Ring particles are typically at most a few meters across. A 5 km body would be much larger than this and therefore rather distinct. Even a modest population of them would also probably not fit into the size distribution of the ring material. And their influence on the ring dynamics isn't like the background ring particle population's. So all in all, it makes sense to think of them as something apart from normal ring material.
Theorists have posited the existance of small moons (~5 km) inside the F ring for some time. They could explain the odd look and behavior of the F ring, although they are not the only possibility. If these new objects are moons and not temporarly clumps of ring material, it will be interesting to see how the models and data agree (or don't agree).
"Further googling (I won't call it research) shows that galactic rotation is both clockwise and anti clockwise."
I'm not sure what you mean by that. Our galaxy has one spin-sense. Which way it seems to go depends on which side you look from, of course. But the disk pretty much all goes in the same direction.
And excellent point about the Milky Way in the night sky. I should have pointed out that it's oriented funky relative to the ecliptic, but you nailed it.:-)
I can't see why it would be impossible, but the effects of scattering are almost always to increase eccentricity. You're giving the planet a fairly random kick, it's hard to imagine that you first have a highly eccentric orbit (which implies a previous kick) which meets the giant planet just right to cancel out the current eccentricity.
Triton is an odd case. It's the only large moon that has a retrograde orbit and it's thought to be captured. A quick tour of the solar system shows that almost everything orbits (which is where the real angular momentum is) and spins in the same direction. There are a handful of exceptions, many of them explained as captured moons, Oort cloud comets, or results of large collisions.
Since I don't think we know the spin direction of the parent stars or the the orbit directions of the planets, I doubt that the statistics about the retrograde planets are availible. However, I can't point out a single major planet (not even Pluto) in our system that orbits retrograde. Minus the comets (which have been reintroduced after significant galactic and stellar purtubations), I can't think of anything that orbits retrograde about the Sun, in fact.
And you'd be wrong, at least for the solar system. We're highly inclined relative to the galaxy. Moreover, multi-star systems are orbit each other at random with respect to the galactic disk. So we conclude that star systems get their angular moment from random motions not systematic galactic ones.
No, it shouldn't be spinning at the current angular velocity initially. But it should be spinning by virtue of the fact that everything in the universe that we've seen spins. As the cloud collapses (and becomes more disk-like), it has to speed up by conservation of angular momentum. (It's the skater pulling her arms in thing.) So that's where that comes from.
Well, we checked on at least one of the transiting planet and no moons were detected. Still, it's possible.
The flip side is that planet migration is hazardous for moons. There are a few effects that might mess with them, including tides from the star (once you're close to the star) the differential Yarkovsky effect (also for close planets), scattering of planetesimals (during migration this might be common), gas drag, and the migration itself.
The planets themselves might host life, but that's been deemed unlikely. There's not a lot of interesting chemistry or useful chemcials per volume of the atmosphere and it's hard to support organisms. (Small stuff can stay aloft and so can really big things, if they're properly designed. But intermediate sizes don't work.)
None of this says either thing is impossible. But it does make the odds longer.
Nope, things don't clump more as you get closer in. Actually if anything you might expect less clumping because collisions speeds are, on the average, higher. But really, what is going on is that the spin counters the star's gravity almost exactly. (The lack of exactness is made up for in the slight gas pressure. The result of this is to slow the orbital speed of the gas down a bit mainly. The pressure effect is compartively minor relative to the gravity/orbit so while the smaller dust grains might feel slight buoyancy, there shouldn't be much. Especially since the gas is also turbulent and probably in possession of a magnetic field, either of which could overwelm the buoyancy behavior.)
Yeah, the stellar ignition will star clearing the gas and small dust out of the disk. By then the planetary cores had better have formed, though. Otherwise there wouldn't be much left to build with. So this is just the end of the planet formation process, it doesn't really have a big effect on what kinds of planets you get where.
Nope, we're not sure. There's a competing model involving a gas instability, but it's not widely adhered to for a variety of reasons. We're not even 100% certain our gas giants didn't for that way, though. The other ones we're mostly extrapolating with.
There are problems with getting spectra from most of the planets found so far, so we're half in the dark to be sure. (Literally and figuratively.) As always in astronomy, you assume things are the same as locally until proven otherwise.:-)
No, it isn't about tides or about denser stuff settling out. (That's a buoancy effect that occurs in fluids with pressure-support. That doesn't really occur in disks, which are mostly just in orbit.)
