Icy medium-sized planets

[h2ouniverse]

We know two ice giants: Uranus and Neptune<br />We know many ice dwarves: Pluto, Eris, 2005FY9, Sedna just to quote the biggest ones<br /><br />Uranus is thought in Nice model to have formed further from the Sun than Neptune (at a mere 15 AU from Sun). But then we come down abruptly from 40000km to 2400! <br /><br />Could intermediate-sized bodies form (and be ejected or sent to highly elliptic orbits)? Or is there a mechanism that would stop accretion process from producing such "ice media", in a very discontinuous way?

 

[JonClarke]

Don't foreget that if they were not orbiting Jupiter, Saturn and Neptune, Europa, Callisto, Ganymede, Titan and Triton would be mdedium sized planets in their own right. All are much larger than the icy "dwarfs" and our Moon, Ganymede, Callisto and Titan are bigger than Mercury.<br /><br />Pluto masses ~10e22 kg, Ganymede ~1023 kg, and Uranus ~10e26kg. I don't see why Mars (~10e24 kg) and Earth (~10e25) mass planets should be impossible.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[3488]

That thought had crossed my mind too.<br /><br />The ice layer on Ganymede is thought to be about <br />1,000 KM deep, overlying a silicate mantle, which makes up approx 56% of Ganymede's mass, <br />with a metal, possibly molten, even double layered core (the only other body other than Earth, thought <br />to have such a core).<br /><br />Ganymede is highly differentiated & internally highly evolved.<br /><br />Callisto, is thought to have an ice crust approx 80 Kmthick, overlying a layer of <br />highly saline water perhaps 50 KM deep,with the rest of the interior a mix of ice, silicate rock & a little<br />metal, witha slight settling towards the centre.<br /><br />Titan appears in this diagram, to be a piggy in the middle. Greater <br />differentiation than Callisto, but less so than Ganymede.<br /><br />BTW is Mercury not larger than our Moon???<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[3488]

Very true, could be.<br /><br />I have my doubts though. I wonder if such large planetary bodies, would <br />have been found by now, by measuring the solar system's centre of gravity?<br /><br />I thought the vast majority of the solar system by mass is now accounted for?<br /><br />Perhaps I'm wrong??<br /><br />If such planets do exist & we find one, perhaps New Horizons 2 should be <br />reinstated right away. <img src="/images/icons/laugh.gif" /><br /><br />I like your idea of such planets being water worlds, closer to their parent stars. This is<br />the sort of thing, I hope we find in the not too distant future.<br /><br />You never know, perhaps Alpha Centauri A or B could have??????<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[h2ouniverse]

Hi Jon,<br /><br />Actually I had in mind something heavier than the big moons of the gas giants, heavy enough to catch an atmosphere. As Eburacum says, "Super-Titans". I would place Titan at the lower end of that category. If Titan had been discovered in the KB, would it have satisfied the "clearance" criterion and got planethood (not dwarfplanethood)? (Even Mercury or Mars would have probably not passed the test...)<br /><br />What I have in mind is a relatively small rocky core (Uranus is thought to have a very small core) topped with hundreds of kms of ices, and thousands of kms of atmosphere.<br />Say 1e24kg to 1e25kg class.<br /><br />Regards.

 

[h2ouniverse]

Hi Andrew,<br /><br />The qualitative change between Mars and Jupiter corresponds to the frost line + destabilization by Jupiter. <br /><br />But the difference between Neptune/Uranus and the KB dwarves is steep. In the Nice model, 99.9% of the KB is thought to have been ejected. That might include such medium-sized bodies, some may be still wandering on elliptical orbits.<br />Otherwise, a mechanism should be imagined to explain the discontinuity. What would stop the accretion process from making such intermediates? <br />Initial lack of matter for a truncated disk? (but KB is said to have been 1000 times heavier, so there was matter...)<br />Critical mass of the rocky core needed to accrete the volatiles cannot be achieved in this less dense area of the disk? (but Uranus has a small core and could make it...)<br />Presence of H2 and He helps increase mass and accretion power? But why shoud H2+He density decrease in the disk with a discontinuity?<br /><br />Regards.

 

[JonClarke]

Both Titan and Triton have atmospheres, Titan a thick one and Triton a very thing one.<br /><br />Since we have icy dwarfs and icy Mercurys, I really can't see any reason why Mars and earth sized icy planets are impossible.<br /><br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

Triton's atmosphere is very thin. Titan's is noticeable indeed. But Titan formed in the mid solar system. And Triton (KBO or not) is not significantly bigger than Pluto and Eris. <br />I can't see any reason either for ice-medium planets not to form beyond Neptune/Uranus... But then where are they (I mean in our Solar Sytem)?<br /><br />Titan demonstrates that at these distances from Sun, 5000km class 90K-cold objects can retain a thick atmosphere... So at further distances that should be even easier.

