If I'm remembering right, there have been recent studies that indicate we do have some genes associated with Neatherals. The idea isn't that we're so much extracted from the speices as there was interbreeding between Cromagnon and Neanderthals. (If they could interbreed, they almost certainly did. That's a fundemental truism for whenever two such species meet.) One finding I do definately recall (as I just read about it the other night) is that the genes for red hair seem to come to us from Neanderthals. The moral might just be that genetics and human evolution isn't nice and simple. Perhaps we should stop seeking the sound-bite sized answers (we are/are not descended from X) and accept that things are inherently more complicated.
The moons of Uranus probably are in the equatorial plane thanks to effects of Uranus's not-quite-spherical shape. Most moons will head towards the equatorial plane in time, even captured ones.
What you are (possibly) forgetting about Neptune is that being farther from the Sun makes it also farther from the Earth. Finding moonsa around Neptune is even more difficult than finding them around Uranus (which is in turn more difficult than finding them around Saturn, etc). Besides being farther away from us, the light out there dimmer. (Neptune is about half-again as far from the Sun as Uranus, which translates to leass than 1/2 the light per area.) Before deducing much about the relative numbers and what they mean, I think we should wait for significantly more complete satellite searches around all 4 giant planets.
Of course, you might be right. Neptune might have fewer moons in the end. Then it could be because of Triton (being both very massive and in an irregular orbit might make it an impedment to other moons' existences). There might also be other effects. Or maybe I was over-generalizing the processes. But I'm not ready to start worrying yet.
Does knowledge about a 21st moon of a remote planet really increase our understanding of anything?
I know. As a matter of fact, it does. If we only had a handful of moons to look at, we'd never really know to what extent the trends we see are just statistics of a few and to what extent they reflect real underlying physical processes at work. Each additional moon adds to the statistics. Individually they aren't wildly important. Collectively, larger numers of moons lead to better theories of where this little guys come from. Brett Gladman, who received the annual Urey Prize for the Division for Planetary Sciences this year, gave a talk about irregular satellites. Having been in the audience, I can tell you that having many moons on there made the trends a lot more believeable than had there been only, say, 5 data points.
If you're asking if each new moon is worth of a headline or even a Slashdot story, I'd agree that it really isn't. But if you're wondering if we should bother looking for these moons, I'd have to say yes, absolutely.
I think perhaps the best way to look at the terrestrial (aka, inner) planets - moon-wise - is that they don't form with moons, so any moons we find are probably anomalous in some senses. Earth's Moon is a bit of a freak, having formed in a very stochastic even. Mars's two moons are most likely captured asteroids. Venus and Mercury are in some ways more like what I'd expect to see in a large fraction of a larger terrestrial planet population.
The outer solar system has it good, moon-wise. First off, the giant planets are thought form with accretion disks about them in the later stages. (I believe Canup and Ward have a paper coming out on this topic in Astrophysical Journal in not too long.) This makes a good place to form moons, it is thought. It gets even better, though. The jovian planets also probably had larger gas envelopes early on, making it easier to capture a moon (like Triton). You need some way to ditch energy in order for capture to occur, and drag is a nice method. And better still: it's easier for giant planets to affect objects in their area. Their Hill spheres (domains of gravitational dominance compared with the Sun's gravity) is larger thanks largely in part due to their greater distances from the Sun. This leaves a larger volume around them in which they can start to mess with small bodies and potentially capture them, under the right conditions.
All in all, if you want to either form (in situ) or capture a moon, the outer solar system is your best bet. It's still possible to pull some tricks in the inner solar system, but they're less likely.
Actually... it does. Astronomers mispronounce a lot of words. (Charon, anyone? Or Io?) I'd know. I am an astronomer. There are a few astronomers out there who make it a minor crusade to try to get the community to recognize the correct pronounciations (Guy Consolmagno comes to mind), but most astronomers don't care. They say things the way they learned them, even knowing it's not the correct pronounciation.
Correct according to whom? http://www.pantheon.org/articles/u/uranus.h tml It's said the way that leads to the juvenile jokes. Quite a few planetary scientists have veered away from this pronounciation, but that doesn't make it correct. Just widely mispronounced.
No, I don't mean that researchers who falsify data are doing good science. But you'll notice that the falsification was caught. And it wasn't just the revelation that they included an incorrect figure and some of their plots had identical noise. Collegues have been growing suspecious of the results for over a year now because they've been unable to reproduce them.
