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
Published in March 2017 Copyright ESA website.

The Boulder movement concerned was, however, first documented in this blog here

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,

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:
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:


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
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
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
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
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.

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.


Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:

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.




Sunday, September 11, 2016

Hallelujah - Philae's been found

Hallelujah - Philae's been found.
The comet landing space probe lost 
Years ago when it went to ground,
Into a shadowy nook tossed.
Out of the sun, it went to sleep.
Mother ship Rosetta searched on.
But from Philae, nary a peep.
Where could the little probe have gone?
Rosetta found the little one,
And sent the good news back to Earth.
Some needed closure thus was done
For the mission - for what it's worth.

Philae with Rosetta in flight,
Cometing into the dark night.

Friday, September 09, 2016

Abydos Orientation

See images to work out what you are looking at and the area of Abydos from many different angles, lighting and magnification.

Colours are an attempt to identify features such as perihelion cliff here, marked in green and orange roughly where I think they are on the Navcam and OSIRIS images below.

Magenta is approximated Philae position. Blue is a prominent egg shaped boulder for reference.

White Quadrangle is roughly the area bounded by the Philae discovery image second image below.


Image Credits
Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
To view a copy of this licence please visit:
All lines and dotted annotations by Marco Parigi