But you can only wedge one these things if they're holding still. A moving rock would need a moving wedge to be effective.
I can envision a system of gates, not unlike locks and dams, to catch a runaway stone. But I also think that those would probably work better on a square-edged stone.
As for Einstein, you're neglecting to mention that he was a patent clerk *with a Ph.D. in physics.* He wasn't some random guy who stumble across relativity, he was a well-trained scientist who had difficulty finding a job (or at least, one he liked) in academia.
No, I think the doubt there is at the idea of *rolling* 2-ton blocks uphill. All it takes is a split second of lost grip on the rock and the vaunted "rock's momentum" suddenly becomes a nightmare.
Remember Sysiphus? It'd be like that, but with a lot more screaming and generally getting smooshed.
Speaking as an actual planetary scientist, we often use "solar system" for planetary systems outside out ours. And we refer to their stars as "suns" rather often, too. As long as you capitalize the proper noun version and not the general term, it's pretty obvious what you mean.
(For that matter, we talk about Jupiter's "moons" a lot. Given that there is only one "the Moon", that shouldn't be, either. But it is, so just get used to it.)
My first reaction upon reading the title mof this article was, "Oh, no. Did the forget the Doppler Shift? Again??" But maybe that's from being a bit too close to the Cassini goings-on.
Incidently, I liked how they said that Mars Express will arrive at Mars "sometime in December". I'm hard-pressed to imagine that they don't have the dates down better than that. (Or was someone just too lazy to look it up?)
Hm, Mitch must have said it in the actual lecture, then.
Then read the book. It's a good read, anyway.
In any event, the event horizon need not be a sphere for the simple reason that you're not worried about how far from the singularity you are, you cannot know that. (Information cannot propogate outward from inside the horizon to any point further out.) What you care about is local spacetime. Since spacetime gets dragged by spinning objects, there is no real reason to expect spinning black holes to look like non-spinning ones.
Re:Theoretical maximum for common stellar material
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Non-Spherical Stars
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· Score: 1
Uh, it isn't a different rotation rate in the interior that creates the Great Red Spot. It's solar and internal heat, causing convection, and the spin, causing belts and zones. Admittedly, the GRS isn't totally understood, but a differentially rotating interior doesn't seem to be required. (As for whether the interior does rotate differentially, it's kind of hard to say. Since you have the belts and zones moving at all different speeds, it turns out to be difficult to define a rotation period for the cloud level. At least 2 attempts were made to define a rotation period based on the clouds, but the rotation period cited is usually the interior rotation perdio. The interior is easy to clock, thanks to the magnetic field and the radio emissions due to it.)
That said, of course you don't expect a star to be rotating as a solid body. As you suggest, there's no reason it has to. But you can make an easier, and far better, case if you just point to the Sun. The Sun's rotation period varies from equator to poles (the equator is fastest, which doesn't help a star stay together any). The interior also rotates differentially, as determined by some of the GONG results.
"Black Hole" isn't a terrifically well-defined term when you come right down to it. If you mean the thing in the middle (the "matter"), that's the singularity. It can have no real shape, as it is, as far as we can figure, a point. (The math goes all wonky, so it's better not to ask too many questions of theorists, as they tend to get kinda touchy about this.) If you mean the edge of where all hell breaks lose, then you're referring to the event horizon. (Formally defined as the point of no return, where spacetime is falling into the black hole faster than the speed of light.) Usually, that's what you care about with a black hole. (Particularly as theory has little to say about the singularity and observations have even less to tell us. And, for that matter, it's the event horizon you need to avoid. If you're dodging the singularity, you're already dead.)
Now, as for the shape of the event horizon, I'm sorry, you're flat out wrong. A spinning black hole will be sqashed at the poles and bulged at the equator. The case of a spinning BH is the Kerr solution to Einstein's equations and it clearly shows this. See http://astronomy.colorado.edu/astr2030/Kerr_files/ v3_document.htm I'd further suggest Kip Thorne's book ("Black Holes and Time Warps"), an excellent read which covers an amazing about of black hole theory while remaining thorougly readable.
Re:Theoretical maximum for common stellar material
on
Non-Spherical Stars
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· Score: 1
A star like the Sun will only convert about 0.01% of it's mass into energy over its entire lifetime. (According to my quick, back of the envelope calculation.) Which means you still have to form very close to the breakup spin rate. Which is still quite difficult to pull off, saith the dynamicists. (The same problem comes up in fusion-formation models of moons.)
