Monday, July 02, 2018

My ideas for Haumea (Plutoid, TNO)

Haumea has been found to be elongated, with two moons, a ring, and not in hydrostatic equilibrium but rotating fast enough that centrifugal forces match mutual gravity near its extremities.

Knowledge about similar objects out at this distance (Pluto, Charon, Enceladus) have been used together with laws of angular momentum to work out what is physically possible. It ignores formation mechanisms at this point so as to concentrate on what is physically and mechanically possible given observations of Haumea and several other well observed analogues.

Pluto, Charon and Enceladus have been found to have ice shells and liquid water oceans beneath. Geysers on Enceladus go to form a ring at Saturn, so this probably explains the formation of Haumea's ring. Out-jetting of water at speed is what is happening at Enceladus, and this would be enough to torque even such a large body as Haumea. A thick ice shell would be enough to hold up to compression at the neck as the centrifugal force, friction, and conservation of Angular Momentum does the rest.








There will be gradual and even stretching of the neck as angular momentum is increased - in the same way as couples ice-skaters do the "spiral of death"

Tidal friction from the moons and ring keeps the motion circularised in the same way as the skating spin.



Sunday, July 01, 2018

Conditions for Contact Binary via collision

This post is to demonstrate that the conditions for CB via collision require highly balanced rotational and translational components in two similarly sized objects for them to retain their individuality as lobes in an otherwise combined object. This to demonstrate both that binary asteroids can not be a source for contact binary asteroids, and that random primordial collisions cannot be either.

1: Formerly connected bodies "reconfiguring"
As shown in a previous blog post, with the real case of couples skaters to demonstrate, bodies twist away from each other to retain angular momentum using their previous independent rotation as a dynamo (at the point of collision in the case of asteroidal bodies)




2: Independently rotating objects colliding from outside each other's hill spheres at "baby crawling" speed.

Inelastic collisions are of course possible for non-rotating (or trivially rotating bodies that collide in the perfect offset to cancel independent rotation). This is because the required collisional/deformation damping is obtained passively and gives a reaction force in the correct direction opposite to motion, and proportionally to motion so that the force stops when the relative velocity between bodies comes to zero.

A head on collision with a random (in observed ranges of possibilities) rotation or offset collision even with no initial rotation makes an inelastic collision impossibly rare given:

Coherent bodies - Mainly solid that can deform but not to the point of liquidity.
The two bodies are of similar size - smaller body is no less than about a third the radius, or no less than a tenth of the moment of inertia in rough figures.


Due to the laws of physics, forces that perform torque on each other must balance.
Overall angular momentum must be conserved.
If work is required to perform torque to change rotation that must be in the amount and direction made possible by friction, reaction force or gravity.

The following is a way to create model to test generated samples to verify this blog's order of magnitude analysis:

http://www.euclideanspace.com/physics/dynamics/collision/threed/index.htm

For a perfectly inelastic collision to ensue, not only relative speeds must be damped to zero, but relative rotation rates must also be damped to zero and still be touching. At the point of touching, the combined bodies' moment of inertia is at the minimum - Therefore, the rotational velocity required to maintain angular momentum is at its maximum. The kinetic energy associated with the required rotation is also at a maximum. There is work required to achieve this synchronised higher rotation unless the initial conditions are perfectly selected. The same fluidity that allows damping of the impact force allows shear perpendicular with the relative spin velocities which would throw the bodies apart further than reactive forces alone could do. In other words, a notionally inelastic collision would convert rotational velocity to inertial frame velocity in all except perfectly tuned cases which are extremely rare given the assumption of random initial spin state.

Friction under tensile stress or associated with outward movement (Stretch) is the only option to passively glue the bodies together keeping coherent orientation. With stretch (or expanding orbit) there is natural damping as the moment of inertia increases for the duo in proportion to its reduced velocity. Whether loosely connected at the neck or two bodies orbiting the barycentre, outward movement from previously connected bodies is the only passive way to stabilise mutual spin.

Pairs skaters use this particular rule of thumb to spectacular effect with the "spiral of death" spin. The technique spirals the (female) skater outwards with her head balanced inches above the ice. The gradual outward release damped with the action of muscles gives exceptional control that appears paradoxical and adds to the appearance of magic levitation of the head off the ice.



