You make the mistake of confusing mathematics with sciences. The two are related, but not the same. Math allows for proof, science does not. Science only permits us to say that we think that one theory is more likely than another.
As to your question, there are 4 ways that have been suggested to make a moon:
1) Form it in place. This is probably true of Juptier's Galilean satellites.
2) Capture it. This is probably true of most of the irregular satellites and possibly Mars's moons.
3) Fission it off of the planet via over-spinning. Suggested first by Darwin's son, by way of interest.
4) Giant impact (or "Big Wack"). Probably true of Earth's Moon and Pluto's Charon.
So why do we opt for number 4? Capture is hard. It is feasible for big gasy planets and small moons because they can get rid of the extra energy by gas drag (we think). There isn't enough angualr momentum in the Earth/Moon system for fission (there might be in Pluto/Charon). The Moon is too big to have formed in place in current formation models and, in any event, ought to be made of the same stuff as Earth. It is composed, almost straight through, of material like Earth's mantel, but not the core.
All in all, the giant impact model seems to beat out the competition soundly. So why does Robin keep doing these simulation? Well, the details are interesting and important for understanding the details of the result. Additionally, we would like see this attention turned to Pluto/Charon now. No one has done that simlulation yet, they've just extrapolated off of the Earth/Moon work. This is risky because Pluto is made of ice, not rock, and behaves differently. Robin has been, when I last spoke to her in May, working on getting the ice behavior right in her models. Hopefully, we'll see about Pluto/Charon soon.
You're forgetting that Galileo is only going to be around another year or two, which isn't many more orbits. Add to that the fact that there are many small perturbations to it's orbit (leaks in the fuel, small impacts, etc), a small change due to Io's plumes would not appear out of the noise.
The plume's density is probably not enough to slow down the spacecraft noticably during its short pass through. Galileo is a large object, and the densities we are talking about here are very low, nanobars of pressure or lower.
I'm having difficulty imagining the spectrometers working better, either. Once a feature is fully resolved, getting closer doesn't make its surface brightness increase, so you don't win there. I'm fairly certain that the plume compositions are pretty well established now (SO2, mostly).
Still, flying through a plume does sound cool, which counts for something.
Nit: Magnetic fields fall off as 1/r^3, not 1/r^2 like gravity and electric fields. This is because magnetic fields are, to lowest order known, dipolar.
This is one of several press-releases I've seen which have come out of NASA about the upcoming pass of Io. I find it interesting that all of them trumpet the plume-pass so highly. Admittedly, it's a "gee-whiz" part of the mission, but there is probably no much science there. As Torrence said in the article, looking at how Tvashtar has changed and making a polar pass to get information of Io's magnetic field are far more interesting scientific goals. Io is the only Galilean moon for which we don't know of the field is intrinsic or induced -- during a polar pass in October of 1999, there was a glitch and the magnetometer was not brought back online in time to do the necessary measurements.
Larger aperture = more light collected = sharper images
Minor quibble, perhaps only with the wording and not the intent: larger apeture means more light. It also means better resolution (sharper images). However, you can get the resolution effect without having a full-sized apeture. The VLA is the classic example: at full extention, it is something like a 20 mile-wide mirror as far as its resolution. But with 27 dishes doing the gathering rather than 1 big one, you don't get the same light gathering power. So increased resoltion does not always equate to increased light gathering power.
For optical telescopes, resolution is not, typically, the reason for building them bigger as much as light gathering power (until adaptive optics started really kicking in, there was no point in getting better resolution in the telescope, since the atmosphere was setting the limit). If you wanted really good resolution in the optical, you would be best advised to use an interferometer, like the VLT. OWL, on the other hand, will have a staggering light gathering power.
I suspect "far" side was intended. The far side of the Moon would have many advantages as an observing site. No atmosphere to absorb light or to refract it and stability are the two biggest. Since there is no atmosphere, daytime observing isn't really a problem because there is not scatting of light and the sky is dark except when you look right at the Sun.
On the other hand, it is far away relative to low Earth orbit. It is expensive to get there and, once there, manned missions to repair and upgrade it would be, at this time, out of the question. Hubble has benefitted massively from such upgrades, from the optics correction package to the replaced gyros and computer upgrade. You could do without them, but it's something to be considered.
