Space Voyage #1 Chatter

[Janus]

I thought this might to bring up some technical points that have come up in recent posts to the Space voyage thread.


The Janus objects

It is extemely unlikely for Io to have four moons of its own for the following reasons:

1. The Hill sphere(the region where moons could exist.) for Io only has a radius of about 10,000 Km. This makes for a small target that any object captured by Io would have to hit.
2. The difference between Io's orbital velocity and escape velocity at Io's orbital distance is greater than Io's surface escape velocity. This means that any object falling in towards Jupiter would be moving too fast to be captured by Io. In order For Io to capture it, it would have to been slowed down by interaction with one or more other moons first.

These two facts combine to make the capture of any object as a moon of Io a very rare.

3. Any moon orbiting Io would be subject to perturbation by other moons.
Io orbits in periodic resonance with Europa and Ganymede. Thus, any perturbation caused by these bodies. Would occur at the same point of Io's orbit. This periodic tugging would eventually disrupt Io's moons out of the Hill sphere.

4. Io's volcanos generate a dust and gas ring that orbits Jupiter with Io.
A fraction of the gases expelled by these volcanos actually reach escape velocity and orbit Jupiter. A moon of Io would have to orbit through this "smoke ring". Over time, the drag would cause its orbit to decay, falling into Io.

Given the low incidence of capture, and the tendancy for captured objects to either drift away or fall into Io, It would be rare to find even one object orbiting Io, let alone four.

One possible solution to this would be that the Janus objects were all captured at once; possibly all that remains of a piece of a comet captured by Jupiter and then Io. They could have been contained in a chunk of frozen gasses ans Ice, which then melted. When the chunk melted in left behind these bodies which then drifted in to their present orbits. There may have been more originally, but these four pieces are now all that are left. As it is, we were lucky to arrive while anything was left at all.

Next post I'll discuss the Brown Dwarf.

[TheBigDog]

Originally Posted by Janus

Next post I'll discuss the Brown Dwarf.

I look forward to it. I had actually been thinking that the four Janus objects might have been from Io itself. Either as a result of impacts, or from extreme volcanic eruption. Would that be a possibility?

Bill

[Mercedes Benzene]

I'm planning on posting an entry soon for the story...

...that is once I find a sufficient amount of time in my full schedule.

[Jay-qu]

I already discussed the issue of the brown dwarf with BD. For it to be practically invisible from Earth it would have to be very small, Im not sure how small, but im thinking that it wouldnt even be burning hydrogen. Technically we shouldnt have been able to see the planets either, no extra-terrestrial planets have been imaged directly yet and even if our new scope was powerful enough, the star isnt throwing out enough light (or IR) to be seen so easily.. Perhaps by saying they are incredibly close to the star, but then you have problems with Roche limits ect...

[Janus]

Originally Posted by Jay-qu

I already discussed the issue of the brown dwarf with BD. For it to be practically invisible from Earth it would have to be very small, Im not sure how small, but im thinking that it wouldnt even be burning hydrogen.

Well, that is the definition of a Brown Dwarf; A failed star that never initiated fusion at its core.

Technically we shouldnt have been able to see the planets either, no extra-terrestrial planets have been imaged directly yet and even if our new scope was powerful enough, the star isnt throwing out enough light (or IR) to be seen so easily.. Perhaps by saying they are incredibly close to the star, but then you have problems with Roche limits ect...

Yes, they would have to be close, not quite Roche Limit close, but close.

[Janus]

The Brown Dwarf

While Brown dwarfs are detectable by a Hubble equivalent telescope, the accidental discovery as described in the story really couldn't happen. The problem is that the dim Brown dwarf just would not show up in an exposure that was meant for the small moon. The moon is moving, so a short exposure is needed to prevent motion blur of the image. A short exposure period would not be long enough for the Brown Dwarf. Remember, this is an object dim enough to have been missed in all previous sky surveys to date. It would take an extended exposure to bring it out. ( In fact, many of those fantastic deep space images we see from Hubble are the results of exposures of weeks or even months.)

