This isn't very deep, but when I first read the title of this story, what leapt to mind was a Sidney Harris cartoon from Einstein Simplified. Two scientists (you can tell they're scientists, they're wearing labcoats) are looking into a cage the size of a rabbit cage. One of them is saying, "Biggest damn virus I've ever seen!" Pity I can't find a copy of it at the moment.
I'd love to see a follow up on that story, because I can recall a fair bit of skepticism at the time. For one thing, newly landed meteors tend to be cold, not warm.
Pardon if I'm being daft, but are you thinking that this hasn't been thought about?
Gamma rays ARE light and can be blocked by about a centimeter (or two) of a reasonably dense metal. And I'm pretty sure that the Sun doesn't give a lot of them off most of the time when it's quiet, being a blackbody peaking in the visible.
Alpha and beta particles won't penetrate a metal heat shield of any appreciable thickness. Since Messanger will spend at least some of it's time inside of Mercury's magnetosphere (I'd need the specs on the orbit to figure out how much, or if it's the entire orbit) alpha and beta particles from the Sun won't be reaching it *anyway*. (The Sun emits electrons and *protons* in abundance as a solar wind. Not quite so much in the way of helium nuclei. But the solar wind doesn't penetrate the magnetosphere proper.)
In any event, these things don't usually do much damage for their heat. They tend to mess with electronics by flipping bits and damaging the electronic substrates. NASA won't let them fly non-radiation hardened electronics. (In fact, all chips will probably have been tested on earlier missions nearer Earth.)
Since I know David Grinspoon, I can assure you that he is not off his nut. Please note the following:
The quotes are from his popular science book, Venus Revealed, not a scientific paper or press release. Context is important. (And the original context is not the linked article, it's the final chapter of a popular book. Many authors have speculated wildly in their last chapters, often far more audaciously than Grinspoon did.)
He explicitly says, several times in the chapter (I know, I have the book opened in front of me.) that he is wildly specultating. He isn't claiming any of these things are true or even saying he believes any of them. He's just thinking out loud about possibility.
Scientists often speculate wildly, especially to each other. In many cases, we don't really believe that our musing are even likely true, but it gives us a chance to explore new territory. Given how often scientists are accused of being stuck in one set of paradigms, I'm surprised that anyone has an objection to our trying to get outside these mindsets.
That said, I don't believe any of the speculations. The only reasonable place I've heard of to look for life on Venus is in the upper part of the atmosphere where it's cooler. (Venus's cloudtops are at something like 250 Kelvin, since they reflect so much of the Sun's light.) Even that is rampant speculation, though.
Of course NASA/APL/LASP has thought through this. The heat shield will do the job. All it has to do is relect the light, after all. The heat can only get to the spacecraft via radiation, so no convection or conduction. (Except a little done the heat-shield holding arms.) The bigger worry is Mercury itself. That chunk of rock is really hot, and the IR radiation coming from it will at some points of orbit be hitting the spacecraft's unshielded side. As I recall, the solution is to not do that for very long and then spend more time away from Mercury, radiating the heat away.
Ah, the term you want is "resonance". The simplist kind of resonance is a "mean motion" resonance wherein the bodies have orbital periods which are small-integer ratios. (3:2 for Pluto/Neptune, for instance.) The planets do not, in general, have orbtial resonances with each other. The fact that Pluto is in resonance with Neptune is, to some, a good reason to not call it a planet. In order to get into resonace, usually one of the bodies needs to be migrating. In Neptune's case, outward.
(The Titus-Bode law, often simply called Bode's law -- which kind of slights poor Titus -- says that the planet's orbits lie in specific plays given by an exponential formula. It was fitted to the then-known planets, but failed increasingly miserably for the subsequently discovered planets. Interestingly, though, simulations have shown that planets do tend to space out exponentially. They don't follow a nice formula, but the distances between each does seem to increase in that general fashion.)
