Just for a change, some EarthArχiv instead of Astronomy.

Still working the backlog, but it looks as if I've got to cut my own HTML to manage Blogger's stylistic incompetence.

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Eclogites

Eclogites and basement terrane tectonics in the northern arm of the Grenville orogen, NW Scotland

Many years ago, I went walking in the highlands, all over. One place I circled around - literally - was the eclogite field on Beinn Sgritheall to the south of Glenelg, on the coast opposite Barrisdale in Knoydart. Wonderful area. And I've always been interested in eclogites, granulites, and ultra-deep metamorphics. Comes of getting started on the Lewisian foreland, I suppose.

(Oh, you've got to love the OS speelung-chokers. I'm sure they have a good reason for having "Barisdale" farm overlooking "Barrisdale Bay". Hang on! Sandaig - the place "Ring of Bright Water" was set - is in the paper's field area too. And I now have a GPX first-draft of a route for getting to the localities, "Eclogites-v1.gpx" ; that'll need some more work.)

Anyway, I spotted this article going by on EarthArxiv (which I don't pay enough attention to, I know). Even if it doesn't contain much in the way of field guides to this eclogite field, it still interests me. I'm sadly out of practice at this stuff - too long looking at (per Mike Lappin) "crustal ephemera which haven't been down to 100km for 100 Myr, and are clearly nowhere near equilibrium, so can be safely ignored. Otherwise known as the oil industry.

So, what is going on here? They seem to have evidence (structural, geochemical) that these eclogites were obducted onto the Lewisian (Laurentian, even) foreland in the Grenvillian orogeny, about 1200 Myr ago - before the Caledonian orogeny that formed most of Scotland ; before the preceding deposition of the Moinian and Torridonian (very approximate correlates) and their orogeny under the Caledonian ; back into the late assembly of the Laurentian foreland itself, these eclogites were obducted onto the foreland as an ophiolite.

Ah, approaching Real Geology : Pressure-temperature estimations obtained from various lithologies, including the eclogites, indicate peak metamorphic conditions of c. 20 kbar and 730-750°C, consistent with burial to depths of c. 70 km.. but do they give locations? "The eclogites are typically composed of garnet + omphacite + rutile + quartz (Sanders, 1989)" sounds like some fun rocks for the collection. "Omphacite grains occur with symplectites of diopside and plagioclase and are replaced around their rims by hornblende. Rutile has been replaced round the rims by ilmenite" sounds like some good hand-specimen textures are possible.

Oh goody - most of their locations are coastal. That turns an area search into a linear search. Where's my maps - sheet 32 or 33, IIRC.

I'd better go pack the tent!

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Thorne-Żytkow Objects

https://arxiv.org/pdf/2410.02896

T-Ż objects are (arguably) theoretical objects where a compact body - a white dwarf or a black hole - becomes entrained in an otherwise normal star, with lots of interesting consequences for both the behaviour of the object and it's evolution. The really interesting thing is, such a peculiar internal state may not be that obvious from the outside.

I wrote a post about these a while ago (2023-05), when some authors discussed whether or not the Sun could actually be hosting such a stellar viper in it's thermonuclear bosom. Their conclusions were that it would be hard to tell, even if the Sun had acquired it's internal parasite early in it's evolution. The energy produced by the accretion of matter onto an asteroid-mass primordial BH would to large degree replace the energy yield from thermonuclear fusion.

Obviously, other people find these objects interesting, in a train-wreck sort of way. This paper is an early version of a chapter on the bodies for an astrophysics textbook/ review forthcoming from Elsevier.

Sections cover :

1. Formation,
2. Internal Structure and Evolution,
3. and their final fates,

Bearing in mind that none of these bodies have been observed (though proposals have been made - and disputed), the constraints of reality upon theory are relatively slight. More ink will be spilt!

Formation

Thorne and Żytkow originally considered the collapse of a large star's core without the normal disruption of it's envelope in nova/ supernova. However doing this without getting a large amount of "thermonuclear ash" ("metals" to an astrophysicist - any nuclei heavier than helium) on the surface of the resulting body seems challenging. And we have a wealth of spectroscopic data from many such events which do reveal various (super-)nova remnants - but no Thorne-Żytkow Objects.

Thorne and Żytkow also considered merger scenarios where a closely orbiting pair of stars, the heavier of which (most-rapidly evolving) becomes a neutron star (or black hole), and which could then inspiral into it's companion (with various requirements for ejecting material from the pair to conserve energy and angular momentum. That's a complex process, inherently variable ; hard to predict. Examples have been proposed. And disputed.

Direct collision is thought (by some) to be the most plausible formation path, particularly in the dense cores of globular clusters or molecular clouds (which the most massive stars don't have time to migrate away from before evolving into compact-body-hood. Again, the details can be complex - closing energy and angular momentum have to be accounted for.

Internal Structure and Evolution,

The main model is that the compact body has a zone near it's surface where the infall energy of the rest of the system releases large amounts of energy, producing a zone where outwards radiation is dominant, and supports the rest of the star's mass against inflow (exactly as Eddington discussed in the 1920s for formation of regular stars, leading to ideas of the Eddington limit. Beyond this "radiative zone" the star is convective as for normal stars. Potentially, with black-hole cored Thorne and Żytkow objects, the accretionary radiative zone can be surrounded by a conventional nuclear-fusing core, then it's radiative-limited zone, then the convective zone. Distinguishing these from conventional giant to super-giant stars could be very "challenging". If, however, this core material gets mixed into the upper parts of the star, that potentially is observable.

Understanding the nuclear reactions in such systems remains both controversial and challenging. Signals from both stable and unstable nuclear species have been considered.

Understanding the evolution of the objects is obviously complex. Some solutions suggest a Thorne-Żytkow object might have a shorter lifetime than the same mass regular star ; some calculations suggest the Thorne- Żytkow object could have a longer lifetime than the regular star.

And their final fates,

Like many large stars, there are multiple routes to mass loss for Thorne- Żytkow object through their evolution. The envelope mass might decrease enough that the accretionary structures can radiate through to the surface, which would rapidly radiate down to being a regular (-ish) neutron star. Or the NS could collapse to a black hole, triggering an (abnormal, ?) supernova. Many of the models produce periods of pulsation in the Thorne- Żytkow object (another potential observable?).

Fun objects, Thorne- Żytkow objects. The universe should contain such strange objects. Whether it does or not remains to be seen.

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A veritable slew of book chapters in preprint.

Wolf-Rayet stars

W-R stars are getting a deal of attention with the focus on recurrent novae and (potential) supernovæ. That's not particularly because being a WR star is associated with the SN process(-es), but because they're by definition evolved massive stars with a strong stellar wind, which means they've already run a lot of their short life. On the other hand, a powerful WR stage can lead to so much mass loss (into a large planetary nebula) that the star falls out of the window in which a SN can occur. The high mass (M_ini >e; ~20 M_☉ (before late-stage mass loss) and high luminosity makes for very short lifetimes (for a 20 M_☉ star, 3.7~5.5 million years ; for a 40 M_☉ star, 2.6 to less than 1.0 million years), which in turn means the stars die (as planetary nebulae, or supernovae) still in their natal molecular clouds. Often they are part of the dismantling process of the collapsing of the cloud. But why am I trying to summarise a review paper?
The death of WR stars - there is some evidence of SN being sourced from WR stars, but other arguments that they are too compact to form SN and instead collapse directly. This latter scenario is argued for from the geometry of SNR-BH couples such as Cygnus X-1.

