Crystalline ice and ammonia...cryovolcanism?

[rhm3]

I've been reading up on the papers and reports on the detection of crystalline ice and ammonia hydrate on the surfaces of Charon and Quaoar. Such has led to conclusions of cryovolcanic activity on both worlds since neither chemical can be maintained at cold temperatures very long, in crystalline ice's case no more than 10 million years. Reasonable enough.<br /><br />But then I found this interesting paper about the surface composition of the major Uranian satellites (sans Miranda):<br /><br />http://www.boulder.swri.edu/~layoung/eprint/Grundy2006uraniansat.pdf<br /><br />Quote from the paper: <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><br />The shapes of the H2O ice absorption bands and their depths relative to one another,<br />especially between 1.50 and 1.57 m and around 1.65 m,<b> confirm that most of the H2O ice<br />on all four satellites is crystalline at the mm depths sampled by these wavelengths</b> (e.g.,<br />Grundy et al. 1999; Hansen and McCord 2004). Amorphous ice lacks 1.57 and 1.65 m<br />absorption bands and exhibits somewhat dierent shapes for the 1.5 and 2 m bands<br />(Grundy and Schmitt 1998; Schmitt et al. 1998). The H2O features in the satellite spectra<br />are consistent with simple Hapke models (e.g., Hapke 1993) having no amorphous ice at all,<br />although we can include up to 10 to 20% amorphous ice before the discrepancies become<br />{ 7 {<br />conspicuous.<br /><b>This predominance of crystalline ice is not surprising, since it is the more<br />thermodynamically stable, lower energy phase. </b> Crystalline H2O has also been reported on<br />other outer solar system surfaces at comparable and greater heliocentric distances, both icy<br />satellites and trans-neptunian objects. In fact, everywhere that the phase of H2O ice on<br />these objects' surfaces has been identied, it is crystalline (e.g., Buie and Grundy 2000;<br />Bauer et al. 2</p></blockquote>

 

[3488]

Hi RHM3.<br /><br />Thanks for starting this thread.<br /><br />I have read your article several times now, very interesting. <br /><br />I am not at all surprised at the presence of crystalline Ice on the major Uranian moons. <br /><br />However, its detection on Umbriel is a surprise however. Voyager 2 clearly imaged a heavily ancient cratered dark surface, with little or no signs of internal activity what so ever.<br /><br />Miranda obviously has seen much action. Likely the slow impact of former co-orbitals created the coronae, but also Miranda may have been smashed apart & re-assembled or both have happened!!<br /><br />Ariel shows much tectonic activity, softening of some features & possibly extinct cryovolcanoes.<br /><br />Titania also shows tectonic activity, softening of some features & possibly extinct cryovolcanoes.<br /><br />Oberon shows cryovolcanic crater floor flooding, tall mountains, softening of some features & possibly extinct cryovolcanoes.<br /><br />Shame New Horizons 2 never happend. After Jupiter, it was to have gone past Uranus on route to the Kuiper Belt. The Uranus system reaches an Equinox in December this year, so New Horizons 2 would have gone past only a few years later, potentially showing the entire surface of all five of the major moons.<br /><br />Just what do the other hemispheres of Miranda & Ariel reveal, or closer views of Titania & Oberon??<br /><br />Voyager 2 did a sterling job, but the Uranus system was at a Solstice & Voyager 2 was travelling pretty quickly as set course for Neptune. <br /><br />Anyway the below may be of interest.<br /><br />http://uplink.space.c</safety_wrapper <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>

 

[rhm3]