Ah, thank you. This explains why theologians are usually responsible for so many of the break-through scientific discoveries and theories and new technologies that improve our life. It's a wonder thepoor scientists can even compete, what with the priests always accurately predicting what the scientists will find decades or centuries in advance!
(Apologies for the sarcasm, but some things just seem to beg for it so much that I can't help myself.)
It's hard to send people to the Moon. They need food, air, sheilding, backup systems, etc. We stopped building rockets of the necessary size 30 years ago, but if we had to, we could probably bring them back in around 5 years (it would take that long to create the infrastructure to build them, not to actually construct one).
On the other hand, we've been to the Moon recently with probes. Remember Clementine (a DoD mission) and Lunar Prospector (carrying a bit of Gene Shoemaker)?
Quite a few "nay-sayers" have advanced science. Einstein decieded he didn't believe in the aether, and did something about it (hello, SR). Galileo didn't believe that big objects fell faster than small ones, and he went out and checked it.
The history of science is replete with skepticism (you call it 'nay-saying', but I find that merely belittling) leading to advancement of our understanding. While science is full of incredibly hard to gasp ideas, it is also the case that scientists shouldn't immediately jump on just any whizzo-cool bandwagon idea of the week that comes along. Science operates under the very premise that any theory or explanation we put forward will be met with skepticism from at least one person. However, we all feel that in the long run, the fittest theories will survive in a sort of Darwinian fashion, the unfit brought done by none other than the skeptics.
Did anyone here analyze the data and do the work? You're right, no we did not. Does that mean that we have no right to be skeptical or to express our skepticism? Don't be absurd. Of course we do, just as we have the right (nay, duty) to hold opinions about what our governments are doing, whether or not we've ever been elected ourselves. I for one plan to try to find the paper on this subject and watch the debate that will almost surely insue. It's science in action, not vandalism.
If you read carefully, you will note that the context of that statement was other scientists. Speaking as one of said, one who has read the major paper on both sides of the debate, I stand by my statment. Scientists disagree on the conclusions, but until you can point me to a credible scientist claiming that McKay et al. are intentionally exaggerating their claims (as opposed to reaching a different conclusion than others), I stand by that claim.
How are you describing this as a crash or a failure? Perhaps I'm mis-reading your first post, but it seem to imply that you consider the landing a failure.
One failed because it crashed, it was landing in an area that hadn't been surveyed. Significantly, Viking DID survey the area before they landed, which is why they missed the July 4 target landing date.
What mission are you talking about? Mars Pathfinder is the only mission that I know of that landed on 4 July (or tried to). And I wouldn't call it a failure by any means.
If you're thinking of Mars Polar Lander, the area had been surveyed and the landing was targeted for late November or early Decemeber of 1999. I still haven't heard NASA give a conclusive explaination of the failure mode, yet.
I must disagree with this. Certainly, NASA trumpets the news it thinks people will get most excited about. But what you have to realize is that NASA, as an organization, does not make these claims. The individual scientists, both at NASA and outside of NASA's immediate control, make claims that NASA then often announces.
Personally, I think that claiming it is a ploy, sucessful for not, is overly cynical and does the scientists a disservice. There continues to rage a very hot debate over life on Mars, especially ALH84001. While the claims are perhaps extraordinay, they aren't wild or unfounded. The scientists involved have repeatedly gotten their analyzes published in peer reviewed journals (not run by NASA) and these papers are given due thought and credit by their peers. Many of us (myself included) do not feel that the data conclusively supports the claim that Martian life has been detected, but I know of no one who claims that these researchers are exaggerating their claims.
NASA spends most of its money on two things: the ISS and the shuttles. Only a small portion of the $14 billion annual budget goes to space exploration beyond near Earth orbit: $2 billion. And they do not focus especially on "pretty pictures." NASA pulls down vast amounts of data that the general public never sees on page 3A of their local paper because the people wouldn't want to see the results from the plasma science package on Galileo, nor would the paper run it. You see pretty pictures because that is what people would like to see. On the other hand, the first thing cut from Galileo's mission when the antenna failure was discovered was the continous cloud imaging. They valued the magnetometer, plasma waves, particles and fields, NIMS and UVS data over pretty pictures of Jupiter (such pretty pictures are now being trotted out from the Cassini fly-by).
