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The Astronomy Thread 
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Joined: Fri Sep 23, 2011 9:33 pm
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Post Re: The Astronomy Thread
Well Karst, that depends on two things:
1) Is your instrument sensitive enough to measure the interaction?
2) Are you personally sturdy enough to survive the slap when the girl realizes that you were weighing her?


Sat Oct 26, 2013 8:02 pm
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Post Re: The Astronomy Thread
Second post, and allow me to put my 2 cents into the earlier discussion about Mars's magnetosphere :) . For those interested :

http://www.newmars.com/forums/viewtopic.php?id=6122&p=1

It seems that making a magnetosphere would not be such a challenge for a human civilization as described in Outsider. To quote orionblade :

"I have done some back of the envelope calculations on this very topic recently, and I will post merely the results - if anyone's interested in seeing the actual calculations, I don't mind scanning and posting an image of my notes at some point.
In any case, I assumed the worst - a single loop of "wire" - the most malleable/ductile superconductor we have currently is niobium-tin, or in some cases niobium-tin-copper compositions. Assuming this is a single large cable to be unspooled in orbit around Mars, "spun up" as an MRI machine's magnet is powered up, and the whole thing encased in a fairly thin, thermally insulating conduit, and provided with a solar shield around its periphery, this should be able to maintain a low orbit at roughly 200-250Km.
I chose this altitude, versus geostationary, since we want to use the lowest current possible to generate a magnetic field, and the least amount of material possible. Further, the rotational motion of the coil relative to the spin of the planet may add a bit to the effective current, if only a negligible fraction.
My calculations left me somewhat disappointed: For an Earth-equivalent field of roughly 70 gauss, a one-meter diameter niobium-tin alloy superconducting cable, assumed to be solid for purposes of calculation, cooled with liquid helium, would be sufficient, but would require roughly 100% of our annual worldwide niobium mine output for a period of roughly a century, and nearly 10 years worth of Tin production. Taking into account mines that are planned or currently under construction, this could be reduced to roughly 65-70 years. The cost is astronomical, just for materials.
On the bright side, this technique is aided by the damn-near absolute-zero of outer space, so the portion of the cable eclipsed by the planet's shadow should provide enough cooling to allow something as simple as peltier junctions mounted every few meters to counteract any solar irradiation incurred beyond what a properly-spaced reflector could not handle on the day side. Since the whole cable would ride through the shadow every 90 minutes or so, and the solar shield/reflector could be composed of solar panels, the feasibility, if not the initial cost, becomes evident.
Further, the calculations assume that there is absolutely no planet in the middle of the coil. Since Mars has quite a bit of iron through its surface, mantle, and core, presumably, this would become a ferromagnetic core, increasing the field strength. Also, I neglected any plasmadynamic effects. If the field were caused to oscillate, or even held steady, but allowed to gather energy as an electric guitar pickup does, from the moving, time-varying plasma current, one could assume that the power for the coil could be had on-site, and only a minimal current required for start-up, with the current building in opposition to the solar wind, so long as seasonal variations were somewhat sizeable. Depending on the effective permeability of the planet as a magnetic core, the entire thing might well be scaled down by an order of magnitude or two. Further, with vastly superior deflection of electrons than protons, an electron-rich solar wind would allow the induced electric field to do most of the work. Another concept I failed to explore further, mathematically, would call for a non-single-loop coil geometry. Multiple turns wouldn't get you very far, but a helical or interlaced loop geometry could enhance local field strengths such that the aforementioned plasmadynamic effects could yeild a higher electric field strength, and thus better shielding. In any case, any shielding effected would be better than nothing, and the atmosphere should build.

