Intrepid librarian (or going to Jupiter)

[Ann]

We used to have a librarian named Birgitta at the school where I work. She got herself another job several years ago and moved away.

Birgitta was - is - a very interesting person. Tall, overweight, stately, cool, and full of unusual hobbies. When she worked at my school she was building fantastic little models of splendid Victorian furniture, at the same time as she herself usually wore colorful and comfortable denim clothes. (So the people who originally owned the Victorian furniture wouldn't have let Birgitta near their elegant chairs and tables.)

We kept in touch for a while after she had moved away, but then she wanted to stay in touch via Facebook. And I just can't do Facebook.

But two nights ago, I met her in person.

She had taken up a new hobby: traveling. She told me, in her typical matter-of-fact way, that her latest journey had gone to Jupiter.

-Jupiter, I said. How's that possible?

-It was NASA, she told me. They are planning manned missions to Jupiter, and they wanted to send a manned "test probe" first, and they were asking for volunteers. I told them I was interested, and they picked me. And a few others too, of course.

As I said, Birgitta is tall. And overweight. She must weigh a few pounds, that's for sure. And she is pushing sixty. But, well, NASA picked her.

-Weren't you scared? I asked. I mean, being locked up inside that tiny capsule for months and months...

-It wasn't so bad, she replied. At first we were basically confined to our bunks, but then we were allowed to move around inside the entire ship.

Move around inside the "entire" ship. That tiny little flying bucket. I felt my claustrophobia working overdrive just thinking about it. I couldn't even ask Birgitta if she hadn't been afraid of dying out in space.

-Wasn't it boring, flying all the way to Jupiter? I asked instead.

-Getting past the orbit of Mars was a bit of a drag, she admitted. But then we seemed to kick into a new gear, and we were at Jupiter in a jiffy.

-Getting there was fun, she continued. I took some really good pictures. Let me show you some...

And she took out her smartphone and started showing me pictures of Jupiter. They really were splendid. I was, of course, particularly fascinated by the blue-gray slightly fan-like patterns in Jupiter's cloud cover - you can see one here, above the moon Io.

And then I woke up.

The dream hasn't quite left me. Of course a manned mission to Jupiter seems like a very remote dream, given that we aren't even close to sending anyone even to Mars. (And if we ever go to Jupiter, we won't send people like Birgitta there - and the round trip won't take just a couple of months - and the shortest part of the journey won't be the one between the orbit of Mars and Jupiter - and so on.)

But let's toy with the idea that we were going. Clearly, if we were going to land on one of the moons, we would choose Europa, since Europa probably has an ocean not too far below its ice cover. But let's assume that we weren't thinking about exploring the possibilities of life inside Europa, but we were only interested in landing on a Jovian moon, any moon, as safely as possible.

What moon would we choose? If we stuck to the Galilean moons, we surely wouldn't choose Io, if we were looking for safety. (We wouldn't want the ground we landed on to erupt from under our feet!) And if we are talking safety only, I don't know how safe Europa would be. Isn't Europa full of sheer ice cliffs? How much fun would that be? As for Callisto, it seems craggly and dark and full ice craters. I don't know, but I think that Ganymede looks safest. It has a variety of terrain to choose from and looks "middle-of-the-road" light brown and well-groomed.

Any thoughts? Where would you land if you went to the Jovian system and wanted to choose the safest landing site?

(And what do you call those bluish fan-like cloud patterns on Jupiter? I know they have a name, but I can't remember it!)

Ann

[neufer]

Where would you land if you went to the Jovian system and wanted to choose the safest landing site?

My primary consideration would be for a small distant moon where the escape velocity for the entire moon/Jupiter system would be less than the escape velocity was for the Apollo astronauts; e.g., Pasiphae (moon). (I'd name my spacecraft the Minotaur.)

[BMAONE23]

If I were planning a manned mission to the Jovian System, The ship would have to be fairly large and likely assembeled in Earth Orbit. It would need to have rotating portion to create artificial gravity for the many years journey. And, since jupiter has So Many Moons I would have a tough time selecting just one so the mission would have to include a set of probes (perhaps 3 per larger moon) that would be deployed to their surfaces and two communications relays to orbit Jupiter

[neufer]

Click to play embedded YouTube video.