This is good science. Scientists individually screw up all the time. I certainly have. Usually, we make honest mistakes. Sometimes, we make dishonest ones. But science is not and has never been about any one person or group. Science is a collective effort. It's not just the group doing the experiment, it's the other groups that try to reproduce it, the reviewers who look at it critically and the opponents who try their hardest to tear it apart. If you want to consider "good science", you need to add all of these into the picture. One of these segments clearly failed in this case (the original researchers) and another didn't catch it (the reviewers), the others did their job.
So, really, while the individual scientist was doing bad work, this illustrates exactly how science should work under real world circumstances.
Actually, the leap from Earth's Moon to other moons isn't a safe one to make. I can think of only one other moon in the solar system believed to have been formed in a giant impact. (Namely, Pluto's Charon.)
Almost all other moons are either believed to be captured (based on their orbits) or giant planet moons, which were believed to have formed in the accretion disks around the planets. In this light, these moons wouldn't collide with their parent planets as accretion occurred because the colliding particles would be in similar orbits about the planet.
First of all, the orbits of stars about the galaxy are Keplerian. They don't orbit as a solid body (like a record) but more like the planets.
What makes this more interesting still is that the spiral arms are not composed of specific stars all the time. The spiral pattern propogates through the stars and gas in the galaxy (triggering star birth along the way). A given star will enter and leave the arms as the star comes up from beind the arm, passes through, and leaves. (Or from the other direction, depending.)
I'm skeptical that we know the pattern speed of the sprial arms that well. When I was doing a paper on the "rare Earth" idea, I was looking up the co-rotation radius (the place where a star would always been inside or outside of a spiral arm because it orbits at the same speed as the pattern) for our galaxy. I found very conflicting numbers quoted in papers.
Because there are no comfortable parking orbits in the Jovian system. There are too many bodies to provide a system we can solve over longer-term. (For a Jovian orbit, that means say a few hundred orbits. Each orbits is of order days, so we're talking a few years.) Beyond any short term, the perturbations to the orbit add up and thanks to the chaotic nature of the orbits, we lose the ability to predict where Galileo will be. Thanks to an almost non-existant fuel supply, nothing can be done to prevent this.
So we lose control of the orbit, so what? So what is that they don't want it to crash into a moon like Europa. While the RTG is relatively safe, it's still warm and would probably work its way down through the ice, saith NASA analysts. (Even if it doesn't, there is a fair chance that the anything on the surface will eventually end up inside the moon.) Once inside, there is the risk of contaminating the moon with not only the radioactive plutonium but also any terrestrial microorganisms that might be left on Galileo. (The spacecraft was not cleaned to the levels that would be required of a lander.) Either way, that runs the risk of contaiminating the whole moon.
Is the risk small? Yes. But the last thing anyone wants is to ruin any extraterrestrial ecosystems for study. Once you contaminate them, all subsequent research is going to be of questionable value.
There is also the risk that Galileo could be ejcted from the system. This has the potential to be bad, as well, as it could (very long term, admittedly) come back and smack Earth. I know, low probability. I was incredulous when I heard the NASA folks worry about that, but it is a risk. And so that's why they're not getting it out of Jupiter orbit, in fact.
Ultimately, I suspect that everyone at NASA would dearly love to save poor Galileo. It's been a trooper and deserves to be enshrined in the Smithsonian. (No offense, but given the choice between that and a few tons of scrap metal and outdate technology, I'd pray they'd bring it home.) But the risks, small though they are, are deemed too great.
Actually, small moons aren't interesting. Well, not in the same way and to the same degree as the Galilean moons. The Galilean moons are large enough to be spherical and to show geological processes and to hold on to trace atmospheres. That means there is probably much more to study with them than with the smaller moons, which have little geology aside from impact cratering. This is not meant to be a value judgement, merely an unfortunate pragmatic fact.
Mission planners also undoubted considered some basic orbital facts, here. The small moons of Jupiter are all either quite a bit outside the Gailean orbits or within Io's orbit. You might think you could sneak visits to the former as the probe swings out from or in to Jupiter on its very elliptical orbit. But ALL of the outer moons have signficant inclinations. The odds of meeting one of them near the equator of Jupiter is slight, given the number of coincidences you'd need. As for the inner moons (Amalthea, Phoebe, Adrestea and Metis), they're all interior to Io. This is actually very bad for Galileo. You'll recall that getting in as close to Jupiter as Io has causes problems, thanks to the magnetosphereic plasma. The farther in you go, the worse it gets. They're only doing this now because Galileo is well past its life expectency and beginning to fail anyway.
Going to the Moon would cost billions of dollars. This project probably costs in the thousands. Arguing that we shouldn't be spending this money because we should be going to the Moon makes little sense, when you look at the numbers.
Not really. Radiation pressure from the Sun only affects dust-sized particles.