Re:Theoretical maximum for common stellar material
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Non-Spherical Stars
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· Score: 4, Interesting
I believe a star has zero tensile strength* (it's just a fluid), so once you're spinning too fast for gravity to hold you together, it's bye-bye time.
The better question is this: how did that star form? If it was spinning too fast to hold together, how did it accrete matter with that much angular momentum at all?
* Barring magnetic fields, mind you. But you'd need an ass-kicking field to hold a star together very long, I would think.
Re:Black holes must be flat dishes
on
Non-Spherical Stars
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· Score: 2, Informative
Er, I don't beleive so, no. You're restricting yourself to the Schwartzschild solution, there. Schwartschild assumed that the black hole wasn't spinning and was uncharged. So of course it's spherically symmetrical, there's nothing to break the symmetry.
Real black holes are likely to be spinning. And then they aren't spherical, as I recall. Also, their horizons start to seperate. Things get a *leeetle* bit weird from there on out.
Actually, there is only one orbital resonance amoung the "planets", and that's the Neptune-Pluto 3:2 one. If I recall my relative positions at Pluto's perihelion correcltly, and if I've done my math right, when Pluto is at its average distance, Neptune is never in the area.
Re:Where's it coming from?
on
Summer on Neptune
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· Score: 2, Informative
Jupiter could never have been that large. It would have had to enveloped all of the inner moons, including the 4 Galilean ones.
I've done the integration and calculation for a homogenous Jupiter (constant density), and the planet would have to have been 25% larger 4.5 billion years ago to have produced the current energy excess that we see today for its entire life. This isn't terribly unreasonable, especially since the transiting extra-solar planets that we've seen have somewhat larger radii than Jupiter does. (The planets can't expand when they get closer to their stars, but they are prevented from contracting as far as Jupiter, say the modellers.)
In fairness, I should note that there are those who think Jupiter's energy excess is due to it's energy of accretion which hasn't leaked out over the past 4.5 billion years. I usually hear the contracting explanation, though.
Re:Where's it coming from?
on
Summer on Neptune
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· Score: 2, Informative
No, the extra-solar planets were a bit of a shock and a sticking point for a bit. But I think most planetary scientists are confident that the giant planets simply migrated inward as part of the formation process. (There were proposals for this years before the first exoplanet was discovered.) The details are still unclear, but I think there's a reasonable consensus that the model still works.
And you're exactly right about the detection method (Doppler shifts in the stars): it's biases towards massive planets with eccentric orbits and small semi-major axes. What we've found isn't likely to be a representative sample.
Re:Where's it coming from?
on
Summer on Neptune
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· Score: 4, Informative
Jupiter does indeed emit about twice as much energy asn it absorbs (not reflects) from the Sun. This indicates an internal heat source. "Core temperature" isn't a very accurate description, based on what we think is going on, though. Jupiter isn't a failed star, especially in the standard planet formation scenario where it forms an icy core before accreting gases. So don't look to fusion to create the heat, the planet's structure is likely (we're not absolutely certain that there is a core) wrong for that. What powers Jupiter is probably slow, continued contraction. As the planet shrinks, it loses gravitational energy and emits that as heat.
Saturn has the same input/output disconnect. In the case of Saturn, I believe that the current model is helium rain. (Also releasing gravitational energy.) And Neptune also emits more energy than it takes in. (Oddly, Uranus doesn't.) Neptune's heat source is somewhat more ambiguous, but helium rain could be it. However, we know that Uranus and Neptune have very large icy cores (well, large proportional to their overall size), so there is definately no fusion there. It's doubtful that the core could be responsible for the extra heat, since there aren't many ways for ices to generate heat.
"Astrobiology" is the term that is usually used in such circles. We actually discussed this the first day of graduate Astrobiology a couple of years ago. The term "exobiology" seems to have fallen by the wayside for whatever reason. (Possibly because "astrobiology" gives an immediate sense of what the field is, while "exobiology" leaves many people wondering "outside of what?")
"So far, all we have seen of Titan is the Orange clouds circling the planet."
If you only count visible wavelengths, true. But we have images from a few other bands, mainly radio and infrared. These can make it to the surface, allowing us to do some sorts of mapping.
