The radius is indeed a guess (it has not been measured), but it's an educated guess based on the planet's mass. The current, best model for planet formation involves rocky material forming a large core early in a stellar system's life. These rocky cores, once they reach a critical mass of 15-20 Earth masses, begin to accrete gas and grow to form giant gas planets like Jupiter and Saturn. As evidence, Uranus and Neptune have around 2 Earth masses of gas and 15 Earth masses of rock. According to this model, GL 876 d is so small (only around 7 Earth masses) that it could not have accumulated significant amounts of gas, so it must be rocky.
From the press release: Though the team has no direct proof that the planet is rocky, its low mass precludes it from retaining gas like Jupiter.
and "The planet's mass could easily hold onto an atmosphere," noted Laughlin, an assistant professor of astronomy at UC Santa Cruz. "It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that's intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune."
Most extrasolar planets are found by the precision radial velocity technique. The orbiting planet induces a reflex motion in the star (like in track & field when the hammer thrower leans back and revolves about the center of mass a little while the hammer moves a lot). We can detect this reflex motion as a change in the star's radial velocity. These velocities have magnitudes of hundreds or even tens of meters per second.
A limitation of this technique is that if a planet orbits its star in the plane of the sky, there will be no radial component to the star's reflex velocity, so we won't detect it. Further, unless the planet orbits with an inclination such that it passes nearly in front of the star, we will measure only a fraction of the total reflex motion.
This means that when we detect a planet, we can only put lower limits on the mass of the planet, since the signal could be from a massive planet in a nearly face-on orbit, or a tiny planet in an edge-on orbit. This ambiguity is proportional to the sine of the inclination (the "tilt"), so what we measure to be the mass of the planet is actually M*sin(i), where M is the true mass of the planet.
What these folks have done is use an instrument on HST to make extremely accurate measurements of the position on the sky of a star known to have planets, and used these measurements to measue the path of the star in the plane of the sky as it wobbles under the influence of the orbiting planet. This measures the missing tangential component of the reflex velocity, resolving the sin(i) ambiguity, and determining M itself. This is only the second time anyone has precisely determined the inclination of one of these planets.
it seems very possible that the planet might have a moon of roughly Earth's size and climate. I believe this is the first discovery that comes close to matching those criteria."
Other planets visit their star's habitable zones, too. Even though most of these other planets have eccentric orbits which would take them in and out periodically, they still "come close to matching those criteria".
Also a much better link to details of the Gamma Cephei system can be found here.
Interesting question: if each civilization emits a 100 light-year thick shell of narrow-band rf, what are the chances that we are in at least one such shell now?
The parent post contains so much flawed logic and bad astronomy, it boggles the mind.
Though how this relates to a 100 light year sphere around earth confuses me: The article is pretty clear that the 100th planet is "symbolic". It's in really big font in a colored box -- you can't miss it! Anyway, it's not this 100th planet that leads to the 30 billion number. It's just a lead in for the article.
While the 300 billion stars is correct, a vast majority of them are on the galatic disk or in the galatic core, where the gravity of the densely packed stars would prevent planet formation according to any currently held theory.: Wow -- that's news to astronomers. We're in the disk, and our sun formed planets, so it can't be that hard!
most of the exo-solar planets that have been found so far are multiple Jupiter-sized and orbiting so close to the star that it doesn't resemble our solar system, the only one we really know about, making any inferences about the existence of other planets useless and pointless
: Oh, so knowing how commonly planets form has nothing to do with how many planets are in the galaxy?!? Knowing that 10 percent of stars near us have detectable planets is astonishing: we can only regularly detect these weird "hot Jupiters" right now. This implies that, unless these systems are for some reason much more common than other planetary systems, a substantial fraction of all stars bear planets. In that case, 30 billion is a reasonable guess -- maybe on the low side!
The final link in the logical chain is provided in the article itself:
But even in this "biased" survey of giants, the smaller worlds predominate - which makes astronomers think that Earth-like worlds do exist. They may even be as common as Jupiter-sized exoplanets.
In other words, if you make a histogram of exoplanets sorted by mass, you see that the least-massive ones are the most common. Go to exoplanets.org and see for yourself. So the above caveat that "hot Jupiters" might be more common than other kinds of planets seems unlikely.
Yes, the author has dumbed down the science to the point where it can be hard to figure out what he's writing about, but that per se doesn't boggle the mind of anyone who reads the science section of any major paper.
> Perhaps the courts are saying the answer is
> "No, everyone should have access to all the
> information that can be provided for them."