Unless you're thinking of the Yarkosky effect, in which the asteroid's spin and re-radiation can cause a drag? It's not clear that the Yarkosky effect is significant, actually. It's a subject of considerable investiagation right right now.
Even if it is, the effect is has will drop like the radius of the body to the minus one power (you radiate proportional to your area, but mass - and thus acceleration - goes like radius cubed). It's usually thought of as potentially important for meteroids, but asteroids probably don't notice much.
You're correct in general that HST (and radio telescopes) are the only ways to looking dayward. But in this case, they talk about the asteroid approaching basically from the Sun-direction. HST isn't allowed to be pointed near the Sun. Mercury has never been observed by HST, for example, for this very reason. Even if HST were slewed to this alignment, I seem to recall that it would automatically shut its door and go into safe mode. (There are ways that this can be overridden, of course. But that they'd risk slamming the door and safing the telescope tells you how seriously they take not looking near the Sun.)
What's worse is that even if you could avoid the Sun and look for such an asteroid, you'd still have a devil of a time. Asteroids are faint to start with, and anything near the Sun-Earth line would be showeing a small crescent phase. So the bugger wouldn't be very bright at all.
I told you very clearly what I was talking about. Where, pray tell, do you get your "facts"? Because they disagree with what I see in published papers and texts.
Jupiter's core: Check out Protostars and Planet IV, page 1087. You'll clearly see that size of Jupiter's core, from measurments. It is nowhere NEAR 100 Earth masses. I've never heard of anyone suggesting that, especially now that we've been there and that's many times outside of the error bars. It's 0-10 Earth masses. If you're arguing against that, the burden of proof is on you, since you're arguing with a MEASURED QUANTITY. (Admittedly, it's an *indirect* measurement. But I am confident they can tell the difference between 10 and 100 Earth masses in the core.)
Your statments about the heat flow and generation don't seem to make sense if you are arguing with me. You're arguing for what pretty much everyone in the planetary community beleives, not what this no theory suggests. Namely that Jupiter's heat comes from a fission reactor in the core. As I've said, there isnt' enough uranium there to do it. (See above.)
I've already addressed the point you repeat in your second paragraph: you're arguing for the status quo theory, in *agreement* with me. This issue here is what these guys are suggesting: an actual fission reaction at the core, not slow radioactive decay.
Yes, the inner core is solid. Unless you can point me to a kosher source claiming otherwise, I'll trust my geology textbooks and my geophysics faculty on this point. Or at least explain how you get differential from the middle of the inner core (you only claim you get it at the outer edge of the core, which is liquid and not important here, since the uranium is going to be in the ceter of the inner core). Both my texts and my faculty have claimed that the inner core is "solid." (Sorces: _Physical Geology_, by Monroe and Wicander, page 264 and _Moons and Planets_ by Wm. K. Hartmann (planetary geologists, for the record), page 211. And statments made in graduate classes by geology faculty.)
And on your final paragraph: then we agree. If we want a radically new paradigm on the Earth's field behavior, it'll be at odds with the theories used on other bodies. Hence the general sense of dissatification with the new theory, espeically seeing as there is a lack of evidence that implies a shift is in order.
So what case are you arguing? For the authors or against them? Three of your paragraphs have turned around and *agreed* with the status quo theory (and with what I'm saying, here). Could you please clearly state your views here, relative to the new theory?
Actually, I'm going to have to say that YOU don't understand Jupiter. Jupiter's core, by current measurements, is 0 to 10 Earth masses. This is based on the gravitational moments measured by Voyagers I and II and Galileo. Now, only around 10% of that is rocky, the rest are hydrogen compounds (water, methane and ammonia ices, mainly). This is based on the composition of comets and the massive abundance of hydrogen. So now you're left with a rocky/metallic bit that is AT MOST the size of Earth. Unless you assume there was a lot more uranium at 5.2 AU than at 1.0 (and all evidence, dynamical and cosmochemical are to the contrary), that uranium core CANNOT be much larger than Earth's. And, yet, it's putting out way more power according to their speculations. Highly unlikely.
So, no, Jupiter's metallic core is NOT larger. Unless you'd like to point me to some papers to the contrary. (For reference: Most of what I know has come from attending the Jupiter Meeting a year ago, assorted DPS talks and my graduate classes in planet formation.)
And, yes THERE WAS mention of differentiation. Implict, perhaps, but it's there. You need to study you're nuclear physics. Uruaniam mixed in with iron won't start a reactor. That's the whole point behind purifying the stuff out of ores (and then isolating U-235) in the first place, when you think about it. The idea that there is radioactive decay in the Earth generating heat is EXACTLY what most geologists believe is going on. If these guys got up and said this, no one would notice since it's an old idea.