I can't find the Science paper referenced (it doesn't seem to have hit the website yet), but from what I'm reading at the BBC site, this isn't news. We've had IR observations of Titan for at over a decade now. (Heck, Griffiths was the author of the papers.) That the surface of Titan wasn't purely methane/ethane oceans was an immediate conclusion from those data. (They also determined that there was a significant amount of water ice on the surface. Which might be what they BBC article means by "like Ganymede".)
I'll have to wait to see the paper to see what's new about their results, but I haven't heard anything yet that I haven't heard before.
That's what I would have thought. But the article very distinctly says "launch" in reference to Nozomi. It also talks about June. (The arrival of the Nozomi-in-transit is December of this year. Which means the fun won't really begin until 2004.)
Which isn't to say that they might not launch a new one in June, I suppose. NASA didn't wait for Voyager 1 to return science data before launching Voyager 2. (Come to think of it, they didn't wait to LAUNCH Voyager 1 before launching Voyager 2. Ah, the subtlties of spacecraft trajectories and timing.) For that matter, NASA has often had more than one mission to Mars in transit/at Mars. (Hence the back-to-back failures in the fall of 1999.) The Japanese space administration might feel that they've learned enough from the first Nozomi to launch a second one.
Call me confused, but I thought Nozomi was already well en route to Mars, having launched in 1998. (It's taking longer than intended to get there due to some technical difficulty; I think they blew too much propellant early on, but don't quote me on that.) I haven't found anything on a second Nozomi mission with Google. Anyone know anything about this new mission?
Yep, they're almost certainly captured. But their lifetimes are probably a lot longer than you think. Tidal effects depend on the mass of the moon creating the tidal bulge and the proximity to Jupiter. Small, distant moons don't raise much in the way of tides and feel little in the way of higher order gravitation moments from Jupiter. So they don't evolve tidal very quickly at all. I'd guess that it would take billions of years to get them in close to Jupiter. In fact, the effects of other bodies (moons, other planets, etc) probably overwelm the tidal effects.
Without tides, retrograde moons are a lot *more* stable than prograde moons. Hamilton and Krivov have a paper where they discuss some of this, but retrograde moons are stable out to about a Hill radius (half an astronomical unit, in the case of Jupiter), while prograde moons are only stable out to about half of a Hill radius.
This points to a pretty good test of whether these are Jovian moons: are they inside the Hill sphere? If "yes", then the are probably fairly well bound. Since I seem to recall Scott Sheppard is searching the Hill sphere (this is from a talk at a meeting, so I'm relying on my memory, here), I'll bet that these fit the bill.
Please explain the logic that lead to your conclusion that these moons are so close to Jupiter? Smaller has NEVER meant closer to the primary. Mars is smaller than Earth. Saturn, Uranus and Neptune are smaller than Jupiter. Kuiper-Belt and Oort Cloud comets are smaller than nearly anything else. I could go on with this listing for quite a while, but you get the point.
If you check the database, all of these newly discovered moons are outside of the orbits of most of the heretofore known moons. Well, well outside, in fact. These irregular moons are probably captured asteroids.
For your calculation to be right, by the way, the moons would be orbiting Jupiter 35 meters from it's barycenter. I'm going to question your orbital semi-major axes. (Also, your mass of Jupiter is incorrect. It's 318 times the mass of Earth.) Also, moons don't rotate about their planet, they revolve. Rotate means to spin.
Translation: "The star is a young fairly massive and hot star 320 light-years away (I'll let you look that one up if you don't already know it:-) in the constellation Libra (which is largely irrelevent, really.). It's brightness seen from Earth (presumably) is about a factor of two fainter than the faintest star you can see on a clear, dark night.
Actually, you can infer that. (Although I don't see it coming from this bit of research.) Simulations indicate that having a Jupiter-ish planet in place helps the formation of the inner solar system along. But, of course, simulations are only so accurate.
Sorry, but not right. The proto-solar nebula was probably pretty well-mixed in elemental abundances. The reason you get rocky/metallic planets in close and icey giant planets further out is purely a matter of temperature. The inner disk is much hotter than the other disk, so that hydrogen compounds like methane, water and ammonia cannot condense into solid forms. Since there are 10 times as much of these compounds as metals and silicates, planets forming father out (past the "frost line" where water first can freeze out) have much more material to build with. Thus this build faster and into more massive bodies. At around 10 Earth-masses, the cores can start to hang on to nebular gasses like hydrogen and helium. And you get a giant planet. Inside the frost line, you're struck building with rocks and metals, and you get a smaller planet.