The difference in planets is due to temperature in the disk. Since it's colder farther out, ices can freeze and be used to build the cores. Once the core is large enough, you get gas capture and jovian planets.
One thing that frustrates me about the articles I've seen on this subject is that they don't explain why formation of big, close-in gas giants precludes formation of Earth-like planets farther out. Accretion disks are really, really big; surely parts of them can clump into gas giants while others slowly form smaller, rocky planets?
Here's the explanation: gas giants have to form farther out, past the "frost-line" where ices can first freeze out of the gas disk. In order to be a hot Jupiter, the have to migrate inward toward the star. That migration is slow, but if the planet encounters a terrestrial planet then the terrestrial planet is in trouble because the giant planet will either scatter it out of its way (either out of system, into the Sun, or at least into a fairly eccentric orbit, none of which is good for habitability) or accrete it. And if there is a terrestrial planet, the giant planet will encounter it on the way in since, by the standard model for planet formation, the terrestrial planets will be in the giant planet's path.
From the Forbes article linked in to the story: "SCO says it discovered the e-mails in a mountain of documents IBM produced in discovery related to SCO's lawsuit against IBM over the Linux operating system."
The inner planets are rocky/metallic because it was too hot for ices to form. Most of the proto-solar disk would have been in the form of hydrogen and helium. The next most abundant elements are oxygen, carbon, and nitrogen. With so my of these and hydrogen, hydrogen compounds (water, ammonia, methane) can do a lot of planet building if they can form solids. Near the proto-Sun, it would habe been too hot for this to happen. Somewhere around 5 AU, water ice could first freeze out. Not surprisingly, you find jovian planets starting around that point. (They have the gases because they were able to get large enough fast enough to trap some of the gas in the disk before the disk dissipated. The terrestrial planets are too small to accomplish this because they never had enough solid materials around to build themselves with.)
You would have found that the composition of the proto-solar disk was probably pretty uniform. The acceration of gravity is higher near the center thanks to the proto-Sun, but that's a red herring. The acceleration is balanced by the orbital motion. The mass of the orbiting object doesn't factor into the motion, so hydrogen gas orbits the same as rock particles. (Well, almost. Gases are subject to gas pressures, but that wouldn't make them move inward or outward, it just slows their orbital speed some.)
Not true. Galileo flew through Jupiter's ring and Voyager 2 and Pioneer 11 flew through a gap in Saturn's ring. (Which is what Cassini just did, albeit a different gap and with full knowledge of what they were doing this time.)
"Chronian" is never used, in my experience, although the stem does work into a few peculiar words, like "perichrone" (closest approach to Saturn in an orbit). Even then, I seldom hear those words used.
What do you mean, variables are what really kill you? You mean unknowns? Things you can't control?
Something can always go wrong with *any* spacecraft. That's not at all unique to being around Saturn. So to be especially nervous about the ring passage would be silly. If anything, I think NASA was more worried about the engine burn going off alright.
If they can't manuver the spacecraft around to position the antenna, they can't manuver it around to make burns or to take data, so it's not a serious concern. (The antenna doesn't move, the whole spacecraft does.)
Overall, they wouldn't be in a lot of danger anyway. Some, but not a lot. Not scientific spacecraft has been lost from meteroid collision and the only case that I know of where one was even messed with by collisions are in comet flybies. (Gitto lost control flying by Halley, which is the case that springs to mind.)
There wasn't much danger of a serious collision. They passed through a gap in the rings and the probe was checking the region out several weeks ago for possible threats. Besides, Cassini will be using the high-gain antenna dish as a shield when passing through the rings, so the spacecraft itself isn't in a lot of danger.
And your point is what? That this somehow automagically makes him not risk adverse now?
No, it explains *why* he got this way, perhaps. But it doesn't address the criticism which amounts, in effect, to saying that he's reacted too far the other way now.
It's important to learn from your mistakes. But make sure that you learn the *right* lessons.
Yep, NASA and O'Keefe have become paranoid by the risks. O'Keefe even brought up the criticism of him that he was "risk-adverse". How did he address it? By beating the fact that 7 astronauts were lost on Columbia into the audience's skulls. (I was there, it was disgusting to watch. It was like the Bush Administration using 9/11 and terrorism to justify pretty much everything it wants to do.) In other words, he told us WHY he was risk-adverse, he didn't argue that he wasn't.