Small Bodies in the Distant Solar System

No, I'm not going to get into the "Is Pluto (♇) a planet?" question. If I'd had my 'druthers, I'd have gone for an intrinsic property of planets vs dwarf planets vs other "small bodies", probably based on the "potato radius", self-rounding or something geological. but I can live with the IAU's extrinsic orbit-clearing definition. Hal Levison's "hand-waving" argument about formation mechanisms holds water too. Argument, as far as I'm concerned, over. Yes, I grew up with 9 planets in my Solar system too. I also watched the discovery of Charon, the increasing puzzlement over Pluto's minuscule size, the initial mapping by mutual occultations, and the discovery of the outer Solar System (3rd or 4th most massive element, to date, is Pluto ♇ ) ; maybe the geometrically largest. Science is a process of improving approximations to the truth, and if the solar system has a 9th planet, we've not seen it yet. That said, @PlutoKiller@Twitter.com (the social media handle of the discoverer of Eris, the most massive (known ; to-date) outer Solar system body) has been quiet lately - maybe he's found something?
Rant over. Debate not engaged with.

This is a proto-chapter for another Elsevier book. Probably not the same astrophysics book as the previous entry, but there's no law against them having multiple in production at one time.

This "key point" is one of the less "stamp collecting" parts of the field : "The sizes and shapes of Kuiper Belt objects tell us about the details of planet formation, while Kuiper Belt orbital distribution puts constraints exactly how and when the giant planets migrated."

That there are now over 3000 known TNOs brings statistics to the subject of the outer Solar system, in the same way that the Kuiper telescope brought statistics to the subject of planetary systems in general. The classical a [semi-major axis ; ∝ orbital energy] vs. eccentricity (e) plot, reveals the sculpting of the Kuiper belt by interaction with Neptune (incidentally, clarifying why Neptune is a planet and Pluto isn't), while the a vs. inclination (i) plot shows that something has been sculpting the Kuiper Belt (Outer Solar system) by dragging everything through the nit-comb of small-number-integer resonances with Neptune.

Detecting, recognising, and calculating the orbits of TNOs is a noisy, bias-prone topic. What the biases are (per instrument/ methodology), how severe they are, and how to de-bias observations towards estimating the underlying population parameters, are important topics. Once orbits have been calculated, they can be classified. But classifications can change over time, as interactions with Neptune (and to a lesser degree, Uranus, Jupiter, Saturn, potentially Planet9 [Brown, Batygin 2016] ...) lead to the orbit evolving over periods of more than a few million years ; few thousand orbits. Classification is a moving goal in many cases, and needs to be tested in all cases. Not all trans-Neptunian Objects are Kuiper Belt Objects ; there are various other classes, some of which enter the inner Solar system (e.g. Centaurs).

The composition of TNOs/ KBOs are generally only available by spectroscopy (if you can get the time on a light-bucket) or colour in different filters (if you can't get the light-bucket time). This gives a hint of evolution, from the polymerisation of surface organic matter to dark-red "tholin" mixtures. The properties of TNOs eventually tend towards those of the dust of the outer Solar system, which can be compared to the dust- and debris- disks surrounding other stars. A 2024 result from the dust-detector on the New Horizons spacecraft [Doner et al (2024), Feb.] suggests that there is more dust than models of the 2010s would suggest, pointing to the Kuiper Belt being more populous and extending further from the Sun than thought in the 2010s.

Atmospheres of Solar System Moons and Pluto

Review article on ... well, as the title says. Io excepted, these are N₂ - CH₄ dominated atmospheres, with the outer bodies (Pluto, Triton) developing seasonal methane frosts. Io is different - it's atmosphere is dominated by SO₂ with minor SO, but these components can freeze out rapidly when Io goes into eclipse behind Jupiter. Complicated systems, worth review.

Detection prospects for the GW background of Galactic (sub)solar mass primordial black holes

The prospect of (sub)solar mass primordial black holes comes up on an almost monthly basis when people are discussing the problem of Dark Matter. Last year someone, for reasons not at all clear, speculated that the putative "Planet9" [of Brown & Batygin, 2016, as modified] might be such a "primordial" black hole. It's a pretty dead idea - if they were present in significant amounts (mass-wise), then we'd have seen them in gravitational lensing experiments (observation projects) like MACHO and OGLE. They're not(MACHO, <25% of necessary dark mass) there. To mis-quote Feynmann, a beautiful hypothesis slain by an ugly fact.

Anyway, this paper suggests that moderste mass, sub-stellar black holes (so, presumably "primordial"), particulalrly those in highly eccentric orbits, might be marginally detectable by the in-work LISA mission, and more detectable by planned missions such as DECIGO.

Back to top. And that, I think is enough for this one. Plough through more backlog now.

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My Favourite Caving

My Favorite Caving

When I were nobbut a spotty young shit-bagger, we had a sudden rush of cavings when CBU. Shakers completely blinded, OBM gushing over the top of the shakers, sand-trap level sensors plummeting - which is why I hauled myself down to the shaker house to see what was going on. The poor shaker hand (Zander, it was ; not long after he was made up to derrickman) was standing on the shakers, desperately shovelling to try to un-blind the shakers, and looking anguishedly at the squwak box to call the driller. So, I phoned upstairs (Terry French on the brake) told Frenchy what was going on, he cut the pumps back and we got things under control.

While we were getting the hole clean, this little beauty came up.

"Block 22" is a licensing district of the North Sea, a little east of the infamous Forties field. I didn't know the stratigraphy of the North Sea very well then, but I'm pretty confident in my assignment of it to the Miocene ; I might even go as far as the "Lark Formation", but I wouldn't go to the gallows over that. It's a thick mudrock series above the productive Forties and Andrew sandstones (new name : Mey Sandstone ; it's not worth trying to keep up with the ever-changing nomenclature).

30cm end-to-end is pretty unhealthily respectable for a caving. This was not a healthy borehole, but we did manage to get the casing down, IIRC. Bit of a struggle, but we did it.

It's not particularly obvious from the pictures, but the caving is strongly curved, concave towards the camera. When measured, the inner diameter was pretty close to 17.5 inches. I didn't realise this at the time, but that was a good sign - which I'll discuss later when we look at the other side. For now, note the sub-parallel sub-horizontal scratches at various places, including just above-right of the printed label. I interpret these as being scratches made by the bit (or possibly some of the downhole tools, but I think we were on a fairly simple BHA because we were on an appraisal well - more or less vertical.

Let's flip it over.

[Hmmm, definite depth-of-field effect there. The "feathered" convex-to-camera surface is in focus in the middle of the field, but towards the edge of the caving it's out of focus.]

From the geometry of the cutting, this was a surface within the rock, which failed because of stresses within the rock which weren't counterbalanced by the drilling mud. That (and 8 other functions) is what mud is for. (The formal title of my job then was "mud logger", not shit-bagger.)

On this surface there is a faint "feather" structure with a central spine running circumfrentially to the wellbore and many plumes splaying out to either side. This is the mark of the propagation of the initial fracture when the rock failed. What triggered the failure isn't clear - maybe a large microfossil, or an existing fracture or vein.

This next picture zooms in on the "feather structure". It's worth putting this into your mental collection of "search images". You see this structure in your cuttings dish (or in more obvious cavings) and you know you've got a pore pressure problem, regardless of what pore pressure modellers, mud men, Uncle Tom Cobbley or even the company man says. They can ignore the problem, or rub woad into their communal belly button and pray for it to go away. But you, youngling-geologist, have to report it.