Thursday, June 28, 2018

Rotational kinematics - possible and impossible spin-ups

In this first case as pictured below, an ice skater takes advantage of the conservation of angular momentum to increase rotational velocity by bringing their arms in. However, forces and torque need to be applied for this to work. The forces must also be balanced with respect to the axis of rotation, otherwise the axis would precess.


A naïve understanding of the forces and torques at play would lead one to believe that pairs skaters (or two co-rotating comet lobes) could come together and corotate quicker due to the conservation of angular momentum. That understanding would be wrong. The main issue is that in the single skater case, the force and torque is made from the outside of the centre of mass. When two co-rotating skaters pull in to each other, there is no way to exert the right forces on each other or the ensemble to torque to the higher speed required for continued co-rotation at a reduced moment of inertia.

This is the same with two co-rotating lobes of a comet or asteroid - neither gravity nor friction (at their points of contact) gives forces in the right direction to provide spin up torque.

Resultant endpoints vary depending on the reaction forces and friction, but none of them end up with the same co-rotating lobes at a faster speed and smaller net moment of inertia (or co-rotating couple at faster speed) 










Monday, June 11, 2018

Why couples figureskaters (and bi-lobe comets) don't do that spin up trick that individual iceskaters do!


It is well known that a figure skater takes advantage of the conservation of angular momentum to achieve incredible speeds of rotation by having their arms outstretched and bringing them in.

Ever wonder why they bring both arms simultaneously?
Or why couples skaters don't/can't pull each other in to achieve spectacular combined rotations?
or why bi-lobe comets don't collapse on the neck and reconfigure to a much faster combined rotation?

In short, the problem is the Coriolis force!
If an ice skater has just one arm outstretched and pulls it in at a rotating reference, the force required to counter the centrifugal force would topple the skater with the skates as the fulcrum and they would precess violently. The equal and opposite arm acting in unison balances the forces required to bring the arms in and all the work exerted on doing this gets converted to torque, spinning up the skilful skater.

With the couples skating this becomes a two body problem. As they pull each other in from outstretched arms, each person's individual moment of inertia is far more than the nominal amount of a single outstretched arm. Therefore, the radial pulling that they can exert on eachother  topples them both over quite effectively. The only way they can exert the torques required to hold them in a configuration is to wrap their arms around each other. Countering the centrifugal force and friction at their contact points is not enough to effect the principle, as it CANNOT prevent the two persons from spinning independently from each other, conserving angular momentum both individually and as a non rigid unit.

This principle, when applied to a bi-lobed comet like 67-P Churyumov-Geramisenko means that a partial collapse of the neck which allows mutual gravity to pull them closer together could not result in a faster rotation keeping the same configuration in the rotating reference frame.

 However, if the lobes rocked at the neck with a slight precession, the same configuration could be kept and the rotation restabilised with less precession if the neck lengthened and the friction caused a slower mutual rotation in the same configuration in the rotating reference frame.

This is exactly the same principle that couple skaters use to stabilise the rotation when doing death defying spins with the female skater's head just inches above the ice. A gradual lengthening of the arm under tension dampens any wobble in the spin allowing complete and graceful control of the spin.

Saturday, February 03, 2018

Anuket Boulder move timing and Cause identified

The 67P C-P change concerned is documented by the ESA here http://sci.esa.int/rosetta/58915-comet-changes-new-fracture-and-boulder-movement-in-anuket/
Published in March 2017 Copyright ESA website.

The Boulder movement concerned was, however, first documented in this blog here http://marcoparigi.blogspot.co.uk/2016/06/anuket-near-crack-changes.html?m=1

This resulted in a lively discussion on the Rosetta Blog regarding the veracity of the observed change, and a detailed photographic demonstration of the move in another blog here


With newly released OSIRIS images released for July and August 2015, detailed analysis shows that an Imhotep style slump occurred centred near the Anuket crack, expanding in a roughly circular direction, and was roughly 5 m deep. Through July, the expanding slump is shown to have reached the Western most boulder, but not as far as the other two boulders of the visible triad. Images get blurrier as Rosetta needed to move further away as perihelion progressed into August 2015. However, the moving ridge front of the circular arc makes a distinct shadow, and the late July 2015 images show the slump to have moved past the boulder, toppling it down the 5m slump and causing it to slide or roll a further 15m or so in a Westerly direction relative to nearby fiduciary points.

