Just to be clear, Nick didn't say there is no ocean. He just said that the ocean is not the source of the plumes. Surprisingly, TFA didn't garble that part of the message; often the popular press will omit important details like that. I don't know if he's published this yet or not.
Now, there are other problems with maintaining an ocean in the long term. From a dynamical standpoint, the observed heat flow can't be maintained indefinitely (Meyer and Wisdom, 2007, Icarus 188, 535-539). And in any event, tidal heating of the ice under present conditions is still too low prevent the ocean from freezing. That's not to say you can't have a transient ocean there right now, but it needs an extra heat source and will freeze in tens of millions of years (Roberts and Nimmo, 2007, Icarus, in press).
Enceladus is too small; the pressure is too low even at the center to get high-pressure phases of ice. The ice on Enceladus is all Ice I. The density of Enceladus is too high to be pure ice, so there has to be some heavier stuff in there as well.
It's important to point out that we don't actually _know_ it's differentiated. Everybody assumes that because the surface ice is clean and there's geologic activity, suggesting that Enceladus was warm enough to differentiate.
Isn't Aragorn like 10 years old at the time of The Hobbit. They might show chibi-Viggo scampering around Rivendell. On second thought, it's probably best not to picture that.
And the number-one threat to Middle-earth? Beorn. He and his Vala-less killing machines are after our honey, they're after our women, and now, they're after our fantasy novels. Why is he helping in the Battle of Five Armies anyway? What do bears need with a stake in that treasure? What heinous bear-plot is this going to finance? I know he seems awesome fighting the orcs and all, but that's just to sucker us in before he tears the Dwarves limb from limb.
Assuming you're making an honest inquiry, and not just cashing in on the joke, it is indeed Saturn. Cassini (on whose data this study was based) went to Saturn, not Uranus. Larry Esposito's the PI for the UVIS instrument on Cassini.
It's the scorps from "The Songs of Distant Earth" by Arthur C. Clarke. Did anybody else read that one? It was set on a planet almost entirely covered in ocean and the human colonists discovered slightly intelligent, 2-meter long lobsters.
A temperature of around 10^8 K should suffice, such that the hydrogen not only fuses into helium, but the triple-alpha process becomes efficient, fusing helium into carbon. The oxygen is largely irrelevant, unless T approaches ~10^9 K, when the C-N-O cycle can happen. The pressures are not so important as the relative abundance of He to H which determines whether triple-alpha takes place. Stars much smaller than the Sun are unlikely to undergo He burning, so a pressure of at least 10^15 dyne cm^-2 is recommended.
Vote Robot Nixon!
Actually, there's gobs more of water down in the mantle than there is on the surface. When oceanic plates subduct, they bring along seawater. At depth the water isn't free-flowing but bonds to the silicates. It's then released back into the wild at mid-ocean ridges and volcanoes at roughly the same rate it's subducted, but there's a huge reservoir in the subsurface. In the transition zone alone (between 410 km and 670 km depth) there's probably 10 times the amount of water as is on the surface.
Water in the Saturnian system is nothing new. Water ice is very abundant beyond the frost line and is a major constituent of most outer solar system satellites. If the satellites are tidally heated, the subsurface ice can melt (e.g. Europa, Ganymede, probably Enceladus).
This picture shows a bright field with dark material down in the craters. That suggests to me that the impacts excavated a bright veneer to uncover dark material beneath, which is at odds with the image caption and the idea that the dark material is debris from other satellites. But I guess that's why I'm not a surfaces person.
It is by far the best accepted theory, although I seem to recall that a few details that haven't been worked. The isotope ratios are a mystery; both the Earth's mantle and the Moon have identical oxygen and silicon ratios are identical. If the impactor had a different source than the Earth, it's hard to explain this unless the two bodies underwent complete mixing, and that's not predicted by the dynamical models. IAAPSBNAGCATIPMAA (I am a Planetary Scientist, but not a Geochemist, and this isn't precisely my area anyway), so this issue may have been resolved without my knowing about it.
Good references in general are:
Asphaug, E., C. B. Agnor, and Q. Williams, Hit-and-run planetary collisions,
Nature439, 155-160, (2006) doi:10.1038/nature04311
Canup, R. M., Dynamics of lunar formation, Annu. Rev. Astron. Astrophys.42,
441-475 (2004).
Canup, R. and E. Asphaug, E., Origin of the Moon in a giant impact near the end of
the Earth's formation, Nature412, 708-712 (2001).
Origin of the Earth and Moon, eds Canup, R. & Righter, K., Univ. Arizona Press,
Tucson, 2000.
Stevenson, D. J., Origin of the moon -- The collision hypothesis, Annu. Rev. Earth
Planet. Sci.15, 271-315 (1987).
"Speeding up" of the battle? In the books it took ~15 pages. In the movies it was something like 45 minutes. I thought the battle scenes in the movies were generally way too long. Sure, it all looks really cool, but at some point it's just too much.
That's not actually an error. SFTU is a commonly accepted abbreviation for "Stop Fighting The Undercurrent", and I assume that means that we should all just accept what's happening. Eventually we'll have to pay each time we play a track we bought, or it will be considered stealing.
Alternate interpretations of SFTU include "Stop Feeding The Unicorns", "Swift Flight To Uruguay", "Stockholm Fails to Understand" and "San Francisco: The Ultimate". None of those make sense in this context.
Yeah, well at least you had matter. We didn't even have space or time yet. When the universe was forged in the crucible of the Big Bang, our race was already 17 years old.
Reviewers don't get paid. In addition to the journal charging a subscription fee, generally the author is also required to pay publication fees. Typically that's paid for by the grant that supported the research, but it still bites the big one. I'm not altogether sure what all the money gets spent on, but I've never recieved a cent as either author or reviewer. Except indirectly, as publication enables employment.