The Sun's field isn't the exactly same as Earths, but the dynamo models have a unifying effect on ALL magnetic fields in astronomy. If you suddenly decieded Earth's field is different, you either are demanding two or more models or need to explain how the Sun fits in to your model. Either way, you're going to get a lot of resistence because you're making the theory messier with no obvious evidence to support it needing the complication.
And, yes, the center of the Earth is solid. I can see you also need to study your geology. We know this from seismic data. The inner core is solid. Since the authors of this work would have us believe that the uranium is differentiating out of the iron because it is denser, they MUST have the uranium in the inner core. So it is solid. And therefore you won't get differnetiation of fission products.
But how do you get the fission products out of a solid chunk of uranium? Solids neither convect nor differntiate.
This theory also doesn't explain why the Sun's magnetic field chances orientation in a 22-year cycle.
I'm not sure about the second point, either. Uranium, as far as I know, chemically reacts with other elements and doesn't necessarily differentiate out of the Earth. If you sliced open Earth, you wouldn't find it layered like an onion, one layer per element. Many of them are chemcially mixed in with the major constituents, like iron.
To add a point: the authors really don't understand energy production or planets (possibly both). Jupiter has to generate about as much energy as it takes in from that Sun. That's or order 10 Watts per square meter, according to my quick calculation. Now, Jupiter's core, IF it has a core at all, is mainly ices. The rocky/metal bit is probably not larger than Earth. So it shouldn't be generating more power than Earth's core. Earth's outward heat flux due to internal heat is 0.01 Watts per square meter. Consider that Jupiter has over 100 times the surface area, and now your core has to be generating 100,000 times the energy that Earth's is, despite being the same size. Does this sound reasonable?
Anything in the core (assuming, as most do, that there *is* a core) is under extreme pressure. Not a great place to live.
The metallic hydrogen is almost certianly there. Something has to be generating that whopping magnetic field. But it's not terribly relevent to the search for life, since hydrogen by itself (metallic or otherwise) doesn't form many interesting compounds.
What bothers me about this is that while there is a quick mention of "formation models," most of the discussion of the potential existence of a terrestrial planet seemed focused on the stability of an orbit in the present configuration. In fact, it isn't clear to me that they've even considered the formation processes at all. (To be honest, I get the opposite sense.)
Why does this bother me, you ask? Because an orbit at 1 AU might be stable NOW, but if you have a giant planet migrating in through the inner solar system to an 15-day orbit, it'll wreck jolly hell with any planets it passes. The migration is slow enough that you are almost guaranteed a close-enounter of some kind. Once a Earth-sized planet gets near a giant planet, the orbit is in the very least highly perturbed. Odds are fair that it could be ejected altogher or will collide with the giant planet and be effectly lost. But even if it isn't, the eccentricity is probably going to be increases substantially. A planet that changes its distance from its star radically over a year is unlikely to be habitable, if you believe current models.
Gravity isn't such an important factor. If you calculate the surface gravity on Jupiter, you'll find it's only 25 m/sec^2, or about 2.5 G's. Humans can tolerate that over short periods, so it's not hard to imagine other organisms evolving in that enviroment.
The problem on jovian planets is lack of biogenic elements, like carbon, nitrogen and oxygen. Sure, they're present, but they're very dilute thanks to a whopping abundance of hydrogen and helium. So terrestrial-sized planets seem to be the way to go.
Oh, no. They really have colors. You get the images from the CCDs in black and white because you have to take one expose through each filter (which is then just a map of intensity at that waveband). But you then add the images to get color.
HST images (as well as other telescopes's outputs) tend to be false colored for two reasons:
1. Because stretching the color tables often brings out subtle details. You can see this is a true and stretched image of Jupiter, for example.
2. Many (most maybe even) HST images include wavelengths that we can't actually see, into the IR and UV. If you want to see those wavelengths, you'll have to false color.
I do sort of wish that they'd always include a little note in the captions stating that the color tables have been stretched or otherwise manipulated. But they seldom do. It's just a dream I have.
Maybe somewhat longer. But complicating matters is that your pupils may dialate to compensate for the lower light levels, letting in more light again. I don't know the numbers, so I couldn't give details.
I figured it was full of it. But I alway prefer to give the benefit of the doubt and act as if he was simply misinformed/ignorant rather than a troll. I'm an incurable optimist about people.
Slashdot Mirror
If I'm remembering right, there have been recent studies that indicate we do have some genes associated with Neatherals. The idea isn't that we're so much extracted from the speices as there was interbreeding between Cromagnon and Neanderthals. (If they could interbreed, they almost certainly did. That's a fundemental truism for whenever two such species meet.)