As JQ has mentioned, the planets, being even dimmer, would take even alonger time to image. I share his misgivings of being able to image such planets.

As to planets around Brown dwarfs, we have discovered at least one Brown dwarf with a planetary disc, so it is a possibility. It is even possible to have "habitable" planets around such a star. By "habitable" I mean planets in that zone where water could be liquid.

As to what conditions would be on such a world, let's consider that Brown Dwarf already mentioned. It has a mass of 15 Jupiters (Brown dwarfs mass from about 10 to 70 Jupiters.) and has a surface temp of 2000°K
This would put the middle of the Habitable Zone at about 4,000,000 Km from the star and give the planet a "year" of about 14 days.

This would be be well outside the Roche limit, but close enough for tidal effects to still be quite strong. In fact, the tidal forces would be around 780 time larger than those our Sun has on us. This is enough to ensure that this planet would be tidally locked. Being tidally locked would give the planet quite a strange climate as very strong convection currents would travel from the day side to the night side (it might even get cold enough on the dark sdie for the very air to freeze).

If the planet wasn't tidally locked and somehow maintained some rotation, the extreme tidal stresses would make it very geologically active place.( just look a what just a little wobble does to Io)
You would also get kilometer high ocean tides sweeping over the land.

All in all you would not get what one would call an "Earthlike" planet.

Another factor to consider is that Brown dwarfs, with no fusion at their cores to maintain temp, cool with time. As they cool, the habitable zone moves in closer to the star. I'm not too sure whether any given planet would stay in that zone long enough to develop life forms.

[Jay-qu]

The wavelength of a black body at 2000C as determined by Weins law would be = 1.3 micrometers, thats in the Infrared range.. while you can have a habitable zone (which is just in terms of liquid water..) how habitable would it actually be to live in an infrared enviroment?

[Janus]

Originally Posted by Jay-qu

The wavelength of a black body at 2000C as determined by Weins law would be = 1.3 micrometers, thats in the Infrared range.. while you can have a habitable zone (which is just in terms of liquid water..) how habitable would it actually be to live in an infrared enviroment?

Right. Another reason that I forgot to mention as to why such a planet would not be "Earthlike".

[TheFaithfulStone]

Okay, don't forget about the Mind-Control robots.

And the AI.

And the rest of the sci-fi junk we've made up.

Maybe we just need to "reboot" the thing, and say - "Oh my god, we've all been having some kind of mass hallucination since we left Earth orbit."

Oh noes! It's teh crazy!

tfs

[Pyrotex]

Originally Posted by Janus

The Brown Dwarf
...the tidal forces would be around 780 time larger than those our Sun has on us. This is enough to ensure that this planet would be tidally locked. Being tidally locked would give the planet quite a strange climate as very strong convection currents would travel from the day side to the night side (it might even get cold enough on the dark sdie for the very air to freeze)....I'm not too sure whether any given planet would stay in that zone long enough to develop life forms.

I can see a scenario that might work. The planet could be in an orbit, say, 10M to 20M km of radius. This might allow a rapid rotation for a small, dense planet. The tides would still be huge (~100 times ours) and would tend to gouge deep canyons around the planet parallel to its equator. Tidal stress on the planet's interior would heat the surface enough to make up for loss of radiant energy from the BD. Given such rotation, temperatures would be fairly even all over, with only slight cooling at the poles of rotation.

There would be no visible light, therefore, no eyes as such. But our critters may have an array of IR receptors on their "carapaces" and they may act like an IR interferometer, enabling detection of objects and motion at some remove, without actually forming "images" which would require hugh imaging structures.

There would be no visible light, only IR. Therefore, no eyes. However, our critters, if they were say, a meter across, might have IR receptors that acted like an IR interferometer. This would give them the ability to detect objects and motion at some remove without the necessity of huge imaging eye structures.

There would be hot spots, perhaps even small volcanic vents, and it would be around these that life might emerge, just like the "smokers" found in our deepest ocean trenches. As the BD cooled, this embrionic life would evolve to cope, crawling or crabbing around in heavily insulated "coats" that might look like a cross between tree bark and styrofoam.