a base on Mercury is scientific exploration of the world without a time delay due to the speed of light. I see no reason not to go there; it is a legitimate scientific target for exploration, and will tell us about the formation of the solar system. It's easier to reach than the outer planets but requires some of the same advanced propulsion systems, so it's a good test for gas-core, VASMR, or whatever is developed.

-- RobS

Shaun Barrett · 2004-01-04 06:45:58

Thanks Robert (Dyck, that is) for the interesting explanation of the relative strengths of the magnetic fields of Mars, Earth, and Mercury. I can see the logic in what you've described and it may yet prove to be the winning hypothesis.
But I've struggled with more than one explanation for the existence of magnetic fields around rocky planets and I get the impression that all the loose ends are far from sewn up.
While not in any way wishing to detract from the information you provided, I believe scientists are still somewhat at a loss to explain the strength of Mercury's field. (I admit I may be behind the times on this, by the way! )

I too was surprised to see your comments about humans on Io, though not for the same reason Cindy mentioned. Io's volcanism is intense and I think much of its surface is largely remodelled by this activity on remarkably short time scales.
Is there anywhere on Io which is sufficiently stable, or even just free of a rain of solidified volcanic ejecta, to contemplate putting people down on the surface?

As for terraforming Venus using bacteria and/or archaea, I think that idea was first put forward by Carl Sagan back in the sixties(?). We've had lively discussions about it in another thread here at New Mars, too, and various difficulties were identified; including what to do with all the carbon from the massive CO2 atmosphere, how to remedy the shortage of water, and how to prevent the high insolation that close to the Sun from quickly reversing our terraforming efforts.
I suppose it all depends on what kind of technology you have access to.

Hi RobS!
It's interesting you should mention winds on Titan with regard to the possible effects of wind-chill-factor. I was reading somewhere just lately that Titan is expected to have "atmospheric tides". I can't remember where I saw the article and they didn't go into the reasons for the hypothesis in any great detail.
Anyway, the important point was that they expected a slight but steady breeze of (I think) 5 or 6 km/hr over much of the surface. They were imagining waves on any sea of liquid hydrocarbons which may exist there!
I'm not sure what effect such air movement would have on the ability of Titan's environment to drain heat from an astronaut standing on the surface. Maybe some of our American cousins here, used to pretty cold conditions in Earth's northern winter, can hazard a guess as to what a 5 km/hr wind at about -180 deg.C (about -290 deg.F) would feel like?!!
:;):

Palomar · 2004-01-04 09:00:31

I too was surprised to see your comments about humans on Io, though not for the same reason Cindy mentioned. Io's volcanism is intense and I think much of its surface is largely remodelled by this activity on remarkably short time scales.
Is there anywhere on Io which is sufficiently stable, or even just free of a rain of solidified volcanic ejecta, to contemplate putting people down on the surface?

*Um, yeah...that too!! (understatement)

--Cindy

Hazer · 2004-01-04 13:20:14

I say that Venus is a great possibility for a planet to colonize aside from Mars.
Sure there's acid there, but I believe Venus may very well be where we write the book on terraforming.
Lots of volatiles to mess around with...

RobertDyck · 2004-01-05 15:30:47

I too was surprised to see your comments about humans on Io, though not for the same reason Cindy mentioned. Io's volcanism is intense and I think much of its surface is largely remodelled by this activity on remarkably short time scales.
Is there anywhere on Io which is sufficiently stable, or even just free of a rain of solidified volcanic ejecta, to contemplate putting people down on the surface?

Underground base with lots of regolith above it to provide radiation protection. You may have to dig out the entrance once in a while.

As for terraforming Venus using bacteria and/or archaea, I think that idea was first put forward by Carl Sagan back in the sixties(?). We've had lively discussions about it in another thread here at New Mars, too, and various difficulties were identified; including what to do with all the carbon from the massive CO2 atmosphere, how to remedy the shortage of water, and how to prevent the high insolation that close to the Sun from quickly reversing our terraforming efforts.

Yup, Carl Sagan wrote the first paper on terraforming in 1961. His idea was to use unmodified algae, but that would only work if Venus had a pressure of 6 bars. Most people thought his idea wouldn't work after they discovered Venus has 92 bars pressure. However, I'm saying we use genetically engineered anaerobic bacteria that excrete a compound that's chemically engineered to sequester CO2; both carbon and oxygen. I initially thought of C3O6, but my chemist friend thinks the molecule won't be stable. He suggested plastic. I'm sure we can engineer a long molecule that's stable in Venus atmosphere and doesn't include hydrogen. We can't afford to sequester hydrogen, but we can use a little sulphur.

Shaun Barrett · 2004-01-05 18:53:31

Weeelll ... I suppose anything's possible if you really set your mind to it! But I think we have a much better chance with Mars than anywhere else.
I still see the terraforming of Venus as being orders of magnitude more technologically challenging and, while the transforming of Mars might see real progress within as little as a century, I tend to think Venus won't be attempted until much later.
I suppose I could be wrong.

Mad Grad Student · 2004-01-05 20:07:24

Here's a rough comparison from Titan to Mars.

Atmosphere: Titan is clearly a better environment. The atmosphere is thick and full of nitrogen with a dash of methane, just like early Earth. Mars' atmosphere is very thin, about 10 millibars, and doesn't give much radiation protection. You would need a large amount of radiation sheilding on Mars, but some temperature sheilding on Titan.

Gravity: It depends on your interests here. Titan's one-seventh gravity is great for structures, less stress, but bad for clacium-depeleted astronauts. Mars, on the other hand, has the opposite issues. The two come to a tie here.