No pushing or pulling of specific elements/compounds is involved.
Why are they misleading? I'm a huge advocate of saying in captions when you've played with the colors (and how you've done so), but doing so is often perfectly good science. Stretching color tables let us see details that would otherwise be too faint for our eyes.
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But you can only wedge one these things if they're holding still. A moving rock would need a moving wedge to be effective.
I can envision a system of gates, not unlike locks and dams, to catch a runaway stone. But I also think that those would probably work better on a square-edged stone.
As for Einstein, you're neglecting to mention that he was a patent clerk *with a Ph.D. in physics.* He wasn't some random guy who stumble across relativity, he was a well-trained scientist who had difficulty finding a job (or at least, one he liked) in academia.
No, I think the doubt there is at the idea of *rolling* 2-ton blocks uphill. All it takes is a split second of lost grip on the rock and the vaunted "rock's momentum" suddenly becomes a nightmare.
Remember Sysiphus? It'd be like that, but with a lot more screaming and generally getting smooshed.
Speaking as an actual planetary scientist, we often use "solar system" for planetary systems outside out ours. And we refer to their stars as "suns" rather often, too. As long as you capitalize the proper noun version and not the general term, it's pretty obvious what you mean.
(For that matter, we talk about Jupiter's "moons" a lot. Given that there is only one "the Moon", that shouldn't be, either. But it is, so just get used to it.)
My first reaction upon reading the title mof this article was, "Oh, no. Did the forget the Doppler Shift? Again??" But maybe that's from being a bit too close to the Cassini goings-on.
Incidently, I liked how they said that Mars Express will arrive at Mars "sometime in December". I'm hard-pressed to imagine that they don't have the dates down better than that. (Or was someone just too lazy to look it up?)
Hm, Mitch must have said it in the actual lecture, then.
Then read the book. It's a good read, anyway.
In any event, the event horizon need not be a sphere for the simple reason that you're not worried about how far from the singularity you are, you cannot know that. (Information cannot propogate outward from inside the horizon to any point further out.) What you care about is local spacetime. Since spacetime gets dragged by spinning objects, there is no real reason to expect spinning black holes to look like non-spinning ones.
Uh, it isn't a different rotation rate in the interior that creates the Great Red Spot. It's solar and internal heat, causing convection, and the spin, causing belts and zones. Admittedly, the GRS isn't totally understood, but a differentially rotating interior doesn't seem to be required. (As for whether the interior does rotate differentially, it's kind of hard to say. Since you have the belts and zones moving at all different speeds, it turns out to be difficult to define a rotation period for the cloud level. At least 2 attempts were made to define a rotation period based on the clouds, but the rotation period cited is usually the interior rotation perdio. The interior is easy to clock, thanks to the magnetic field and the radio emissions due to it.)
That said, of course you don't expect a star to be rotating as a solid body. As you suggest, there's no reason it has to. But you can make an easier, and far better, case if you just point to the Sun. The Sun's rotation period varies from equator to poles (the equator is fastest, which doesn't help a star stay together any). The interior also rotates differentially, as determined by some of the GONG results.
"Black Hole" isn't a terrifically well-defined term when you come right down to it. If you mean the thing in the middle (the "matter"), that's the singularity. It can have no real shape, as it is, as far as we can figure, a point. (The math goes all wonky, so it's better not to ask too many questions of theorists, as they tend to get kinda touchy about this.) If you mean the edge of where all hell breaks lose, then you're referring to the event horizon. (Formally defined as the point of no return, where spacetime is falling into the black hole faster than the speed of light.) Usually, that's what you care about with a black hole. (Particularly as theory has little to say about the singularity and observations have even less to tell us. And, for that matter, it's the event horizon you need to avoid. If you're dodging the singularity, you're already dead.)
/ v3_document.htm I'd further suggest Kip Thorne's book ("Black Holes and Time Warps"), an excellent read which covers an amazing about of black hole theory while remaining thorougly readable.
Now, as for the shape of the event horizon, I'm sorry, you're flat out wrong. A spinning black hole will be sqashed at the poles and bulged at the equator. The case of a spinning BH is the Kerr solution to Einstein's equations and it clearly shows this. See http://astronomy.colorado.edu/astr2030/Kerr_files
A star like the Sun will only convert about 0.01% of it's mass into energy over its entire lifetime. (According to my quick, back of the envelope calculation.) Which means you still have to form very close to the breakup spin rate. Which is still quite difficult to pull off, saith the dynamicists. (The same problem comes up in fusion-formation models of moons.)
