Phoebe, Comet Moon of Saturn?

3488 · Dec 29, 2008

This was started over on The Spaceport forums & the below was copied from there. Thought it would be very interesting to bring here also. "Images from the Cassini spacecraft near Saturn indicate that Phoebe may have originated in the outer Solar System. When astronomers first discovered it photographically, a first for the technique, they believed it to be a captured asteroid. However, Phoebe's irregular surface, retrograde orbit, unusually dark surface, assortment of large and small craters, carbon dioxide content, and low average density are consistent with Phoebe once being a part of the Kuiper belt of icy comets before Saturn captured it. Its surface shows different places of clays and primitive organic chemicals. Cassini took this image 30,000 kilometers out from this 214-kilometer diameter moon. Phoebe is 13 million kilometers from Saturn, four times as far as its nearest moonly neighbor Iapetus The International Astronomical Union, IAU officially named 24 craters on Phoebe in 2005. Phoebe’s low 1.9 grams per cubic centimeter density indicates it is half rock and half ice. It is an icy remnant of the solar system’s birth 4,500 million years ago. Its warm daytime temperature is 163 degrees below zero Celsius. Its nighttime temperature is a bit chilly. Icy planetesimals like Phoebe came together to form the planets, although Phoebe itself escaped that end. One guess is that young Saturn’s gravity captured it and kept it out of the process."APOD 12/02/06. Astrobiology article on Phoebe. It will be interesting to compare Phoebe with the Pluto moons Nix & Hydra when New Horizons makes it to the Kuiper Belt & rendezvous with the Pluto system. Also Phoebe appears to be similar in size to the Eris moon Dysnomia. Are they indeed siblings?? I've a few interesting Phoebe images below.Phoebe both sides Voyager 2. <img src="http://sitelife.space.com/ver1.0/Content/images/store/3/4/93daeb78-d5f3-481f-b4e4-fe234ab012db.Medium.jpg" alt="" /> Phoebe both sides Cassini. <img src="http://sitelife.space.com/ver1.0/Content/images/store/7/12/a7721c0a-9c9c-46b5-acb2-0fb1af11cab5.Medium.jpg" alt="" />Phoebe another approach image from Cassini. <img src="http://sitelife.space.com/ver1.0/Content/images/store/11/3/ebb4c0fb-0cd7-4ad6-a3f7-5bc2e7d7e2ac.Medium.jpg" alt="" />Phoebe yet another approach image from Cassini. <img src="http://sitelife.space.com/ver1.0/Content/images/store/10/15/2af6e3f6-ca56-43b1-8f69-95a15d2ec774.Medium.jpg" alt="" />Phoebe 12 KM wide crater & surrounding terrain. <img src="http://sitelife.space.com/ver1.0/Content/images/store/2/8/92172593-5fb2-4a90-b879-d30b5be77274.Medium.jpg" alt="" />13 KM wide crater on Phoebe. <img src="http://sitelife.space.com/ver1.0/Content/images/store/5/8/552d9904-0042-464e-98ec-c63b10703fb4.Medium.jpg" alt="" /> 13 KM wide crater floor with large ice boulders. <img src="http://sitelife.space.com/ver1.0/Content/images/store/14/7/2ee49c4d-38c8-4921-970d-cd1ace3b3a16.Medium.jpg" alt="" />Phoebe ice hills & craters. <img src="http://sitelife.space.com/ver1.0/Content/images/store/5/5/c506bb5e-28ac-4f56-85b2-c3816d05621c.Medium.jpg" alt="" />Phoebe close up of limb showing craters & mountains in profile. <img src="http://sitelife.space.com/ver1.0/Content/images/store/15/2/3f9a4781-cb46-4ae7-a2e5-848030d213e5.Medium.jpg" alt="" /> Phoebe 16 KM tall cliff with slumping. <img src="http://sitelife.space.com/ver1.0/Content/images/store/4/5/b4740847-3bbc-4f0d-b57b-02525b4b9edc.Medium.jpg" alt="" />Phoebe mountains & craters rotating into the night. <img src="http://sitelife.space.com/ver1.0/Content/images/store/15/11/4fc17b65-540e-45ea-8ba3-7af1a20a5713.Medium.jpg" alt="" /> Phoebe ice boulders & craters. <img src="http://sitelife.space.com/ver1.0/Content/images/store/11/10/6be1de97-42da-49ff-9a55-33b4d5fece6c.Medium.jpg" alt="" /> Phoebe closer view of above. <img src="http://sitelife.space.com/ver1.0/Content/images/store/15/4/7fc5ee16-012f-4de0-a471-c8774f1bd68c.Medium.jpg" alt="" />Phoebe south polar depression. <img src="http://sitelife.space.com/ver1.0/Content/images/store/15/5/df2c9d18-447e-4a3e-b5dd-43a6ef642aab.Medium.jpg" alt="" />Phoebe, Three two KM wide craters each in a different state of preservation. The centre one looks the oldest by far. <img src="http://sitelife.space.com/ver1.0/Content/images/store/14/1/5eb503a1-897b-41d6-b131-a2a8e91812ba.Medium.jpg" alt="" />  Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

silylene old · Dec 29, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>........Images from the Cassini spacecraft near Saturn indicate that Phoebe may have originated in the outer Solar System. When astronomers first discovered it photographically, a first for the technique, they believed it to be a captured asteroid.  Andrew Brown. Posted by 3488</DIV>Andrew thanks for the reminder about this strange moon, and the nice collection of photos (good to review them again!).  Are there any more Cassini close approaches in the future? <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

3488 · Dec 29, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Andrew thanks for the reminder about this strange moon, and the nice collection of photos (good to review them again!).  Are there any more Cassini close approaches in the future? Posted by silylene</DIV>Hi Silylene,Phoebe certainly is of immense added scientific interest. Unfortunately, Cassini will not be passing Phoebe again or much closer in Iapetus for that matter as they are far too far out from Saturn to be included in the extended Cassini Equinox Mission. However if the Cassini Solstice Extended Mission is approved, an enormous 7.5 year extention, to continue just past the Saturn system Northern Summer Solstice, then perhaps possibilities may open up to rendezvous with Saturn's outer moons from Iapetus outwards or even one of the smaller outlier new founds.Myself I think Phoebe will not be  approached until a future Saturn system craft arrives, such as a future Titan & / or Enceladus craft, or perhaps NH2 / ARGO if approved that could potentially encounter Phoebe inbound. Also Phoebe may help enable to approve an encounter with 2060 Chiron or 5145 Pholus, two Centaurs that may have also been ex KBOs, though 5145 Pholus appears very red, one of the reddest known bodies in the solar system. Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

h2ouniverse · Mar 1, 2009

hi andrew

this paper to come at EGU, in favour of the captured-KBO theory:
http://meetingorganizer.copernicus.org/ ... -11192.pdf
(Phoebe's shape: implications for internal structure and origin)

best regards.

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