Zooming in further, I wonder what dragged across the caving to cause this tool mark. I was pretty careful handling it - "Pretty! Precioussss!" - keeping it in a paper bag to slow it's drying, avoiding point sources of heat, carefully wrapped in my kit bag to go home. I don't know if this happened coming up the hole, or on surface.

The Company Man got a batter cutting - nearly 50% of the wellbore circumference. But he kept it on the shelf above the radiator in his office and it crumbled to dust the day before my crew change. He tried bribery and corruption to get mine. Once. " Precioussss!" Didn't work. Again, I did tell him "don't dry it too aggressively". Not responsible for advice not taken.

cm and mm scale ; the other side of this scale has American bananas. I've had to do too many conversions for people who can't handle a different unit system to what they grew up with.

This last picture is taken with "oblique illumination" to show the "feather structure" better. It has around a half-mm relief from the general surface.

End of Document
Back to List.

Filed under geoPr0n, which is a very specific type of Pr0n.

Weird deep-sea plesiosaur

https://twitter.com/Prehistorica_CM/status/1416089188563406857?s=09

High lung capacity - but does that help with compression?

Skull features mentioned.

I read the paper, but it starts a long, deep dive into the literature to get to why they think it's specifically deep-diving adaptations. Needs considerably more work.

I roughtly translated a Russian paper about this.

Iceland Bathymetry

I've always been interested in bathymetry - well, at least since needing to produce meaningful "location map" inserts for well logs at work. I've used things ranging from a geology server on Cornell.edu 's system to (since I left work) a tool called GeoMappApp (GeoMapApp (www.geomapapp.org) / CC BY).

This morning someone posted on Twitter a partial picture of Heezen & Tharpe's 1968 seabed topography map (to be more precise, Heinrich Berann's 1977 painting of Heezen & Tharpe's 1968 cross-ocean profiles), which prompted a question by another user about the "ring around Iceland". Which is why I'm interrogating the GIS.

Firstly, we need a bit motre detail on the bathymetry. Note that we're over 50 years later than the data Heezen and THarpe were working with, so we've a lot more data than they had. But it has to be said, Iceland has always valued - and therefore mapped - it's nearshore fishing grounds. So their data in the mid-1960s was probably pretty good for the first 300-odd km.

Bathymetry map of North Atlantic, centred on Iceland. White line is the associated N-S depth profile.

The white line shows the position of this profile. Note that sealevel is 3/4 up the vertical axis. Also note the vertical exaggeration is 125× ; distances are south from the origin, near Scoresby Sund on the East coast of Greenland.

You can see a definite "surface" around Iceland close to shore - between km marks 600 and 700 - which is very typical for around islands. (Damn, I forgot to put a scale on the bathymetry plot.) It's where wave action breaks up rock and moves boulders around until the sediment "falls off the edge" into the abyssal deeps. (This also appears on the next profile, alonf the Scottish margin, which is mainly composed of multi-billion-year old high-grade metamorphic rocks - much more consolidated than fresh lavas which erupted into seawater.)

From 700 to 1200 km from the start point, you can see that the seabed level (above some particular level in the mantle) declines failry steadily. Not uniformly, it looks more like what the mathemeticians call an "asymptotic" curve - always approaching a certain lline, but never quite getting there. If you, dear reader, want to play with the numbers yourself, I have the data file along this track line under the name "IS-profile-NS.txt". Some header lines :

GMRT Grid Version 4.11
Longitude Latitude Distance (km) Elevation (m)
-20.88 69.50 0.0 -378.21484
-20.88 69.48 2.9305084 -374.4984
-20.88 69.45 5.864622 -379.54816

(The original file is tab-separated, not space-separated, but that shouldn't cause any significant problems.

The general opinion of this profile is that the predictable decrease in the seabed level is the result of the deper parts of the crust slowly cooling as they move away from the heat inputs at the mid-ocean ridge. That's very compliant with the rest of physics - density changes with temperature, Archimedes and his post-bath streak through the streets of Syracuse, all that jazz.

But I have to admit that for the specific case of Iceland, I had to select my profile fairly carefully, because to the NW and SE are complicating structures - the Fareoes (DK : "Far Islands") ridge and the Iceland-Greenland ridge. These are the surface traces of the movement of the comtinental shelves and newly-created oceanic crust over the margins of the Icelandic hotspot, which has resulted in the accumulation of considerable thicknesses of lavas on the surface (I've drilled oil wells on the UK side of this region ; basalt and eroded lava beds and intrusions are common for the top several kilometres.) and sub-surface heating from some flow away from the hotspot. The textbook image of a hotspot is that they're circularly symmetrical, but as seismic data improves it is becoming increasingly clear that they're not simple, or circularly symmetrical. Or even, verticallt straight. By coincidence I was reading a paper on the topic just a few days ago ("Imaging deep-mantle plumbing beneath La Réunion and Comores hot spots: Vertical plume conduits and horizontal ponding zones", Dongmo Wamba et al., Sci. Adv. 9, eade3723 (2023) 25 January 2023) which gives a much more geological "feeling", complex structure. That this SW Indian Ocean example shows plumbing structures in the mantle of several thousand km size N-S, E-W and Up-Down feels - to me - more realistic than simple cartoons of circular structures. In the volume of the Earth, nothing is the "spherical cow in a vacuum" that physicists (stereotypically) start with ; everything has a history, which affects it's present and future. Complications of the "Icelandic hotspot" stretch at least as far as the island of Lundy in the Bristol Channel, the line of "Tertiary Volcanic Districts" (as the regional geological memoirs are titled) from Ulster to Arran to Mull to Skye to the Forties oilfield (intimately associated with the whole Central North Sea oil province), a slew of seamounts and dead volcanoes between Orkeny and the Faroes, the Faroes themselves, and I literlally do not know what is further up the Norwegian Atlantic coast. Really quite comparable with that paper's Comoros-Mayotte-Reunion-Marion-Crozet-Kerguelen sub-crustal plumbing.

Taking a profile perpendicularly across the Ridge direction, from the mountain rim of Greenland, through Iceland, over the Faroes to the Shetland Islands, shows a more complicated set of elements :

Within Iceland, dips to almost sealevel speak to marine and ice erosion to that (approximate) base level (probably with some filling by sediments, also accumulating to approximately sealevel), then continuing to the East (increasing distance from the start point), between about 700km and 1300km the seabed sinks along a similar shaped profile to the N-S profile, though at a devreased rate. Then is a interval going above sealevel - the Faroes - which appear to have either a lot of build-up, or some thermal support from below. Then there is a trough (not a subduction trench, but probably fault-controlled) which reaches down to approximately meet the previous "thermal sinking" curve. Then there is the Scottish continental slope, and the wave-cut surrounds of the continentals shelf around a relatively small island group. (Text file of plot data is IS-profile-NWSE.txt)

This final set of images is across the Reykjanes ridge, a few hundred km SW of Iceland, and somewhat away from the complications of the hotspot.

Here the decrease in seabed level away from the ridge is much more clearly symmetrical about the ridge axis. The axis is still a thousand metre tall range above the "abyssal plain" - compare it with the Greenland mountains above sealevel.

The data file for this plot is "/home/aidank/winxferdir/Portable/geomapapp/GMA outputs/IS-ReykjanesRidge-Profile-NWSE.txt"

I've uploaded all the images and data files to a folder on "Box", but I'm not sure how that is visible from the outside world. https://app.box.com/s/skg097kuinerqy52b89xvuain2d7qweb Suck it and see!