I believe a star has zero tensile strength* (it's just a fluid), so once you're spinning too fast for gravity to hold you together, it's bye-bye time.
The better question is this: how did that star form? If it was spinning too fast to hold together, how did it accrete matter with that much angular momentum at all?
* Barring magnetic fields, mind you. But you'd need an ass-kicking field to hold a star together very long, I would think.
Er, I don't beleive so, no. You're restricting yourself to the Schwartzschild solution, there. Schwartschild assumed that the black hole wasn't spinning and was uncharged. So of course it's spherically symmetrical, there's nothing to break the symmetry.
Real black holes are likely to be spinning. And then they aren't spherical, as I recall. Also, their horizons start to seperate. Things get a *leeetle* bit weird from there on out.
Actually, there is only one orbital resonance amoung the "planets", and that's the Neptune-Pluto 3:2 one. If I recall my relative positions at Pluto's perihelion correcltly, and if I've done my math right, when Pluto is at its average distance, Neptune is never in the area.
Jupiter could never have been that large. It would have had to enveloped all of the inner moons, including the 4 Galilean ones.
I've done the integration and calculation for a homogenous Jupiter (constant density), and the planet would have to have been 25% larger 4.5 billion years ago to have produced the current energy excess that we see today for its entire life. This isn't terribly unreasonable, especially since the transiting extra-solar planets that we've seen have somewhat larger radii than Jupiter does. (The planets can't expand when they get closer to their stars, but they are prevented from contracting as far as Jupiter, say the modellers.)
In fairness, I should note that there are those who think Jupiter's energy excess is due to it's energy of accretion which hasn't leaked out over the past 4.5 billion years. I usually hear the contracting explanation, though.
No, the extra-solar planets were a bit of a shock and a sticking point for a bit. But I think most planetary scientists are confident that the giant planets simply migrated inward as part of the formation process. (There were proposals for this years before the first exoplanet was discovered.) The details are still unclear, but I think there's a reasonable consensus that the model still works.
And you're exactly right about the detection method (Doppler shifts in the stars): it's biases towards massive planets with eccentric orbits and small semi-major axes. What we've found isn't likely to be a representative sample.
Jupiter does indeed emit about twice as much energy asn it absorbs (not reflects) from the Sun. This indicates an internal heat source. "Core temperature" isn't a very accurate description, based on what we think is going on, though. Jupiter isn't a failed star, especially in the standard planet formation scenario where it forms an icy core before accreting gases. So don't look to fusion to create the heat, the planet's structure is likely (we're not absolutely certain that there is a core) wrong for that. What powers Jupiter is probably slow, continued contraction. As the planet shrinks, it loses gravitational energy and emits that as heat.
Saturn has the same input/output disconnect. In the case of Saturn, I believe that the current model is helium rain. (Also releasing gravitational energy.) And Neptune also emits more energy than it takes in. (Oddly, Uranus doesn't.) Neptune's heat source is somewhat more ambiguous, but helium rain could be it. However, we know that Uranus and Neptune have very large icy cores (well, large proportional to their overall size), so there is definately no fusion there. It's doubtful that the core could be responsible for the extra heat, since there aren't many ways for ices to generate heat.
"Astrobiology" is the term that is usually used in such circles. We actually discussed this the first day of graduate Astrobiology a couple of years ago. The term "exobiology" seems to have fallen by the wayside for whatever reason. (Possibly because "astrobiology" gives an immediate sense of what the field is, while "exobiology" leaves many people wondering "outside of what?")
"So far, all we have seen of Titan is the Orange clouds circling the planet."
If you only count visible wavelengths, true. But we have images from a few other bands, mainly radio and infrared. These can make it to the surface, allowing us to do some sorts of mapping.
I can't find the Science paper referenced (it doesn't seem to have hit the website yet), but from what I'm reading at the BBC site, this isn't news. We've had IR observations of Titan for at over a decade now. (Heck, Griffiths was the author of the papers.) That the surface of Titan wasn't purely methane/ethane oceans was an immediate conclusion from those data. (They also determined that there was a significant amount of water ice on the surface. Which might be what they BBC article means by "like Ganymede".)