Please consider this one key fact that is often overlooked: Mars' atmosphere is in a state of dynamic stability - it is continually losing atmospheric gas to nonthermal loss mechanisms, yet its atmosphere continues to remain at a stable, if low, pressure and density. If we inhibit even a small fraction of the loss, the atmosphere would build. If on the other hand, we build the atmosphere, we will be losing, perhaps the same percentage, but much more of the atmosphere. We'll be driving the reaction towards loss by adding gas to a lossy system. If we instead reduce loss mechanisms, the gases will add themselves, from whatever surface or subsurface sources are already in operation (anyone notice the detection of subsurface Methane sources not too long ago?). I'll have to look up the effective velocities, and calculate turning angles required for various orbits, perhaps writing up a system of equations and optimizing them for minimum material required (low loop current vs. shorter cable). It may very well be that a geostationary ring would require vastly lower current to achieve an adequate turning angle of maximum solar wind velocity, since it is further from the planet, or it could be that we would be better off with a larger diameter cable much lower in orbit, permitting a larger field but with considerably less cable length to encircle the planet at a lower altitude.
Either way, i would point out that any solution with a multitude of orbital components that are not physically connected, will be subject to magnetic attraction, or at least torques, which would require continual energy input to overcome. I think a single loop, or some variation on this Dyson-like ring is a better bet, since the loop would auto-inflate to a nearly perfect circle under the influence of its own magnetic field, much like a loop of string floating on a soap bubble. Individual magnets would pull together, and multitudes of loops would at the very least rotate to become a toroidal magnetic field, and the gaps between the loops would actually cause a degree of focusing.
It has also occurred to me that a slightly weak magnetic field might result in protection near the tropics, but deposition of solar wind components near the poles - thus heating the poles somewhat, but also adding hydrogen and helium to the atmosphere. Admtitedly, these would boil off rather quickly, but there should be enough radical production that water vapor would be created, and gravitationally retained within the atmosphere... I am uncertain as to the equilibrium state with high incidence angles for stellar wind particles on the atmosphere, if they would eject atmospheric particles more, or if they would be captured at a greater rate than the loss mechanisms... it's an interesting mathematical problem."

Seems like all we'd need is some tin and niobium. Well.....lots of it.


Tue Oct 29, 2013 1:09 pm
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Post Re: The Astronomy Thread
hi hi

Maybe if you put a magnet around the surface, or drilled a bore hole through the poles it might be more feasible, but solid ring structures are inherently unstable. It would be very difficult to keep the thing in place, as perturbations will have positive feedback in pulling the ring out of position.

Mars does have a very weak electromagnetic signature, which is left over from the last time it had an active magnetic field. Scientists can use this as one of their means to calculate how long ago the magnetic field failed, as meteor impacts damage the local magnetic field.

Lastly, the assertion that Mars' atmosphere is dynamically stable is debatable. While there is some level of conjecture involving Mars' historical atmosphere, the models that I have seen suggest that Mars will eventually lose its entire atmosphere.


Tue Oct 29, 2013 2:38 pm
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Post Re: The Astronomy Thread
For a project like this, a century's worth of current production of any material should probably be considered quite cheap, since we're presumably talking about something that would be done only once a large volume of either Mars-based or space-based production capacity is built up.

As for orbits, if you're willing to shuffle Mar's moons around then you might be able to implement a shepherd pair to keep the ring in position. If you're willing to move Ceres, then you can use it to keep them in position with fewer maintenance needs (it could also help stabilize Mar's eon-scale orbit).

Of course, if you aren't willing to do all of this, you could also go the Transmetropolitan route, by building tall arcology structures that support a dome structure to hold in air, gradually enlarging the covered area until you get the whole thing.


Thu Oct 31, 2013 1:22 am
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Post Re: The Astronomy Thread
Cassini image from the shadow of Saturn (click for larger image). It's interesting that you can see stars in this image, which gives you an idea of how low the light level is.

Image

http://www.jpl.nasa.gov/news/news.php?release=2013-329
http://www.jpl.nasa.gov/spaceimages/det ... d=PIA17172

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Tue Nov 12, 2013 11:24 am
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Post Re: The Astronomy Thread
see that dot right below the right side of saturn rings?
that us! :D


Tue Nov 12, 2013 3:13 pm
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Post Re: The Astronomy Thread
This I can't think of any place better to announce I still live... Ohhhh, Saturn! A most awesome picture!


...Also; Telepanties.

That is all.

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Sun Nov 17, 2013 5:12 pm
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Post Re: The Astronomy Thread
A video of comets ISON and Encke taken from the solar observatory spacecraft STEREO-A. You can clearly see the solar wind and how it drives and interacts with the comets' tails.

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Sun Nov 24, 2013 12:14 pm
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Post Re: The Astronomy Thread
With a little luck (read, no breakup of the comet), I'll have a good chance at seeing it first hand when it rounds the sun. ;)

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Mon Nov 25, 2013 4:42 am
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Post Re: The Astronomy Thread
Awesome!