Hey 3488, thanks for the response. <br /><br />From what I've understood, crystalline ice would indicate remodeling of surface in the past 10 million years. I definitely can't dispute that the Uranian satellites (sans Umbriel) have had extensive geological activity...but that recently? Based on the Voyager 2 images I would compare them more to Ganymede, with resurfacing ending no later than 500 million years...hardly recent enough to be the cause of the current crystalline ice. Plus Umbriel has very few signs at all.<br /><br />Which is why I think the crystalline ice can be explained by external impacts of some sort, as the article suggests. Miranda is a little more interesting to me because in addition to crystalline ice, there are hints of ammonia or ammonia hydrate...which may mean Miranda has been recently resurfaced from internal activity. Although the idea you brought up that co-orbitals smashed into the satellite is interesting...maybe that happened very recently and welled up ammonia leftover from its geological era that was present not too far under its crust? If that is a process that could bring ammonia to a surface, then perhaps Quaoar and Charon experienced recent similar impacts.<br /><br />Oh another thing, I just learned that there are strong signs of crystalline ice on Orcus too (no ammonia though). If this keeps showing up on these outer objects, especially smaller ones, I would think that it's caused by impact and sputtering...which would be expected in a chaotic place like the Kuiper Belt. <br /><br />EDIT: There's evidence of crystalline ice on 2002 TX300 too. Hexagonal crystalline ice is also present on the trailing hemisphere of Iapetus (which we know is geologically dead object). I'm really starting to think there's a common exogenic process here.

 

[3488]

Was not aware of crystalline ice being found on the Saturn moon Iapetus!!!<br /><br />I am trying to get the Cassini encounter with Iapetus distance this September reduced, this revelation may strengthen the case (as well as the weird equatorial ridge, Cassini Regio, etc).<br /><br />You may be aware, there has been much discussion on this board about Saturn's third largest & outermost large moon!!<br /><br />Andrew Brown.<br /> <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>

 

[rhm3]

Thanks for linking that thread...very interesting stuff and I totally support your persuasion of reducing the flyby distance. <img src="/images/icons/smile.gif" /><br /><br />Crystalline ice on Iapetus may actually not be that surprising...the temperature on the light material reaches 100K (-280F) which isn't too far from the point where water ice is crystalline anyways. The dark material (some which extends on the trailing hemisphere in the middle) reaches as high as 112K (-258F). The rest of the colder satellites of Saturn have crystalline ice as well, but that can be explained by the constant fresh spray of Enceladus material. <br /><br />Sans the Saturnian satellites which have a unique source of fresh water...have you noticed that albedo generally correlates positively with geological age? Very evident on the Uranian satellites:<br /><br />Umbriel - 0.21<br />Oberon - 0.23<br />Titania - 0.27<br />Miranda - 0.32<br />Ariel - 0.39<br /><br />Triton is a much fresher 0.76 and no surprise, it's active today. <br /><br />And this makes sense. Darker objects in the outer solar system imply thicker coating of external material and surfaces more processed by UV rays. To acquire both takes long geological time, so it would need to be dead...whereas active objects constantly replenish the surface and keep it fresh. <br /><br />So let's apply this theory to some ice dwarfs. Charon's albedo is almost identical to that of Ariel (not to mention so is its radius and density). I believe the crystalline ice found on the Uranian satellites is fresh ice excavated by external bombardment that was left from the cryovolcanism...Ariel's was the most recent with the highest albedo...and I think the same can be applied to Charon.<br /><br />So I expect Charon will look a lot like Ariel...dead now, but clear evidence of extensive geological activity not too far in the distant past. <br /><br />Quaoar is even darker than Umbriel though! I don't see how it would still be cryovolcanically active today with tha

 

[rhm3]

