Tidal dissipation occurs when the tidal forces vary with time, generally due to the orbit of the secondary being eccentric. That brings it alternately closer to and farther from the primary, stretching and squeezing the interior.
However, the orbit of Charon about Pluto is circular (Buie et al., 2012), so the tidal bulge is constant. There's no time-varying deformation and no dissipation.
The solar wind never gets anywhere near Jupiter's atmosphere. Jupiter has an absurdly strong magnetic field. The magnetopause is between 50 about 100 Jupiter radii from the planet, and the solar wind is deflected around it (Khurana et al., 2004). The jovian aurorae are powered by currents entirely within the magnetosphere (Jupiter's rotation and Io's plasma).
According to the IAU definition, the north pole for a major planet (or one of its satellites) is the pole on the same side of the ecliptic as the Earth's north pole, the North Celestial Hemisphere. By this definition, Venus and Uranus are retrograde rotators -- they rotate clockwise about their north poles.
For comets and minor planets (including Dwarf planets), the north pole is the pole about which the body rotates counterclockwise. So the north pole of a retrograde-rotating asteroid points into the South Celestial Hemisphere.
This brings us (as do all topics that mention the IAU) to Pluto. Pluto rotates retrograde. It was once considered a major planet, so it's north pole would have been on the same side of the ecliptic as ours. But as a dwarf planet, the opposite definition applies. Even before the 2006 decision, the convention was inconsistently applied. Papers have been published using each definition of the north pole, and they're not always good about stating which convention they used. With New Horizons on the doorstep, we're going to need consistency for mapping and navigation. So I believe the mission has decided to use the current IAU definition consistently to avoid any confusion. There was a huge fight over the coordinate system of Vesta on the Dawn mission, and we don't want that.
I've never found the antipodal argument convincing. Seismic waves converge at the antipode of an impact only if the target is spherically symmetric and isotropic. In the actual Earth, you have reflections off all kinds of laterally varying boundaries. Also, the sound speed differs substantially between continental and oceanic crust, so the path matters quite a bit.
The Chixulub impact is also not that big (as planetary-scale impacts go). The projectile was what, 10 km? Shock heating is only significant within a few times the projectile diameter.
It's not clear from the summary (or the linked article), but this isn't a mission at this point. This is a concept selected for Phase I study.
From the NASA Innovative Advanced Concepts (NIAC) news release: "NIAC Phase I awards are approximately $100,000, providing awardees the funding needed to conduct a nine-month initial definition and analysis study of their concepts. If the basic feasibility studies are successful, proposers can apply for Phase II awards, which provide up to $500,000 for two more years of concept development."
This effort is independent of the ongoing Europa mission studies (e.g. the Clipper concept.) The Draper concept may end up getting a mission if the results prove promising. Personally, I have doubts that this will prove credible, but that's the whole point of the NIAC studies.
Not the whole ring system. Only the A-D rings are within the Roche limit. But the phenomenon discussed here is happening in the A-ring, so this limitation does indeed apply. I don't understand how a moon could accrete here.
Actually, I always had wanted Stewart cast as Denethor. Not only could he have played the character much closer to how he's portrayed in the book, he'd have been a great foil to McKellen's Gandalf.
A prolate spheroid doesn't taper to points on the end. You'd need an infinite series of spherical harmonics to describe an American football, not just the degree-2 term. Though it's sufficiently elongated that spherical harmonics might not be the best basis set. Bessel functions?
1. The major heat-producing elements are all lithophiles, preferentially bounding to silicates. So there's virtually no radioactive decay in the core. It's all in the crust and mantle.
2. Thorium is an important heat source now due to its long half-life (14 Gy IIRC). But back in the day, Uranium and Potassium-40 were much more abundant, and produced the majority of the radioactive heating.
3. Assuming the Earth and Mars initially had similar bulk compositions, they would have similar rates of radioactive heating. But Mars surely cooled more quickly. The heat production scales as the mass, and therefore the volume. Heat loss scales as the surface area. So smaller planets have the lower surface to mass ratio and cool more quickly.
Earth already had its iron core at the time of the Moon forming impact. Most of the impactor accreted onto the Earth and the cores of the two bodies merged (Canup and Asphaug, 2001, Nature). A fraction of the silicate crust and mantle of the impactor and target was ejected into orbit. That debris accreted into the Moon. Since it is largely made of the silicate portion of the original bodies, it is depleted in metal, and has a relatively small core.
That's actually not an error. It's a contraction of "Space September", the name of a time unit in the early attempts at a Space Calendar or "Spalendar" that wouldn't be tied to solar or lunar cycles as viewed on Earth. It never caught on, which is too bad, because "Spock-tober" would be awesome.
Slashdot Mirror
Tidal dissipation occurs when the tidal forces vary with time, generally due to the orbit of the secondary being eccentric. That brings it alternately closer to and farther from the primary, stretching and squeezing the interior.
However, the orbit of Charon about Pluto is circular (Buie et al., 2012), so the tidal bulge is constant. There's no time-varying deformation and no dissipation.