The resultant slump is visible in the post perihelion pictures here, http://sci.esa.int/science-e-media/img/23/ESA_Rosetta_CometChanges_FractureBoulder.jpg






















Sunday, January 08, 2017

Liquid water on comets assertion

With regards to liquid water on comets, my thoughts conclude that although evidence is circumstantial in the terms of supposed solar system origins, liquid water as mud in comets interior will eventually be proven - most likely in the next couple of decades. The corollaries to this is that the only possible way to reconcile this to measured data is to include life in comets, stretch as a way that bilobate shapes are formed, and tectonic style surface movements to explain surface features.


Objections to liquids on comets addressed:

1. There is no evidence for liquid water: 

This is not strictly correct at all, as there is indirect evidence from many comet missions. Panspermia advocates are a group of scientists who note that the evidence is entirely consistent with there being liquid water in comets. There are no contradictions from Rosetta, and many otherwise unexplained surface features that have easy explanations if internal liquid water mud is hypothesised.

2. The connection between O2 and water rules out liquid water because liquid water cannot dissolve a level of O2 that high: 

O2 was in fact considered impossibly unlikely until the Rosetta mission discovered it. Liquid water, molecular oxygen and life are all considered impossibly unlikely on small bodies, but all three are abundant on Earth and are connected to each other - ie. Life needs O2 and water - forms of life generate O2 and require water etc. An alternate explanation for both O2 and Water abundances is a pressurised interior, with abundant life which generates O2 among other respiration byproducts.

3. The temperatures and pressures both within and outside small body categorically rule out liquid water:

Clearly the surface is exposed to vacuum, which rules out surface liquid water. At hydrostatic equilibrium, the interior also cannot hold liquid water. However, if the interior was somehow sealed and able to hold at least .006 Atm pressure, and was, for whatever reason, warmer than the surface average temperature over its orbital cycle, then liquid water would be certain, given outgassing patterns.

4. Incredible claims require incredibly convincing evidence.

This is a common theme when alien life is posited as part of a narrative of what is happening. There are two possibilities - alien life is either 100% true or 100% false (in a comet in this case) If it is 100% true, then it isn't an incredible claim. Since we surmise the probability of life on a body based on the surmised possibility of liquid water, the argument that O2 is inconsistent its liquid water is a circular argument based on the assumption that alien life on a comet is impossible.
Ie. There is no liquid water because the O2 rules it out, there can be no life because there is no liquid water, therefore life cannot explain the O2.
So liquid water should not be ruled out until an actual internal measurement is made.

5. Comets are unchanged remnants from the early solar system. This rules out narratives where comets could evolve into what they are now.

All the factors that lean towards comets being pristine remnants (until the recent epoch of entering the inner solar system) can have other explanations, especially if life is part of the explanation. For instance, low density leans towards these not having been part of larger bodies. The activities of life within these bodies could have reduced the density (increased porosity) over time, meaning they could have been fragments of larger bodies (perhaps that had life as larger bodies)

Sunday, November 06, 2016

Recombinant Fission in 67P comet nucleus

As suggested in a recent peer reviewed paper:


http://www.nature.com/nature/journal/v534/n7607/full/nature17670.html
Hirabayashi et al

Stresses due to "rocking" of the lobes of 67P are likely to cause "fission" - that is a complete separation of the two lobes, but then "reconfiguration" of the two lobes due to their relative velocity being less than escape velocity.

What hasn't yet been considered is that at an instantaneous level, this process is happening repeatedly already! The fractures are causing the two lobes to instantaneously act as separate bodies. Internal frictional forces only then come into play and have a rebalancing effect. The rebalancing is effected by an exchange of angular momentum as the lobes rock relative to each other. Instantaneously fluidised material near the core of the nucleus is attracted outwards by the gravity of the closest lobe rather than the centre of gravity of the entire nucleus. The net effect of this stepwise recombinant fission is that the centres of gravity of the individual lobes move slightly further apart. While the outgassing of the comet is speeding the rotation considerably, the recombinant fission  is effecting a slight braking manoeuvre due to the conservation of angular momentum. 

Friction has the dual effect of damping the precession, and rebalancing the lobes on the neck, a little like a spinning top keeps upright if it can keep spinning. A spinning top has the disadvantage of not having jet "propulsion" and the friction eventually slows a top down to a speed that topples it, while the comet nucleus has a net propulsive torque that keeps the neck balanced even as it gets skinnier due to repeated recombinant fission.

The changes I have found on Anuket are the surface evidence that this recombinant fission is ongoing. The other points of evidence are that there is no torque free precession - implying the damping necessary is evident.


