Mab, the Enceladus of Uranus?

[h2ouniverse]

<p><font size="2">hi all,</font></p><p><font size="2">Very surprising new results have been reported about the small uranian moons at the European Planetary Science Congress this week.</font></p><p><font size="2">http://www.cosis.net/abstracts/EPSC2008/00254/EPSC2008-A-00254-1.pdf?PHPSESSID=03adbd528bb6ae9057ed3d7eee9ca64e</font></p><p><font size="2">They include a surprisingly set of clues about Mab, a recently discovered moonlet:</font></p><p><font size="2">* the&nbsp;mu ring, which corresponds to Mab's orbit, is as blue as Saturn's E-ring (the one generated by Enceladus plumes); Uranus' mu-ring and Saturn's E-ring are the only known blue rings.</font></p><p><font size="2">* Mab's RMS astrometric signal is clearly exceptionally fuzzy among all moonlets, <font face="TimesNewRomanPSMT">indicating that it is responding to a large and un-modeled perturbation.</font></font></p><p><font size="2">* Mab's orbit is strongly non-Keplerian: "<font face="TimesNewRomanPSMT">Mab is the single most severely perturbed moon in the Solar System, showing orbital deviations of ~100 km over intervals as brief as 6 days. No known moons orbit nearby, and no resonances have been identified that might produce these deviations."</font></font></p><p><font face="TimesNewRomanPSMT" size="2">Also, Mab is located between the main rings and the closest "large" moon (Ariel), as is Enceladus in the Saturnian system.</font></p><p><font face="TimesNewRomanPSMT" size="2">A sizable&nbsp;difference though: Enceladus is 500km-wide. Mab is believed to be ludicrously small (10-20km).</font></p><p><font face="TimesNewRomanPSMT" size="2">Either there is:</font></p><p><font face="TimesNewRomanPSMT" size="2">*&nbsp;hidden mass to account for non-Keplerian motion, plus meteoritic bombardement to generate the blue ring</font></p><p><font face="TimesNewRomanPSMT" size="2">* or it is active Enceladus-style (cometary activity), but the thrust needed to account for non-Keplerian motion would be very high...</font></p><p><font size="2">* another potential explanation from the author is that Mab might be far bigger (hence globally darker) than believed, with a bright spot on its surface that would be misinterpretated as its optical center, leading to the illusion of non-Keplerian motion; but the author has pointed that the diameter would have to be a whopping 1100km (how could Voyager2 miss it?) and the albedo would have to be ridiculously low, far lower than any body in the Solar System => unlikely</font></p><p><font face="TimesNewRomanPSMT" size="2">&nbsp;Other guesses?</font></p>

 

[3488]

<p><font size="2"><strong>Hi Joel, fascinanting topic, I'm glad you have bought it here.</strong></font></p><p><font size="2"><strong>Regarding Mab as being 1,100 KM wide, Like you, I think that is nonsense. Even if Mab was darker than coal at that size, Voyager 2 would have seen it without trouble & the fact Voyager 2 did not see Mab, though of courase Mab may be sitting in the images, but not identified as yet, makes me think Mab is small. Perhaps possibly larger than 10 - 20 KM as quoted, but is certainly not a 1,100 KM wide monster. That's about the size of Dione or Ariel or even a size akin to Mimas, Enceladus or Miranda. No way, Voyager 2 would not have missed an object of that size, even if very dark.</strong></font></p><p><font size="2"><strong>Even if Mab was over on the other side of Uranus to Voyager 2 at periuranion, Mab at that size would have been clearly seen during the approach.&nbsp; &nbsp;</strong></font></p><p><font size="2"><strong>So no, I do not think for one moment Mab is several hundred KM wide, let alone over a thousand KM wide.</strong></font></p><p><font size="2"><strong>&nbsp;There is some other expantaion as to the sourse of the ice within the 'blue ring' of Uranus. <br />A large Mab is not it. Peraps Ariel is active & that ice particles are shepherded by Miranda & Mab into that orbit around Uranus??? </strong></font></p><p><font size="2"><strong>I dunno. </strong></font><img src="http://sitelife.space.com/ver1.0/Content/images/store/15/6/bf0be0f7-6bf3-436c-b6f0-e9cbda0934ed.Medium.gif" alt="" /></p><p><font size="2"><strong>Andrew Brown.&nbsp;</strong></font></p> <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]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Regarding Mab as being 1,100 KM wide, Like you, I think that is nonsense. Posted by 3488</DIV><br /><br />Yes.</p><p>The author just mentioned it as an absurd assumption too, for the sake of being exhaustive.</p><p>I would rather bet for a cometary activity on Mab. Or a larger mass of the ring (the author mentionned a need for particles denser than titanium for such an assumption to explain the phenomena, without believing it really himself). But both scenarii are quite astounding per se.</p><p>The mu ring is really really on Mab's orbit. Far from Ariel. I don't think Ariel can be at play there.</p><p>best regards.</p>