Hot Jupiters migrated inwards. I've never thought about what would happen if they captured a terrestrial planet into resonance as the move, but any such capture would have to be inside of the jovian planet. Making such a planet REALLY hot once the hot Jupiter parked itself. I'm a bit dubious about whether you could capture a planet in such migration, though. The jovan planet migration timescales that I see tossed about (for the hot Jupiter; ignore Uranus and Neptune for now) is fairly short, tens to hundreds of thousands of years, usually. To capture something in a resonance, you have to sort of creep up on it. If you move to fast, the resonace sweeps right over the body and soon the hot Jupiter gets to close and either absorbs the planet or ejects it.
The usual mechanism for hot Jupiter migrations is disk torques, actually. A massive prot-stellar disk well feel the giant planets. In return, the disk pulls back on the planet. If the torques don't balance out, the planet migrates. (The other popular mechanism is scattering a lot of small bodies out of the system. I'm a bit more skeptical of this mechanism because you have scatter a LOT of small bodies to make it work.)
That actually depends. If the planet were spinning rapidly, like Jupiter or Saturn, the planet would probably be pretty nearly isothermal. There is some doubt on that point, though, since planets this close to their primaries are likely tidally locked (in a 1:1 spin-orbit resonance), or at least in some low-order resonance (a la Mercury).
(Also, if it is spinning rapidly and NOT isothermal, you'll still get the bulk of the escape occuring off to one side of the planet-star line. It takes a while for an atmosphere to heat to it's maximum daily temperature. Which is why noon is seldom the hottest part of the day.)
Even if it isn't spinning rapidly, the heat could easily be well-distributed. Venus's temperature is pretty nearly constant across the planet, and it spins excurciatingly slowly.
Still, interesting idea. I should run the numbers through on that one.
Interesting. It's totally different in the sciences. The intro. texts tend to be everything books written by a fairly small number of people, often just one.
There are plenty of "everything" undergrad textbooks, though. Those were the ones I was maning thinking of, in fact. For instance, there are dozens of introductory astronomy textbooks on the market, most of them decent. The people who write them have to cover a lot of different subjects, only in one or two of which they are likely to be experts. The same is true of intro. physics, chemistry or biology books.
(It is also not the case that they make a whole lot of money on the textbooks. Unless the book becomes hugely popular, the time investment is probably larger than the pay would merit. Nor is the the case that no professor makes a career of being a generalist. I can point out a number of people - Chandrasaker for instance - who flit from topic to topic rather than become absorbed by one. They are in a minority, to be sure, but they most certainly exist.)
The article claims that textbooks at the K-12 level are usually written by committees. This is probably true, based on my limited recollections. So why is this so very different from college textbooks, which are usually written by a small number of authors? (Usually, there are one, two or at most, three.)
There must be some driving force that makes the committee system work better for the K-12 textbooks, but what is it, I wonder?
In as much as Cassini never got all that terribly close to Jupiter (it just barely slipped inside the magnetosphere, which is huge), I don't think you're seeing Cassini's best work. At Saturn, it will be in orbit, which means it will get a lot closer to the planet.
Even if its instruments were only of Voyager quality (and they aren't, they're better), it would still be a very useful mission simply because it will be able to take a lot more data over it's lifetime.
Well, the answer we give intro astro students goes something like this:
To get a magnetic field, you need three things:
1. A liquid, metallic* interior (so it can move and carry charges about) 2. A reasonably fast rotation rate 3. Convection in the liquid metal.
* (Actually, any charge carrier works, as far as I know. Salty water might be able to do it, I suppose.)
Mars meets criterion 2. And now apparently it meets 1. It isn't clear that there is convection going on, though, so that itself might be keeping the field from being present.
Then again, dynamo theory is pretty shaky stuff. (As someone already said.) I tend to trust it in the big picture (the stuff I outlined above), but not in the details. So exactly how much a planet needs to meets the three criteria is anybody's guess. (That is, how fast does it need to rotate? How metallic does the interior have to be? How much convection?) Mercury and Venus certainly create certain... issues... with this theory, for a start.
People have already answered the question pretty well, but I'm going to try to offer a slightly broader picture. (Why, yes I do teach. Why do you ask?)