Alright continuing my odd spurt of obsession (I go through these)...I've looked into a few more distant bodies.<br /><br />Orcus's spectrum displays some water ice, and indications are that it is crystalline. It's estimated that about 15-30% of its surface is covered in water ice...less than Charon. There are some carbonaceous compounds as well, probably other materials that haven't yet been identified. It's albedo is assumed to be 0.09 per wikipedia but I think it's higher. As mikeemert noted in another thread...Ixion has a measured albedo of 0.15 and it's covered in dark, processed tholins...completely lacks water ice. On the other hand, Orcus has less water ice than Charon which has an albedo around 0.36...so I estimate Orcus's albedo is in the middle, between 0.20-0.30. <br /><br />The surface composition and albedo both match the Uranian satellite Oberon very well...perhaps Umbriel or Titania depending on the exact albedo. So I think Orcus has been dead for billions years...but with some of the old cryovolcanic ice excavated by bombardment.<br /><br />TX300 is a bit smaller than these other objects discussed in this thread...probably smaller than Ceres. Nonetheless, its surface apparently has no volatiles. In fact, the spectrum indicates about 60% of its surface is covered in large water ice particles...indicative of crystalline ice. The albedo hasn't been measured so (as with Orcus) it's a little tougher to nail this one down...but the coverage of ice on its surface is similar to Charon. So I expect an albedo similar to Charon and thus a similar geological record: extensive cryovolcanism ending (rough estimate) about 500 million years ago. Gardening or lager impacts would be capable of excavating this fresh ice to the surface, similar to what is seen on Ariel and what is speculated to occur on Charon.<br /><br />EL61 is interesting...it rotates very rapidly and thus has a shape like an American football (even though its one of the largest ice dwarfs). This is almost c

 

[rhm3]

Hey borman, thanks for posting that, I did read it earlier...interesting article nonetheless.<br /><br />Oddly enough though, I actually think Quaoar has been dead for billions of years. The reason being it only reflects 10% of the light that hits its surface...that's even darker than Umbriel. So the crystalline ice must only cover a small part of its surface...otherwise it'd be much brighter. The best bet is that it's a fresh impact crater that exposed subsurface ice...spectrascopic observations showing an albedo variation supports this idea.

 

[rhm3]

<blockquote><font class="small">In reply to:</font><hr /><p>One needs some caution in comparing Uranian moons to general icy bodies. Even if Miranda has a NH3 signature, one needs to remember the radiolytic environment due to Uranus’ magnetosphere as well as heat produced by impact to such a moon located deep within the gravity well of Uranus. Impacts on Miranda are likely to be more energetic than on outlying Quaoar due to focusing by Uranus. Quaoar also lacks the radiolytic environment found near Uranus. Using the moons as a prototype may be mixing apples with oranges. <p><hr /></p></p></blockquote><br /><br />That is a very good point...<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>While the idea behind the loss of crystal water on trailing hemispheres on Uranus moons being due to radiation striking from behind seems quite reasonable, I am a little less convinced as to the source of crystal water and CO2 there. There is no observational evidence of ongoing geyser action spraying the moons leading edge such as seen currently with Enceladus. It would need to have occurred within the past 10 million years. <p><hr /></p></p></blockquote><br /><br />...I'm a little confused here, perhaps I'm just not following what you're saying. If the Uranian satellites are subject to higher energy impacts and a radiolytic environment induced by the planet's magnetosphere...doesn't that only support the idea that impacts are excavating their crystalline ice? The crystalline ice could have been produced billions of years ago due to cryovolcanism...but as you pointed out, impacts in the Uranian system are pretty intense. It's not hard to imagine that the impacts penetrate to the warmer ice. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Also, if the moons formed early in the solar systems history, they may have had a complement of Al26 to help them differentiate. Uranus has its magnetic field locked to its rotation which is faster than the moons’ orbits. So there may</p></blockquote>

 

[3488]

Thanks RHM3 & borman.<br /><br />I have printed this entire thread & will read it properly when I have time.<br /><br />mikeemmert suggested that the different types of KBOs, Plutinos, Cubewanos, etc shared albedos & spectra, bolstering the theory of KBO families. I believe very strongly that mikeemmert is correct. <br /><br />We see similar in the main asteroid belt between Mars & Jupiter, such as the 8 Flora family of which asteroid 951 Gaspra (visited by the Jupiter bound Galileo spacecraft) is a member.<br /><br />This fascinating thread started by alokmohan, will help to throw light on this too.<br /><br />RHM3, I am convinced the feature in the Charon map is an impact basin. When New Horizons arrive, we will know for sure. <br /><br />Thank you for posting those links.<br /><br />Andrew Brown.<br /><br /> <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>