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There's an annoyance - the Wikipedia page for Marie Tharpe cites her as having "discovered the Mid-Atlantic Ridge", while the page for the Mid-Atlantic Ridge correctly cites the discovery to the Challenger oceanographic survey voyage in 1872 - some decades before Tharpe, and probably her parents, were born. I'm fed up with correcting Wiki and being reverted, so do what you want with the correction. I'm not disputing Tharpe's contribution, but the first awareness of a tall mid-Atlantic underwater topography feature came from laying trans-Atlantic telegraph cables in the 1860s, and has been incredibly well reported. Amongst people who know what physics is. Well, ::SHRUG:: if someone more dedicated to Wikipedia wants to fix it, feel free.

2023-05 May Science Readings

2023 May Science Readings

May the 11th, and I have only just started. This isn't going to be a productive month.
A bit of progress by thw 18th.

Articles studied this May - some of which might go to Slashdot.

WTF is a Magrathea planet?

Thorne-Żytkow objects

Sporadic rotation in tightly-packed planetary systems

Some Tweets.

Replacing Areceibo?

The Winchcombe Meteorite.

Mantle structure below HotSpots

End of document

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I've got my keyboard better set up for accenting etc, and that's worth remembering. But it's not really a thing for this page. And I need to work on the redshift calculator (online version). [I still can't see what I was concerned about.]

Well, now I've got a problem. Why are my changes to my CSS not updating?

P …

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WTF is a "Magrathea Planet"?

ArXiv : Statistics of Magrathea exoplanets beyond the Main Sequence

Do people these days need to reference that Magrathea is a fictional planet in Douglas Adams' "Hitchhiker's Guide To The Galaxy"? Hopefully not, but if so, follow the link.

From the radio series/ books/ TV series/ films, the planet is sufficiently Earth-like for an unmodified tea-drinking slightly furry English-person to walk across the surface, picking his way between the lumps of confused sperm whale, armoured in a slightly battered dressing gown. So, essentially, Earth-like.

But what is a "Magrathea planet", according to these astronomers? Well, I'm not sure exactly how they got from the book description to a "system[s] in which the planet survived the [white dwarf] formation of the stars in the binary." In particular they're looking at planets around double-white dwarf systems, of which "No exoplanet has been found orbiting double white dwarf (DWD) binaries yet." That terminal "yet" suggests they have some reason to believe that there will be an announcement, some time "soon". Watch, as they say, this space.

There is a hint in the books etc that the Magrathea "civilisation" (Adams' own expressed doubt) is quite old in human - and "galactic" - terms. Which goes with a relatively old stellar system … there are a lot of caveats to put in there, but it's fiction, so not worth getting too bothered about. These scientists seem to have priority on re-using the term in an astronomical context, and I guess we pretty much have to accept it. They're a moderately interesting type of planet, but ultimately not going to be that common, compared to main sequence star's planets.

The "gas giant" aspect of the definition is in contradiction to Adams' earth-like scenario, but does mean the class is of relatively detectable planets. The main difficulty is likely to be in finding "DWD" systems, because by definition, they're going to be dim. The closest WD to Earth is the Sirius (absolute magnitude +1.43) and it's companion WD, ("Sirius B" sometimes called the "Pup", absolute magnitude +11.83, on a 50-year orbit about the primary) which is about 10.4 magnitudes (a factor of 14400-fold) fainter. As a "DWD" system, we certainly wouldn't have spotted tis until the 1700s, if not 1800s, while as it exists today, it's the brightest star i nthe sky after the Sun.

As a class of planets, it's a logical class, and this is a name for it. But it's not ever going to be a particularly common class, compared to those around G₀- or M- stars.

There are other science uses of "Magrathea" in software ("Magrathea-Pathfinder: A 3D adaptive-mesh code for geodesic ray tracing in N-body simulations") and experiment ("Magrathea: Dust growth experiment in micro-gravity conditions"). Both are in the field of "building planets", which was the business area of Adams' Magratheans. Which is all good fun.

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Observational predictions for Thorne–Żytkow objects

https://arxiv.org/pdf/2305.07337.pdf

Well, I had to search my note to remind me how to type the (capital-Z-upside-down-caret) character. (It's Super-.,z on my machine.) But that's not the big point. What the fsck is a Thorne-Żytkow object? Thorne–Żytkow objects (TŻO) are potential end products of the merger of a neutron star with a non-degenerate star. Ohh, so, the popular trope every time there is some science news about a black hole or neutron star, "What would happen if this entered the Solar system? is right up this street.

There has obviously been theoretical work in the past on this, because the paper doesn't start with the NS entering a photosphere. They seem to have their NS already at the core of the "non-degenerate" star ("the Sun" for the Internet wail). Previous work (1975 to 1991) suggests that Depending on the mass of the combined star, it can be supported either via nuclear burning on/or near the surface of the NS and by accretion onto the NS. Which is rather what you'd expect, if you think about it for a few seconds. The situation isn't that far from what happens to a NS in a binary system, as it accretes material from the non-compact star, except (this is important) there is enough material compressing the burning area to not go down the SNIA route of a thermonuclear "standard" candle, but it burns in a quasi-steady state. The normal scenario of a SNIa is for a white dwarf (WD) to be doing the accreting, but you could try doing it with a NS too. The difference in surface area between a WD (approximately Earth-size) and a NS (typically 3km in radius) is going to change things a lot though.

TZOs may be news to me (though I've got to say, I had wondered about the question myself, but never researched it), but they've been a subject of work since the mid-70s, have a Wiki page, and I (probably you too, dear reader, should you exist) would be best advised to read that first. A TŻO has an estimated lifespan of 10^5–10^6 years. Given this lifespan, it is possible that between 20 and 200 Thorne-Żytkow objects currently exist in the Milky Way. answers several very obvious questions. What happens then? It has been theorized that mass loss will eventually end the TŻO stage, with the remaining envelope converted to a disk, resulting in the formation of a neutron star with a massive accretion disk. Very well and good.

A candidate TŻO was proposed in 2014, and they've been linked to other classes of odd stars (Wolf-Rayet stars, RCrB variables ... ), but that attribution has been challenged with an alternative candidate proposed. There are now a half-dozen eight candidates, some of which are well-known RCrB variables.

From Wiki, they're also associated (potentially) with "strange" stars (in the quantum chromodynamics sense), and hence tetraquarks and pentaquarks, all of which have appeared in my reading lists over the last few years.

So, what does this paper add, now that I've dragged myself up to speed on the base phenomenon?
By using different computer models for the nuclear chemistry that would go on on the stellar core to NS boundary, this paper makes different predictions for the nuclear make up (and so, eventually, spectroscopy) of the star. And ... it's over to the observational astronomers.

I've dropped the data into the TŻO wiki page "talk" section. I've had too many snotty responses from Wikipeople to waste effort putting it in myself.

Dramatis Personae

An obvious question is, who are Żytkow and Thorne? I don't recognise Żytkow's name, but is the "Thorne" "Kip" Thorne of various GR and gravity text books? And indeed, it seems to be him. The other author, Anna Żytkow, is a new name to me. See her Wiki page.

Edit : connected to this article from Jan 2024.