However, I'm predicting as ISS resumes contruction and deadlines loom, they'll be taking ever bigger gambles with the shuttles and the lives of the astronauts to build it. Keep an eye on the details when they return to flight and see how many of the CAIB's recommendations are really followed. O'Keefe promised that every one of them had to be done (which is why, he claims, SM4 is too dangerous), but I'm betting that if we go back and check we'll see that many weren't taken care of. For example, see if they have that autonomous repair kit when they fly to ISS.
At the AAS meeting, someone said to me that -- having seen the cost estimates on the robotic repair mission -- it would, in fact, be cheaper to build and launch a new HST. We could use the spare parts, including Kodak's backup mirror (the one that DIDN'T have the flaw) and the good gyros. Hell, sending astronauts there would be cheaper than the robotic mission. (A typical shuttle flight costs about $200 million, as I recall.)
On the one had, I applaude NASA's attempt to get the robotic technology to this point. On the other, this is NOT the mission. We have a deadline that has to be met and an instrument that will be lost if we screw it up. It would be better to pick a nontime-critical project with fewer worries about breaking something valuable if something goes wrong. Worse, this is about the most tricky project you could try for a beginning. HST was designed to be serviced by astronauts, that's true. But it doesn't make it easy to do. As I recall, the astronauts had great difficulty manuvering stuff in and out, not to mention getting the door on HST closed afterward. A robot doesn't stand a chance.
Frankly, I don't think O'Keefe is out to save HST. I think he only hopes to de-orbit it. That's the way he prioritized it (rightly) and I suspect that at the end of the summer we're going to hear something like, "Oh, dear. While we can deorbit Hubble, the repair looks too difficult/expensive. Oh, well." Meanwhile, the dogs have been called off of O'Keefe and when he makes the final decision there will be less of a chance to reverse it.
I'm especially not surprised, since I've read reports of bacteria that have been found in the cooling pools for the spent nuclear fuel rods at reactor sites. Apparently, the little buggers are related to the guys that live in the hypersaline environments. The same celluar repair machinery works for both the saline damage and the radiation damage.
Actually, Latin was the language of the... Latins! Rome was but one city in that region (approximately what is now Lazio in Italy). Rome eventually become the most important city, and then an empire proper. But culturally, it was just part of Latium.
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Ring particles are typically at most a few meters across. A 5 km body would be much larger than this and therefore rather distinct. Even a modest population of them would also probably not fit into the size distribution of the ring material. And their influence on the ring dynamics isn't like the background ring particle population's. So all in all, it makes sense to think of them as something apart from normal ring material.
Theorists have posited the existance of small moons (~5 km) inside the F ring for some time. They could explain the odd look and behavior of the F ring, although they are not the only possibility. If these new objects are moons and not temporarly clumps of ring material, it will be interesting to see how the models and data agree (or don't agree).
"Further googling (I won't call it research) shows that galactic rotation is both clockwise and anti clockwise."
:-)
I'm not sure what you mean by that. Our galaxy has one spin-sense. Which way it seems to go depends on which side you look from, of course. But the disk pretty much all goes in the same direction.
And excellent point about the Milky Way in the night sky. I should have pointed out that it's oriented funky relative to the ecliptic, but you nailed it.
I can't see why it would be impossible, but the effects of scattering are almost always to increase eccentricity. You're giving the planet a fairly random kick, it's hard to imagine that you first have a highly eccentric orbit (which implies a previous kick) which meets the giant planet just right to cancel out the current eccentricity.
Triton is an odd case. It's the only large moon that has a retrograde orbit and it's thought to be captured. A quick tour of the solar system shows that almost everything orbits (which is where the real angular momentum is) and spins in the same direction. There are a handful of exceptions, many of them explained as captured moons, Oort cloud comets, or results of large collisions.
Since I don't think we know the spin direction of the parent stars or the the orbit directions of the planets, I doubt that the statistics about the retrograde planets are availible. However, I can't point out a single major planet (not even Pluto) in our system that orbits retrograde. Minus the comets (which have been reintroduced after significant galactic and stellar purtubations), I can't think of anything that orbits retrograde about the Sun, in fact.
And you'd be wrong, at least for the solar system. We're highly inclined relative to the galaxy. Moreover, multi-star systems are orbit each other at random with respect to the galactic disk. So we conclude that star systems get their angular moment from random motions not systematic galactic ones.
No, it shouldn't be spinning at the current angular velocity initially. But it should be spinning by virtue of the fact that everything in the universe that we've seen spins. As the cloud collapses (and becomes more disk-like), it has to speed up by conservation of angular momentum. (It's the skater pulling her arms in thing.) So that's where that comes from.