 

[alokmohan]

2700 km in diameter.Give the poor chap its due. Its no KBO.

 

[h2ouniverse]

2700 is not that bigger vs the (still only guessed) 2400km of Eris. <br />I mentionned Triton as a potential KBO (captured by Neptune) as this is a hypothesis floated by many planetologists.

 

[JonClarke]

I can't see any reason for icy planets not forming anywhere outside the solar system snowline. Hence the significance of the icy Galileans and Titan. They don't have to be as far out as Neptune or Saturn.<br /><br />As for atmospheres, I suspect thet galileans would have more were it not for the sputtering from particles trapped in Jupiter. An earth-sized icy planet at Jupier distance would have a very decent atmosphere, I would expect. <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

My point is: why nothing in this category beyond Uranus/Neptune? <br /><br /><br />In reply to<br />------------<br />"An earth-sized icy planet at Jupier distance would have a very decent atmosphere, I would expect. "<br />----------<br />Me too! How cool would it be if we could find one! As the H2O layer in Uranus is very hot (supercritical) and the H2O layer in Pluto/Eris is cold (ice), why not dream for an intemediate situation, an open air ocean of water-ammonia, isolated from the coldness of space by a very thick H2-rich atmosphere, in an everlasting night?<br /><br />Regards.

 

[3488]

I wonder if the accretion process beyond Uranus was too slow (it is thought that <br />Uranus & Neptune have swapped places, so Uranus was at one time the outermost planet).<br /><br />Yes I too think that, an Earth sized ice planet at Jupiter distance & beoyond, would have a<br />very dense atmosphere. <br /><br />I also think at one time Ganymede had a respectable atmosphere too (not as dense as <br />Earth's or Titan's, but more so than present day Mars), before it was lost. <br /><br />It is my own theory, not anything official or necessarily correct, just a theory.<br /><br />This is a most fascinating thread. Thank you very much Joel for starting it.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[h2ouniverse]

Hi Andrew,<br /><br />in reply to<br />-------------<br />"the vast majority of the solar system by mass is now accounted for"<br />-------------<br /><br />You are probably right. But... Some say the Oort cloud is 30 Earth masses: how evenly distributed is it, and how accurately is this figure known? <br />Plus: Alpha Centauri system exerts more gravity force on us than would an Earth-massed object at 325 AU. Sirius system exerts more gravity force on us than would an Earth-massed object at 550 AU.... I am not sure we can detect the gravitational effect of something at 2500AU unless we can observe drifts over several centuries, as objects at 2500AU would orbit sun in 125,000 years.<br /><br />Best regards.

 

[bguth]

I also agree with that analogy, but how about an incoming rogue 4000 km icy protomoon of 8.5e22 kg, as having rather nicely glanced off Earth for a little icy lithobraking? <br />-- Brad Guth

 

[h2ouniverse]

in reply to<br />--------------<br />"but how about an incoming rogue 4000 km icy protomoon of 8.5e22 kg, as having rather nicely glanced off Earth"<br />--------------<br /><br />Very unlikely. One such body in every cube 580AU-edged on average, would multiply the average density of galaxy by 5! <br />And even so (i.e. assuming all dark matter is in fact made of "4000km icy protomoons of 8.5e22kg"), and assuming relative velocities vs Earth of about 100km/s, that would mean one chance out of 27 millions that there is an encounter with Earth over a 4.5 billion years period. (as a very rough order of magnitude)<br /><br />Best regards.

 

[bguth]

That's not what I'd asked, but even those are relatively good random cosmic happenstance odds, especially if our solar system were associated with and every so often cruising nearby another system that had been going a little red giant postal(sort of speak), as perhaps shortly before its primary 5~6 solar mass star became a white dwarf.<br /><br />However, how about if there was just a little divine intelligence or orchestrated intentions working those interstellar migration odds?<br /><br />Of course, with a good enough supercomputer that's already loaded with all of the required physics of complex orbital dynamics, as such would make this conjecture/argument a whole lot easier to figure out. Too bad there's no such supercomputer nor hardly any physics software to be found within any American owned and operated agency, or even those of public collage or private consideration that's either taboo/nondisclosure rated or perhaps not worth squat. <br />-- Brad Guth

 

[h2ouniverse]