There are basically 4 ways to heat a planet: 1. Heat of accretion. As stuff comes from a long ways a way and smashes into the planet, the graviational potential energy is turned into heat. Important early on for all planets. This heat is leaked out over time. 2. Differentiaion. If the planet is liquid (or gaseous), the heavier elements/compounds will tend to sink to the middle and the light components will rise to the top. This reduces the overall graviational potential energy, releasing more heat. Most planets have differentiated about as far as they are likely to, so this doesn't really help much anymore, either. Saturn and Neptune might be having a form of this happening today, with a helium rain in their atmospheres. 3. Contraction. If a planet shrinks in radius, gravitational potential energy is released. (Yet again.) This is possibly what is keeping Jupiter warmer than solar heating alone would make it. 4. Radioactive decay. This depends on composition, of course (gas giants, being mostly hydrogen, aren't terribly prone to this one). Rocky/metallic planets experience a fair bit of this after 4.5 billion years, mainly from potassium and uranium isotopes. (He says, trying desperately to remember his planetary geology class 4 years ago.)
Note that friction and pressure are not in the above list. Higher pressure does not always mean more heat! (The ideal gas law doesn't always work!) Friction requires moving bits inside the planet. In fact, that is where the frictional heat comes from. So you still need a source of energy to get things moving, meaning friction can't be the ultimate source of energy.
That might be more information that you wanted, but I wanted to give a bit of context for the answer.
Jupiter's moons are all named (saith the official Internation Astronomers' Union rules) after paramours of Jupiter/Zeus. There are a few exceptions, named for the nurses of the young Jupiter.
But even with Zeus's... er... excesses, we're running out of names.
(Saturn's moons are all titans, I believe, Neptune's are minor gods and goddess associated with, well, Neptune, and Uranus's are named for Shakespeare and Pope characters. Mostly sprites, I think.)
"S/2002 J1- Catchy name, eh? Beats the hell out of say, Europa or Ganymede."
That won't be its permanent name. All bodies are given temporary names of that kind until the Internation Astronomer's Union confirms their permanent names. Besides some slight beaurcratic overhead intended to keep astronomical nomenclature standardized, this is also because they want to be sure it's really a new object.
There *is* a natural limit to how far out you can get and still be orbiting a planet, like Jupiter. That limit (roughly) is the Hill radius*, which goes like (m/3 M)^(1/3) a, where m is the mass of the planet, M is the mass of the Sun, a is the planet's orbital semi-major axis and 3 is 3. For Jupiter, this is about half of an astronomical unit. That's actually a pretty big sphere of influence, since Jupiter is only 5.2 AU from the Sun to start with.
There are some who would call objects in the same helicentric orbit as the planet "moons". This class of objects includes the Trojan asteroids of Jupiter, as well as Earth's "second" moon. On the whole, however, astronomers seem to prefer to only consider something a moon if it really orbits the planet.
* It's actually a eeensy bit more interesting than that. Prograde moons can't seem to orbit stably much further than half of a Hill radius from their planet, while retrograde moons can orbit up to about a full Hill radius.
Re:How do people figure this stuff out?
on
Collecting Stardust
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· Score: 4, Informative
The usual way to trace the place of origin of a sample (meteorites, dust, whatever) is to look at the ratio of isotopes of certain elements. In this case, they used two oxygen isoptopes. Objects in our solar system tend to have a particular ratio, all the material having formed from the same nebula 4.6 billion years ago. Material with a very different isotope ratio probably comes from outside the system, then.
This method isn't without it's risks, of course. There are processes which might enhance or deplete a body in a particular isotope over it's kin. But I'm not thinking of any that would work on a dust grain, assuming it had ever been part of a planet.
Yeah, I can't argue with the showmanship aspect to science. I'm actually slightly guilty of playing the astrobiology card in a paper that I've written.
I'm not sure you'll see heat build-up, though. The sparks probably won't produce much energy, certainly less than the thermal energy produced directly by the impact. And that diffuses away fairly quickly at these temperatures. I forget the the exact timescales, but recall that passing into and out of Jupiter's shadow is enough time for the moons to heat and cool significantly. That timescale is of order a day or few.