Well, we checked on at least one of the transiting planet and no moons were detected. Still, it's possible.
The flip side is that planet migration is hazardous for moons. There are a few effects that might mess with them, including tides from the star (once you're close to the star) the differential Yarkovsky effect (also for close planets), scattering of planetesimals (during migration this might be common), gas drag, and the migration itself.
The planets themselves might host life, but that's been deemed unlikely. There's not a lot of interesting chemistry or useful chemcials per volume of the atmosphere and it's hard to support organisms. (Small stuff can stay aloft and so can really big things, if they're properly designed. But intermediate sizes don't work.)
None of this says either thing is impossible. But it does make the odds longer.
Nope, things don't clump more as you get closer in. Actually if anything you might expect less clumping because collisions speeds are, on the average, higher. But really, what is going on is that the spin counters the star's gravity almost exactly. (The lack of exactness is made up for in the slight gas pressure. The result of this is to slow the orbital speed of the gas down a bit mainly. The pressure effect is compartively minor relative to the gravity/orbit so while the smaller dust grains might feel slight buoyancy, there shouldn't be much. Especially since the gas is also turbulent and probably in possession of a magnetic field, either of which could overwelm the buoyancy behavior.)
Yeah, the stellar ignition will star clearing the gas and small dust out of the disk. By then the planetary cores had better have formed, though. Otherwise there wouldn't be much left to build with. So this is just the end of the planet formation process, it doesn't really have a big effect on what kinds of planets you get where.
Nope, we're not sure. There's a competing model involving a gas instability, but it's not widely adhered to for a variety of reasons. We're not even 100% certain our gas giants didn't for that way, though. The other ones we're mostly extrapolating with.
:-)
There are problems with getting spectra from most of the planets found so far, so we're half in the dark to be sure. (Literally and figuratively.) As always in astronomy, you assume things are the same as locally until proven otherwise.
No, it isn't about tides or about denser stuff settling out. (That's a buoancy effect that occurs in fluids with pressure-support. That doesn't really occur in disks, which are mostly just in orbit.)
The difference in planets is due to temperature in the disk. Since it's colder farther out, ices can freeze and be used to build the cores. Once the core is large enough, you get gas capture and jovian planets.
One thing that frustrates me about the articles I've seen on this subject is that they don't explain why formation of big, close-in gas giants precludes formation of Earth-like planets farther out. Accretion disks are really, really big; surely parts of them can clump into gas giants while others slowly form smaller, rocky planets?
Here's the explanation: gas giants have to form farther out, past the "frost-line" where ices can first freeze out of the gas disk. In order to be a hot Jupiter, the have to migrate inward toward the star. That migration is slow, but if the planet encounters a terrestrial planet then the terrestrial planet is in trouble because the giant planet will either scatter it out of its way (either out of system, into the Sun, or at least into a fairly eccentric orbit, none of which is good for habitability) or accrete it. And if there is a terrestrial planet, the giant planet will encounter it on the way in since, by the standard model for planet formation, the terrestrial planets will be in the giant planet's path.
From the Forbes article linked in to the story:
"SCO says it discovered the e-mails in a mountain of documents IBM produced in discovery related to SCO's lawsuit against IBM over the Linux operating system."
It appears legit, then.
Not quite, no.
The inner planets are rocky/metallic because it was too hot for ices to form. Most of the proto-solar disk would have been in the form of hydrogen and helium. The next most abundant elements are oxygen, carbon, and nitrogen. With so my of these and hydrogen, hydrogen compounds (water, ammonia, methane) can do a lot of planet building if they can form solids. Near the proto-Sun, it would habe been too hot for this to happen. Somewhere around 5 AU, water ice could first freeze out. Not surprisingly, you find jovian planets starting around that point. (They have the gases because they were able to get large enough fast enough to trap some of the gas in the disk before the disk dissipated. The terrestrial planets are too small to accomplish this because they never had enough solid materials around to build themselves with.)
You would have found that the composition of the proto-solar disk was probably pretty uniform. The acceration of gravity is higher near the center thanks to the proto-Sun, but that's a red herring. The acceleration is balanced by the orbital motion. The mass of the orbiting object doesn't factor into the motion, so hydrogen gas orbits the same as rock particles. (Well, almost. Gases are subject to gas pressures, but that wouldn't make them move inward or outward, it just slows their orbital speed some.)