One finding I do definately recall (as I just read about it the other night) is that the genes for red hair seem to come to us from Neanderthals.
The moral might just be that genetics and human evolution isn't nice and simple. Perhaps we should stop seeking the sound-bite sized answers (we are/are not descended from X) and accept that things are inherently more complicated.
The moons of Uranus probably are in the equatorial plane thanks to effects of Uranus's not-quite-spherical shape. Most moons will head towards the equatorial plane in time, even captured ones.
What you are (possibly) forgetting about Neptune is that being farther from the Sun makes it also farther from the Earth. Finding moonsa around Neptune is even more difficult than finding them around Uranus (which is in turn more difficult than finding them around Saturn, etc). Besides being farther away from us, the light out there dimmer. (Neptune is about half-again as far from the Sun as Uranus, which translates to leass than 1/2 the light per area.) Before deducing much about the relative numbers and what they mean, I think we should wait for significantly more complete satellite searches around all 4 giant planets.
Of course, you might be right. Neptune might have fewer moons in the end. Then it could be because of Triton (being both very massive and in an irregular orbit might make it an impedment to other moons' existences). There might also be other effects. Or maybe I was over-generalizing the processes. But I'm not ready to start worrying yet.
Does knowledge about a 21st moon of a remote planet really increase our understanding of anything?
I know. As a matter of fact, it does. If we only had a handful of moons to look at, we'd never really know to what extent the trends we see are just statistics of a few and to what extent they reflect real underlying physical processes at work. Each additional moon adds to the statistics. Individually they aren't wildly important. Collectively, larger numers of moons lead to better theories of where this little guys come from. Brett Gladman, who received the annual Urey Prize for the Division for Planetary Sciences this year, gave a talk about irregular satellites. Having been in the audience, I can tell you that having many moons on there made the trends a lot more believeable than had there been only, say, 5 data points.
If you're asking if each new moon is worth of a headline or even a Slashdot story, I'd agree that it really isn't. But if you're wondering if we should bother looking for these moons, I'd have to say yes, absolutely.
Ok, lots to say here.
I think perhaps the best way to look at the terrestrial (aka, inner) planets - moon-wise - is that they don't form with moons, so any moons we find are probably anomalous in some senses. Earth's Moon is a bit of a freak, having formed in a very stochastic even. Mars's two moons are most likely captured asteroids. Venus and Mercury are in some ways more like what I'd expect to see in a large fraction of a larger terrestrial planet population.
The outer solar system has it good, moon-wise. First off, the giant planets are thought form with accretion disks about them in the later stages. (I believe Canup and Ward have a paper coming out on this topic in Astrophysical Journal in not too long.) This makes a good place to form moons, it is thought.
It gets even better, though. The jovian planets also probably had larger gas envelopes early on, making it easier to capture a moon (like Triton). You need some way to ditch energy in order for capture to occur, and drag is a nice method.
And better still: it's easier for giant planets to affect objects in their area. Their Hill spheres (domains of gravitational dominance compared with the Sun's gravity) is larger thanks largely in part due to their greater distances from the Sun. This leaves a larger volume around them in which they can start to mess with small bodies and potentially capture them, under the right conditions.
All in all, if you want to either form (in situ) or capture a moon, the outer solar system is your best bet. It's still possible to pull some tricks in the inner solar system, but they're less likely.
Just to toss in another good site, I'm very partial to:
http://ssd.jpl.nasa.gov/
As you can no doubt tell, it's maintained by JPL, so it has pretty much the best orbital and physical data around.
Actually... it does. Astronomers mispronounce a lot of words. (Charon, anyone? Or Io?) I'd know. I am an astronomer. There are a few astronomers out there who make it a minor crusade to try to get the community to recognize the correct pronounciations (Guy Consolmagno comes to mind), but most astronomers don't care. They say things the way they learned them, even knowing it's not the correct pronounciation.
Correct according to whom?h tml
http://www.pantheon.org/articles/u/uranus.
It's said the way that leads to the juvenile jokes. Quite a few planetary scientists have veered away from this pronounciation, but that doesn't make it correct. Just widely mispronounced.
No, I don't mean that researchers who falsify data are doing good science. But you'll notice that the falsification was caught. And it wasn't just the revelation that they included an incorrect figure and some of their plots had identical noise. Collegues have been growing suspecious of the results for over a year now because they've been unable to reproduce them.