Textbooks are often wrong in the details. If that is your only point, you went through a lot of trouble to say nothing remotely new to anyone here. And you phrased it extraordinarily badly, too.
As for "choices", I was -admittedly- anthropomorphicizing somewhat. I imagine you are smart enough to know that, though. Right? You can replace "chose" with "life came to use", if you are a stickler for undue precision.
The point of the Urey-Miller experiment wasn't to show the way organics were produced, it was to demonstrate that they CAN be produced by such methods. Similar experiments have been run with dozens of permutations on the atmosphere and energy sources, and they generally produce organics. In fact, a range of different experiments with a variety of catalysts, like some clays, have also been performed, with similar results. A quick literature search would have told you that.
The point of these experiments is not to reproduce the early-Earth conditions exactly. We still don't know what those are. But the fact that such a wide variety of conditions produce organics is an indication that the goop is easy to form and probably did so on the early-Earth, regardless of the conditions.
(Your point about the chirality of the amino acids is a red herring. There is no reason to think that life was formed in a soup of only one chirality. All we know is that somehow life on Earth has evolved to use only one of those. It isn't hard to imagine that one or the other might have a slight advantage or even that life had to - at some early stage - chose just one and use it. Dealing with both L and D forms all the time would probably require a lot more effort than it's worth.)
This result is certainly interesting, but I don't think it really pushes the case of organics on Europa much farther than it already was. I'm a little skeptical that electric sparks in an ice matrix will do a lot to generate organic molecules, for starters. (With compounds in the ice, there is very limited mobility, so that chemical reactions just don't occur very often. My guess is that you can spark it all you like, but in most case, nothing will happen.) Research needs to be done on that problem before they have much of a case.
Even then, this is hardly ground-breaking. Electric sparks are not the only way to generate organics. Urey and Miller also showed that UV light can do the same thing. All you really need is a high-energy source to break up some bounds and allow new ones to form. Heck, even the particle radition in Jupiter's magnetosphere can probably do some of that. The UV flux is down by a factor of 27 from that at Earth (top of the atmosphere, now at the surface where ozone and other molecules have attenuated it), but I'd bet you can provide more activation energy that way than with little electric shocks from impacts.
That said, it's a damn cool result without all the "Life on Europa" hype.
Excellent point. In fact, let me add to it: Many citiations now are copied from ONLINE SOURCES. We read the papers, but we hate typing in our bibliography from scratch. I can just go to ADS (http://adsabs.harvard.edu) and have it print out the reference in BIBTeX format for me. Now, there are quite a few typos in that database. I know because we're finding them while creating a bibliography for the upcoming Juptier book.
None of this implies that we're not reading papers we cite. In fact, from experience, people in my field (astronomy) know the papers they reference pretty well, as a rule. There are times when we don't read an entire paper because we're just taking a few numbers or an equation, but as a whole, it pays to know the papers. If you don't, you'll usually find yourself under fire from your collegue who wrote the mis-quoted paper. Quite often, that collegue will be the journal referee who is reviewing the paper before publication. This is *not* a position you want to be in, so people generally work to avoid it.
It is very unlikely that either comet or meteorites would have survived that long. Even at 1 AU, the Sun would have long ago made most of the volatiles on the comet disappear. Failing that, 4.5 billion years is plenty long enough for some sort of collision to have occured, removing comet/meteorites from circulation. Besides, what would the connection actually be? Comets don't come from rocky bits, they're mainly ice. So you wouldn't have probably formed any cometary material in the giant impact that formed our Moon. And even if you did, it is difficult to get it onto such a highly eccentric orbit. All in all, it doesn't seem a likely area of interet. But it's still a pretty meteor shower.
The article is actually rather scant on details. But it is my guess that they are NOT going to be generating small-scale detailed models. So no views of planet surfaces. I'm guessing that they're going to use the planetary parameters as inputs and see how different organisms thrive or die off. The alternative is just much too complex and full of unknow parameters. Which means that this project is inherently very limited in its abilities. They'll have to work on averaged and estimated behaviors for the biota and they can't investigate detailed niches. Most disturbing from a biological perspective is that they are really only investigating "live as we know it", since we have no idea how other life forms might exist. So in a very real sense they aren't really learning a whole lot that is new.