That is what the First Amendment says, basically, although the courts are not saying that the government has any obligation to provide such information.
The court decided that the Internet was a close analog to the Founders' idea of "the press" and that terminals in public libraries were government-sponsered fora for the free exchange of ideas, like parks and sidewalks (I'm summarizing, read the article). This, the court said, is the kind of speach that gets some of the strongest First Amendment protection of all, and so the court was able to use very strict tests to determine if the law is constitutional. Since the law effectively inhibited some lawful speach to prohibit some unlawful speach, it failed.
> The 1/r^2 law is only true for isotropic
>radiation -- not for a directed laser beam,
>which can remain well-collimated over great
>distances.
Note that unless the laser beam is perfectly collimated you still lose as 1/r^2. The inverse square law is not unique to isotropic radiation. Think about it: the area of the base of a cone goes as the height squared no matter how narrow the cone is, just like the area of a sphere goes as the radius squared.
As long as all of the laser light is hitting the sail it doesn't matter, of course, but once you're far enough away that the laser beam is bigger than your sail, you start to lose. This isn't really a bad thing, though, since presumably you can only point the laser with some fixed accuracy, so you need bigger and bigger beams for more and more distant ships. Although I suppose the ships could try to actively stay on the beam, it's still a rather strict stability requirement for the laser to have to hit an object light years away and keep it steady for years.
I don't know as I'd consider any adult in the prime of their life who could go 3+ years without sexual release to be particularly sane. Or were you just thinking they'd send an equal balance of the sexes so that no one needs any sex toys?
All I meant was that the original poster's implication that NASA was somehow encouraging alcoholics and sex-addicts to sign up for important missions was far-fetched. I didn't mean to imply that booze and blow-up dolls would be inappropriate on such trips -- quite the opposite.
> Dont send all that stuff to Mars with these people, folks..really.
Who's going to Mars? The post is about a trip to the arctic.
> We shouldnt be sending people who'll need their booze and blowup dolls by any means.
For any potential Mars mission no one who "needs" booze and blow-up dolls would be selected. Luxury items will certianly be included, however, since the crew will have to stay sane, comfortable, and amicable on the 3+ years the mission would take.
>We should be sending Marines there and oil rig miners...
Oh, like in Aliens and Armageddon!
> Dont think their aren't sci fi hacks who couldnt get published sitting at CIA analyst desks right now thinking about this stuff.
...or posting on Slashdot. I'm sorry... why on Earth (or Mars) would the CIA care about the social dynamics of a colony that won't even exist for at least a century?
We have found that the excursion
times between X-ray minima in Cyg X-2 can be characterized as a series of integer multiples of the 9.8 binary orbital period... In the black hole candidate system LMC X-3, the excursion times are shown to be related to each other by rational fractions. We find that the long
term light curve of the unusual galactic X-ray jet source Cyg X-3 can also be described as a series of intensity excursions related to each other by
integer multiples of a fundamental underlying clock. In the latter cases, the clock is apparently not related to the known binary periods.
But that doesn't mean that the model is wrong. Their model involves a third object with its own orbital period that disturbs the disk, causing the flares. This would have a period unrelated to the orbital period of the binary, and the multipliers would not be completely random but would have a predictable propability distribution.
The measurements of extrasolar planets don't constrain alternate gravities very well, since the distances at which these are detected from their parent stars is similar to those of our planets around the Sun, whose positions we can measure much more accurately.
Gravity at short ranges is being tested now (on scales of, like, inches) as a test of some superstring theories.
If gravity does not have a 1/r^2 dependence, things get really messy, really fast. First of all if you have to introduce a new length scale into the universe (such as a length within or beyond which a different law applies) then you have basically introduced a new constant of nature.
Secondly, it means that GR is wrong in some fundamental ways, so you have to work very hard to recover the successful tests of GR while still scrapping the guts theory itself.
Finally, remember that we HAVE tests of gravity at the ranges we're talking about -- Pluto's orbit is pretty well-determined, and Neptune and Uranus are out there, and Earth and Mars turn out to put very strong constraints on this, too (see the article for details, p.77); galaxies attract each other about the way we expect; there are plenty of long-period binary stars with this sort of separation that have been studied; etc.
I'm not saying that there's no way that gravity itself could be the culprit in the anomolous position of the craft; I'm just saying that the nature of gravity is pretty tightly constained by observation, so throwing stuff off like "it's different at large distances" opens a whole can of worms that have to be shoved back into some new theory.