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Wed Nov 27, 2013 10:46 am
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Post Re: The Astronomy Thread
GeoModder wrote:
With a little luck (read, no breakup of the comet), I'll have a good chance at seeing it first hand when it rounds the sun. ;)



care to elaborate on that?


Thu Nov 28, 2013 7:16 pm
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Post Re: The Astronomy Thread
I simply flew to a place with less chance of cloudy weather. Sofar, I feel rain here, which is pretty rare. :(

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Fri Nov 29, 2013 12:24 pm
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Post Re: The Astronomy Thread
hi hi

Something interesting I just saw in the papers today. The IceCube South Pole Observatory has detected several neutrinos that are thought to have come from outside the solar system, and possibly outside of the galaxy. At about a billion times more energetic than the neutrinos detected from our Sun, it'll be interesting to find out what could have produced them.

Unprecedented Neutrino Discovery


Sun Dec 01, 2013 4:27 pm
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Post Re: The Astronomy Thread
I think the assumption is that they're from a galactic core black hole, or a distant gamma-ray burst.

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Sun Dec 01, 2013 8:38 pm
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Post Re: The Astronomy Thread
Recently discovered HD 106906 b is a newly-formed gas giant (still glowing from the heat of its formation) of some 11 Jupiter masses, orbiting at a whopping distance of 650 AU (more than 20 times the distance of Neptune). It is the most distant planet from its primary yet discovered.

The system primary is an F5 pre-main-sequence yellow-white star of 1.5 solar masses. The system is very young, about 13 million years old.

Image

The astronomers seem puzzled at how such an object can have formed so far from the primary, but it seems to me that it has to be the same process by which binary stars form. It's possible that the planet's orbit may be very eccentric, and that it passes much closer to the primary than it is currently. In our own solar system, the dwarf planet Sedna has an aphelion of 937 AU (perihelion is 76 AU), so these distances are not unheard of.

Compare Kappa Andromedae b, at 55 AU and 12.8 Jupiter masses (the system primary is a 2.5 solar mass B9 blue-white subgiant).

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Fri Dec 06, 2013 1:03 pm
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Post Re: The Astronomy Thread
Yeah, 11 Jm's is getting close to the boundary between gas giants and brown dwarfs.
Another possibility of course is that this planet is a captured wanderer.

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Sat Dec 07, 2013 1:09 am
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Post Re: The Astronomy Thread
GeoModder wrote:
Another possibility of course is that this planet is a captured wanderer.

If it were captured, it probably wouldn't still be glowing from the heat of formation.

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Sat Dec 07, 2013 2:46 am
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Post Re: The Astronomy Thread
True... unless it came from another nearby young star system. 13 million years sounds young enough in order to still float near the rest of its 'birth siblings'.

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Sat Dec 07, 2013 5:45 am
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Post Re: The Astronomy Thread
hi hi

If it didn't form in that orbit, I would say it is more likely that orbital interactions with other planets pushed it into the higher orbit. Little nudges can really build up over time, especially before everything has a chance to settle into a stable place.


Sat Dec 07, 2013 8:48 am
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Post Re: The Astronomy Thread
Galactic ballet, in music
http://www.youtube.com/watch?v=eF02Nhix ... E5&index=5
More in same youtube playlist. YMMMV


Thu Jan 30, 2014 12:58 am
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Post Re: The Astronomy Thread
Found a little simulator of galactic proportions :)

www.youtube.com/watch?v=3bH4KleneFM

http://en.spaceengine.org/


Thu Feb 27, 2014 3:41 pm
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Post Re: The Astronomy Thread
As it passed in front of a star, the centaur asteroid Chariklo revealed that it has rings.

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Wed Mar 26, 2014 1:31 pm
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Post Re: The Astronomy Thread
Should make a fine target for an Asteroid Mission. :mrgreen:

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Thu Mar 27, 2014 9:15 am
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Post Re: The Astronomy Thread
GeoModder wrote:
Should make a fine target for an Asteroid Mission. :mrgreen:

I think they'd want one that's a little closer. This one is between Saturn and Uranus.

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Thu Mar 27, 2014 10:57 am
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Post Re: The Astronomy Thread
I know. Let's get us some really advanced propulsion... :mrgreen:

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Fri Mar 28, 2014 9:03 am
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