Recently I've been in communication with @ChasAstro on Twitter. He wrote some interesting information on Pluto.
He opened my eyes to something new. We were discussing the possibility of Charon being a Pluto captured object and the difficulties facing the theory of satellite capture. These difficulties are as follows. |
He pointed out how “things in solar orbit tend to be moving really fast relative to each other”.
For two objects to get as close as Pluto is to Charon, upon their approach, they will tend to either collide as their collective masses will gravitationally drive them toward each other ever faster leading to collision or they will miss causing them to get flung apart. These same two points of view are expressed in Wikipedia. The thing is, there are quite a number of Transneptunian Binary (TNB) pairs in and around the Kuiper belt. To the left are eight such objects. |
In addition to the above 8 binaries, 3/4 down this page is a list of eight newly studied Transneptunian Objects (TNO) which are actually Transneptunian Binaries (TNB).
This gif shows a small moon of asteroid 2004 BL86 passing into view. I just noticed the moon appears to be orbiting perpendicular to the equator of 2004 BL86. That indicates its a really recently acquired moon as its relatively tiny by comparison and isn't orbiting its parent body's equator. |
<<<<<<<<<< (136617) 1994 CC, a trinary asteroid with two moons. >>>>>>>>> 243 Ida and its moon Dactyl. Yeah that little dot off to the right is a moon. |
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This video of asteroid 2014 JO25 was generated by NASA's Goldstone Solar System Radar on April 18th 2017.
Credits: NASA/JPL-Caltech/GSSR This is a bi-lobe asteroid nearly identical to comet 67p. While capturing satellites may be a difficult process, it isn't that uncommon in the outer solar system. One possible reason binaries occur commonly in the Kuiper belt is because objects are far from the Sun thus moving slower than objects near to the Sun. |
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This is how most people tend to view collisions between bodies in space and while it is inevitable many collisions take place in a manner similar to this, I, however, see another form of collision that takes place and is much less disruptive or cataclysmic. The relatively large number of similarly sized conjoined objects seem to indicate binaries of dissimilar size join in a way that would appear violent since the small object obliterates on impact to be absorbed by the larger body but bodies of similar size enter a tug of war dance each offsetting the gravitational pull of the other until they gently merge into one odd shape. |
Conservation of momentum suggests that as the two bodies come closer their orbital spin speed increases creating increased centrifugal force which in turn is trying to fling them apart.
The closer they get the faster they spin, the faster they spin, the slower they impact. If Pluto and Charon's orbital spin speed around their collective barycenter is increasing over time they are coming closer together. Conversely, if their barycentric orbital rotation is decreasing they're separating. Everything I've read so far seems to indicate their orbital speeds are stable. |
Just as comet 67p and Neptune's largest moon Triton are/were Kuiper Belt Object's (KBO) so too are Pluto and Charon. Comet 67p was a binary pair until two distinctly different objects gently merged and married into one. Their collision was so gentle in fact they maintained their individually aligned strata while merging into one body.
Over time, dust and other particles began filling in the connecting neck. Then something kicked comet 67p into an extreme short period orbit around the Sun causing it to become a comet as it then sublimated away ices by the heat of the Sun. |
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Triton is the second outermost moon of Neptune and it has some peculiar features which suggest strongly that it is a captured KBO, whereas, Neptune's smaller inner moons are reasoned to be accreted from debris. @ChasAstro "Nereid is actually the outermost satellite of Neptune. Some people have hypothesized that Nereid might have originally been a regular satellite in a circular orbit but was displaced to its present wide irregular orbit during Triton’s capture."