Your biochemistry is perfectly correct. However, your conclusion is wrong this time, but for a subtle reason: Chyba's point (I have the paper in question in front of me right now) is that O2 in Europa's ocean would provide a source of energy. Molecular oxygen is seldom in equilibrium with any environment and tends to "want" to react quickly (which is a lot of what made it so dangerous for life). If you can provide a source of molecular oxygen to the oceans, the recombination reactions would represent a way that life could support itself. It is similar to how bacteria around geothermal vents at the bottom of the ocean can use sulfar compunds that are spurted out of the vents in disequilibrium concentrations to live.
Upon what do you base your odds? We have one case of a planet or moon that we know has been hospitable to life as we know it (Earth) and that developped life. If you like, you can throw in Mars and make the odds 50%, but we don't know that there hasn't been life there (quite a few prominenet astrobiologists have staked their reputations and careers on ALH84001 as showing evidence of life).
Further, you might consider that life on Earth couldn't form and persist until after the [late?] heavy bombardment ended, about 0.5 billion years into Earth's history, or 4 billion years ago. Current isotopic evidence points to life as having been present on Earth by 3.85 billion years ago (see Steve Moizjis's work). That's a REALLY quick developpment. If that's any indication, Europa has had plenty of time to develop life IF it has the right conditions to support life.
Of course, all of this is based essentially on statistics of one. Even astronomers balk at drawing conclusions form this. Stating that if conditions are good on Europa implies there must be life is foolish. So is stating that the odds "make ``astronomical'' look humdrum (try worse than 1 in 10E300)."
Sorry, but that's just not true. Jupiter's magentic field almost certainly doesn't penetrate that far for starters. Europa's ocean is laddened with salts, it appears, and this causes it to act as a barrier to the penetrate of field into the interior.
Second, the field isn't that strong at Europa. Jupiter's surface field at the equator is 20 times Earth's. Field falls off as r-3 for a dipole (admittedly, the dipole approximation actually starts to get off at around Europa's distance, but this is an order of magnitude calculation). Europa's orbit is about 10 Jovian radii, so that's down from Jupiter's surface field by a factor of 1000. That is to say, Jupiter's field at that distance is much less than the field we feel from the Earth here. I don't see an tearing apart of things on Earth's surface.
Finally, I know of no mechanism to tear appart a moon's core, even WITH a strong field. A metallic core would just generate currents and exclude the field by Lenz's law, not tear appart.
You might be thinking of tidal heating, which is by far the dominant heating mechanism here. As I've stated elsewhere, that is unlikely to be a factor deep within Europa, and is likely only at work in the ice shell.
Given the induced magnetic field in Europa, as seen by the Galileo magnetometer team this past year, I think the existence of an ocean on Europa is getting pretty hard to contest. The surface features and (weaker) chemistry point that way, too.
The issue now is more a matter of 'is there enough energy to support life?' If all the tidal heat is dissipated in the ice, there will be no deep-sea geothermal vents, spewing out of equilibrium compounds out all over the place. Current models for Europa seem to favor this senario, although it's not certain by any means. But in the absense of these sources for energy, another is need. Chris Chyba's oxygen might provide such a source, although his number seem low to get a really interesting ecosystem going.
That's completely different. Colonizing the methane deposits isn't really different than colonizing a rock: they still use water like all life on Earth.
Water might not be necessary, but no one has really been able to find another solvent in which to suspend the organics needed. Water has some really remarkable properties that are hard to get in other liqids, particularly in its abundance and its polarity (handy in disolving minerals, salts and other polar molecules).
Triton is the large moon of Neptune. However, I think that the post in question refered to *Titan*, the large moon of Saturn. The trouble with life on Titan is that while there might well be a ton of organic sludge, there isn't any water and the temperature is quite cold.
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As to your question, there are 4 ways that have been suggested to make a moon:
1) Form it in place. This is probably true of Juptier's Galilean satellites.
2) Capture it. This is probably true of most of the irregular satellites and possibly Mars's moons.
3) Fission it off of the planet via over-spinning. Suggested first by Darwin's son, by way of interest.
4) Giant impact (or "Big Wack"). Probably true of Earth's Moon and Pluto's Charon.