If I were planning a manned mission to the Jovian System, The ship would have to be fairly large and likely assembeled in Earth Orbit. It would need to have rotating portion to create artificial gravity for the many years journey. And, since jupiter has So Many Moons I would have a tough time selecting just one so the mission would have to include a set of probes (perhaps 3 per larger moon) that would be deployed to their surfaces and two communications relays to orbit Jupiter

[orin stepanek]

Ann! If I were planning a trip to Jupiter; - - - well, I just wouldn't! I'll stay home and have a couple of 's

[neufer]

Click to play embedded YouTube video.

Ann! If I were planning a trip to Jupiter;

- - - well, I just wouldn't!

I'll stay home and have a couple of 's

[list]Ahhh...so peaceful and quiet! [/list]

[Chris Peterson]

But let's toy with the idea that we were going. Clearly, if we were going to land on one of the moons, we would choose Europa, since Europa probably has an ocean not too far below its ice cover.

"ALL THESE WORLDS ARE YOURS—EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE."

[Beyond]

Did they know something about Europa way back then, that we don't, even now

Hey Chris, you broke the 6000 barrier. Now, you're twice as posted as i am.

[TNT]

But let's toy with the idea that we were going. Clearly, if we were going to land on one of the moons, we would choose Europa, since Europa probably has an ocean not too far below its ice cover.

"ALL THESE WORLDS ARE YOURS—EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE."

Darn, I ran out of water on my way here. Oh well, I guess there's always Io.

[neufer]

But let's toy with the idea that we were going. Clearly, if we were going to land on one of the moons, we would choose Europa, since Europa probably has an ocean not too far below its ice cover.

"ALL THESE WORLDS ARE YOURS—EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE."

Darn, I ran out of water on my way here. Oh well, I guess there's always Io.

[b][color=#0000FF]Ganymede pouring Jupiter a libation[/color][/b]

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• But Ganymede is Jupiter's cup-bearer!

<<Ganymede (Greek: Γανυμήδης) was the cup-bearer in Olympus. Ganymede was afterwards also regarded as the genius of the fountains of the Nile, the life-giving and fertilizing river. Thus the divinity that distributed drink to the gods in heaven became the genius who presided over the due supply of water on earth. Zeus granted him eternal youth and immortality and the office of cupbearer to the gods, supplanting Hebe. Zeus later put Ganymede in the sky as the constellation Aquarius, which is associated with that of the Eagle (Aquila). A moon of Jupiter, the planet named for Zeus's Roman counterpart, was named Ganymede by modern-era astronomers.>>

<<The average density of Ganymede, 1.936 g/cm³, suggests a composition of approximately equal parts rocky material and water, which is mainly in the form of ice. The mass fraction of ices is between 46–50%, slightly lower than that in Callisto. Ganymede's surface has an albedo of about 43%. Water ice seems to be ubiquitous on the surface, with a mass fraction of 50–90%, significantly more than in Ganymede as a whole. Near-infrared spectroscopy has revealed the presence of strong water ice absorption bands at wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0 μm. The grooved terrain is brighter and has more icy composition than the dark terrain. Galileo results have also shown magnesium sulfate (MgSO₄) and, possibly, sodium sulfate (Na₂SO₄) on Ganymede's surface. These salts may originate from the subsurface ocean. A saltwater ocean is believed to exist nearly 200 km below Ganymede's surface, sandwiched between layers of ice.>>

[b][color=#0000FF]Callista Gingrich explains her husband's moon base[/color][/b]

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<<The average density of Callisto, 1.83 g/cm³, suggests a composition of approximately equal parts of rocky material and water ice, with some additional volatile ices such as ammonia. The mass fraction of ices is between 49–55%. Callisto's surface has an albedo of about 20%. Its surface composition is thought to be broadly similar to its composition as a whole. Near-infrared spectroscopy has revealed the presence of water ice absorption bands at wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0 micrometers. Water ice seems to be ubiquitous on the surface of Callisto, with a mass fraction of 25–50%. Spectral data indicate that the moon's surface is extremely heterogeneous at the small scale. Small, bright patches of pure water ice are intermixed with patches of a rock–ice mixture and extended dark areas made of a non-ice material.>>

[Moonlady]

Neufer, I didnt know that Mrs Gingrich's husband is an elephant!

