Safe journey to Mars with Mod Ring?; Spin rate of gas giants and angular momentum transfer; Supergravity and physics breakthrough prize; Night out under the stars with Kenny G and Jupiter

Greetings from Palmia Observatory


Well this week we can report on a space habitat presentation and review some planet rotation rates and finish with some supergravity and Kenny G and saxophone under the stars.


We got a note from Gravity Guy & part-time Las Vegan, Ken, about his paper on the ModRing concept for future generation space habitats that provide for safe journeying to Mars for example.  When I heard that the paper had been accepted and would be presented at the AIAA Propulsion conference in Indianapolis, I wanted to put that trip on my calendar too, but got to busy and forgot all about it.  I Way back in August 11, 2018, we posted some discussion about one of Ken's initial presentation about the Mod Ring concept, which he made at a local AIAA meeting.  You can check out the details of that event, and for a comment about upcoming mathematics of supergravity, you can see some comments by Sabine Hossenfelder, who writes in her book, "Lost in Math" that physics is being lead astray by mathematics, given that even after 40 years effort it has not resulted in any observational corroboration.  That post is at: http://www.palmiaobservatory.com/2018/08/smoky-skies-value-of-image-stacking.html

Anyway, Ken's presentation in Indianapolis last week was apparently good and we can share a couple of slides from that presentation.  In the slide you can see that the central issue is how to protect the astronauts from cosmic radiation from the long time in space and how the structure can be constructed in space and transported to Mars, etc.

ModRing concept and goals (Source: K. Macleod & J. Martin, AIAA Propulsion Conference, 21 Aug 2019)

Other large rotating space stations, like von Braun's rotating space station concept, would be way to expensive and heavy to build and get into orbit.  Hence, this one of the many new concepts being floated is constructed to address the cost of getting into orbit and of building the structure in space with low cost.

The ModRing approach is outlined in the slide below.  Construction of pairs of habitats could be moved into position and installed in the rotating ring as pairs in order to keep the rotating structure stable.  The rotation rate would provide some nominal value of artificial gravity and the habitat construction would include radiation blocking material.  There are tradeoffs between the rotation rate to achieve full one G of artificial gravity and having that rate cause nausea and on the overall size and diameter of the ModRing.

That is a great idea and it looks promising.  Congratulations on a successful paper, Ken and James!

Mod Ring concept and goals (Source: K. Macleod & J. Martin, AIAA Propulsion Conference, 21 Aug 2019)

Separately, there was another interesting article on a similar topic, not rotating structures like Mod Ring, but planets and why they don't rotate as fast as they should.  I have pasted the front page of the article below and you can get the whole article by Jenny Calahan at the astrobites website or just click: https://astrobites.org/2019/08/21/why-are-jupiter-and-saturn-spinning-so-slowly/

Why are Jupiter and Saturn spinning so slowly? (Source: Jenny Calahan, https://atrobites.org)

Recall from the August 20, 2019 post of this blog we mentioned how each of the planets has its own rotation rate and some of the planets have really weird rotation rates and rotation axis orientations.  The graphic by Dr. James O'Donoghue is reproduced here for comparison.  In the previous blog post the demonstration of Kepler's 3rd law and relationship between orbital distance and rotation period was the key point but the strange orientation of the spin axis and different rotary spin rates is the key topic for this discussion.

Axial tilts of the planets, mostly line up, but there are oddballs! (Source: Dr. James O'Donoghue,  @physicsJ)

The spin rate of the large gas giants both spin at about 9-10 hours per revolution and the question is why they spin so slowly.  Hmm, they spin a bit more than twice as fast as the Earth does, so what is the big deal?  The issue is that according to planetary accretion theory and planet formation theory, the larger planets should have acquired more angular momentum with more and more gas and stuff accreting on the forming planet and should be found to rotate much faster.  Recall that the law of conservation of angular momentum says that as a planet contracts and gets smaller, for the angular momentum to be conserved the planet must spin up faster, just as the same for the ice skater model when she draws her arms inward.  The angular momentum is the product of the angular velocity and the  moment of inertia, which scales up as the square of the planet's radius.  Nonetheless after considering all of these variables and more, the measured rotational speed of the larger planets seemed to be quite a bit lower than was expected.  So what was going on?  Well, the conservation of momentum rule assumes that no other torques are applied to the planet, but in these papers we find that a magnetic torque between the planet and the ionized protoplanetary disk from which it formed can transfer momentum away from the planet, hence slowing it down.