> I've seen several posts already saying the
> number of violent crimes committed by youth has
> dropped. Oh yay us. Let's give kids more violent
> games. Well.. yes the pure numbers show
> that. However, there is also a lot less kids
> than then there were. So while the rates go
> up.. the numbers are going down.
*BZZT* Wrong, but thanks for playing. Numbers AND rates for violent crime among youth have dropped:
Pay particular attention to the section "Arrest rates":
Studies of changes in juvenile crime should always consider the
possibility that fluctuations in the juvenile population may be
responsible for trends seen in the number of arrests reported by law
enforcement.
This was not the case during the recent crime drop. Even controlling
for changes in the population, the rate of decline in juvenile arrests
outpaced that of other age groups.
But now this statement is easily testable. According to the RIAA, sales of singles should jump 39% now that Napster is shut down. Or something like that...
Without the tests, your poor kid with the 4.0 but no APs because they aren't offered and no SAT scores to back him up doesn't get in, but the kids from the private schools with 3.6 GPAs with a reputation for excellence do.
The UC system already allows the top 4% of students from any California school to bypass the SATs entirely, so it DOES recognize that a 4.0 from a bad school can mean a lot.
Also, the UC system would not ignore SATs under the new plan, it would just make them optional. Students could still submit them to demonstrate potential, and most who did well probably would.
Your statements that Mr. Atkinson "wants to hurt" students like you and "HAS NOT thought through his situation" are unfounded exaggerations.
Then the gov't does not have that particular compelling interest and the producer's individual rights carry more weight in the balancing. After all just saying a sentence like "Child pornographers explicitly depict children engaged in sexual activity" is itself a depiction of said activity (albiet a very abstract one), but it would not be covered by virtual child pornography laws. The government is allowed to write laws that are subject to interpretation and descretion.
That same argument IS made for so many things. e.g.: in times of civil unrest curfews restrict freedom of movement and association, and "the end result is that legitimate actions and expressions are criminalized to make it easier for the police." Encryption is another good example. The point is that it's not unconstitutional for the government to make these kinds of laws when it has a compelling interest, which is why the appeal will fail and "virtual" kiddie porn will remian illegal. The law is bad, but not unconstitutional.
Remember, the ULTIMATE source of the wisdom of our laws was supposed to be the voice of the people through the legislature, not the chanelling of constitutional guarantees through the courts. The constitution protects against tyrrany, not folly.
Anyway, the "slippery slope" argument is a red herring. The courts have to balance on a slippery slope all the time. The alternative is that individual rights overwhelm ANY national or social interest, which undermines the whole social contract the Framers intended. There's a slippery slope down the other side of the hill, as well.
The government certainly has the right (and, more importantly, a compelling interest) to procescute true child pornographers. If "virtual" kiddie porn makes it impossible or much more difficult to do that ("that's not a real kid, your honor! honest! i used photoshop!") then the government has an interest in banning that, too. It's a balancing issue: the government is claiming that society's need to punish real child pornographers outweighs an individual's rights to produce virtual kiddie porn.
That's the government's position, according to news reports, at least. It's not unreasonable that the SC will agree with that position: the other federal courts (except the 9th appeals) have.
Slashdot Mirror
http://newton.nap.edu/books/0309075742/html/
http://www.ipcc.ch/pub/reports.htm
The radius is indeed a guess (it has not been measured), but it's an educated guess based on the planet's mass. The current, best model for planet formation involves rocky material forming a large core early in a stellar system's life. These rocky cores, once they reach a critical mass of 15-20 Earth masses, begin to accrete gas and grow to form giant gas planets like Jupiter and Saturn. As evidence, Uranus and Neptune have around 2 Earth masses of gas and 15 Earth masses of rock. According to this model, GL 876 d is so small (only around 7 Earth masses) that it could not have accumulated significant amounts of gas, so it must be rocky.
From the press release:
Though the team has no direct proof that the planet is rocky, its low mass precludes it from retaining gas like Jupiter.
and
"The planet's mass could easily hold onto an atmosphere," noted Laughlin, an assistant professor of astronomy at UC Santa Cruz. "It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that's intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune."
A limitation of this technique is that if a planet orbits its star in the plane of the sky, there will be no radial component to the star's reflex velocity, so we won't detect it. Further, unless the planet orbits with an inclination such that it passes nearly in front of the star, we will measure only a fraction of the total reflex motion.
