There is a much easier way to get an order of magntitude estimate of G: you know g (accererlation of gravity on Earth), Earth's radius and you can estimate the mass of Earth to (as it turns out) within a factor of 2 by knowing rock/metal typically has a density of about 3-4 g/cm^3. (You can do better if you understand how rocks and metals compress under pressures.) From that, you get G to within about a factor of 2.
Of course, that isn't nearly as fun as doing the experiment!
So what's the "natural" fraction of c? 1/100? That'd be just an accident of our having 10 fingers.
And what's the base unit of mass? A solar mass? Seems natural to me, as an astronomer. In that case, gravity wins. And length? You could claim Plank units, I suppose, but they're not really tied to anything physical, as such.
So before you compare, you need an actual situation set up to look at. This isn't like saying "Blue light has a shorter wavelength than red light." That statment is always true, totally meaningful and useful. Saying "Gravity is weaker than electrostatic forces," is often untrue, not really well-defined in meaning and (being untrue in so many situations we encounter) not useful.
The trouble here is that people just have this inate itch to rank things, even when any such rankings can only be made on a case-by-case basis.
It's a far more interesting story than that. I get really frustrated/angry by glib comments (and you see them everywhere, including in textbooks) that compare the strengths of the 4 forces. In order to do that, you'd need a common reference for amount of mass/charge, and that simply doesn't exist. Sure, the electromagnetic force due to a single electron is much larger than the gravitational force. But on the other hand, the gravity of Earth greatly overwelms the electrostatic force. If you specify a physical situation, the comparison is prefectly apt (recommended, in many cases). But until you do, saying that "gravity is the weakest force" doesn't really mean anything.
As for black holes, they have no magnetic fields. It's part of the "hair" that they shed on their formation. The only physical properties they have are angular momentum, mass and charge.
Small one first: Pathfinder, as an intended lander, was heavily decontaminated to prevent it from carrying terrestrial organics. There exists a non-zero probability that it still carried some chlorophyll-bearing organisms, but the odds are small. The odds that it carried enough to be noticed are much, much smaller still.
Big point: spacecraft instruments are NOT lab instruments. While the spectrum from chlorophyll might be distinctive in the lab with a very precise spectrum, things get much hairier on a small spacecraft with mass and power limitations. Spectra in planetary science are often too poorly resolved to really uniquely identify the source. Generally, we use some knowledge of the surface characteristics to help narrow down the candidates. (For example, you can bet that the spectrum of Venus's surface has no water in it, so that's out as a surface material.) That some mineral might look, through bad luck and trick of data, like chlorphyll at the spectral resolution that Pathfinder managed doesn't seem that unlikely.
Whether they work for NASA or not is irrelevent, really. NASA employs plenty of scientists, none of whom have much to do with sending people to the Moon or anything else in that vein. NASA's scientists are, on the whole, no better or worse than the ones you'll find at every university and college in the country. And even if they did have a brighter population on the average, that doesn't mean that they can't be wrong. Espeically since they so often disagree with each other at NASA. (Remember ALH84001, the Martian meteorite that may have had life on it? Most of the people most strongly for and against those claims are at Ames.)
Put simply, arguing from authority is poor science. Particularly when the authority is an acronymn.
You're still thinking the heating has been going on forever and has reached steady-state. It probably hasn't done the latter since the former is untrue. Exactly your point about spring, in fact. And the center will NEVER get hotter than the upper layers if the heating is being done in the upper layers. (Simple physics, that: equilibrium is the same temperature throughout.)
I totally fail to see your coffee point. Yes, you can heat it by stirring, just like you can heat silly-putty by flexing it. There is no fundemental different between water/ice and rock, except that the former experience much more flexing. (It is true that if you flex rock by the SAME AMOUNT, it heats more. But again, this is probably NOT happening on Europa.) So if you don't think the former will heat up, then you need to reject the latter, too. So I am at a loss why you're rejecting this.
(The tidal heating due to the Moon is way, way, way down from Europa, since the mass of the tide-inducing body comes into the formula in a huge way, (like mass to the 7/2 power); since Jupiter is 100,000 times the mass of Earth, a priori, the heating is expected to be fantasically higher.)