This is just my impression and interpretation, though. If they can do more detailed models, I'd be deeply, deeply impressed.
Slashdot Mirror
This isn't very deep, but when I first read the title of this story, what leapt to mind was a Sidney Harris cartoon from Einstein Simplified. Two scientists (you can tell they're scientists, they're wearing labcoats) are looking into a cage the size of a rabbit cage. One of them is saying, "Biggest damn virus I've ever seen!" Pity I can't find a copy of it at the moment.
I'd love to see a follow up on that story, because I can recall a fair bit of skepticism at the time. For one thing, newly landed meteors tend to be cold, not warm.
Pardon if I'm being daft, but are you thinking that this hasn't been thought about?
Gamma rays ARE light and can be blocked by about a centimeter (or two) of a reasonably dense metal. And I'm pretty sure that the Sun doesn't give a lot of them off most of the time when it's quiet, being a blackbody peaking in the visible.
Alpha and beta particles won't penetrate a metal heat shield of any appreciable thickness. Since Messanger will spend at least some of it's time inside of Mercury's magnetosphere (I'd need the specs on the orbit to figure out how much, or if it's the entire orbit) alpha and beta particles from the Sun won't be reaching it *anyway*. (The Sun emits electrons and *protons* in abundance as a solar wind. Not quite so much in the way of helium nuclei. But the solar wind doesn't penetrate the magnetosphere proper.)
In any event, these things don't usually do much damage for their heat. They tend to mess with electronics by flipping bits and damaging the electronic substrates. NASA won't let them fly non-radiation hardened electronics. (In fact, all chips will probably have been tested on earlier missions nearer Earth.)
Since I know David Grinspoon, I can assure you that he is not off his nut. Please note the following:
That said, I don't believe any of the speculations. The only reasonable place I've heard of to look for life on Venus is in the upper part of the atmosphere where it's cooler. (Venus's cloudtops are at something like 250 Kelvin, since they reflect so much of the Sun's light.) Even that is rampant speculation, though.
Of course NASA/APL/LASP has thought through this. The heat shield will do the job. All it has to do is relect the light, after all. The heat can only get to the spacecraft via radiation, so no convection or conduction. (Except a little done the heat-shield holding arms.) The bigger worry is Mercury itself. That chunk of rock is really hot, and the IR radiation coming from it will at some points of orbit be hitting the spacecraft's unshielded side. As I recall, the solution is to not do that for very long and then spend more time away from Mercury, radiating the heat away.
Ah, the term you want is "resonance". The simplist kind of resonance is a "mean motion" resonance wherein the bodies have orbital periods which are small-integer ratios. (3:2 for Pluto/Neptune, for instance.) The planets do not, in general, have orbtial resonances with each other. The fact that Pluto is in resonance with Neptune is, to some, a good reason to not call it a planet. In order to get into resonace, usually one of the bodies needs to be migrating. In Neptune's case, outward.
(The Titus-Bode law, often simply called Bode's law -- which kind of slights poor Titus -- says that the planet's orbits lie in specific plays given by an exponential formula. It was fitted to the then-known planets, but failed increasingly miserably for the subsequently discovered planets. Interestingly, though, simulations have shown that planets do tend to space out exponentially. They don't follow a nice formula, but the distances between each does seem to increase in that general fashion.)
Hot Jupiters migrated inwards. I've never thought about what would happen if they captured a terrestrial planet into resonance as the move, but any such capture would have to be inside of the jovian planet. Making such a planet REALLY hot once the hot Jupiter parked itself. I'm a bit dubious about whether you could capture a planet in such migration, though. The jovan planet migration timescales that I see tossed about (for the hot Jupiter; ignore Uranus and Neptune for now) is fairly short, tens to hundreds of thousands of years, usually. To capture something in a resonance, you have to sort of creep up on it. If you move to fast, the resonace sweeps right over the body and soon the hot Jupiter gets to close and either absorbs the planet or ejects it.