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Day ‘N’ Nite: Habitability of Tidally Locked Planets with Sporadic Rotation

https://arxiv.org/pdf/2303.14546.pdf

Quite a short one here. In a "compact" planetary system - lots of planets in close orbits tight arouind a (typically) small star, it has generally been thought that the planets woulf be tidally locked - rotating about their own axis in the same time (and sense) as they orbit the star - so that one part of the ground points permanently to the star while it's antipode points permanently to outer space. A number of SF authors have used such planets as interesting locations to set their stories, including (just two I remember) "Proxima" and "Ultima" by Stephen Baxter. In a different setting, Larry Niven looks at the "star unmoving in the sky" in different artificial habitats on "Ringworld" (1970) and on the "Bowl of Heaven" (2012). Is there something about SF authors that makes them interested in "abnormal daylight hours"? Chronic insomnia and disturbed sleep patterns, maybe?

The work here is a mathematical study of the influnce of one planet upon another in such systems. The authors find a significant number of planets can interact to torque each other between locked rotation (do I need to point out that in tidally-locked couples, both bodies are actually rotating, just at the same rate?), and rotating at various rates. The transition between rotating (with respect to the star) and non-rotating can be chaotic, with periods of chaotic rotation occupying around ⅕ of the time between periods of tidally-locked rotation - which can put a reference location near the "sub-solar point", or the "anti-solar point", fairly rapidly.

Which would make for an interestingly different place to live.

Whether it's an interesting place for an SF author to drop some small furry Centaurian creatures into (with a criminally negligent pre-colonisation survey) ... well that's a question. The "chaotic rotation" doesn't mean that one day the "Sun" rises in the middle of the sky as normal, then it starts to move to the east, does that for a couple of days, then reverses to travel to the west. However the small furry Centaurians define "sunrise", "east" and "west". No, the chaos of rotation state swaps for periods of thousands of years (orbits), not on a day by day basis. With orbital periods of a few weeks, that's maybe not such a dramtic problem. And the Good Doctor himself managed at least one story with a once-in-10,000-year event ( Nightfall)

Is there much more to the science? FTFAbstract, A recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations of the substellar point possible for these planets, which are usually assumed to be tidally locked. - which is basically what I put above. Also in TFAbstract : Our findings show that tidally locked planets with sporadic rotation are able to be in both long-term persistent states and chaotic states: where rapid transitions between behaviors are present. Quasi-stable spin regimes, where the planet exhibits one spin behavior for up to hundreds of millennia, are likely able to form stable climate systems while the spin behavior is constant. Which gives the SF fraternity somewhere to set their "playground". Many studies have shown that with sufficient heat circulation in the atmosphere and/or oceans, these planets may not have a temperature dichotomy as extreme as was once thought between their day and night side It would also seem that the paper's authors have noticed the "dramatic" potential :

An illustrative example would be a planet that was previously tidally locked for a long period of time, hundreds to thousands of years, whatever is long enough that the climate has settled into a stable state. Such a planet in the habitable zone around a TRAPPIST-1-like star could have an orbital period of around 4-12 Earth days – the approximate orbital periods of T-1d and T-1g, respectively. Due to the TLSR [’tidally locked with sporadic rotation’] spin state, this planet may, rather abruptly, start to rotate, albeit slowly – on the order of one rotation every few Earth years. The previous night side of the planet, which had not seen starlight for many Earth years, will now suddenly be subjected to variable heat with a day-night cycle lasting a few years. The day side would receive a similar abrupt change and the climate state that prevailed for centuries would suddenly be a spinning engine with momentum but spark plugs that now fire out-of-sync with the pistons. In this analogy, the spark plugs and the subsequent ignition of fuel correspond to the input of energy from starlight. The response of ocean currents, prevailing winds, and weather patterns may be quite dramatic.

It's an interesting idea. Much fun to play with. The big dramtic laibility I can see is that the onset of rotation would be fairly slow, so frozen air from "dark side" is likely to be evaporating from the terminator (day/ night boundary line) as it gradually progresses into long-untouched areas ; not freshly exposed to the heat of the noon-day sun. That terminator evaporation is going to rapidly increase the heat-transporting capabilities of the atmosphere, both into the newly-lit regions and back to the newly dark regions. Which ... is exactly where the SF author can slice and dice the "science" and "fiction" parts of their business.

For perfectly good reasons, authors are very chary about receiving "interesting ideas" from the general public. Too much chance of a "plagiarism" lawsuit. Baxter suggests mailing via "c/o Christopher Schelling, Selectric Artists, 56 Planetarium Station, New York NY 10024, USA, Email: Christopher Schelling ; if his Google-fu is strong, he'll get some notification from Google that people are talking about him. Maybe. I'll see if there's any response before the end of the month. 19th - haven't heard anything yet. I'll have to get into doing the edit-before-publish thing instead of republishing as I edit.

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Some Tweets - and Toots

Hands up who loves a good B-Z reaction? No, sorry, that's unfair. Everyone loves a good - or even a bad, BZ reaction. Well, how about this one?

The Frederick lab has perfected disposal of used luminol-based ECL reagent. After the Western is developed, inject the ECL into a solution containing 10% bleach. Chemistry is awesome! pic.twitter.com/fa9z7XEQkl

— Dr. Kendra Frederick (@kendrakf13) June 14, 2018

That's not a B-Z reaction, but it is quite dramatic, isn't it? It's obviously a light-emitting oxidation reaction (10% "bleach" is a it stronger than regular supermarket bleach (my under-sink bottle says it's less than 5%), but you could get to 10% using a freezer. What are the other reagents? Byproducts or waste products from a "Western". Which is a "Western Blot Test", I think - a way of "fingerprinting" genetic material. Or, as Wiki puts it, a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detecting the proteins, this technique is also utilized to visualize, distinguish, and quantify the different proteins in a complicated protein combination. That latter is pretty much where I got the "fingerprinting" idea from. This would seem to be a mixture that is used for chemiluminescent detection, but this surplus solution has clearly not reacted with the "reporter" part of the detection antibody. "Luminol" is mentioned, with this structure :

(Structural diagram of luminol molecule, a bicyclic with benzene coupled to a nitrogen-nitrogen containing ring.) So I guess getting any supply of luminol, in an appropriate solution , then injecting it into an oxidising solution, and you should indeed get this sort of display. P Ah, I thought I recognised that name - the compound is one that gets cited in every second "true crime" programme as the "magic blood detecting spray". The Luminol can react (briefly, but it can be photographed) with oxygenated haemoglobin in blood, producing this same glow.

So if I need to clean up a site from a blood splatter, a reducing agent that reacts with haemoglobin should make the SOCO's job harder. (Scene Of Crime Officer.)

Well, that's a technique I can't use after I publish this. [Shrug]

It's a fun piece of chemistry, but I doubt I'll ever have the materials to do it. If I'm ever ordering from the BDH (or Aldrich, or whoever) catalogue, I'll maybe get some Luminol, but I doubt that'll ever happen.

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The Next Generation Arecibo Telescope: A preliminary study

link

Finally nearing "up to date".

The 1960s-designed Arecibo radio telescope sufferec catastrophic failure of one of it's three support towers on December 1^st 2020. It's loss meant the loss of observational capability in three major fields

• planetary science,
• space and atmospheric sciences
• radio astronomy

The radio astronomy work can, to a significant degree, be performed at other sites (including the recently comissioned Chinese 500m Telescope, "FAST"), but few sites have the capability to transmit high power radio signals into the sky with high accuracy, which was used for radar imaging of passing asteroids, radar mapping of Venus, and studies of the Earth's atmosphere.

Proposals are now being made for a replacement to continue astronomical observations on the site. This proposed structure uses a large number (102) of identical 13m steerable parabolic dishes mounted on a separately pointable base structure about 150m in diameter. The "base plate" would deform under it's own weight (and wind loads ; Arecibo remains in hurricane territory), which the individual dishes can be re-pointed to accommodate as the telescope tracks a target across part of the sky. (The paper doesn't say "commodity satellite base-stations" - but with over 100 required including spares, that's the industry that would probably fill the order, even if the design is specific for this job.)