The article can mention volcanoes all it likes. Most of what I've heard lately implies the opposite. Researchers WANT their to be volcanoes for astrobiological reasons, but indications I've seen are that there are not any. The reason you keep hearing about this is that people want them there.
(To get a volcano, you need to heat the rock to more like 1200 K, vs. 300 K for water. If you want a MOLTEN interior, that's a lot more heating still. )
In any event, you refuse to believe the current research because your intuition is probably wrong for this case. Since nothing I can present will ever convince you otherwise, we should drop this.
Wrong on both counts. I've already given you a prefectly good case of where the outer layer of something is warmer than the interior (Earth's surface vs. a few meters down). Dig down, you'll see what I mean.
You're intuition about the flexing is equally wrong. Flex your sand by millimeters and jostle the water by tens of cm. The water heats more, for obvious reasons. Doubt this all you like, it is quite simply the case. So I'm trusting the computer models and geophysics degrees of my officemate over your intuititions on this one. Sorry.
And I didn't mean that the exact surface (the space/ice interface) was warmest, it's pretty cold. I meant that the icey/watery outer shell is warmer than the rocky/metallic interior since the former is where the tidal energy is deposited (aka, the heat is disipated). All the current research I've read points to this, despite your doubts.
The problem is that the out layers can flex indepently of the inner layers, particularly if an ocean is involved. (In fact, the ice shell might be totally decoupled from the mantle and core, a thought which usally causes me to need a good lie-down.) Even if they are coupled, the ice and water flex more, being father out, and so take more energy in. (Think of tides on Earth: the ocean response more than the rock does.)
Where this really gets interesting is that different materials also are better at disipating heat. In fact, ice is much better than rock and metal, so the ice layers take most of the heating. Warm, mushy ice and water are better than cold ice (the latter being, at the temperatures of most of the outer solar system, a rock for all intents). So the ice shell and ocean would take the brunt of the heating, not the core. In fact, it's far from clear that the core or mantle heat up in any significant way. Since the heat probably gets dumped into the ice, perhaps even in a narrow layer (as my officemater, a Europa modeller, is starting to suspect), the heat works its way out quickly, not heating the core much at all. (Just like how the sunlight on Earth's surface does very little to heat the crust a few tens of meters down.)
So as incredible as it might seem, particularly given our intuition based on Earth and other rocky planets, the outer, icey layer is probably the warmest on Europa. (The same is true with the Sun's corona, of course, but we actually kind of understand Europa...)
But hasn't been happened that long. The tidal flexing only occurs because of the Laplace resonance with Io and Ganymede. The capture into this resonance is a relatively recent event in Galilean moon history. So "still" is inaccurate.
Also inaccurate is "core". The tidal heat is most probably disappated in the outer layers, since tidal forces are proportional the the diameter of the layer. (Cores are small, so don't get flexed much.) Also, since the ice can turn to mush and even melt, it makes it easier to dump the heat there.
No, no and no. Radio/radar have nothing to do with it. Nor does a "still hot core." Any body the size of Europa would have cooled by now, even with radiactive heat. (Mars, being much larger, is also largely cooled.)
We are pretty sure that there is a liquid ocean because 1) The pattern of cracks imaged on the surface. 2) The types of surface features, which are generally held to be consistent with a liquid ocean under the ice. And 3) the Galileo magnetometer measurements of an induced magnetic field, indicating a lquid interior. Modelling indicates that the field is only consistent with a liquid near the surface, not the in the core.
The heat needed to keep the water liquid comes from tidal flexing due to the forced eccentricity of Europa's orbit, unlike the usual situation for rocky bodies
Let's see.. 58 ft is about 17.7 meters. With a revolution every 4 seconds, &omega = 1.6 1/sec. So the acceleration is about 43.6 m/sec², or 4.45 times g. That theses numbers agree stands to reason: both formulae are the same, if you remember that &omega = v/r.
First I've heard about this claimed descrepency. It certain isn't in Carroll and Ostile, or any of my other astrophysics texts I have on my shelf. (Including Thorne's and Clifford Wills's books, the latter about tests of GR). All texts claim that GR agrees with the measured precession to a high accuracy. That GR would match this measurment that accurately when it was the higher moments of the Sun causing the orbital precessionis highly unlikely.