I'll have to wait to see the paper to see what's new about their results, but I haven't heard anything yet that I haven't heard before.
That's what I would have thought. But the article very distinctly says "launch" in reference to Nozomi. It also talks about June. (The arrival of the Nozomi-in-transit is December of this year. Which means the fun won't really begin until 2004.)
Which isn't to say that they might not launch a new one in June, I suppose. NASA didn't wait for Voyager 1 to return science data before launching Voyager 2. (Come to think of it, they didn't wait to LAUNCH Voyager 1 before launching Voyager 2. Ah, the subtlties of spacecraft trajectories and timing.) For that matter, NASA has often had more than one mission to Mars in transit/at Mars. (Hence the back-to-back failures in the fall of 1999.) The Japanese space administration might feel that they've learned enough from the first Nozomi to launch a second one.
Call me confused, but I thought Nozomi was already well en route to Mars, having launched in 1998. (It's taking longer than intended to get there due to some technical difficulty; I think they blew too much propellant early on, but don't quote me on that.) I haven't found anything on a second Nozomi mission with Google. Anyone know anything about this new mission?
Yep, they're almost certainly captured. But their lifetimes are probably a lot longer than you think. Tidal effects depend on the mass of the moon creating the tidal bulge and the proximity to Jupiter. Small, distant moons don't raise much in the way of tides and feel little in the way of higher order gravitation moments from Jupiter. So they don't evolve tidal very quickly at all. I'd guess that it would take billions of years to get them in close to Jupiter. In fact, the effects of other bodies (moons, other planets, etc) probably overwelm the tidal effects.
Without tides, retrograde moons are a lot *more* stable than prograde moons. Hamilton and Krivov have a paper where they discuss some of this, but retrograde moons are stable out to about a Hill radius (half an astronomical unit, in the case of Jupiter), while prograde moons are only stable out to about half of a Hill radius.
This points to a pretty good test of whether these are Jovian moons: are they inside the Hill sphere? If "yes", then the are probably fairly well bound. Since I seem to recall Scott Sheppard is searching the Hill sphere (this is from a talk at a meeting, so I'm relying on my memory, here), I'll bet that these fit the bill.
Please explain the logic that lead to your conclusion that these moons are so close to Jupiter? Smaller has NEVER meant closer to the primary. Mars is smaller than Earth. Saturn, Uranus and Neptune are smaller than Jupiter. Kuiper-Belt and Oort Cloud comets are smaller than nearly anything else. I could go on with this listing for quite a while, but you get the point.
If you check the database, all of these newly discovered moons are outside of the orbits of most of the heretofore known moons. Well, well outside, in fact. These irregular moons are probably captured asteroids.
For your calculation to be right, by the way, the moons would be orbiting Jupiter 35 meters from it's barycenter. I'm going to question your orbital semi-major axes. (Also, your mass of Jupiter is incorrect. It's 318 times the mass of Earth.) Also, moons don't rotate about their planet, they revolve. Rotate means to spin.
Translation: :-) in the constellation Libra (which is largely irrelevent, really.). It's brightness seen from Earth (presumably) is about a factor of two fainter than the faintest star you can see on a clear, dark night.
"The star is a young fairly massive and hot star 320 light-years away (I'll let you look that one up if you don't already know it
Actually, you can infer that. (Although I don't see it coming from this bit of research.) Simulations indicate that having a Jupiter-ish planet in place helps the formation of the inner solar system along. But, of course, simulations are only so accurate.
Sorry, but not right. The proto-solar nebula was probably pretty well-mixed in elemental abundances. The reason you get rocky/metallic planets in close and icey giant planets further out is purely a matter of temperature. The inner disk is much hotter than the other disk, so that hydrogen compounds like methane, water and ammonia cannot condense into solid forms. Since there are 10 times as much of these compounds as metals and silicates, planets forming father out (past the "frost line" where water first can freeze out) have much more material to build with. Thus this build faster and into more massive bodies. At around 10 Earth-masses, the cores can start to hang on to nebular gasses like hydrogen and helium. And you get a giant planet. Inside the frost line, you're struck building with rocks and metals, and you get a smaller planet.
No pushing or pulling of specific elements/compounds is involved.
Why are they misleading? I'm a huge advocate of saying in captions when you've played with the colors (and how you've done so), but doing so is often perfectly good science. Stretching color tables let us see details that would otherwise be too faint for our eyes.