This is good science. Scientists individually screw up all the time. I certainly have. Usually, we make honest mistakes. Sometimes, we make dishonest ones. But science is not and has never been about any one person or group. Science is a collective effort. It's not just the group doing the experiment, it's the other groups that try to reproduce it, the reviewers who look at it critically and the opponents who try their hardest to tear it apart. If you want to consider "good science", you need to add all of these into the picture. One of these segments clearly failed in this case (the original researchers) and another didn't catch it (the reviewers), the others did their job.
So, really, while the individual scientist was doing bad work, this illustrates exactly how science should work under real world circumstances.
Actually, the leap from Earth's Moon to other moons isn't a safe one to make. I can think of only one other moon in the solar system believed to have been formed in a giant impact. (Namely, Pluto's Charon.)
Almost all other moons are either believed to be captured (based on their orbits) or giant planet moons, which were believed to have formed in the accretion disks around the planets. In this light, these moons wouldn't collide with their parent planets as accretion occurred because the colliding particles would be in similar orbits about the planet.
First of all, the orbits of stars about the galaxy are Keplerian. They don't orbit as a solid body (like a record) but more like the planets.
What makes this more interesting still is that the spiral arms are not composed of specific stars all the time. The spiral pattern propogates through the stars and gas in the galaxy (triggering star birth along the way). A given star will enter and leave the arms as the star comes up from beind the arm, passes through, and leaves. (Or from the other direction, depending.)
I'm skeptical that we know the pattern speed of the sprial arms that well. When I was doing a paper on the "rare Earth" idea, I was looking up the co-rotation radius (the place where a star would always been inside or outside of a spiral arm because it orbits at the same speed as the pattern) for our galaxy. I found very conflicting numbers quoted in papers.
Because there are no comfortable parking orbits in the Jovian system. There are too many bodies to provide a system we can solve over longer-term. (For a Jovian orbit, that means say a few hundred orbits. Each orbits is of order days, so we're talking a few years.) Beyond any short term, the perturbations to the orbit add up and thanks to the chaotic nature of the orbits, we lose the ability to predict where Galileo will be. Thanks to an almost non-existant fuel supply, nothing can be done to prevent this.
So we lose control of the orbit, so what? So what is that they don't want it to crash into a moon like Europa. While the RTG is relatively safe, it's still warm and would probably work its way down through the ice, saith NASA analysts. (Even if it doesn't, there is a fair chance that the anything on the surface will eventually end up inside the moon.) Once inside, there is the risk of contaminating the moon with not only the radioactive plutonium but also any terrestrial microorganisms that might be left on Galileo. (The spacecraft was not cleaned to the levels that would be required of a lander.) Either way, that runs the risk of contaiminating the whole moon.
Is the risk small? Yes. But the last thing anyone wants is to ruin any extraterrestrial ecosystems for study. Once you contaminate them, all subsequent research is going to be of questionable value.
There is also the risk that Galileo could be ejcted from the system. This has the potential to be bad, as well, as it could (very long term, admittedly) come back and smack Earth. I know, low probability. I was incredulous when I heard the NASA folks worry about that, but it is a risk. And so that's why they're not getting it out of Jupiter orbit, in fact.
Ultimately, I suspect that everyone at NASA would dearly love to save poor Galileo. It's been a trooper and deserves to be enshrined in the Smithsonian. (No offense, but given the choice between that and a few tons of scrap metal and outdate technology, I'd pray they'd bring it home.) But the risks, small though they are, are deemed too great.
Actually, small moons aren't interesting. Well, not in the same way and to the same degree as the Galilean moons. The Galilean moons are large enough to be spherical and to show geological processes and to hold on to trace atmospheres. That means there is probably much more to study with them than with the smaller moons, which have little geology aside from impact cratering. This is not meant to be a value judgement, merely an unfortunate pragmatic fact.
Mission planners also undoubted considered some basic orbital facts, here. The small moons of Jupiter are all either quite a bit outside the Gailean orbits or within Io's orbit. You might think you could sneak visits to the former as the probe swings out from or in to Jupiter on its very elliptical orbit. But ALL of the outer moons have signficant inclinations. The odds of meeting one of them near the equator of Jupiter is slight, given the number of coincidences you'd need. As for the inner moons (Amalthea, Phoebe, Adrestea and Metis), they're all interior to Io. This is actually very bad for Galileo. You'll recall that getting in as close to Jupiter as Io has causes problems, thanks to the magnetosphereic plasma. The farther in you go, the worse it gets. They're only doing this now because Galileo is well past its life expectency and beginning to fail anyway.
Going to the Moon would cost billions of dollars. This project probably costs in the thousands. Arguing that we shouldn't be spending this money because we should be going to the Moon makes little sense, when you look at the numbers.