Temperature: Mars is naturally friendlier, with temperatures around the same as Antarctica (Getting colder at the poles). By contrast, Titan is a cryonics lab, others here have shown how cold it gets. However, Titan is steadier in its weather, so that puts less strain on materials than the up to 100 degree F temperature swing on Mars between day and night.

While Titan will pose a challenge, going there is doable. Even if it takes more sturdy spacesuits we should have the technology in a short time.

RobertDyck · 2004-01-05 21:55:18

Weeelll ... I suppose anything's possible if you really set your mind to it! But I think we have a much better chance with Mars than anywhere else.
I still see the terraforming of Venus as being orders of magnitude more technologically challenging and, while the transforming of Mars might see real progress within as little as a century, I tend to think Venus won't be attempted until much later.
I suppose I could be wrong.

I've was converted from the cause of Venus to Mars several years ago. You don't have to convince me now.

Mars is the easiest to terraform, and has the great advantage that you can colonize now and terraform later. Venus has to be terraformed first, unless you want to wonder about in multi-hundred pound suits with liquid nitrogen for coolant. Venus has 90% of Earth's surface gravity while Mars has 38%, true. Venus has plenty of atmosphere including several times as much nitrogen as Earth, true. But you how do you live on a planet with 92 bars pressure, 850?F (454?C) temperature, and carbonyl sulphide (COS) in the atmosphere? In fact, the lowest 30 miles (48 kilometres) of Venus atmosphere glows red from the heat and chemical breakdown of COS. Scientists used to think Venus had sulphuric acid in the atmosphere, but modern probes found sulphuric acid only in the clouds. But carbonyl sulphide is more corrosive than sulphuric acid!

But I would still like to see Mars colonized now and genetically engineered bacteria seeded into Venus atmosphere so decades in the future Venus could be colonized.

Palomar · 2004-01-06 06:10:24

I too was surprised to see your comments about humans on Io, though not for the same reason Cindy mentioned. Io's volcanism is intense and I think much of its surface is largely remodelled by this activity on remarkably short time scales.
Is there anywhere on Io which is sufficiently stable, or even just free of a rain of solidified volcanic ejecta, to contemplate putting people down on the surface?
Underground base with lots of regolith above it to provide radiation protection. You may have to dig out the entrance once in a while.

*But isn't the radiation of Jupiter which Io is awash in so lethal that it would kill a person within 40 minutes? I have read that before, and that seems to have been verified (not by you) previously here, as well.

Is this estimation of the lethal potential of Jupiter's radiation belts wrong?

If not, then I can't see how humans will be able to live long enough to even approach Io, let alone have time to "dig themselves in," as it were.

?

Not unless technology can advance to such a point that radiation can be kept at bay by advanced suits, etc., but then those explorers would have to be bound head to toe in such a garment all the time...if it'll even be possible to manufacture such a suit to begin with (given the nature of radiation), etc...

--Cindy

RobertDyck · 2004-01-06 12:48:58

*But isn't the radiation of Jupiter which Io is awash in so lethal that it would kill a person within 40 minutes? I have read that before, and that seems to have been verified (not by you) previously here, as well.
Is this estimation of the lethal potential of Jupiter's radiation belts wrong?
If not, then I can't see how humans will be able to live long enough to even approach Io, let alone have time to "dig themselves in," as it were.
Not unless technology can advance to such a point that radiation can be kept at bay by advanced suits, etc., but then those explorers would have to be bound head to toe in such a garment all the time...if it'll even be possible to manufacture such a suit to begin with (given the nature of radiation), etc...

I must admit I haven't looked at the detailed radiation of Io. When I was a teenager I read a book about homesteading on Ganymede (Farmer in the Sky, but Robert A. Heinlein). At that time Ganymede was thought to have a greater density, so surface gravity almost equal to Mars. Since Voyager and Galileo, we discovered it's lower. I thought Mars gravity was the reason it had a low atmospheric pressure, so terraforming would be difficult. I thought if we could terraform Mars we could terraform Ganymede. Venus certainly doesn't have a problem with gravity or air pressure. That's why I've studied these three bodies. I haven't studied Io with as much detail.

I believe a magnetosphere is required to preserve water and atmosphere. Once we have technology to create an artificial planetary magnetosphere, it can be applied to Io. Io certainly has an active, liquid core. Io, like the other Galilean moons, is tide locked so the same side always faces Jupiter. Since it doesn't rotate, where is the flex that causes heating? According to Solar Views, Io is directly in a radiation belt of Jupiter, and gets impacted by so much radiation that its thin atmosphere glows with a planet-wide aurora. Could all that energy be harnessed to generate a magnetosphere? Could the magnetosphere deflect the radiation in such a way as to increase the strength of the magnetosphere? That would power the radiation deflector with the same radiation it is deflecting.

Josh Cryer · 2004-01-06 13:16:02

Shaun,

I still see the terraforming of Venus as being orders of magnitude more technologically challenging and, while the transforming of Mars might see real progress within as little as a century, I tend to think Venus won't be attempted until much later.

There's one thing Venus has more of than Mars, and that's solar energy. Granted, I agree that it would be technologically mroe challenging, but as far as energy requirements are concerned, I think Venus is in a little bit better shape.

Robert,

Mini-magnetosphere are really helped by fine particles or gasses, since Io is covered with that sort of stuff, wouldn't you imagine that simply creating a strong magnetic field would create the magnetosphere we'd want? I think it's in the relm of possiblity.

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