The solar wind never gets anywhere near Jupiter's atmosphere. Jupiter has an absurdly strong magnetic field. The magnetopause is between 50 about 100 Jupiter radii from the planet, and the solar wind is deflected around it (Khurana et al., 2004). The jovian aurorae are powered by currents entirely within the magnetosphere (Jupiter's rotation and Io's plasma).
So, no water, no salt.
I highly recommend Good Omens, co-authored with Neil Gaiman.
NIXON'S BACK!
According to the IAU definition, the north pole for a major planet (or one of its satellites) is the pole on the same side of the ecliptic as the Earth's north pole, the North Celestial Hemisphere. By this definition, Venus and Uranus are retrograde rotators -- they rotate clockwise about their north poles.
For comets and minor planets (including Dwarf planets), the north pole is the pole about which the body rotates counterclockwise. So the north pole of a retrograde-rotating asteroid points into the South Celestial Hemisphere.
This brings us (as do all topics that mention the IAU) to Pluto. Pluto rotates retrograde. It was once considered a major planet, so it's north pole would have been on the same side of the ecliptic as ours. But as a dwarf planet, the opposite definition applies. Even before the 2006 decision, the convention was inconsistently applied. Papers have been published using each definition of the north pole, and they're not always good about stating which convention they used. With New Horizons on the doorstep, we're going to need consistency for mapping and navigation. So I believe the mission has decided to use the current IAU definition consistently to avoid any confusion. There was a huge fight over the coordinate system of Vesta on the Dawn mission, and we don't want that.
I've never found the antipodal argument convincing. Seismic waves converge at the antipode of an impact only if the target is spherically symmetric and isotropic. In the actual Earth, you have reflections off all kinds of laterally varying boundaries. Also, the sound speed differs substantially between continental and oceanic crust, so the path matters quite a bit.
The Chixulub impact is also not that big (as planetary-scale impacts go). The projectile was what, 10 km? Shock heating is only significant within a few times the projectile diameter.
It's not liquid, it's not hot, and it's not magma.
To be fair, this is basically what's happening.
It goes down every day on its own. They just went way out west and built the lab in the spot where the Sun sets.
What's in your wallet?
It's not clear from the summary (or the linked article), but this isn't a mission at this point. This is a concept selected for Phase I study.
From the NASA Innovative Advanced Concepts (NIAC) news release:
"NIAC Phase I awards are approximately $100,000, providing awardees the funding needed to conduct a nine-month initial definition and analysis study of their concepts. If the basic feasibility studies are successful, proposers can apply for Phase II awards, which provide up to $500,000 for two more years of concept development."
This effort is independent of the ongoing Europa mission studies (e.g. the Clipper concept.) The Draper concept may end up getting a mission if the results prove promising. Personally, I have doubts that this will prove credible, but that's the whole point of the NIAC studies.
And for goodness sake, don't let them drive the bus.
Not the whole ring system. Only the A-D rings are within the Roche limit. But the phenomenon discussed here is happening in the A-ring, so this limitation does indeed apply. I don't understand how a moon could accrete here.
Actually, I always had wanted Stewart cast as Denethor. Not only could he have played the character much closer to how he's portrayed in the book, he'd have been a great foil to McKellen's Gandalf.
We certainly will be observing this comet with our Mars spacecraft. http://www.nasa.gov/jpl/mars/c...
In fact, there was a practice run with ISON last year. I think the goal is to point every telescope in the solar system at this thing during the pass.
Well, at least the Canadian pennies should stop being such a problem. They stopped making them a couple years ago. http://www.cbc.ca/news/canada/...
A prolate spheroid doesn't taper to points on the end. You'd need an infinite series of spherical harmonics to describe an American football, not just the degree-2 term. Though it's sufficiently elongated that spherical harmonics might not be the best basis set. Bessel functions?
Well, you have to admire the restraint, but I think this calls for a more forceful protest.
Like how Jor-El sent his only son to Earth to save mankind?
I'd also be confused if this site were in my current directory.
It's always bothered me when a radio program is called a "show". What exactly are you showing me?
A few points of clarification.
1. The major heat-producing elements are all lithophiles, preferentially bounding to silicates. So there's virtually no radioactive decay in the core. It's all in the crust and mantle.
2. Thorium is an important heat source now due to its long half-life (14 Gy IIRC). But back in the day, Uranium and Potassium-40 were much more abundant, and produced the majority of the radioactive heating.
3. Assuming the Earth and Mars initially had similar bulk compositions, they would have similar rates of radioactive heating. But Mars surely cooled more quickly. The heat production scales as the mass, and therefore the volume. Heat loss scales as the surface area. So smaller planets have the lower surface to mass ratio and cool more quickly.
Earth already had its iron core at the time of the Moon forming impact. Most of the impactor accreted onto the Earth and the cores of the two bodies merged (Canup and Asphaug, 2001, Nature). A fraction of the silicate crust and mantle of the impactor and target was ejected into orbit. That debris accreted into the Moon. Since it is largely made of the silicate portion of the original bodies, it is depleted in metal, and has a relatively small core.
That's actually not an error. It's a contraction of "Space September", the name of a time unit in the early attempts at a Space Calendar or "Spalendar" that wouldn't be tied to solar or lunar cycles as viewed on Earth. It never caught on, which is too bad, because "Spock-tober" would be awesome.