The usual mechanism for hot Jupiter migrations is disk torques, actually. A massive prot-stellar disk well feel the giant planets. In return, the disk pulls back on the planet. If the torques don't balance out, the planet migrates. (The other popular mechanism is scattering a lot of small bodies out of the system. I'm a bit more skeptical of this mechanism because you have scatter a LOT of small bodies to make it work.)
What do you mean by "harmony"? And Bode's law (as I've always seen it) doesn't work.
A hot Jupiter would have destroyed/removed any smaller inner planets as it migrated in. So there's no real issue there.
That actually depends. If the planet were spinning rapidly, like Jupiter or Saturn, the planet would probably be pretty nearly isothermal. There is some doubt on that point, though, since planets this close to their primaries are likely tidally locked (in a 1:1 spin-orbit resonance), or at least in some low-order resonance (a la Mercury).
(Also, if it is spinning rapidly and NOT isothermal, you'll still get the bulk of the escape occuring off to one side of the planet-star line. It takes a while for an atmosphere to heat to it's maximum daily temperature. Which is why noon is seldom the hottest part of the day.)
Even if it isn't spinning rapidly, the heat could easily be well-distributed. Venus's temperature is pretty nearly constant across the planet, and it spins excurciatingly slowly.
Still, interesting idea. I should run the numbers through on that one.
Interesting. It's totally different in the sciences. The intro. texts tend to be everything books written by a fairly small number of people, often just one.
There are plenty of "everything" undergrad textbooks, though. Those were the ones I was maning thinking of, in fact. For instance, there are dozens of introductory astronomy textbooks on the market, most of them decent. The people who write them have to cover a lot of different subjects, only in one or two of which they are likely to be experts. The same is true of intro. physics, chemistry or biology books.
(It is also not the case that they make a whole lot of money on the textbooks. Unless the book becomes hugely popular, the time investment is probably larger than the pay would merit. Nor is the the case that no professor makes a career of being a generalist. I can point out a number of people - Chandrasaker for instance - who flit from topic to topic rather than become absorbed by one. They are in a minority, to be sure, but they most certainly exist.)
The article claims that textbooks at the K-12 level are usually written by committees. This is probably true, based on my limited recollections. So why is this so very different from college textbooks, which are usually written by a small number of authors? (Usually, there are one, two or at most, three.)
There must be some driving force that makes the committee system work better for the K-12 textbooks, but what is it, I wonder?
In as much as Cassini never got all that terribly close to Jupiter (it just barely slipped inside the magnetosphere, which is huge), I don't think you're seeing Cassini's best work. At Saturn, it will be in orbit, which means it will get a lot closer to the planet.
Even if its instruments were only of Voyager quality (and they aren't, they're better), it would still be a very useful mission simply because it will be able to take a lot more data over it's lifetime.
Well, the answer we give intro astro students goes something like this:
To get a magnetic field, you need three things:
1. A liquid, metallic* interior (so it can move and carry charges about)
2. A reasonably fast rotation rate
3. Convection in the liquid metal.
* (Actually, any charge carrier works, as far as I know. Salty water might be able to do it, I suppose.)
Mars meets criterion 2. And now apparently it meets 1. It isn't clear that there is convection going on, though, so that itself might be keeping the field from being present.
Then again, dynamo theory is pretty shaky stuff. (As someone already said.) I tend to trust it in the big picture (the stuff I outlined above), but not in the details. So exactly how much a planet needs to meets the three criteria is anybody's guess. (That is, how fast does it need to rotate? How metallic does the interior have to be? How much convection?) Mercury and Venus certainly create certain... issues... with this theory, for a start.
People have already answered the question pretty well, but I'm going to try to offer a slightly broader picture. (Why, yes I do teach. Why do you ask?)
There are basically 4 ways to heat a planet:
1. Heat of accretion. As stuff comes from a long ways a way and smashes into the planet, the graviational potential energy is turned into heat. Important early on for all planets. This heat is leaked out over time.
