Space Voyage #1 Chatter

[TheBigDog]

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]

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]

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]

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.

[Pyrotex]

(continued) 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.

[ronthepon]

What do you guys think of... um... less developed life forms?

[TheBigDog]

I was also thinking that the light source on the planet could be prismatic aurora. So while the brown dwarf is like an ember in space with almost no light, its radiation causes the planet's atmosphere to glow. This is also why the planet was visible, because it is actually brighter than the star it orbits.

 

This is of course hypothetical. While the methods of finding the planet and dwarf in the story may not be realistic, and the probability of these things happening may be remote, my contention is that we are continually suprised by what we actually have found as we explore new places. And that all we need for the sake of the story is plausibility.

 

When I said that the planet was earth like, what that meant was that the chemical and heat signatures and the mass are all within 5% of the earth. That doesn't mean it is habitable. Part of this whole exercise is the exploration of the ideas of space exploration. Walking the process, and trying to use our imaginations and our intellect to make the process more real. Along the way we are throwing in some intreague and sci-fi stuff. But that is in the nature of keeping it fun.

 

So, given the couple of ideas I threw into play, the Janus objects and the planet/dwarf combination, how do we utilize this information in the story? The facts that everyone is bringing up should be confirmed by our research in the story. How would the news of an "earth twin" play out among the crew and on earth?

 

This is a great vehicle for learning about space. And it should be fun along the way.

 

Bill

[Janus]

I was also thinking that the light source on the planet could be prismatic aurora. So while the brown dwarf is like an ember in space with almost no light, its radiation causes the planet's atmosphere to glow. This is also why the planet was visible, because it is actually brighter than the star it orbits.

 

 

 

Bill

 

This would be akin to fluorscence. However, in fluorscence it is higher energy radiation, such as ultraviolet, which is absorbed and then released at a lower energy as visible light. Our brown dwarf will emit little or no ultraviolet to drive fluorescence.

 

I know of no mechanism that would allow the process to go the other way - absorbing lower energy radiation (infrared) and re-emitting it as a higher energy radiation (visible light).

[Janus]

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.

 

At those distances the tides would range from between 50 to 6 times ours (tidal forces vary by the cube of distance), But I understand what you're getting at.

 

The question is whether you can find that perfect balance of far enough away to prevent tidal locking, yet close enough for the tidal forces to compensate for the loss of radiant energy from the Sun through geological heating, While at the same time not having so much geological activity that the atmosphere isn't choked by volcanic ash and gases. How much geological activity is needed for a particular rise in surface temperture?

[Jay-qu]

What if there was a larger planet, tidally locked to the BD and it had a moon, could the moon be more habitable?

[Janus]

What if there was a larger planet, tidally locked to the BD and it had a moon, could the moon be more habitable?

 

Let's examine that.

 

Say we have a Jupiter-sized world orbiting at 4,000,000 km (in the Habitable zone), with an earth sized moon orbiting it.

 

First we'll establish the orbital limits of the moon's orbit. The Roche limit would be around 110,000 km and the Hill sphere limit a little under 600,000 km.

 

This would put the period of the moon at between 6 hrs and 3 days. The moon would be likely to be tidally locked to the planet, so this would also be the length of its (sidereal)"day".

 

The moon would still be subject to tides from the BD, so it will be subject to a lot of tidal heating, and if its a ocean covered world, huge ocean tides. ( I'll talk more about these later)

 

Another issue is that, with the planet being tidally locked to the BD, the moon's period will be shorter than the planet's "year" of about fourteen days. (incidentally, this makes the synodic period of the moon a little longer than the sidereal period I gave for the moon's day above. For instance, the Synodic (noon to noon) day for the 3 day orbit would be 3.8 days.)

This situation causes the reverse of what happens with our moon, this moon would spiral in towards the planet over time.

 

With the much stronger tidal interaction between the two bodies, I think that it is safe to assume that this process will occur much faster. If we assume that it happens 10 times faster, this means that it wold take about 1.25 billion years for the moon to go from its furthestmost orbital distance to inside the Roche limit where it would break up into a ring. (it could be more or it could be less). This means that such a world would have to be younger than the Earth.

 

 

Now let's go back to those ocean tides. The oceans would be subject to two tides, that caused by the BDm and that caused by the planet itself. The planet would cause tidal bulges that stay stationary with respect to the moon, always pointing away from and towards the planet. These bulges would be quite high, measured in kilometers. This would result in most or all of the dry land to exist in a band at the "low tide" points.

The BD adds a complication to this as the moon orbits the planet. At various points of thre orbit, its tidal effect will either add to or subtract from the tidal bulge formed by the planet. The effect would be that the width of our band of dry land would vary over the course of a day, Possibly by as much as tenss or hundreds of km. This would make for a very fast tide. (for instance, assume that the length of the day is 90 hrs ( about the maximum possible length) and the tidal zone was 50 km wide. The tide would have top go from low to high in 22.5 hrs, meaning it would have to travel at about 2 km per hr.

This is a slow waliking speed. This would also mean that a "oceanview" would actually only be able to see the ocean for a small fraction of every day.

 

Also we still need to consider the tidal heating and geological activity this creates, so we might have to move our whole system outwards from the BD to compensate.

[TheBigDog]

This would be akin to fluorscence. However, in fluorscence it is higher energy radiation, such as ultraviolet, which is absorbed and then released at a lower energy as visible light. Our brown dwarf will emit little or no ultraviolet to drive fluorescence.

 

I know of no mechanism that would allow the process to go the other way - absorbing lower energy radiation (infrared) and re-emitting it as a higher energy radiation (visible light).

This brings us a nice possibility to the story: illimination of the planet than cannot be explained. If this were the case, would it not compell us to want to explore it further?

 

Otherwise, is it possible for the BD to emit higher level energy, but not in the visible spectrum?

 

Bill