Are the moons of Jupiter not affected by gravitational instability?

I would like the chance to make a trip to Jupiter, I know earth now long enough, Mars would be dull but hey if someone says come with us, I wouldnt say no.

I would prefer a space station around Jupiter, a big comfy one, with and a lounge for Beyond so he doesn't get left behind!

Ann, you so need an own b.... you know the word! he he

[neufer]

Are the moons of Jupiter not affected by gravitational instability?

• Surprisingly not.

The most remarkable resonance involving Io-Europa-Ganymede includes the following relation locking the orbital phase of the moons:

The Io-Europa-Ganymede Laplace resonance:



where are mean longitudes of the moons. This relation makes a triple conjunction impossible. (The Laplace resonance in the Gliese 876 system, in contrast, is associated with one triple conjunction per orbit of the outermost planet.)

[Ann]

Where would you land if you went to the Jovian system and wanted to choose the safest landing site?

My primary consideration would be for a small distant moon where the escape velocity for the entire moon/Jupiter system would be less than the escape velocity was for the Apollo astronauts; e.g., Pasiphae (moon). (I'd name my spacecraft the Minotaur.)

Pasiphaë about to enter the artificial cow made for her by Daedalus.
Painting by Giulio Romano

Pasiphaë, wife of king Minos, had a spell cast on her by Poseidon, the god of the sea, in retaliation for her husband's refusal to sacrifice a white bull that had been sent to him by Poseidon.

The spell cast on her made Pasiphaë fall in love with one of her husband's bulls. (The white one, the one he had refused to sacrifice, I think.) So she tried to seduce the bull, but his bovine instincts weren't interested. Therefore she approached the master inventor, Daedalus, father of Icarus, and had him make a "cow costume" for her. Dressed up as a cow, she did indeed make the bull interested in her, and later she gave birth to Asterius, also known as the Minotaur.

Ann

[Chris Peterson]

Are the moons of Jupiter not affected by gravitational instability?

Very much so. It is gravitational perturbation and tidal effects that has placed most of them in orbits that are resonant with other moons, and which has tidally locked them into rotational resonance with Jupiter itself. All naturally occurring orbital systems containing more than two bodies are unstable, and will eventually collapse due to the effects of gravitational perturbation.

It is virtually certain that earlier in the history of the Solar System there were more planets (maybe many more), and the gas giants had more moons. But all the planets and moons that were located at positions of greater instability were either ejected or relocated within the system. What's left now, after a few billion years, are bodies in almost stable orbits... which is why the Solar System appears (on our scale of time) to be so stable. But that's an illusion.

[neufer]

Are the moons of Jupiter not affected by gravitational instability?

Very much so. It is gravitational perturbation and tidal effects that has placed most of them in orbits that
are resonant with other moons, and which has tidally locked them into rotational resonance with Jupiter itself.

Tidally locked them into rotational resonance with Jupiter itself

• What exactly does that mean?

All naturally occurring orbital systems containing more than two bodies are unstable,
and will eventually collapse due to the effects of gravitational perturbation.

Define collapse? (And if it takes trillions of years "to collapse" does that still count?)

It is virtually certain that earlier in the history of the Solar System there were more planets (maybe many more), and the gas giants had more moons. But all the planets and moons that were located at positions of greater instability were either ejected or relocated within the system.

Relocated within the system

(Is that some sort of witness protection program?)
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Art (Definitely not N-body) Neuendorffer

[Ann]

Chris Peterson wrote:

It is virtually certain that earlier in the history of the Solar System there were more planets (maybe many more), and the gas giants had more moons. But all the planets and moons that were located at positions of greater instability were either ejected or relocated within the system.