Neptune orbits around 30 AU from the sun. One Astronomical Unit (AU) is the distance of the Earth to the Sun so Neptune is 30 times further away from the Sun as the Earth. KBO's reside in a relatively circular doughnut ring orbiting approximately 40-50AU from the Sun at an inclination of less than 5 degrees relative to the ecliptic plane (orbital plane of Earth to Sun). So why is it thought Triton's a captured KBO when it should normally exist 15 AU further away from the Sun than Neptune? And how did it drop 15 AU closer to the Sun to become captured by Neptune? |
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This is the orbit of Nereid compared to that little tiny orbital blue circle which is Triton going around Neptune. Wiki says Nereid orbits Neptune in the prograde direction at an average distance of 5,513,400 km (3,425,900 mi), but its high eccentricity of 0.7507 takes it as close as 1,372,000 km (853,000 mi) and as far as 9,655,000 km (5,999,000 mi). The gravitational influence of a body is reduced by the square of its distance. Doubling the distance means quadrupling the weakness of the gravitational torque force. |
This short video demonstrates how moons that orbit near to a parent planet like Jupiter (in this example) remain closely aligned around the planet's equatorial plane.
Jupiter's axis is only tilted 3 degrees off its orbital plane but its nearest moons align with its 3 degree tilted rotation. Saturn is tilted 27 degrees and its rings and inner moons mostly all align with its equator while further out moons are more random in their orbital paths. Orbiting bodies further out tend to orbit in more random spherical patterns. |
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When Nereid reaches periapsis (closest to Neptune) in its orbit, it is also closest to Triton and speeds up. Each orbit near periapsis the potential exists for Nereid to receive a resonant push from Triton both elongating and creating its inclined orbital angle relative to Neptune's equator. Neptune's other moons are puny, close to and inline with its equator. Triton is 99.5% of the entire mass orbiting Neptune so its not too difficult to believe it has perturbed Nereid into its current orbit.. |
Relative to Neptune Triton orbits in a retrograde or backward spin while it's other moons orbit in a prograde direction in line with Neptune's equator.
Triton is compositionally very similar to Pluto which is also a KBO that is in a 2:3 resonance with Neptune. Pluto orbits the Sun 2 times while Neptune orbits 3 times hence 2:3 resonance. Triton is very geologically active, the majority of it's surface is mostly smooth or recently resurfaced by roiling activity or cryovolcanism and its shell is too thin to support elevated structures. |
Like Pluto, Triton has a very thin atmosphere. Triton is primarily made of the same stuff as other KBO mostly nitrogen, methane, carbon monoxide, water ice and rocky material. Triton's density is 2.06 g/cm3 while Pluto's is 1.86 g/cm3. A moon composed strictly of water ice would be 1 g/cm3. A density greater than one indicates heavier materials like silicate rock (rock density = 2.5-3.5 g/cm3) are present. Like Pluto, Triton is composed of heavier materials than water ice meaning Triton's silicate rock mass is about 66% (Pluto = 67%) 36-40% by volume. Triton's massive cantaloupe looking thin skin and cryovolcanic activity depositing dark minerals on the surface suggest it's core is fully differentiated and there is a warm ocean keeping the outer shell soft enough to lack impact craters and elevated structures. |
Triton is locked to Neptune so one side always faces Neptune and the eccentricity of its orbit is a near perfect circle at .000016 yet Triton is geologically extremely active for the following reason. Triton's orbit is angled -23 degrees relative to Neptune's equator. Triton is 99.5 % of all the mass orbiting Neptune. Neptune has 14 moons and only Triton is big enough to make itself round. |
Wiki quote
The presence of Neptune has a profound effect on the Kuiper belt's structure due to orbital resonances... Neptune's gravity destabilizes the orbits of any objects that happen to lie in certain regions. Cold KBOs reside primarily around 42 – 50 AU maintaining a fairly circular orbit (blue Classical ring in image) around the Sun with low inclinations <5° to the ecliptic plane. Classical Kuiper Belt Objects (KBO), also known as Cold KBOs or Cubewanos they are typically more red (tholin covered) than Hot inclined Transneptunian Objects (TNO) (not named for temperatures rather orbital inclinations of greater than 5 degrees). TNO's and KBO's may overlap but typically KBO's sit in the quiet doughnut shaped blue ring while TNO's are often objects scattered by Neptune into resonance, extreme inclinations and/or extreme eccentric orbits. Hot TNOs are more varied in their color ranges from grays to reds with inclinations from 5 to 40 degrees and eccentricities up to .85 which is massive. |
Known objects in the Kuiper belt beyond the orbit of Neptune. (Scale in AU; epoch as of January 2015.)