For that matter, so do the gravity wave based energy losses in pulsar PSR 1933+16, which netted Taylor and Hulse the Nobel prize in physics. The measurements of the pulsar continue to track the prediction very precisely (I've seen the yet-unpublished data: it's bang-on). These measurements actually go so far as to make GR the most precisely tested theory in physics, to something like one part in ten to the eleventh.
Once upon a time (well, 4 years ago), I was being trained for pulsar research. It's a topic that I still find fascinating, if even I rarely worry about things outside this solar system these days. But I have a few thoughts to offer: It isn't as if pulsar spin-down ages have ever been that trustworthy, anyway. As far as I know, no one is putting much faith in them, beyond a factor a few. This work indicates that the spin-down ages is off from the dynamic age by a factor of 2. For astrophysics, that's bang-on (as Carl Hansen likes to say). Basically, the weaknesses of the spin-age are pretty obvious: you assume the pulsar started spinning infinitely fast (well, obviously not) and that the field isn't decaying in time. In fact, it is known that dynamic ages are smaller than spin-down ages for older pulsars (around a million years), possibly due to field decay. (Er, "dynamic ages" has previously been determined by how far the pulsars have moved above/below the galactic disk and how fast they are moving.)
I was also a little irked by the statment that this is the first pulsar were we've been able to find the supernova remenant it is moving out of. The wording seemed to me to imply that we've never been able to associate a pulsar with a SN remenant before, but both the Veil pulsar and the Crab pulsar are clearly associated with known SN remenants. However, I don't believe that either of them is moving. (Flip side, we know exactly how old the Crab pulsar is, since the Chinese recorded the SN in 1054 AD.)
That's enough from me, for now. Other than to say that I'm kind of impressed that they did this on the VLA. It really isn't the best instrument for pulsar work. (But there aren't many radio dishes far enough north to cover the northern sky.)
No, again: microwaves. These guys are millimeters to centimeters wavelength. (To convert, remember Wien's law: 0.29cm-K/T = peak wavelength) T = 2.78 K, so peak wavelength ~.1cm = 1 mm.
But most of the energy in the universe is NOT from the CMB. Remember the Stefan-Boltzmann law: energy per unit area goes like sigma T^4. 3 K is barely a blimp. The billions of stars in each of the billions of galaxies are at 1500 K or more (the sun is 5800 K, blue stars are hotter still). That T^4 comes in like a demon and means that most of the energy we perceive does NOT come from the CMB.
Signal degredation is not really an issue. The solar wind isn't going to affect radio waves that much. Witness Galileo's abilty to send back signals during solar maximum and continuing contact with Pioneer 10 and Voaygers I and II.
Oh, the solar wind isn't (much of?) an issue. Probes have survived solar maximum near Earth (SOHO, for instance), and the wind becomes less intense like 1/r2 as you move away from the Sun.
Tectonics? Not really. If there is, we can't really see evidence of it, with all the volcanoes. Perhaps you mean volcanic activity, which is a (somewhat) different beast?
Sulphur Volcanoes.
The more recent evidence (past couple of years) points to silicate volcanism, rather than sulphuric. This is because we have higher resolution IR images of the surface, and the lava is really hot (1200 K, I think). This points to silicates rather than sulphur. Also, Io's topography has long been known to be too varied to be supported by sulphur.
you'd get a fatal tan
Nope. Sorry, but I get frustated when people seem to perpetually confuse particle radiation and electromagnetic radiation. The latter can give tans. The former will simply kill you, in high enough dosage. It's particles that are trapped in the Jovian magnetosphere and which pepper the surface of Io.
Actually, what you said is correct (if not what you meant): Jupiter's magnetic axis is more or less aligned with the spin axis. (It is, in fact, tipped 10 degrees towards 202 degrees System III longitude.) The mangetic field does spin with the planet, just like Earth's. This means that the Galilean moons experience different magnetic fields over the 9.92 hour rotation period of Jupiter, as the field sweeps over them.
On the other hand, opposite Earth's current field, Jupiter's mangetic north pole is in the northern hemisphere. (On Earth, just think about that fact that a compass's north is attracted to Earth's 'north', making the latter secretly south.)
If you want some wild magnetic axis action, with a really massive tilt relative to the spin axis, check out Uranus and Neptune. Both have wicked tilts, around 60 degrees.