2. Differentiaion. If the planet is liquid (or gaseous), the heavier elements/compounds will tend to sink to the middle and the light components will rise to the top. This reduces the overall graviational potential energy, releasing more heat. Most planets have differentiated about as far as they are likely to, so this doesn't really help much anymore, either. Saturn and Neptune might be having a form of this happening today, with a helium rain in their atmospheres.
3. Contraction. If a planet shrinks in radius, gravitational potential energy is released. (Yet again.) This is possibly what is keeping Jupiter warmer than solar heating alone would make it.
4. Radioactive decay. This depends on composition, of course (gas giants, being mostly hydrogen, aren't terribly prone to this one). Rocky/metallic planets experience a fair bit of this after 4.5 billion years, mainly from potassium and uranium isotopes. (He says, trying desperately to remember his planetary geology class 4 years ago.)
Note that friction and pressure are not in the above list. Higher pressure does not always mean more heat! (The ideal gas law doesn't always work!) Friction requires moving bits inside the planet. In fact, that is where the frictional heat comes from. So you still need a source of energy to get things moving, meaning friction can't be the ultimate source of energy.
That might be more information that you wanted, but I wanted to give a bit of context for the answer.
Jupiter's moons are all named (saith the official Internation Astronomers' Union rules) after paramours of Jupiter/Zeus. There are a few exceptions, named for the nurses of the young Jupiter.
... er... excesses, we're running out of names.
But even with Zeus's
(Saturn's moons are all titans, I believe, Neptune's are minor gods and goddess associated with, well, Neptune, and Uranus's are named for Shakespeare and Pope characters. Mostly sprites, I think.)
"S/2002 J1- Catchy name, eh? Beats the hell out of say, Europa or Ganymede."
That won't be its permanent name. All bodies are given temporary names of that kind until the Internation Astronomer's Union confirms their permanent names. Besides some slight beaurcratic overhead intended to keep astronomical nomenclature standardized, this is also because they want to be sure it's really a new object.
There *is* a natural limit to how far out you can get and still be orbiting a planet, like Jupiter. That limit (roughly) is the Hill radius*, which goes like (m/3 M)^(1/3) a, where m is the mass of the planet, M is the mass of the Sun, a is the planet's orbital semi-major axis and 3 is 3. For Jupiter, this is about half of an astronomical unit. That's actually a pretty big sphere of influence, since Jupiter is only 5.2 AU from the Sun to start with.
There are some who would call objects in the same helicentric orbit as the planet "moons". This class of objects includes the Trojan asteroids of Jupiter, as well as Earth's "second" moon. On the whole, however, astronomers seem to prefer to only consider something a moon if it really orbits the planet.
* It's actually a eeensy bit more interesting than that. Prograde moons can't seem to orbit stably much further than half of a Hill radius from their planet, while retrograde moons can orbit up to about a full Hill radius.
The usual way to trace the place of origin of a sample (meteorites, dust, whatever) is to look at the ratio of isotopes of certain elements. In this case, they used two oxygen isoptopes. Objects in our solar system tend to have a particular ratio, all the material having formed from the same nebula 4.6 billion years ago. Material with a very different isotope ratio probably comes from outside the system, then.
This method isn't without it's risks, of course. There are processes which might enhance or deplete a body in a particular isotope over it's kin. But I'm not thinking of any that would work on a dust grain, assuming it had ever been part of a planet.
Yeah, I can't argue with the showmanship aspect to science. I'm actually slightly guilty of playing the astrobiology card in a paper that I've written.
I'm not sure you'll see heat build-up, though. The sparks probably won't produce much energy, certainly less than the thermal energy produced directly by the impact. And that diffuses away fairly quickly at these temperatures. I forget the the exact timescales, but recall that passing into and out of Jupiter's shadow is enough time for the moons to heat and cool significantly. That timescale is of order a day or few.
Textbooks are often wrong in the details. If that is your only point, you went through a lot of trouble to say nothing remotely new to anyone here. And you phrased it extraordinarily badly, too.
As for "choices", I was -admittedly- anthropomorphicizing somewhat. I imagine you are smart enough to know that, though. Right? You can replace "chose" with "life came to use", if you are a stickler for undue precision.