Sun - Yel Jupiter trojans - Gray Giant planets: J · S · U · N - Red dots Centaurs - Green dots Kuiper belt - Blue Scattered disc - Beige Neptune trojans - Purple Distances but not sizes are to scale Source: Minor Planet Center, www.cfeps.net and others |
About one third of known Kuiper belt objects exist as binary pairs. I've been reading some of Francis Nimmo's paper's this one in particular. Five New and Three Improved Mutual Orbits of Transneptunian Binaries In this paper, Kuiper Belt Object's which exist as binary pairs orbiting around a shared barycentric point are studied. Quote - "most of these systems consist of near equal-sized pairs" Triton is shown below in false color while Pluto is displayed in natural color in reality Triton's color looks nearly identical to Pluto. The image below is for size comparison. Triton's radius = 1.353 km, Pluto's radius = 1,188 km. |
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The more we explore space the more we find binary pairs of near equal size, mass and composition either attached or orbiting each other. Below quote is from an article issued by the space telescope science institute in Baltimore, Maryland dated Sept 21st, 2017 Quote Hubble was used to image the asteroid, designated 300163 (2006 VW139/288P), in September 2016 just before the asteroid made its closest approach to the Sun. Hubble’s crisp images revealed that it was actually not one, but two asteroids of almost the same mass and size, orbiting each other at a distance of 60 miles. Transneptunian Binaries (TNB) are binary pairs mostly loosely bound as they orbit each other and most of them are similar in size mass and composition just like Pluto and Triton. Below is an image of the TNB object's studied in F. Nimmo's paper with their shared orbits. Logos and Zoe are the first TNB in this chart. |
From this information I choose to speculate on a possible interaction scenario between Pluto, Triton, Charon & Neptune. What if? Pluto and Triton were a binary pair of cold classical KBO with their similar sizes, compositions, densities and colors minding their own business in the Kuiper Belt then Neptune migrated close enough and regular enough (resonance) to gently perturbed them out of their classical Kuiper belt comfort zone causing them to slowly experience an increasingly eccentric orbit. Each pass Neptune made near to them it's gravitational mass increased Pluto/Triton's angle of inclination and eccentricity pushing them into an orbital zone we call a Neptune 3:2 resonance (Plutino zone) along with other similarly clustered 3:2 resonant objects including Charon. |
As Neptune gravitationally pushed or pulsed Pluto/Triton it changed their orbital eccentricity along with their orbital inclination (Kozai mechanism). Pluto and Charon are currently in an eccentric orbit around the Sun that places them closer to the Sun than Neptune periodically.
The orbit of Pluto is the most eccentric of any planet in our Solar System. Pluto's orbital eccentricity is 0.2488. Back in the day when the binary pair Pluto/Triton got close enough to Charon in the 3:2 resonant zone, the three set up an imbalanced system that caused Triton to exit the trio. |
If the ejection occurred while they were closer to the Sun than Neptune it would have placed Triton into Neptune's orbital path. Charon latched onto Pluto while Triton fell into Neptune's grasp. This jostling created tidal flex on all three planets.
Something like this >>>>>>>>>> Which eventually turned into Pluto/Charon doing this |
Pluto travels faster at perihelion (nearest the Sun) than at aphelion (farthest from Sun) so depending on where Triton exited the trio (Pluto, Charon, Triton) would determine whether Triton needed to leave faster or slower to get dropped into Neptune's path so it's a more complex scenario than to simply say Triton sped up or slowed into Neptune's orbit.
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The conditions could have been such that Triton got pushed into Neptune's orbit.