Hi Andrew,<br /><br />in reply to<br />-----------<br />"I wonder if such large planetary bodies, would <br />have been found by now, by measuring the solar system's centre of gravity?"<br />-----------<br /><br />recently I could check the following: Barnard's star exerts on us as much gravity as would an Earth-massed object at 1640 AU (about 6e-15 m/s2 (*)). And it travels very fast, with an apparent angular drift of about 0.0029 degree per year viewed from Sun. Whereas the potential unknown object at 1640 AU would have an average drift of 0.0054°/yr around the the Sun (and us...). i.e. comparable in magnitude.<br /><br />If we want to take the same angular drifting speed of 0.0029°/yr, we would then have to consider an object at 2500AU, (125,000 year period), which then exerts on the central Solar system bodies 2.6e-15m/s2 that is less than half the grav attraction by Barnard's star.<br /><br />Are the measurements of the movements of the center of gravity of the known bodies of the Solar System accurate enough to detect the effect of Barnard's star?<br /><br />If yes, then your argument holds: we should have detected Earth-massed objects at less than 2500 AU. Otherwise, this means such objects would have remained easily unnoticed.<br /><br />Best regards.<br /> <br /><br />(*) note: 6e-15 is about 1/25000th of the gravity force exerted by the Milky Way! So that is already well in the surrounding noise...

 

[alokmohan]

H20 is correct.

 

[alokmohan]

Forget not europa.Jupiter's moon Europa is just as far away as ever, but new research is bringing scientists closer to being able to explore its tantalizing ice-covered ocean and determine its potential for harboring life. <br /><br />"We've learned a lot about Europa in the past few years," says William McKinnon, professor of Earth and Planetary Sciences at Washington University in St. Louis, Mo. <br /><br />"Before we were almost sure that there was an ocean, but now the scientific community has come to a consensus that there most certainly is an ocean. We're ready to take the next step and explore that ocean and the ice shell that overlays it. We have a number of new discoveries and techniques that can help us do that." <br /><br />McKinnon is discussing some of these recent findings and new opportunities for exploring Europa in a news briefing today at the meeting of the American Geophysical Union in San Francisco. He is joined by colleagues Donald Blankenship, research scientist at the Institute for Geophysics at the University of Texas at Austin's Jackson School of Geosciences., and Peter Doran, associate professor of Earth and Environmental http://www.spaceref.com/news/viewpr.nl.html?pid=24294<br />

 

[h2ouniverse]

no risk I forget Europa, Europa Orbiter is so long in the making... I hope that at the AGU they showed enough progress. (that may favour Laplace mission). But it is a pity ESA picks only one between Laplace and Tandem...<br /><br />However I would not rank Europa in "Icy medium-sized planets" category but as an "Icy dwarf planetary object".<br />By "Icy medium-sized planets" I mean an Earth-massed object.<br />

 

[JonClarke]

Europa falls between Pluto and Mercury, mass wise. It has more than twice the mass of Pluto and roughly a 5th the mass of Mercury. <br /><br />However, Europa has a lower density that Mercury. So at 3120 km it is almost exactly haf way between Pluto's 2380 km and Mercury's 4880 km.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[3488]

Hi Jon,<br /><br />Europa has 63% of the Moon's mass, Pluto has only 16%, so Europa has four<br />times Pluto's mass.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[JonClarke]

Your right!<br /><br />Thanks<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

Hi Andrew,<br /><br />yes. However it seems that a Mars-sized object, if discovered in KB, would be probably ranked still in "dwarf-planet" category.<br />A Mars-MASSED object may probably be the limit.<br />That would trigger another row of bitter debaes between planetologists (who privilege constitution and structure) and dynamicists (who privilege influence on orbits of other objects, role in the solar system, and won last time in Prague...).<br /><br />To me, if we consider not "planets" but "planetary-massed objects" (ie independently from the fact that the primary is the Sun or another planet, not to offend dynamicists), the limit between categories should be the presence of liquid water or water/ammonia ON THE SURFACE.<br /><br />We would then have IMHO as "Icy planetary object" an object that is differentiated between rock and ices and is:<br />A) Ice dwarf planetary object = rocky core + layer of ices (with or without subsurface ocean) + no atmosphere (Ceres, Ganymede) or an atmosphere (thin: Triton, or thick: Titan)<br />B) Icy medium planetary object = rocky core + a layer of warm ices + an open-air liquid ocean + a thick atmosphere (probably hydrogen-rich)<br />C) Ice giant planetary object = rocky core + (potentially) a layer of warm ices + an open-air supercritical ocean + a very thick hydrogen-rich atmosphere (e.g; Uranus, Neptune)<br /><br />With this categorisation we would have in Solar System for now:<br />A) Ceres(TBC), Europa, Ganymede, Callisto, Enceladus, Dione, Tethys, Rhea, Titan, Ariel, Umbriel, Titania, Oberon, Triton, Pluto, Charon, 2003EL61(TBC), 2005FY9, Eris, Sedna, and many TNOs<br />B) Nothing for now<br />C) Uranus, Neptune.<br /><br />Jupiter and Saturn, having hydrogen layer thick enough so that it gradually liquefy/solidify, do not enable hydrogenated ices to form layers, and are therefore Hydrogen Giants.<br /><br />The Moon, Vesta (TBC), Ceres (TBC, if not differentiated) and Io would then be Rocky dwarf planetary objects.<br /><br />Best regards.