Yes, it is the tidal tugs of Jupiter that heat the ice, as far as most models are concerned. I have some considerable background here, my thesis is on orbital dynamics and my officemate's is on tidal heating and ice convection in Europa.
Saying that the core will melt belies a serious misunderstanding of tidal heating. The core is too small to feel tides nearly as strongly as the outer icey shell or, to a lesser degree, the mantle. The mantle *might* get heated. But most models I've seen in the past few years point to the heat being dissapated in the icey shell. Thus, leaving the rocky bits untouched and usless for an energy source.
As for biogenic elements: just because they are generally abundant does not meant that they are accessible. If they're locked into the rocks or frozen as ices, they're useless for life. Particularly for the genesis of life.
Well, to start with, we've no idea if our planets are representative of the overall planet population or not. Not understanding that point makes it hard to really put our planet formation theories in context, as well as the issues of planet evolution (geological, atmospheric, etc). Life is another biggie, finding it or not. Even a null detection gives us statistics on the likihood of life developping. We have one known case where we know life (as we know it, which is all we are really able to talk about right now) could have formed, and it did in fact form there: Earth. I'll leave off Mars because the question of whether it had life when it was habitable is still open. Statistics of 1 are very bad news, especially when we are that statistic of 1 (we being the observers introduce a massive bias, no?).
As I said earlier, I don't expect we'll ever find Earths with Doppler techniques. The spectral lines in the stars are broadened by the activity on the stellar surfaces by more than the amount of the shifts due to planets. This makes it extraordinarily difficult to pick out the planet's effects.
Astrometery probably won't help much, either, as long as the point-spread function of the telescopes blurs out the star's light by well more than the amount that the stars move. Even without that effect, it's tricky. I spent a summer doing astrometry. You have to do it differentially (relative to nearby objects) rather than absolutely (position on the sky) because exact positions are too imprecise. But even that was tough, given all of the instrumental and atmospheric effects.
Thanks, but the topic isn't using telescopes (which generally don't utilize lenses anymore), but lensing. In this context, it refers to the bending of light by massive objects. Planet searches are underway using this technique, but none have been successful.
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There is a much easier way to get an order of magntitude estimate of G: you know g (accererlation of gravity on Earth), Earth's radius and you can estimate the mass of Earth to (as it turns out) within a factor of 2 by knowing rock/metal typically has a density of about 3-4 g/cm^3. (You can do better if you understand how rocks and metals compress under pressures.) From that, you get G to within about a factor of 2.
Of course, that isn't nearly as fun as doing the experiment!
So what's the "natural" fraction of c? 1/100? That'd be just an accident of our having 10 fingers.
And what's the base unit of mass? A solar mass? Seems natural to me, as an astronomer. In that case, gravity wins. And length? You could claim Plank units, I suppose, but they're not really tied to anything physical, as such.
So before you compare, you need an actual situation set up to look at. This isn't like saying "Blue light has a shorter wavelength than red light." That statment is always true, totally meaningful and useful. Saying "Gravity is weaker than electrostatic forces," is often untrue, not really well-defined in meaning and (being untrue in so many situations we encounter) not useful.
The trouble here is that people just have this inate itch to rank things, even when any such rankings can only be made on a case-by-case basis.
It's a far more interesting story than that. I get really frustrated/angry by glib comments (and you see them everywhere, including in textbooks) that compare the strengths of the 4 forces. In order to do that, you'd need a common reference for amount of mass/charge, and that simply doesn't exist. Sure, the electromagnetic force due to a single electron is much larger than the gravitational force. But on the other hand, the gravity of Earth greatly overwelms the electrostatic force. If you specify a physical situation, the comparison is prefectly apt (recommended, in many cases). But until you do, saying that "gravity is the weakest force" doesn't really mean anything.
As for black holes, they have no magnetic fields. It's part of the "hair" that they shed on their formation. The only physical properties they have are angular momentum, mass and charge.
Two points--
Small one first: Pathfinder, as an intended lander, was heavily decontaminated to prevent it from carrying terrestrial organics. There exists a non-zero probability that it still carried some chlorophyll-bearing organisms, but the odds are small. The odds that it carried enough to be noticed are much, much smaller still.