There have been suggestions in the Breaking Space News folder that some really major reshuffling of the planets in the solar system has taken place over the circa four billion years it has existed. I remember, for example, that one astronomer suggested that Mars may be so puny because Jupiter moved inwards during the childhood of the solar system and stirred up the planetesimals that ought to have been fattening up Mars. Then, either when Jupiter and Saturn hit some sort of resonance, or when the solar system disk ran out of gas, Jupiter stopped moving inwards and turned back again.

Ann

[neufer]

Click to play embedded YouTube video.

There have been suggestions in the Breaking Space News folder that some really major reshuffling of the planets in the solar system has taken place over the circa four billion years it has existed. I remember, for example, that one astronomer suggested that Mars may be so puny because Jupiter moved inwards during the childhood of the solar system and stirred up the planetesimals that ought to have been fattening up Mars. Then, either when Jupiter and Saturn hit some sort of resonance, or when the solar system disk ran out of gas,

Jupiter stopped moving inwards and turned back again.

[Ann]

Said by a Swedish teetotaler in the early twentieth century:

-Every time I see a young man leave a bar, I want to shout out to him: "Young man, mend thy ways! Turn back!!!"

Ann

[Chris Peterson]

Tidally locked them into rotational resonance with Jupiter itself

• What exactly does that mean?

I mean they are locked into some resonance between their rotational period and orbital period around Jupiter (typically 1:1, but I think there might be other resonances).

All naturally occurring orbital systems containing more than two bodies are unstable,
and will eventually collapse due to the effects of gravitational perturbation.

Define collapse? (And if it takes trillions of years "to collapse" does that still count?)

Bodies in the system enter new orbits- including hyperbolic orbits that take them out of the system completely. Any period "counts", but models for the Solar System project chaotic instabilities over a time scale of several tens of billions of years, not trillions.

It is virtually certain that earlier in the history of the Solar System there were more planets (maybe many more), and the gas giants had more moons. But all the planets and moons that were located at positions of greater instability were either ejected or relocated within the system.

Relocated within the system :?:

In some cases. The Nice model certainly requires in-system relocations. But more general simulations (reported in these forums not long ago) suggest that more than half of the planetary bodies produced in a new system are ejected into interstellar space quite early in the evolution of the system.

[Moonlady]

Thank you for the explanation!

Unfortunately I see my spelling errors too late, it should be "effected" and not "affected", hmmm I was reading a novel before, really

[geckzilla]

Affect was correct, actually.

[Ann]

Ann wrote:

(And what do you call those bluish fan-like cloud patterns on Jupiter? I know they have a name, but I can't remember it!)

Festoons on Jupiter.
Photo: Ed Grafton

Hah! I remember what they are called. They are called festoons! Read the fourth paragraph here!

Ann

[neufer]

Festoons on Jupiter.
Photo: Ed Grafton

(And what do you call those bluish fan-like cloud patterns on Jupiter?
I know they have a name, but I can't remember it!)

...................................

Hah! I remember what they are called. They are called festoons!
Read the fourth paragraph here!

[b][color=#0000FF]Spanish Festoon[/color][/b]

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[b][color=#0000FF]Southern Festoon[/color][/b]

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<<A Festoon (from French feston, Italian festone, from a Late Latin festo, originally a festal garland, Latin festum, feast), is a wreath or garland, and so in architecture a conventional arrangement of flowers, foliage or fruit bound together and suspended by ribbons, either from a decorated knot, or held in the mouths of lions, or suspended across the back of bulls heads as in the Temple of Vesta at Tivoli. The motif is sometimes known as a swag when depicting fabric or linen. The design was largely employed both by the Ancient Greeks and Romans and formed the principal decoration of altars, friezes and panels. The ends of the ribbons are sometimes formed into bows or twisted curves; when in addition a group of foliage or flowers is suspended, it is called a drop or margent. Its origin is probably due to the representation in stone of the garlands of natural flowers, etc., which were hung up over an entrance doorway on fête days, or suspended round the altar. The motif was later used in neo-classical architecture and decorative arts, especially ceramics and the work of silversmiths.>>