So why do we opt for number 4? Capture is hard. It is feasible for big gasy planets and small moons because they can get rid of the extra energy by gas drag (we think). There isn't enough angualr momentum in the Earth/Moon system for fission (there might be in Pluto/Charon). The Moon is too big to have formed in place in current formation models and, in any event, ought to be made of the same stuff as Earth. It is composed, almost straight through, of material like Earth's mantel, but not the core. All in all, the giant impact model seems to beat out the competition soundly. So why does Robin keep doing these simulation? Well, the details are interesting and important for understanding the details of the result. Additionally, we would like see this attention turned to Pluto/Charon now. No one has done that simlulation yet, they've just extrapolated off of the Earth/Moon work. This is risky because Pluto is made of ice, not rock, and behaves differently. Robin has been, when I last spoke to her in May, working on getting the ice behavior right in her models. Hopefully, we'll see about Pluto/Charon soon.
You're forgetting that Galileo is only going to be around another year or two, which isn't many more orbits. Add to that the fact that there are many small perturbations to it's orbit (leaks in the fuel, small impacts, etc), a small change due to Io's plumes would not appear out of the noise.
I'm having difficulty imagining the spectrometers working better, either. Once a feature is fully resolved, getting closer doesn't make its surface brightness increase, so you don't win there. I'm fairly certain that the plume compositions are pretty well established now (SO2, mostly).
Still, flying through a plume does sound cool, which counts for something.
Nit: Magnetic fields fall off as 1/r^3, not 1/r^2 like gravity and electric fields. This is because magnetic fields are, to lowest order known, dipolar.
This is one of several press-releases I've seen which have come out of NASA about the upcoming pass of Io. I find it interesting that all of them trumpet the plume-pass so highly. Admittedly, it's a "gee-whiz" part of the mission, but there is probably no much science there. As Torrence said in the article, looking at how Tvashtar has changed and making a polar pass to get information of Io's magnetic field are far more interesting scientific goals. Io is the only Galilean moon for which we don't know of the field is intrinsic or induced -- during a polar pass in October of 1999, there was a glitch and the magnetometer was not brought back online in time to do the necessary measurements.
Minor quibble, perhaps only with the wording and not the intent: larger apeture means more light. It also means better resolution (sharper images). However, you can get the resolution effect without having a full-sized apeture. The VLA is the classic example: at full extention, it is something like a 20 mile-wide mirror as far as its resolution. But with 27 dishes doing the gathering rather than 1 big one, you don't get the same light gathering power. So increased resoltion does not always equate to increased light gathering power.
For optical telescopes, resolution is not, typically, the reason for building them bigger as much as light gathering power (until adaptive optics started really kicking in, there was no point in getting better resolution in the telescope, since the atmosphere was setting the limit). If you wanted really good resolution in the optical, you would be best advised to use an interferometer, like the VLT. OWL, on the other hand, will have a staggering light gathering power.
On the other hand, it is far away relative to low Earth orbit. It is expensive to get there and, once there, manned missions to repair and upgrade it would be, at this time, out of the question. Hubble has benefitted massively from such upgrades, from the optics correction package to the replaced gyros and computer upgrade. You could do without them, but it's something to be considered.
(Apologies for the sarcasm, but some things just seem to beg for it so much that I can't help myself.)
On the other hand, we've been to the Moon recently with probes. Remember Clementine (a DoD mission) and Lunar Prospector (carrying a bit of Gene Shoemaker)?
The history of science is replete with skepticism (you call it 'nay-saying', but I find that merely belittling) leading to advancement of our understanding. While science is full of incredibly hard to gasp ideas, it is also the case that scientists shouldn't immediately jump on just any whizzo-cool bandwagon idea of the week that comes along. Science operates under the very premise that any theory or explanation we put forward will be met with skepticism from at least one person. However, we all feel that in the long run, the fittest theories will survive in a sort of Darwinian fashion, the unfit brought done by none other than the skeptics.
Did anyone here analyze the data and do the work? You're right, no we did not. Does that mean that we have no right to be skeptical or to express our skepticism? Don't be absurd. Of course we do, just as we have the right (nay, duty) to hold opinions about what our governments are doing, whether or not we've ever been elected ourselves. I for one plan to try to find the paper on this subject and watch the debate that will almost surely insue. It's science in action, not vandalism.