Big point: spacecraft instruments are NOT lab instruments. While the spectrum from chlorophyll might be distinctive in the lab with a very precise spectrum, things get much hairier on a small spacecraft with mass and power limitations. Spectra in planetary science are often too poorly resolved to really uniquely identify the source. Generally, we use some knowledge of the surface characteristics to help narrow down the candidates. (For example, you can bet that the spectrum of Venus's surface has no water in it, so that's out as a surface material.) That some mineral might look, through bad luck and trick of data, like chlorphyll at the spectral resolution that Pathfinder managed doesn't seem that unlikely.
Whether they work for NASA or not is irrelevent, really. NASA employs plenty of scientists, none of whom have much to do with sending people to the Moon or anything else in that vein. NASA's scientists are, on the whole, no better or worse than the ones you'll find at every university and college in the country. And even if they did have a brighter population on the average, that doesn't mean that they can't be wrong. Espeically since they so often disagree with each other at NASA. (Remember ALH84001, the Martian meteorite that may have had life on it? Most of the people most strongly for and against those claims are at Ames.)
Put simply, arguing from authority is poor science. Particularly when the authority is an acronymn.
It probably is already spinning, since pretty much any celestial body you can name does. This is the basis of the Yarkosky effect, in fact.
You're still thinking the heating has been going on forever and has reached steady-state. It probably hasn't done the latter since the former is untrue. Exactly your point about spring, in fact. And the center will NEVER get hotter than the upper layers if the heating is being done in the upper layers. (Simple physics, that: equilibrium is the same temperature throughout.)
I totally fail to see your coffee point. Yes, you can heat it by stirring, just like you can heat silly-putty by flexing it. There is no fundemental different between water/ice and rock, except that the former experience much more flexing. (It is true that if you flex rock by the SAME AMOUNT, it heats more. But again, this is probably NOT happening on Europa.) So if you don't think the former will heat up, then you need to reject the latter, too. So I am at a loss why you're rejecting this.
(The tidal heating due to the Moon is way, way, way down from Europa, since the mass of the tide-inducing body comes into the formula in a huge way, (like mass to the 7/2 power); since Jupiter is 100,000 times the mass of Earth, a priori, the heating is expected to be fantasically higher.)
The article can mention volcanoes all it likes. Most of what I've heard lately implies the opposite. Researchers WANT their to be volcanoes for astrobiological reasons, but indications I've seen are that there are not any. The reason you keep hearing about this is that people want them there.
(To get a volcano, you need to heat the rock to more like 1200 K, vs. 300 K for water. If you want a MOLTEN interior, that's a lot more heating still. )
In any event, you refuse to believe the current research because your intuition is probably wrong for this case. Since nothing I can present will ever convince you otherwise, we should drop this.
Wrong on both counts. I've already given you a prefectly good case of where the outer layer of something is warmer than the interior (Earth's surface vs. a few meters down). Dig down, you'll see what I mean.
You're intuition about the flexing is equally wrong. Flex your sand by millimeters and jostle the water by tens of cm. The water heats more, for obvious reasons. Doubt this all you like, it is quite simply the case. So I'm trusting the computer models and geophysics degrees of my officemate over your intuititions on this one. Sorry.
And I didn't mean that the exact surface (the space/ice interface) was warmest, it's pretty cold. I meant that the icey/watery outer shell is warmer than the rocky/metallic interior since the former is where the tidal energy is deposited (aka, the heat is disipated). All the current research I've read points to this, despite your doubts.
The problem is that the out layers can flex indepently of the inner layers, particularly if an ocean is involved. (In fact, the ice shell might be totally decoupled from the mantle and core, a thought which usally causes me to need a good lie-down.) Even if they are coupled, the ice and water flex more, being father out, and so take more energy in. (Think of tides on Earth: the ocean response more than the rock does.)
Where this really gets interesting is that different materials also are better at disipating heat. In fact, ice is much better than rock and metal, so the ice layers take most of the heating. Warm, mushy ice and water are better than cold ice (the latter being, at the temperatures of most of the outer solar system, a rock for all intents). So the ice shell and ocean would take the brunt of the heating, not the core. In fact, it's far from clear that the core or mantle heat up in any significant way. Since the heat probably gets dumped into the ice, perhaps even in a narrow layer (as my officemater, a Europa modeller, is starting to suspect), the heat works its way out quickly, not heating the core much at all. (Just like how the sunlight on Earth's surface does very little to heat the crust a few tens of meters down.)