Not really. Radiation pressure from the Sun only affects dust-sized particles.
Unless you're thinking of the Yarkosky effect, in which the asteroid's spin and re-radiation can cause a drag? It's not clear that the Yarkosky effect is significant, actually. It's a subject of considerable investiagation right right now.
Even if it is, the effect is has will drop like the radius of the body to the minus one power (you radiate proportional to your area, but mass - and thus acceleration - goes like radius cubed). It's usually thought of as potentially important for meteroids, but asteroids probably don't notice much.
You're correct in general that HST (and radio telescopes) are the only ways to looking dayward. But in this case, they talk about the asteroid approaching basically from the Sun-direction. HST isn't allowed to be pointed near the Sun. Mercury has never been observed by HST, for example, for this very reason. Even if HST were slewed to this alignment, I seem to recall that it would automatically shut its door and go into safe mode. (There are ways that this can be overridden, of course. But that they'd risk slamming the door and safing the telescope tells you how seriously they take not looking near the Sun.)
What's worse is that even if you could avoid the Sun and look for such an asteroid, you'd still have a devil of a time. Asteroids are faint to start with, and anything near the Sun-Earth line would be showeing a small crescent phase. So the bugger wouldn't be very bright at all.
I told you very clearly what I was talking about. Where, pray tell, do you get your "facts"? Because they disagree with what I see in published papers and texts.
Jupiter's core: Check out Protostars and Planet IV, page 1087. You'll clearly see that size of Jupiter's core, from measurments. It is nowhere NEAR 100 Earth masses. I've never heard of anyone suggesting that, especially now that we've been there and that's many times outside of the error bars. It's 0-10 Earth masses. If you're arguing against that, the burden of proof is on you, since you're arguing with a MEASURED QUANTITY. (Admittedly, it's an *indirect* measurement. But I am confident they can tell the difference between 10 and 100 Earth masses in the core.)
Your statments about the heat flow and generation don't seem to make sense if you are arguing with me. You're arguing for what pretty much everyone in the planetary community beleives, not what this no theory suggests. Namely that Jupiter's heat comes from a fission reactor in the core. As I've said, there isnt' enough uranium there to do it. (See above.)
I've already addressed the point you repeat in your second paragraph: you're arguing for the status quo theory, in *agreement* with me. This issue here is what these guys are suggesting: an actual fission reaction at the core, not slow radioactive decay.
Yes, the inner core is solid. Unless you can point me to a kosher source claiming otherwise, I'll trust my geology textbooks and my geophysics faculty on this point. Or at least explain how you get differential from the middle of the inner core (you only claim you get it at the outer edge of the core, which is liquid and not important here, since the uranium is going to be in the ceter of the inner core). Both my texts and my faculty have claimed that the inner core is "solid." (Sorces: _Physical Geology_, by Monroe and Wicander, page 264 and _Moons and Planets_ by Wm. K. Hartmann (planetary geologists, for the record), page 211. And statments made in graduate classes by geology faculty.)
And on your final paragraph: then we agree. If we want a radically new paradigm on the Earth's field behavior, it'll be at odds with the theories used on other bodies. Hence the general sense of dissatification with the new theory, espeically seeing as there is a lack of evidence that implies a shift is in order.
So what case are you arguing? For the authors or against them? Three of your paragraphs have turned around and *agreed* with the status quo theory (and with what I'm saying, here). Could you please clearly state your views here, relative to the new theory?
Actually, I'm going to have to say that YOU don't understand Jupiter. Jupiter's core, by current measurements, is 0 to 10 Earth masses. This is based on the gravitational moments measured by Voyagers I and II and Galileo. Now, only around 10% of that is rocky, the rest are hydrogen compounds (water, methane and ammonia ices, mainly). This is based on the composition of comets and the massive abundance of hydrogen. So now you're left with a rocky/metallic bit that is AT MOST the size of Earth. Unless you assume there was a lot more uranium at 5.2 AU than at 1.0 (and all evidence, dynamical and cosmochemical are to the contrary), that uranium core CANNOT be much larger than Earth's. And, yet, it's putting out way more power according to their speculations. Highly unlikely.
So, no, Jupiter's metallic core is NOT larger. Unless you'd like to point me to some papers to the contrary. (For reference: Most of what I know has come from attending the Jupiter Meeting a year ago, assorted DPS talks and my graduate classes in planet formation.)
And, yes THERE WAS mention of differentiation. Implict, perhaps, but it's there. You need to study you're nuclear physics. Uruaniam mixed in with iron won't start a reactor. That's the whole point behind purifying the stuff out of ores (and then isolating U-235) in the first place, when you think about it. The idea that there is radioactive decay in the Earth generating heat is EXACTLY what most geologists believe is going on. If these guys got up and said this, no one would notice since it's an old idea.