This approach of "many small receivers, linked" has long been used in radio telescopy. Big, fully steerable structures like Jodrell Bank and Green Bank have to some degree been superceded by large arrays such as the Allen Telescope Array and https://en.wikipedia.org/wiki/Square_Kilometre_Array . Improvements in radio sensitivity have moved the emphasis from the "light bucket" approach to improving angular resolution by widely-spaced receivers. The ultimate end of this approach is using telescopes at opposite points on the Earth for a receiver spacing of up to 12,000km. Until, of course someone puts a significant radio telescope in space.

Part of the purpose of science papers is to provoke questions. This approach makes me think - could the operations phase of the (proposed) NGAT130 (Next Generation Arecibo Telescope-130m) be brought forward into the construction phase by mounting the first 13m dishes around the rim of the "bowl" to start doing science while the tiltable platform is built within the "bowl".

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The Winchcombe Fireball—that Lucky Survivor

https://arxiv.org/pdf/2303.12126.pdf

On February 28, 2021 a bright fireball was seen over SW England, by many eyewitnesses and by a considerable number of sky-observing "fireball cameras" which allowed the rapid calculation of the fall location. The next day, 0.6kg of relatively lightly contaminated meteorite was recovered, including one bodt which fell onto a paved driveway. The number of instrumental records allowed the reconstruction of the original orbit, and also the calculation of the strains imposed on the body at the times of it's several fragmentation events. The initial mass of the meteor was estimated at 13kg, with about 4% of it's mass recovered.

The observing cameras were parts of 5 different camera networks, all 14 cameras grouped into the UK Fireball Alliance (UKFAll) (3 from SCAMP (System for the Capture of Asteroid and Meteorite Paths) ; 3 from UKFN (UK Fireball Network) ; 3 from UKMON (UK Meteor Network) ; 2 from NEMETODE (Network for Meteor Triangulation and Orbit Determination) and 3 from GMN (Global Meteor Network). Fortunately the camera networks have common standards and procedures for reporting and combining data, allowing the networks to work together in real time. Their joint PR mechanisms managed to coordinate reporting on news media so that amateurs in the fall area recognised and collected, with anti-contamination procedures, the meteorites.

On analysis, the meteorite was classified as a CM2 carbonaceous chondrite, which is a fairly uncommon type of meteorite. (Analyses continue.) The body's pre-impact orbit was moderately eccentric (e≃0.61), which with a semi-majjor axis of 2.598 AU gave an orbit that touches Earth's orbit near it's perihelion and has an aphelion near the orbit of Jupiter (0.98 and 4.18 AU respectively). The orbit was in the same direction as the Earth's, approaching it from it's trailing quarter, which lead to the relatively low impact velocity of 13.8 km/s (the Earth's orbital velocity is 18km/s, which is a more typical lower limit for impact velocity of meteors. That low closing velocity with Earth is why it experienced realtively low stresses in flight. Even so it fragmented several times in flight, each fragmentation being accompanied by a flare of the fireball.

The meteor's pre-impact orbit falls between the 3:1 and 5:2 mean motion resonances with Jupiter, which suggests how the body may have evolved its orbit before entering on it's final orbit.

What strikes me - and slightly worries me, is the number of distinct groups of fireball cameras involved. This time they seem to have had good coordination, but with recent screaming from "online communities" about "do more, do it faster, do it quicker" (Slashdot story of 2023-05-10), I anticipate it will take considerable time to tie people from this burst of enthusiasm into the necessary networks of coordination and information exchange. Then again, that noise is from "UFO-hunters", so it probably wouldn't amount to much value anyway.

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Imaging deep-mantle plumbing beneath La Réunion and Comores hotspots: Vertical plume conduits and horizontal ponding zones

I forgot to save the link, but it's Open Access.Search for "Dongmo Wamba et al., Sci. Adv. 9, eade3723 (2023) 25 January 2023"

Over the last few decades the questions in deep mantle petrology have somewhat shifted from "Do hotspots really exist?" to "What is the structure of hotspots>". In the process the image has shifted from the cartoonish idea of a single jet of hot material rising from (where? That's always been a question) to play in the underside of the crust (or lithosphere - not the same thing!), creating particular melts, and causing a circular area of thermal uplift, to the much more complex ideas expressed in this 3-d seismic tomogrpahy exercise described in this paper.

For several years, a protracted sequence of earthquakes under the Indian Ocaen island of Mayotte. I thought I'd written about the Meyotte events previously - I've certainly prepared some diagrams - but if I did, I can't find it.

Short version : there have been a lot of earthquakes under the island group of Mayotte in the arm of the Indian Ocean separating Madagascar from Africa. Lots of earthquakes. Enough earthquakes to raise very real concerns about the stability of the atoll's flanks, as well as the simple risk of unadorned ground shaking.

Mayotte is a départemnt of France, so their government have to take the threat seriously. It may be unlikely to uproot the Eifel Tower, but a major earthquake (or eruption, or sector collapse) would seriously affect, or even kill substantial numbers of French citizens (and no small number of refugees and economic migrants from across the Mozambique Channel). So of course, they French take it seriously.

One part of that taking seriously has been the establisjhment of a dense array of seismographs, which assist in locating earthquakes in the body of the volcano. But it also allows the recording of changes in seismic waves from distant earthquakes which pass through and below the volcano and are affected by changes in the rock properties. This is the essence of the subject of "seismic tomography", which acquires a very thick accretion of mathematics to deconvolve the signal from the raw seismic. But that's what computers are for.

What this paper reveals is that below the SW corner of the Indian Ocean there are conduits of relatively hot, low seismic velocity rock

• moving up from the core-mantle boundary …
• to pool at the 1000km to 600km (depth) "low velocity zone" …
• then to move up further to pool again at another "low velocity zone" …
• then finally erupt (or intrude) to (near) surface

Which is fairly conventional "hotspot" theory. But there is one problem - the vertical conduits between each storage level are offset horizontally from each other by several hundred kilometres, if not more. That definitely isn't in the conventional story of hotspots.

This diagram (from Mantleplumes.org - guess their point of view!) shows - on the left panel - the traditional view of plumes ascending more or less directly from the CMB (Core-Mantle Boundary) to the base of the crust. In the right-hand panel several "low velocity zones" (LVZs) are indicated at different levels in the mantle, associated with various levels of dismemberment of subsiding plates. In contrast, the model from this Mayotte paper postulates that the same LVZs are actually conduits for horizontal movement of magma ascending from the CMB towards the surface, potentially displacing the position of the conduit hundreds or thousands of km between each level.

In short, the plumbing store has supplied the same parts, but they're now arranged differently.

The previous diagrams have been cartoons. Now comes the actual data, rendered as a cube of [difference in seismic velocity] versus northing and easting (I'm avoiding "latitude" and "longitude" because that could get really complex where you're comparing radii that differ by a factor of 2).

What do we see here? Well, it's typical geology - obviously it bears some resemblence to the cartoon (there wouldn't have been much point drawing the cartoon otherwise …), but it's also a lot more complex. The "levels" where there is horizontal melt (heat) transfer aren't level, and the "pipes" where there is vertical melt (heat) transfer aren't vertical. The "lava lamp" appearence … well, isn't the physics in both actually quite similar. It has been a long time since I had a lava lamp, but now I'm thinking that a vacuum-walled (reduce lateral heat losses) lava lamp with 3 immiscible liquids (continuum transparent; two opaque colours) would be really intereasting. I'd put a beer on it that at least one of the offices or labs of the authors has a lava lamp of some sort.