So as incredible as it might seem, particularly given our intuition based on Earth and other rocky planets, the outer, icey layer is probably the warmest on Europa. (The same is true with the Sun's corona, of course, but we actually kind of understand Europa...)
But hasn't been happened that long. The tidal flexing only occurs because of the Laplace resonance with Io and Ganymede. The capture into this resonance is a relatively recent event in Galilean moon history. So "still" is inaccurate.
Also inaccurate is "core". The tidal heat is most probably disappated in the outer layers, since tidal forces are proportional the the diameter of the layer. (Cores are small, so don't get flexed much.) Also, since the ice can turn to mush and even melt, it makes it easier to dump the heat there.
No, no and no.
Radio/radar have nothing to do with it. Nor does a "still hot core." Any body the size of Europa would have cooled by now, even with radiactive heat. (Mars, being much larger, is also largely cooled.)
We are pretty sure that there is a liquid ocean because 1) The pattern of cracks imaged on the surface. 2) The types of surface features, which are generally held to be consistent with a liquid ocean under the ice. And 3) the Galileo magnetometer measurements of an induced magnetic field, indicating a lquid interior. Modelling indicates that the field is only consistent with a liquid near the surface, not the in the core.
The heat needed to keep the water liquid comes from tidal flexing due to the forced eccentricity of Europa's orbit, unlike the usual situation for rocky bodies
Let's see.. 58 ft is about 17.7 meters. With a revolution every 4 seconds, &omega = 1.6 1/sec. So the acceleration is about 43.6 m/sec², or 4.45 times g. That theses numbers agree stands to reason: both formulae are the same, if you remember that &omega = v/r.
First I've heard about this claimed descrepency. It certain isn't in Carroll and Ostile, or any of my other astrophysics texts I have on my shelf. (Including Thorne's and Clifford Wills's books, the latter about tests of GR). All texts claim that GR agrees with the measured precession to a high accuracy. That GR would match this measurment that accurately when it was the higher moments of the Sun causing the orbital precessionis highly unlikely.
For that matter, so do the gravity wave based energy losses in pulsar PSR 1933+16, which netted Taylor and Hulse the Nobel prize in physics. The measurements of the pulsar continue to track the prediction very precisely (I've seen the yet-unpublished data: it's bang-on). These measurements actually go so far as to make GR the most precisely tested theory in physics, to something like one part in ten to the eleventh.
Once upon a time (well, 4 years ago), I was being trained for pulsar research. It's a topic that I still find fascinating, if even I rarely worry about things outside this solar system these days. But I have a few thoughts to offer:
It isn't as if pulsar spin-down ages have ever been that trustworthy, anyway. As far as I know, no one is putting much faith in them, beyond a factor a few. This work indicates that the spin-down ages is off from the dynamic age by a factor of 2. For astrophysics, that's bang-on (as Carl Hansen likes to say).
Basically, the weaknesses of the spin-age are pretty obvious: you assume the pulsar started spinning infinitely fast (well, obviously not) and that the field isn't decaying in time. In fact, it is known that dynamic ages are smaller than spin-down ages for older pulsars (around a million years), possibly due to field decay. (Er, "dynamic ages" has previously been determined by how far the pulsars have moved above/below the galactic disk and how fast they are moving.)
I was also a little irked by the statment that this is the first pulsar were we've been able to find the supernova remenant it is moving out of. The wording seemed to me to imply that we've never been able to associate a pulsar with a SN remenant before, but both the Veil pulsar and the Crab pulsar are clearly associated with known SN remenants. However, I don't believe that either of them is moving. (Flip side, we know exactly how old the Crab pulsar is, since the Chinese recorded the SN in 1054 AD.)
That's enough from me, for now. Other than to say that I'm kind of impressed that they did this on the VLA. It really isn't the best instrument for pulsar work. (But there aren't many radio dishes far enough north to cover the northern sky.)
No, again: microwaves. These guys are millimeters to centimeters wavelength. (To convert, remember Wien's law: 0.29cm-K/T = peak wavelength) T = 2.78 K, so peak wavelength ~ .1cm = 1 mm.
Further than that. It's microwave, so it's already into the radio.