Slashdot Mirror
Just to be clear, Nick didn't say there is no ocean. He just said that the ocean is not the source of the plumes. Surprisingly, TFA didn't garble that part of the message; often the popular press will omit important details like that. I don't know if he's published this yet or not.
Now, there are other problems with maintaining an ocean in the long term. From a dynamical standpoint, the observed heat flow can't be maintained indefinitely (Meyer and Wisdom, 2007, Icarus 188, 535-539). And in any event, tidal heating of the ice under present conditions is still too low prevent the ocean from freezing. That's not to say you can't have a transient ocean there right now, but it needs an extra heat source and will freeze in tens of millions of years (Roberts and Nimmo, 2007, Icarus, in press).
Enceladus is too small; the pressure is too low even at the center to get high-pressure phases of ice. The ice on Enceladus is all Ice I. The density of Enceladus is too high to be pure ice, so there has to be some heavier stuff in there as well.
It's important to point out that we don't actually _know_ it's differentiated. Everybody assumes that because the surface ice is clean and there's geologic activity, suggesting that Enceladus was warm enough to differentiate.
Wait, _audio_ isn't for _looks_? That explains a lot. Now could somebody help me get these hearing aids out of my eyes?
Isn't Aragorn like 10 years old at the time of The Hobbit. They might show chibi-Viggo scampering around Rivendell. On second thought, it's probably best not to picture that.
And the number-one threat to Middle-earth? Beorn. He and his Vala-less killing machines are after our honey, they're after our women, and now, they're after our fantasy novels. Why is he helping in the Battle of Five Armies anyway? What do bears need with a stake in that treasure? What heinous bear-plot is this going to finance? I know he seems awesome fighting the orcs and all, but that's just to sucker us in before he tears the Dwarves limb from limb.
Gimli will be replaced by an annoying CGI sidekick.
Replaced? In other words, no change.
Assuming you're making an honest inquiry, and not just cashing in on the joke, it is indeed Saturn. Cassini (on whose data this study was based) went to Saturn, not Uranus. Larry Esposito's the PI for the UVIS instrument on Cassini.
Super-retro. It totally sucks there.
It's the scorps from "The Songs of Distant Earth" by Arthur C. Clarke. Did anybody else read that one? It was set on a planet almost entirely covered in ocean and the human colonists discovered slightly intelligent, 2-meter long lobsters.
A temperature of around 10^8 K should suffice, such that the hydrogen not only fuses into helium, but the triple-alpha process becomes efficient, fusing helium into carbon. The oxygen is largely irrelevant, unless T approaches ~10^9 K, when the C-N-O cycle can happen. The pressures are not so important as the relative abundance of He to H which determines whether triple-alpha takes place. Stars much smaller than the Sun are unlikely to undergo He burning, so a pressure of at least 10^15 dyne cm^-2 is recommended. Vote Robot Nixon!
Well, Pong actually exists. In that sense it's better.
See, this is exactly why they don't want you looking at the code.
Exact? In some cases you're doing well to get even the right order of magnitude.
Actually, there's gobs more of water down in the mantle than there is on the surface. When oceanic plates subduct, they bring along seawater. At depth the water isn't free-flowing but bonds to the silicates. It's then released back into the wild at mid-ocean ridges and volcanoes at roughly the same rate it's subducted, but there's a huge reservoir in the subsurface. In the transition zone alone (between 410 km and 670 km depth) there's probably 10 times the amount of water as is on the surface. Water in the Saturnian system is nothing new. Water ice is very abundant beyond the frost line and is a major constituent of most outer solar system satellites. If the satellites are tidally heated, the subsurface ice can melt (e.g. Europa, Ganymede, probably Enceladus).
This picture shows a bright field with dark material down in the craters. That suggests to me that the impacts excavated a bright veneer to uncover dark material beneath, which is at odds with the image caption and the idea that the dark material is debris from other satellites. But I guess that's why I'm not a surfaces person.
It is by far the best accepted theory, although I seem to recall that a few details that haven't been worked. The isotope ratios are a mystery; both the Earth's mantle and the Moon have identical oxygen and silicon ratios are identical. If the impactor had a different source than the Earth, it's hard to explain this unless the two bodies underwent complete mixing, and that's not predicted by the dynamical models. IAAPSBNAGCATIPMAA (I am a Planetary Scientist, but not a Geochemist, and this isn't precisely my area anyway), so this issue may have been resolved without my knowing about it.
Good references in general are:
"Speeding up" of the battle? In the books it took ~15 pages. In the movies it was something like 45 minutes. I thought the battle scenes in the movies were generally way too long. Sure, it all looks really cool, but at some point it's just too much.
I'm sure you intended to type 'third-degree murder'. Though I'd have never noticed the typo had I not been looking for one based on the posts.
Alternate interpretations of SFTU include "Stop Feeding The Unicorns", "Swift Flight To Uruguay", "Stockholm Fails to Understand" and "San Francisco: The Ultimate". None of those make sense in this context.
For Web 2.0 you have to synergize thinking outside the box while shifting some paradigms.
I work at UC Santa Cruz; why do I have to find out about this on Slashdot?
Shouldn't the frozen pizza be in the freezer? I'm just saying.
Had he dunked his face into a deep fat fryer for comparison?
Yeah, well at least you had matter. We didn't even have space or time yet. When the universe was forged in the crucible of the Big Bang, our race was already 17 years old.
Reviewers don't get paid. In addition to the journal charging a subscription fee, generally the author is also required to pay publication fees. Typically that's paid for by the grant that supported the research, but it still bites the big one. I'm not altogether sure what all the money gets spent on, but I've never recieved a cent as either author or reviewer. Except indirectly, as publication enables employment.