Since Pluto crosses inside and outside Neptune's orbital range, it crosses Neptune's orbital distance twice each orbit around the Sun. If Triton ejected near either of these two locations, Neptune could have latched onto and picked it up. Think of it like a gravity assist which we use with space probes to gain velocity. If Triton ejected from the trio at perihelion it would have been traveling faster than Neptune and could have caught up with it or if Triton ejected at an orbit further from the Sun it would have been moving slower than Neptune and slowed into it's orbital and gravitational range. |
Our Moon's avg semi major axis around Earth
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384,402 km (238,856 miles)
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Triton's semi major axis around Neptune
Titan's semi major axis around Saturn
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354,759 km (220,437 miles)
1,221,870 km (759,235 miles)
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Iapetus' semi major axis around Saturn
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3,560,820 km (2,212,591 miles)
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Charon's semi major axis around Pluto
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19,591 km (12,173 miles)
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Saturn's moon Titan is massive compared to all the others.
Several tiny moons that orbit inside Saturn's rings are forming by acting like a vacuum cleaner sucking up ice particles from the rings. They exhibit a round central bulge shape with a flat disc extending around their equator. This disc is formed by accretion. Three of these tiny moons are named Atlas, Daphnis and Pan. |
Iapetus has an equatorial ridge 20km or 12 miles high and is thought to be created by the accretion of ices similar to what we see on Atlas and Pan. This suggests Iapetus was at some point closer to Saturn and inline with its orbital plane collecting ices from its rings.
Iapetus is compositionally the same as the other small moons of Saturn while Titan is different suggesting Titan is a captured moon not an in-situ (in place) accreted moon. The ridge on Iapetus strongly suggest accretion took place previously which implies Iapetus was orbiting much closer to Saturn and in line with its equatorial plane at an earlier date. |
This chart shows how moons become larger farther out from Saturn.
Iapetus' is the third largest moon of Saturn, its large size relative to other moons indicate it developed toward the outer edges of Saturn's inner rings. The fact that its bulging ridge only extends three quarters of the way around its equator suggests it was tidally locked when it was closer to Saturn just as it is today. Iapetus was likely an inner moon of Saturn until something resonantly perturbed or knocked it into a higher orbit. Titan sits between Saturn and Iapetus. |
Hyperion is more than twice as close as Iapetus is to Saturn and is 0.003 times less massive (or 3 thousandths of a percent) and Hyperion is not tidally locked with one side always facing Saturn while Iapetus is locked.
Smaller closer bodies lock sooner to their parent planet than larger farther bodies. Some scientists believe Hyperion is not locked to Saturn because Titan delivers resonant pulses to Hyperion but this doesn't make sense as a resonant pulse would more likely induce orbital oscillations (eccentricity) not axial spin. If Hyperion at its current close distance and small mass relative to Iapetus is spinning but Iapetus is locked it says to me that Iapetus was closer to Saturn at one point, its spin got locked but then was perturbed by Titan into its current orbit where it remains locked with a bulging ridge around its equator. Distance from Saturn along with resonant pulses from Titan along with Iapetus being outside Saturn's Laplace radius could have all worked together to create Iapetus' inclined orbit. |
Considering the proximity of our Earth and Moon to the Sun's gravitational influence, Earth has pulled our Moon as close to the equator as it can. Our Moon is a little farther away from Earth (384,399 km) than Triton is from Neptune (354,759 km).
Our Moon has about three times the mass (7.342×10^22 kg) of Triton (2.14×10^22 kg) (heavier objects are harder to move) so it would be more difficult for our Earth's gravity to place the Moon around its equator than it would be for Neptune to adjust Triton around its equator but then there's also the matter of the parent body's mass. |
This seems similar to what I've suggested happened with Pluto. Pluto was in an eccentric dance with Charon which previously generated relevant tidal flex energy but is now not significant. But both Pluto and Triton still show signs of recent activity suggesting to me they both could have been involved in the same process around the same time and not 4 billion years ago based on Triton's orbital inclination dating this process at less than 1 bya. Triton's surface is mostly smooth meaning the crust is too thin to support mountains and is renewing itself. The surface is relatively young yet we see black streaks on it indicating much younger volcanic eruptions have deposited the black mineral based material on top of a young surface. |
You might want to read my Eruptions page 77 as it explains some significant information related to Triton and Pluto.
Update December 8th 2018. Bummer! I just read a paper dated 2006 that hypothesizes this same theory I'm proposing here on this page for Triton's capture.
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