But most of the energy in the universe is NOT from the CMB. Remember the Stefan-Boltzmann law: energy per unit area goes like sigma T^4. 3 K is barely a blimp. The billions of stars in each of the billions of galaxies are at 1500 K or more (the sun is 5800 K, blue stars are hotter still). That T^4 comes in like a demon and means that most of the energy we perceive does NOT come from the CMB.
Signal degredation is not really an issue. The solar wind isn't going to affect radio waves that much. Witness Galileo's abilty to send back signals during solar maximum and continuing contact with Pioneer 10 and Voaygers I and II.
Oh, the solar wind isn't (much of?) an issue. Probes have survived solar maximum near Earth (SOHO, for instance), and the wind becomes less intense like 1/r2 as you move away from the Sun.
Tectonics? Not really. If there is, we can't really see evidence of it, with all the volcanoes. Perhaps you mean volcanic activity, which is a (somewhat) different beast?
Sulphur Volcanoes.
The more recent evidence (past couple of years) points to silicate volcanism, rather than sulphuric. This is because we have higher resolution IR images of the surface, and the lava is really hot (1200 K, I think). This points to silicates rather than sulphur. Also, Io's topography has long been known to be too varied to be supported by sulphur.
you'd get a fatal tan
Nope. Sorry, but I get frustated when people seem to perpetually confuse particle radiation and electromagnetic radiation. The latter can give tans. The former will simply kill you, in high enough dosage. It's particles that are trapped in the Jovian magnetosphere and which pepper the surface of Io.
Actually, what you said is correct (if not what you meant): Jupiter's magnetic axis is more or less aligned with the spin axis. (It is, in fact, tipped 10 degrees towards 202 degrees System III longitude.) The mangetic field does spin with the planet, just like Earth's. This means that the Galilean moons experience different magnetic fields over the 9.92 hour rotation period of Jupiter, as the field sweeps over them.
On the other hand, opposite Earth's current field, Jupiter's mangetic north pole is in the northern hemisphere. (On Earth, just think about that fact that a compass's north is attracted to Earth's 'north', making the latter secretly south.)
If you want some wild magnetic axis action, with a really massive tilt relative to the spin axis, check out Uranus and Neptune. Both have wicked tilts, around 60 degrees.
Yes, it is the tidal tugs of Jupiter that heat the ice, as far as most models are concerned. I have some considerable background here, my thesis is on orbital dynamics and my officemate's is on tidal heating and ice convection in Europa.
Saying that the core will melt belies a serious misunderstanding of tidal heating. The core is too small to feel tides nearly as strongly as the outer icey shell or, to a lesser degree, the mantle. The mantle *might* get heated. But most models I've seen in the past few years point to the heat being dissapated in the icey shell. Thus, leaving the rocky bits untouched and usless for an energy source.
As for biogenic elements: just because they are generally abundant does not meant that they are accessible. If they're locked into the rocks or frozen as ices, they're useless for life. Particularly for the genesis of life.
Well, to start with, we've no idea if our planets are representative of the overall planet population or not. Not understanding that point makes it hard to really put our planet formation theories in context, as well as the issues of planet evolution (geological, atmospheric, etc). Life is another biggie, finding it or not. Even a null detection gives us statistics on the likihood of life developping. We have one known case where we know life (as we know it, which is all we are really able to talk about right now) could have formed, and it did in fact form there: Earth. I'll leave off Mars because the question of whether it had life when it was habitable is still open. Statistics of 1 are very bad news, especially when we are that statistic of 1 (we being the observers introduce a massive bias, no?).
As I said earlier, I don't expect we'll ever find Earths with Doppler techniques. The spectral lines in the stars are broadened by the activity on the stellar surfaces by more than the amount of the shifts due to planets. This makes it extraordinarily difficult to pick out the planet's effects.
Astrometery probably won't help much, either, as long as the point-spread function of the telescopes blurs out the star's light by well more than the amount that the stars move. Even without that effect, it's tricky. I spent a summer doing astrometry. You have to do it differentially (relative to nearby objects) rather than absolutely (position on the sky) because exact positions are too imprecise. But even that was tough, given all of the instrumental and atmospheric effects.
Thanks, but the topic isn't using telescopes (which generally don't utilize lenses anymore), but lensing. In this context, it refers to the bending of light by massive objects. Planet searches are underway using this technique, but none have been successful.