Summary

It's a much more "realisitic" feeling model. I've always been rather uncomfortable with the "cartoon" hotspot model, because the idea of such a norrow conduit persisting for so long - as well as "how the fsck do they get started?" really seemed to ask quite a lot of Earth's materials (well, any other planet's too). But the basic idea seems to have som many things going for it too. Seamount chains ; Wrightman's triple junctions ; the Yewllowstone trace under America ... it's all very tempting.

This model makes that look a lot more reasonable. It is a much more "geologically reasonable" model. "More seismic data under other complexes!" I'd really like to look underneath the incipient rift zone of East Africa - and this can't have escaped the authors either. The Yellowstone trace, OTOH would tell us a lot more about how cells (and walls and conduits) fade away. If we we're still allowed to think about basin studies and the timing of generation in petroleum provinces, this would probably get a lot of traction there.

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New Year, New ArXivery

I've been a bit slack on keeping up with Arxiv for a while, so let's see what's hiding in the in-box.

2022-01-04

Hyper-Fast Positive Energy Warp Drives

Now that sounds like a challenge to anyone not wanting to "out-geek their inner Trekkie", or however they describe it.

What's it all about? It's on the "gr-qc" section of Arxiv, which is "general relativity & quantum cosmology", so from the off, I'm not expecting a claim of a working model, ready to go out and speak to Vulcans.

Abstract

Solitons in space–time capable of transporting time-like observers at superluminal speeds have long been tied to violations of the weak, strong, and dominant energy conditions of general relativity. This trend was recently broken by a new approach that identified soliton solutions capable of superluminal travel while being sourced by purely positive energy densities.

Yes, previous suggestions of how to travel faster than light have been "hampered" by needing some way of generating "negative energy density" volumes of space, which nobody has any idea of what it means, or how to make one. So staying on the positive side of that question is probably a good idea - at least if you're wanting to talk about things that might actually be realisable.

[continued] This is the first example of hyper-fast solitons satisfying the weak energy condition, reopening the discussion of superluminal mechanisms rooted in conventional physics. This article summarizes the recent finding and its context in the literature. Remaining challenges to autonomous superluminal travel, such as the dominant energy condition, horizons, and the identification of a creation mechanism are also discussed.

OK, it's more of a review article than a research report, but that's OK.

The first 18 references are about the negative energy density thing. It still doesn't mean much to me, but at least I got that bit right. A soliton is a shaped block of space time that in some way differes from the surrounding smooth space time by means of it's rapidly varying curvature. I think. What does Wiki say? a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity - so it's not just a space-time thing, but a general wave phenomenon. And then ... the paper goes down a rabbithole of maths, way over my head.

There are still numerous challenges between the current state of physical warp drive research and a functioning prototype.

Ohhh, that sounds fun ...

The most glaring challenge is the astronomical energy cost of even a modest warp drive, currently measured in solar masses where kilograms is closer to the threshold of human technology.

Spoilsports!

the next hurdle to approach is modeling the full life cycle of a physical warp drive (creation, acceleration, inertial motion, deceleration, and diffusion).

Similarly more spoilsportery. Such tedious attention to uninteresting mere engineering. How are we meant to vibrate the dilithium crystals if someone insists that we make the damend things first?

The last hurdle I will mention is the full characterization of the sourcing fields, whether it be a plasma or other state of matter and energy. [...] the specification of the drive geometry only is an incomplete description of the full solution. Stress-energy sources must be specified to close the system.

More mere engineering. Is this paper meant ot be an inspiration to dreamers, or some sordid little chain which we have to slip, to touch the rest of the universe.

It sounds fascinating, but it's not a huge rallying cry to the Trekkies of the world. Sad. but they're used to it, I'm sure.

On thermodynamics of compact objects

ArXiv (where I recently discovered that the "X" isn't an "X" but a "chi", so the pronunciation is "archive"). Sounds dull, but since we can't yet find a way around those pesky laws of thermodynamics, I suppose we'd better pay attention to them. My first question is, are they talking about "compact bodies" which aren't gases, or bodies that are compact enough to have gone out the other side of atoms to being piles of fundamental particles. with no free internal space? Oh, it's black holes, so the inner workings of the bodies are thoroughly hidden from us. How convenient! No details to worry about.

Oh, no, they're not hiding the details : "focusing on self-gravitating compact systems without event horizons" means they don't have any convenient "Veil of Cosmic Censorship" (a.k.a "event horizon") to hde the details from the rest of the universe. How do they manage that? "The key step is the appropriate identification of thermodynamic volume [...] which is in general different from the geometric volume." Ah, that makes a degree of sense to me - if the spacetime were flat, a metre here is the same size as a metre over there, and a right angle to this straight line here defines a plane which is parallel to a right angle from the same straight line over there ; but explicitly they're not looking at a flat space time but a curved one, so you can't rely on either of those identities of translation. And 75 equations later, we get to a summary. Which is expressed i nterms of the Equation of State. of the material. (They're looking at photon gases, or fundamental particles, not atoms, so we shouldn't need to worry about "chemistry".)

Sidebar - Equation of State

I remember seeing these in Mike "Plutokiller" Brown's planetary science course, but I need to refresh mt memory. They provide a link between the pressure on a material and it's density. Wiki puts it slightly differently : "an equation of state is a thermodynamic equation relating state variables, which describe the state of matter under a given set of physical conditions, such as pressure, volume, temperature, or internal energy." That included the pressure-density relation (density being related to volume for a particular bit of matter), plus others. The classical ideal gas law EoS is
p * V = n * R * T (Eq. 1 ; pressure, volume, number of moles in system, Rydberg constant and temperature, respectively)
or
p = R * T * (n/V) (Eq 2)
where n/V is clearly an expression of density.

If you're holding volume constant (so, doing no work, because the pressure vector doesn't move (if you think in terms of a piston model) you get a temperature- pressure relation. If you hold the temperature constant, you get a pressure volume (or pressure-density) relationship.

When you get into QM systems, you have to worry about Fermi or Bose-Einstein statistics. which is a more complicated study.

"For relativistic gas in particular, i.e. with EoS ρ = 3p" How did they get from Eq 2 (or one of the more complex QM expressions) to implying that R * T = 1 / 3 ?

So ... I don't understand what this paper is trying to say. It reminds me that I need to go back to Plutokiller's class notes - and it was a good class! - because I remember thinking I understood the EoS stuff then, but I don't seem to any more.

Rumour has it that Plutokiller is revising and updating that class. No mention on Coursera's website, but I'll keep ear open.

The influence of a fluid core and a solid inner core on the Cassini sate of Mercury

There's a sudden flurry of papers about "Cassini states", also for the Moon. It's something to do with the rotational interactions between outer and inner components. I guess there was a conference recently. Mercury behaves like a rigid body (in terms of how it's spin axis and it's axis of rotation about the Sun relate - the so-called Cassini state) BUT we know it has a substantial liquid core (umm, how? I'll havve to check --- magnetic field?) so what is going on. The authors infer that there may be a large interior solid inner core. Earth has one, but at rather different T & P conditions. So ... probably the chemical composition of Mercury's core is different ot Earth's. Since there are still arguments going at the ~10% level about the composition of the Earth's core, that's not wildly constraining.