The Sun's field isn't the exactly same as Earths, but the dynamo models have a unifying effect on ALL magnetic fields in astronomy. If you suddenly decieded Earth's field is different, you either are demanding two or more models or need to explain how the Sun fits in to your model. Either way, you're going to get a lot of resistence because you're making the theory messier with no obvious evidence to support it needing the complication.
And, yes, the center of the Earth is solid. I can see you also need to study your geology. We know this from seismic data. The inner core is solid. Since the authors of this work would have us believe that the uranium is differentiating out of the iron because it is denser, they MUST have the uranium in the inner core. So it is solid. And therefore you won't get differnetiation of fission products.
But how do you get the fission products out of a solid chunk of uranium? Solids neither convect nor differntiate.
This theory also doesn't explain why the Sun's magnetic field chances orientation in a 22-year cycle.
I'm not sure about the second point, either. Uranium, as far as I know, chemically reacts with other elements and doesn't necessarily differentiate out of the Earth. If you sliced open Earth, you wouldn't find it layered like an onion, one layer per element. Many of them are chemcially mixed in with the major constituents, like iron.
To add a point: the authors really don't understand energy production or planets (possibly both). Jupiter has to generate about as much energy as it takes in from that Sun. That's or order 10 Watts per square meter, according to my quick calculation. Now, Jupiter's core, IF it has a core at all, is mainly ices. The rocky/metal bit is probably not larger than Earth. So it shouldn't be generating more power than Earth's core. Earth's outward heat flux due to internal heat is 0.01 Watts per square meter. Consider that Jupiter has over 100 times the surface area, and now your core has to be generating 100,000 times the energy that Earth's is, despite being the same size.
Does this sound reasonable?
Anything in the core (assuming, as most do, that there *is* a core) is under extreme pressure. Not a great place to live.
The metallic hydrogen is almost certianly there. Something has to be generating that whopping magnetic field. But it's not terribly relevent to the search for life, since hydrogen by itself (metallic or otherwise) doesn't form many interesting compounds.
Pressure is only that extreme near the center of the planets. Near the surface, you smoothly go to essentially zero pressure.
What bothers me about this is that while there is a quick mention of "formation models," most of the discussion of the potential existence of a terrestrial planet seemed focused on the stability of an orbit in the present configuration. In fact, it isn't clear to me that they've even considered the formation processes at all. (To be honest, I get the opposite sense.)
Why does this bother me, you ask? Because an orbit at 1 AU might be stable NOW, but if you have a giant planet migrating in through the inner solar system to an 15-day orbit, it'll wreck jolly hell with any planets it passes. The migration is slow enough that you are almost guaranteed a close-enounter of some kind. Once a Earth-sized planet gets near a giant planet, the orbit is in the very least highly perturbed. Odds are fair that it could be ejected altogher or will collide with the giant planet and be effectly lost. But even if it isn't, the eccentricity is probably going to be increases substantially. A planet that changes its distance from its star radically over a year is unlikely to be habitable, if you believe current models.
Gravity isn't such an important factor. If you calculate the surface gravity on Jupiter, you'll find it's only 25 m/sec^2, or about 2.5 G's. Humans can tolerate that over short periods, so it's not hard to imagine other organisms evolving in that enviroment.
The problem on jovian planets is lack of biogenic elements, like carbon, nitrogen and oxygen. Sure, they're present, but they're very dilute thanks to a whopping abundance of hydrogen and helium. So terrestrial-sized planets seem to be the way to go.
Oh, no. They really have colors. You get the images from the CCDs in black and white because you have to take one expose through each filter (which is then just a map of intensity at that waveband). But you then add the images to get color.
HST images (as well as other telescopes's outputs) tend to be false colored for two reasons:
1. Because stretching the color tables often brings out subtle details. You can see this is a true and stretched image of Jupiter, for example.
2. Many (most maybe even) HST images include wavelengths that we can't actually see, into the IR and UV. If you want to see those wavelengths, you'll have to false color.
I do sort of wish that they'd always include a little note in the captions stating that the color tables have been stretched or otherwise manipulated. But they seldom do. It's just a dream I have.
Maybe somewhat longer. But complicating matters is that your pupils may dialate to compensate for the lower light levels, letting in more light again. I don't know the numbers, so I couldn't give details.
I figured it was full of it. But I alway prefer to give the benefit of the doubt and act as if he was simply misinformed/ignorant rather than a troll. I'm an incurable optimist about people.