Sunday, October 23, 2016

Timing for Anuket (Sah) collapse. - NOT perihelion

This is an extension of the changes noted in this post:

And

These changes were thought more likely to have occurred during the time of greatest activity, in mid to late 2015, but the evidence points to a far later collapse.

Image of region in January 2015 

Image in December 2014 for verification of ridge shape:

Image in February (18th) 2016 below: Main rockfall not happened.

Following image shows the Sah area on the February 21st 2016 but angle is not ideal:




Image on March 1st 2016 clearly shows rockfall. 

The conclusion from these images is that the rockfall happened no earlier than 18th of February 2016, and no later than the 1st of March 2016.  OSIRIS WAC and NAC images could narrow this down considerably.

Image Credits
FOR NAVCAM
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
http://creativecommons.org/licenses/by-sa/3.0/igo/
FOR OSIRIS
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DyASP/IDA/
All lines and dotted annotations by Marco Parigi







Sunday, October 02, 2016

Anuket Sobek Border Confusion

Some aspects of cometary science of 67P are more critical than others regarding accuracy. This is because measurements, maps, feature identification and so forth are shared among many scientists and used as inputs in many papers. Errors, mis-identification and inaccuracies in maps can trickle down and cause problems far into the future for seemingly unrelated papers.

The border of Anuket and Sobek is a case in point. There is a pre to post perihelion change near Anuket's southern border very closely associated with outbursts. There are three almost parallel ridges that look very similar in post perihelion images. These straddle the border, and are also close to the border with Neith. 

However, due to the different latitude of these ridges, most images do not show all three. The ones that do have all three, them in have different lighting angle which means they look different enough in the same image, but are easily confused when in separate images.

As can be seen below, the first map shown is overlaid onto a pre-perihelion image in which the northern most ridge has distinctive pointy overhangs. The border is (correctly, I believe) past the next Southerly ridge which is straighter.

The second map below is overlaid onto a *Post* perihelion image (because they show the southern areas better), but the ridges pointy overhangs have collapsed and the ridge looks like the next southern ridge because the overhang collapses have straightened the ridge. The map is therefore very misleading because it changes the region in which very important outburst have taken place. The highly publicised short outburst lands in Anuket in the top map, but Sobek in the bottom map.

This sort of error can be extremely embarrassing for science, and expensive to fix once papers have used both of the maps separately to come to different conclusions. I think an urgent audit of these maps is in order. It appears peer review has not picked up this and several other discrepancies.







Image Credits
FOR NAVCAM
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
http://creativecommons.org/licenses/by-sa/3.0/igo/
FOR OSIRIS
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DyASP/IDA/
All lines and dotted annotations by Marco Parigi

Wednesday, September 28, 2016

67P nucleus changes citizens vs scientist

Before and after perihelion images are a great way to verify theories about the connection between outbursts/outgassing/dust flow and the physical evidence of effects on the cometary nucleus surface. Figure 8 from the following paper:

'Are fractured cliffs the source of cometary dust jets? Insights from OSIRIS/Rosetta at 67P/Churyumov-Gerasimenko.'
Vincent, J.-B., et al.
http://arxiv.org/pdf/1512.03193.pdf

shows a before and after. However, after discussing features *thought* to be fractured cliffs and their detritus, the before and after images show what is *thought* to be evolving flows and *thought* to be partial collapse of a fractured cliff without detritus evidence.

Little effort is made to connect the dots for the reader to try to work out for themselves exactly what is happening and why. I think surface changes are the most fascinating things about comets.




 


Following is the images and annotations from this blog about a fairly clear overhang collapse.

Further down are the original images for context and for the reader to work out changes/evolution for themselves.




After

PHOTO CREDITS
FOR NAVCAM
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
http://creativecommons.org/licenses/by-sa/3.0/igo/
FOR OSIRIS
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DyASP/IDA/

Wednesday, September 14, 2016

Anuket Crack remodelling

Following is an image of Anuket taken well before perihelion in 2014


Note the triangle of boulders and the shortish shadows.
Also a triangular platform near the main crack.






Following is a July 2016 post perihelion image of the same area in about the same resolution and a similar angle.Shadows are a bit longer. Changes are quite obvious. Boulders have moved, The triangular platform near the main crack has collapsed.
 These are videos overlaid to help see the changes trans perihelion. One is slow, and one is fast.