The point of the Urey-Miller experiment wasn't to show the way organics were produced, it was to demonstrate that they CAN be produced by such methods. Similar experiments have been run with dozens of permutations on the atmosphere and energy sources, and they generally produce organics. In fact, a range of different experiments with a variety of catalysts, like some clays, have also been performed, with similar results. A quick literature search would have told you that.
The point of these experiments is not to reproduce the early-Earth conditions exactly. We still don't know what those are. But the fact that such a wide variety of conditions produce organics is an indication that the goop is easy to form and probably did so on the early-Earth, regardless of the conditions.
(Your point about the chirality of the amino acids is a red herring. There is no reason to think that life was formed in a soup of only one chirality. All we know is that somehow life on Earth has evolved to use only one of those. It isn't hard to imagine that one or the other might have a slight advantage or even that life had to - at some early stage - chose just one and use it. Dealing with both L and D forms all the time would probably require a lot more effort than it's worth.)
This result is certainly interesting, but I don't think it really pushes the case of organics on Europa much farther than it already was. I'm a little skeptical that electric sparks in an ice matrix will do a lot to generate organic molecules, for starters. (With compounds in the ice, there is very limited mobility, so that chemical reactions just don't occur very often. My guess is that you can spark it all you like, but in most case, nothing will happen.) Research needs to be done on that problem before they have much of a case.
Even then, this is hardly ground-breaking. Electric sparks are not the only way to generate organics. Urey and Miller also showed that UV light can do the same thing. All you really need is a high-energy source to break up some bounds and allow new ones to form. Heck, even the particle radition in Jupiter's magnetosphere can probably do some of that. The UV flux is down by a factor of 27 from that at Earth (top of the atmosphere, now at the surface where ozone and other molecules have attenuated it), but I'd bet you can provide more activation energy that way than with little electric shocks from impacts.
That said, it's a damn cool result without all the "Life on Europa" hype.
Excellent point. In fact, let me add to it:
Many citiations now are copied from ONLINE SOURCES. We read the papers, but we hate typing in our bibliography from scratch. I can just go to ADS (http://adsabs.harvard.edu) and have it print out the reference in BIBTeX format for me. Now, there are quite a few typos in that database. I know because we're finding them while creating a bibliography for the upcoming Juptier book.
None of this implies that we're not reading papers we cite. In fact, from experience, people in my field (astronomy) know the papers they reference pretty well, as a rule. There are times when we don't read an entire paper because we're just taking a few numbers or an equation, but as a whole, it pays to know the papers. If you don't, you'll usually find yourself under fire from your collegue who wrote the mis-quoted paper. Quite often, that collegue will be the journal referee who is reviewing the paper before publication. This is *not* a position you want to be in, so people generally work to avoid it.
It is very unlikely that either comet or meteorites would have survived that long. Even at 1 AU, the Sun would have long ago made most of the volatiles on the comet disappear. Failing that, 4.5 billion years is plenty long enough for some sort of collision to have occured, removing comet/meteorites from circulation.
Besides, what would the connection actually be? Comets don't come from rocky bits, they're mainly ice. So you wouldn't have probably formed any cometary material in the giant impact that formed our Moon. And even if you did, it is difficult to get it onto such a highly eccentric orbit.
All in all, it doesn't seem a likely area of interet. But it's still a pretty meteor shower.
The article is actually rather scant on details. But it is my guess that they are NOT going to be generating small-scale detailed models. So no views of planet surfaces. I'm guessing that they're going to use the planetary parameters as inputs and see how different organisms thrive or die off. The alternative is just much too complex and full of unknow parameters.
Which means that this project is inherently very limited in its abilities. They'll have to work on averaged and estimated behaviors for the biota and they can't investigate detailed niches. Most disturbing from a biological perspective is that they are really only investigating "live as we know it", since we have no idea how other life forms might exist. So in a very real sense they aren't really learning a whole lot that is new.
This is just my impression and interpretation, though. If they can do more detailed models, I'd be deeply, deeply impressed.