Now I have seen the author of the published paper many times before at various conferences, so I looked up Konstaintin Batygin's (Caltech) article for some more of the details and rely on it for the remaining comments.

So Konstaintin goes into all of the heavy details, even though as he says the paper is only semi-analytical.  There is a lot of physics in the various stages of star formation and planet formation out of the original solar disk.  The main point is there is a way that magnetic torqueing could transfer some of the planet's angular momentum, and hence slow it down.  In the figure below you can see how the planet's magnetic field interacts with the thermally ionized disk of gas and dust that surrounds the young planet.  It was surprising to see that the solar energy, so much diluted by the long distance from the sun, can be used to ionize, maybe not hydrogen, but some of the metals in the disk.  The rotating ionized disk generates a magnetic field which interacts with the planet's magnetic field.

Interaction of planetary magnetic field with ionized disk can slow rotation rate (Source: K. Batygin, arXiv:1803.07106v1)

In the calculated curves below you can see that the magnetic breaking takes place during one phase of planet formation and later on some additional infall and accretion of material continues and begins to speed up the spin.  But when the breaking and speed up are all done, the rate of spin is lower than expected and matches up fairly well with observed values.  These effects cover about a millions years in the evolution of the planet.  More detailed work and simulation hopefully will close out any outstanding details and deficiencies.  Thanks for the interesting discussion, Jenny and Konstaintin!

Interaction of planetary magnetic field with ionized disk can slow rotation rate (Source: K. Batygin, arXiv:1803.07106v1)

Ok, enough for now about angular momentum and magnetic torqueing to slow down planet rotation rates, especially since an early morning parcel delivery, requiring a signature, has interrupted our breakfast on the patio.  The package had a book on the "Ideas and Methods of Supersymmetry and Supergravity".  You will recall that this year the special breakthrough prize in fundamental physics was awarded to physicists Peter van Nieuwenhuizen, Sergio Ferrara and Dan Freedman for their 40 years of work on supergravity.  Some critics, like the aforementioned, Sabine Hossenfelder, ask how long physics can go without getting any experimental verification?   Now never mind that this has been no experimental evidence for any part of supersymmetry or supergravity, but their work has been very instrumental in structuring the theoretical research into the topic.  So, as a physicist wannabe, I wanted to see if I could understand what it was all about and had to find some "easy" book on the subject.  Well my friends at Amazon quickly recommended this one.  I didn't realize that I was going to have to sign for the delivery, which usually only happens with wine delivery, but here I had to sign for the book and also noticed that the package had to be x-rayed for security.  Hmm, I didn't realize that supergravity was such a topic.  But, now after trying to read the book and having got stuck at about page 17, I now see why you might want some control over it!  It is not that the topic of supermathematics is that difficult, but that it is very abstract and requires a lot of definitions and abstract concepts, none of which I was familiar with, to make any progress.  Hmm, maybe the signature line on the package should have said, "Warning, abstract mathematics is inside; Open at your own risk"!

Textbook by Buchbinder and Kuzenko tries to describe supersymmetry and supergravity (Source: Palmia Observatory)

Ok, luckily after getting stuck trying to read the book, it was time for a night out and let the brain cool down.  So it is off to the Newport Beach Hyatt Regency, where we met up with Science Nerd & Theatre Impresario, Scott and Sandy, for a jazz concert by Kenny G with saxophone and group.  Here Resident Astronomer, Peggy and I stop at the 94.7 FM, The Wave, free photo booth.

Resident Astronomers pose at 94.7 FM booth at Newport Jazz Series (Source: Palmia Observatory)

It was a lot of fun being out under the stars in the amphitheater and listening to some cool jazz.  I also couldn't resist doing a little, teeny weeny amount of iPhone astroimaging there as you can just barely see Jupiter in the upper left sky with Kenny G and group playing down below.  So, it was a great evening out, even saw Jupiter, and its back to physics in the morning!

Jupiter can be seen in upper left while Kenny G plays at Newport Hyatt Regency Jazz Series (Source: Palmia Observatory)

Until next time,

Resident Astronomer George

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