This means that when we detect a planet, we can only put lower limits on the mass of the planet, since the signal could be from a massive planet in a nearly face-on orbit, or a tiny planet in an edge-on orbit. This ambiguity is proportional to the sine of the inclination (the "tilt"), so what we measure to be the mass of the planet is actually M*sin(i), where M is the true mass of the planet.
What these folks have done is use an instrument on HST to make extremely accurate measurements of the position on the sky of a star known to have planets, and used these measurements to measue the path of the star in the plane of the sky as it wobbles under the influence of the orbiting planet. This measures the missing tangential component of the reflex velocity, resolving the sin(i) ambiguity, and determining M itself. This is only the second time anyone has precisely determined the inclination of one of these planets.
You believe wrongly.
HD28185 b and IotaHor b both could support moons with liquid water, year-round.
HD27442 b (aka Epsilon Reticulum) could also do it.
Other planets visit their star's habitable zones, too. Even though most of these other planets have eccentric orbits which would take them in and out periodically, they still "come close to matching those criteria".
Also a much better link to details of the Gamma Cephei system can be found here.
Ummm..... 100%?
Though how this relates to a 100 light year sphere around earth confuses me:
The article is pretty clear that the 100th planet is "symbolic". It's in really big font in a colored box -- you can't miss it! Anyway, it's not this 100th planet that leads to the 30 billion number. It's just a lead in for the article.
While the 300 billion stars is correct, a vast majority of them are on the galatic disk or in the galatic core, where the gravity of the densely packed stars would prevent planet formation according to any currently held theory.:
Wow -- that's news to astronomers. We're in the disk, and our sun formed planets, so it can't be that hard!
most of the exo-solar planets that have been found so far are multiple Jupiter-sized and orbiting so close to the star that it doesn't resemble our solar system, the only one we really know about, making any inferences about the existence of other planets useless and pointless :
Oh, so knowing how commonly planets form has nothing to do with how many planets are in the galaxy?!? Knowing that 10 percent of stars near us have detectable planets is astonishing: we can only regularly detect these weird "hot Jupiters" right now. This implies that, unless these systems are for some reason much more common than other planetary systems, a substantial fraction of all stars bear planets. In that case, 30 billion is a reasonable guess -- maybe on the low side!
The final link in the logical chain is provided in the article itself:
In other words, if you make a histogram of exoplanets sorted by mass, you see that the least-massive ones are the most common. Go to exoplanets.org and see for yourself. So the above caveat that "hot Jupiters" might be more common than other kinds of planets seems unlikely.
Yes, the author has dumbed down the science to the point where it can be hard to figure out what he's writing about, but that per se doesn't boggle the mind of anyone who reads the science section of any major paper.
> "No, everyone should have access to all the
> information that can be provided for them."
That is what the First Amendment says, basically, although the courts are not saying that the government has any obligation to provide such information.
The court decided that the Internet was a close analog to the Founders' idea of "the press" and that terminals in public libraries were government-sponsered fora for the free exchange of ideas, like parks and sidewalks (I'm summarizing, read the article). This, the court said, is the kind of speach that gets some of the strongest First Amendment protection of all, and so the court was able to use very strict tests to determine if the law is constitutional. Since the law effectively inhibited some lawful speach to prohibit some unlawful speach, it failed.
>radiation -- not for a directed laser beam,
>which can remain well-collimated over great
>distances.
Note that unless the laser beam is perfectly collimated you still lose as 1/r^2. The inverse square law is not unique to isotropic radiation. Think about it: the area of the base of a cone goes as the height squared no matter how narrow the cone is, just like the area of a sphere goes as the radius squared.
As long as all of the laser light is hitting the sail it doesn't matter, of course, but once you're far enough away that the laser beam is bigger than your sail, you start to lose. This isn't really a bad thing, though, since presumably you can only point the laser with some fixed accuracy, so you need bigger and bigger beams for more and more distant ships. Although I suppose the ships could try to actively stay on the beam, it's still a rather strict stability requirement for the laser to have to hit an object light years away and keep it steady for years.
All I meant was that the original poster's implication that NASA was somehow encouraging alcoholics and sex-addicts to sign up for important missions was far-fetched. I didn't mean to imply that booze and blow-up dolls would be inappropriate on such trips -- quite the opposite.
Who's going to Mars? The post is about a trip to the arctic.
> We shouldnt be sending people who'll need their booze and blowup dolls by any means.
For any potential Mars mission no one who "needs" booze and blow-up dolls would be selected. Luxury items will certianly be included, however, since the crew will have to stay sane, comfortable, and amicable on the 3+ years the mission would take.