If you read carefully, you will note that the context of that statement was other scientists. Speaking as one of said, one who has read the major paper on both sides of the debate, I stand by my statment. Scientists disagree on the conclusions, but until you can point me to a credible scientist claiming that McKay et al. are intentionally exaggerating their claims (as opposed to reaching a different conclusion than others), I stand by that claim.
How are you describing this as a crash or a failure? Perhaps I'm mis-reading your first post, but it seem to imply that you consider the landing a failure.
What mission are you talking about? Mars Pathfinder is the only mission that I know of that landed on 4 July (or tried to). And I wouldn't call it a failure by any means.
If you're thinking of Mars Polar Lander, the area had been surveyed and the landing was targeted for late November or early Decemeber of 1999. I still haven't heard NASA give a conclusive explaination of the failure mode, yet.
Personally, I think that claiming it is a ploy, sucessful for not, is overly cynical and does the scientists a disservice. There continues to rage a very hot debate over life on Mars, especially ALH84001. While the claims are perhaps extraordinay, they aren't wild or unfounded. The scientists involved have repeatedly gotten their analyzes published in peer reviewed journals (not run by NASA) and these papers are given due thought and credit by their peers. Many of us (myself included) do not feel that the data conclusively supports the claim that Martian life has been detected, but I know of no one who claims that these researchers are exaggerating their claims.
Your biochemistry is perfectly correct. However, your conclusion is wrong this time, but for a subtle reason: Chyba's point (I have the paper in question in front of me right now) is that O2 in Europa's ocean would provide a source of energy. Molecular oxygen is seldom in equilibrium with any environment and tends to "want" to react quickly (which is a lot of what made it so dangerous for life). If you can provide a source of molecular oxygen to the oceans, the recombination reactions would represent a way that life could support itself. It is similar to how bacteria around geothermal vents at the bottom of the ocean can use sulfar compunds that are spurted out of the vents in disequilibrium concentrations to live.
Further, you might consider that life on Earth couldn't form and persist until after the [late?] heavy bombardment ended, about 0.5 billion years into Earth's history, or 4 billion years ago. Current isotopic evidence points to life as having been present on Earth by 3.85 billion years ago (see Steve Moizjis's work). That's a REALLY quick developpment. If that's any indication, Europa has had plenty of time to develop life IF it has the right conditions to support life.
Of course, all of this is based essentially on statistics of one. Even astronomers balk at drawing conclusions form this. Stating that if conditions are good on Europa implies there must be life is foolish. So is stating that the odds "make ``astronomical'' look humdrum (try worse than 1 in 10E300)."
Second, the field isn't that strong at Europa. Jupiter's surface field at the equator is 20 times Earth's. Field falls off as r-3 for a dipole (admittedly, the dipole approximation actually starts to get off at around Europa's distance, but this is an order of magnitude calculation). Europa's orbit is about 10 Jovian radii, so that's down from Jupiter's surface field by a factor of 1000. That is to say, Jupiter's field at that distance is much less than the field we feel from the Earth here. I don't see an tearing apart of things on Earth's surface.
Finally, I know of no mechanism to tear appart a moon's core, even WITH a strong field. A metallic core would just generate currents and exclude the field by Lenz's law, not tear appart.
You might be thinking of tidal heating, which is by far the dominant heating mechanism here. As I've stated elsewhere, that is unlikely to be a factor deep within Europa, and is likely only at work in the ice shell.
The issue now is more a matter of 'is there enough energy to support life?' If all the tidal heat is dissipated in the ice, there will be no deep-sea geothermal vents, spewing out of equilibrium compounds out all over the place. Current models for Europa seem to favor this senario, although it's not certain by any means. But in the absense of these sources for energy, another is need. Chris Chyba's oxygen might provide such a source, although his number seem low to get a really interesting ecosystem going.
Water might not be necessary, but no one has really been able to find another solvent in which to suspend the organics needed. Water has some really remarkable properties that are hard to get in other liqids, particularly in its abundance and its polarity (handy in disolving minerals, salts and other polar molecules).
>WTF is Triton?
Triton is the large moon of Neptune. However, I think that the post in question refered to *Titan*, the large moon of Saturn. The trouble with life on Titan is that while there might well be a ton of organic sludge, there isn't any water and the temperature is quite cold.