Not true. Galileo flew through Jupiter's ring and Voyager 2 and Pioneer 11 flew through a gap in Saturn's ring. (Which is what Cassini just did, albeit a different gap and with full knowledge of what they were doing this time.)
You can also find pictures at the CICLOPS site.
"Saturnian" is correct.
"Chronian" is never used, in my experience, although the stem does work into a few peculiar words, like "perichrone" (closest approach to Saturn in an orbit). Even then, I seldom hear those words used.
M-W has you covered. Most astronomers I know pronounce it like "Hoi-gens" (hoi like in "a-hoy", gens with a hard g).
What do you mean, variables are what really kill you? You mean unknowns? Things you can't control?
Something can always go wrong with *any* spacecraft. That's not at all unique to being around Saturn. So to be especially nervous about the ring passage would be silly. If anything, I think NASA was more worried about the engine burn going off alright.
If they can't manuver the spacecraft around to position the antenna, they can't manuver it around to make burns or to take data, so it's not a serious concern. (The antenna doesn't move, the whole spacecraft does.)
Overall, they wouldn't be in a lot of danger anyway. Some, but not a lot. Not scientific spacecraft has been lost from meteroid collision and the only case that I know of where one was even messed with by collisions are in comet flybies. (Gitto lost control flying by Halley, which is the case that springs to mind.)
There wasn't much danger of a serious collision. They passed through a gap in the rings and the probe was checking the region out several weeks ago for possible threats. Besides, Cassini will be using the high-gain antenna dish as a shield when passing through the rings, so the spacecraft itself isn't in a lot of danger.
And your point is what? That this somehow automagically makes him not risk adverse now?
No, it explains *why* he got this way, perhaps. But it doesn't address the criticism which amounts, in effect, to saying that he's reacted too far the other way now.
It's important to learn from your mistakes. But make sure that you learn the *right* lessons.
Yep, NASA and O'Keefe have become paranoid by the risks. O'Keefe even brought up the criticism of him that he was "risk-adverse". How did he address it? By beating the fact that 7 astronauts were lost on Columbia into the audience's skulls. (I was there, it was disgusting to watch. It was like the Bush Administration using 9/11 and terrorism to justify pretty much everything it wants to do.) In other words, he told us WHY he was risk-adverse, he didn't argue that he wasn't.
However, I'm predicting as ISS resumes contruction and deadlines loom, they'll be taking ever bigger gambles with the shuttles and the lives of the astronauts to build it. Keep an eye on the details when they return to flight and see how many of the CAIB's recommendations are really followed. O'Keefe promised that every one of them had to be done (which is why, he claims, SM4 is too dangerous), but I'm betting that if we go back and check we'll see that many weren't taken care of. For example, see if they have that autonomous repair kit when they fly to ISS.
At the AAS meeting, someone said to me that -- having seen the cost estimates on the robotic repair mission -- it would, in fact, be cheaper to build and launch a new HST. We could use the spare parts, including Kodak's backup mirror (the one that DIDN'T have the flaw) and the good gyros. Hell, sending astronauts there would be cheaper than the robotic mission. (A typical shuttle flight costs about $200 million, as I recall.)
On the one had, I applaude NASA's attempt to get the robotic technology to this point. On the other, this is NOT the mission. We have a deadline that has to be met and an instrument that will be lost if we screw it up. It would be better to pick a nontime-critical project with fewer worries about breaking something valuable if something goes wrong. Worse, this is about the most tricky project you could try for a beginning. HST was designed to be serviced by astronauts, that's true. But it doesn't make it easy to do. As I recall, the astronauts had great difficulty manuvering stuff in and out, not to mention getting the door on HST closed afterward. A robot doesn't stand a chance.
Frankly, I don't think O'Keefe is out to save HST. I think he only hopes to de-orbit it. That's the way he prioritized it (rightly) and I suspect that at the end of the summer we're going to hear something like, "Oh, dear. While we can deorbit Hubble, the repair looks too difficult/expensive. Oh, well." Meanwhile, the dogs have been called off of O'Keefe and when he makes the final decision there will be less of a chance to reverse it.
I'm especially not surprised, since I've read reports of bacteria that have been found in the cooling pools for the spent nuclear fuel rods at reactor sites. Apparently, the little buggers are related to the guys that live in the hypersaline environments. The same celluar repair machinery works for both the saline damage and the radiation damage.
Actually, Latin was the language of the... Latins! Rome was but one city in that region (approximately what is now Lazio in Italy). Rome eventually become the most important city, and then an empire proper. But culturally, it was just part of Latium.