>We should be sending Marines there and oil rig miners...
Oh, like in Aliens and Armageddon!
> Dont think their aren't sci fi hacks who couldnt get published sitting at CIA analyst desks right now thinking about this stuff.
...or posting on Slashdot. I'm sorry... why on Earth (or Mars) would the CIA care about the social dynamics of a colony that won't even exist for at least a century?
But that doesn't mean that the model is wrong. Their model involves a third object with its own orbital period that disturbs the disk, causing the flares. This would have a period unrelated to the orbital period of the binary, and the multipliers would not be completely random but would have a predictable propability distribution.
The best informed comment is probably the article itself. Check out pp.76-78 and the conclusions section.
Gravity at short ranges is being tested now (on scales of, like, inches) as a test of some superstring theories.
If gravity does not have a 1/r^2 dependence, things get really messy, really fast. First of all if you have to introduce a new length scale into the universe (such as a length within or beyond which a different law applies) then you have basically introduced a new constant of nature.
Secondly, it means that GR is wrong in some fundamental ways, so you have to work very hard to recover the successful tests of GR while still scrapping the guts theory itself.
Finally, remember that we HAVE tests of gravity at the ranges we're talking about -- Pluto's orbit is pretty well-determined, and Neptune and Uranus are out there, and Earth and Mars turn out to put very strong constraints on this, too (see the article for details, p.77); galaxies attract each other about the way we expect; there are plenty of long-period binary stars with this sort of separation that have been studied; etc.
I'm not saying that there's no way that gravity itself could be the culprit in the anomolous position of the craft; I'm just saying that the nature of gravity is pretty tightly constained by observation, so throwing stuff off like "it's different at large distances" opens a whole can of worms that have to be shoved back into some new theory.
> I've seen several posts already saying the
> number of violent crimes committed by youth has
> dropped. Oh yay us. Let's give kids more violent
> games. Well.. yes the pure numbers show
> that. However, there is also a lot less kids
> than then there were. So while the rates go
> up.. the numbers are going down.
*BZZT* Wrong, but thanks for playing. Numbers AND rates for violent crime among youth have dropped:
http://www.urban.org/crime/module/butts/youth-crim e-drop.html.
Pay particular attention to the section "Arrest rates":
But now this statement is easily testable. According to the RIAA, sales of singles should jump 39% now that Napster is shut down. Or something like that...
The UC system already allows the top 4% of students from any California school to bypass the SATs entirely, so it DOES recognize that a 4.0 from a bad school can mean a lot.
Also, the UC system would not ignore SATs under the new plan, it would just make them optional. Students could still submit them to demonstrate potential, and most who did well probably would.
Your statements that Mr. Atkinson "wants to hurt" students like you and "HAS NOT thought through his situation" are unfounded exaggerations.
Then the gov't does not have that particular compelling interest and the producer's individual rights carry more weight in the balancing. After all just saying a sentence like "Child pornographers explicitly depict children engaged in sexual activity" is itself a depiction of said activity (albiet a very abstract one), but it would not be covered by virtual child pornography laws. The government is allowed to write laws that are subject to interpretation and descretion.
That same argument IS made for so many things. e.g.: in times of civil unrest curfews restrict freedom of movement and association, and "the end result is that legitimate actions and expressions are criminalized to make it easier for the police." Encryption is another good example. The point is that it's not unconstitutional for the government to make these kinds of laws when it has a compelling interest, which is why the appeal will fail and "virtual" kiddie porn will remian illegal. The law is bad, but not unconstitutional.
Remember, the ULTIMATE source of the wisdom of our laws was supposed to be the voice of the people through the legislature, not the chanelling of constitutional guarantees through the courts. The constitution protects against tyrrany, not folly.
Anyway, the "slippery slope" argument is a red herring. The courts have to balance on a slippery slope all the time. The alternative is that individual rights overwhelm ANY national or social interest, which undermines the whole social contract the Framers intended. There's a slippery slope down the other side of the hill, as well.
The government certainly has the right (and, more importantly, a compelling interest) to procescute true child pornographers. If "virtual" kiddie porn makes it impossible or much more difficult to do that ("that's not a real kid, your honor! honest! i used photoshop!") then the government has an interest in banning that, too. It's a balancing issue: the government is claiming that society's need to punish real child pornographers outweighs an individual's rights to produce virtual kiddie porn.
That's the government's position, according to news reports, at least. It's not unreasonable that the SC will agree with that position: the other federal courts (except the 9th appeals) have.