There's an update there for Mercury's properties. Stick that into the big astronomy database file.

Otherwise, not a lot of news.

Isostatic Modelling, Vertical Motion Rate Variation and Potential Detection of Past-Landslide in the Volcanic Island of Tahiti

What's this doing on Arxiv - it should be on Earth Arxiv. Anyway, In Tahiti, a coastline uplift of 80-110 m occurred 872 kyr ago after a giant landslide - that sounds like a bad hair day. Tahiti is considered a "stable" island and a tie point for reconstructing global eustatic sealevel variations, so finding a point deformation of the surface there and modelling the post-landslide deformation of the mantle underpinning of the island affects all the rest of the world's sealevel curves. Not by a lot, but definitely by a bit.

Is Tahiti really 6000m above sea level? That sounds incredible. I don't trust GeoMapApp's data sources. Wikipedia says "Highest elevation ... 2,241 m (7352 ft)" Ah, maybe they've got a ft elevation model, and attached it to a metres bathymetry model. That's a bit un-funny.

Update 2022-01-16 - Volcanic eruption, high explosivity in neighbouring Tonga yesterday. These "high islands" of the Pacific are active volcanoes.

What sort of size of volcano are we talking about? (Link to seabed image https://app.box.com/s/4omk3pi5roy1lui05sz8mw3rsowmpbtv ) It's about a 10km wide structure rising 750-800m above the seabed, 50-odd km behind the Tonga Trench. There's a line of volcanoes (and "high islands") close to the trench, and this is a step further back, sourced from deeper off the descending slab. (link to cross section (You can also see the trench-edge primary melt volcanoes and the more distal more andesitic line of volcanoes including the erupting one. "Andesitic volcano" and "good neighbour" don't generally appear in the same sentence.) Volcanism is reported as andesitic, which is appropriate to the reported explosivity of the eruption. The surface islands enclosed two sides (about 1/5) of the perimeter of the summit caldera. SI Global Volcanism database entry

2022-01-08

Gravity-Assist as a Solution to Save Earth from Global Warming https://arxiv.org/pdf/2201.02879.pdf

Well, it sounds serious. But ... if you're wanting to move the Earth outwards by (so much), you need to transfer a comparable amount of material inwards from wherever (the asteroid belt, in this discussion). But the asteroid belt weighs, about 1/2000 of the Earth. If you move that amount (several million asteroids) all the way to the surface of the Sun, you'd expect to move the Earth out by a corresponding amount - fractions of a percent.

What the energy and pollution costs of that would be, to not even address the actual outstanding problem of global warming, let alone the next generation's contribution ... Mr Sohrab Rahvar doesn't seem to have considered that. He calculates an expression for the change of power of light delivered to the Earth proportional to the asteroid mass and a factor for the change of angle - as my gut feeling at the start told me. And the temperature change would be the 4th root of that.

There's a minor point buried away in the details - the impact factor (how close the asteroid close-passer gets to Earth is set to 6400 km - a comfortable miss by 30km. For certain values of "comfortable" which many people wouldn't find very comfortable. That''l be fun.

Someone is trying to steal Avi Loeb's thunder!

This may be a suitable one for Slashdot's peanut gallery.

Two-step nucleation of the Earth’s inner core

I did this one as a comment, attached to "Giant lasers simulate exoplanet cores prove they're more likely to have life, which was a fairly overblown piece about high pressure EoS for iron and it's magnetic effects. Great, you can generate a magnetic field at bigger planet sizes than Earth, but so what? The Earth gets most of it's radiation protection from it's atmosphere, not it's magnetic field. (More of an issue for Mars-size bodies, but so? The overblowing is about super-Earths and sub-Neptunes, not Mars-a-likes.)

A recent paper on ArXiv addresses the question of how you for an inner solid iron core in the molten iron core of a planet - which is believed to be necessary to produce the turbulent flow necessary to produce a self-stimulating dynamo.

The problem is that the "iron catastrophe" involved in separating the iron of a protoplanet from the rock it is mixed with, and it then settling to the middle of the planet, releases quite a lot of energy. (Depending on the composition, possibly enough to melt essentially all the protoplanet.) That leaves the initial core hot and molten, and you then need to nucleate iron crystals to form the solid core. Which would normally need a significant degree of undercooling (cooling the mixture below it's nominal melting point). Which is hard to achieve in the middle of a planet, possibly under thousands of km of magma ocean.

So, a new paper models a different way of forming the necessary crystals. Rather than going from the melt directly to a hexagonal close-packing (hcp) crystal (which is the energetically most favourable end product), they propose a two stage process of first forming a body-centred-cubic (bcc) close packing crystallite, which then rearranges to a hcp as it's growing. They propose that the energy barriers to that two step process would be lower, so the process rates would be higher.

Which is an interesting wrinkle on the details of core formation, but probably a bit less than practically useful, since people are still arguing at the several-percent level on the composition-temperature-pressure phase diagram for core formation. I haven't followed the details for years, but the last time I looked people were still arguing over whether the Earth's core contained several % (atom) of oxygen, sulphur, potassium, or all three (in addition to bulk iron and nickel) to get the right combination of viscosity, radiogenic heating, resistivity (conductivity) and magnetic permittivity, at appropriate temperatures and pressures.

Of course, the crystals formed would probably be quite pure iron, because you're essentially running a planet-scale zone refining process. So your melt composition is going to be constantly changing. Regardless of any continuing additions to/ losses to the overlying mantle bottom layer. Don'tcha just love reality against theory?

And I'm just about caught up with IArxiv.

Glancing impacts on Earth

There is this guy who appears regularly on Twitter, trying to fill the shoes of Archimedes Plutonium, and the Expanding Earth guy, who asserts ad nauseam that the Puerto Rico back-arc basin and some structures in the Southern Andes are the product of glancing impacts by cosmic projectiles. He's a bit irritating - typically very dismissive of counter evidence, totally dismissive of plate tectonics possibly operating in "his" (I assume it's a "he" ; safe bet) area, but somewhat content that plate tectonics operate in the rest of the world. He's got a bit of and "Electric Universe" or "plasma physics" hang up too, associated with his putative impacts. He's probably also afraid of 5G telephones, and I think he's spoken approvingly of Expanding Earth ideas too.

A bog-standard, run of the Internet kook, in other words.

Well, I'm not saying that this piece's author is the same guy, or even knows of his existence, but this is the sort of thing that would greatly encourage the kook. I found this while checking for references about the potential "glancing impact" origin of Mars' Borealis (North Polar) basin.

On a Possible Giant Impact Origin for the Colorado Plateau

This is an Arxiv preprint, for a paper that was submitted to EPSL ("Earth and Planetary Science Letters" - a medium-hitter of a journal in the field) but with no mention of it actually being published. I'm not surprised.

So, firstly, it's a single-author paper. It would seem that Xiaolei Zhang hasn't managed to persuade any of his GMU (George Mason University, wherever that is) colleagues that his theory is valid. He's got a reasonable track record of publishing in "galaxy dynamics" (which he shoehorns into this paper too - confirming the identity of the author), but AFAICT, this is his only foray into geology/ planetary science. In itself, this isn't a disbarring factor, but it is a warning sign.

What is the theory? That about 750 Myr ago (in the Neoproterozoic era), the Earth suffered a "glancing blow" by an impactor to produce an astrobleme of about 640km diameter, which we now call the "Colorado Plateau". 

Aside : digging out the "area under discussion" was surprisingly hard - the author clearly thinks his audience has the same familiarity with the area that he does. There is a map - labelled as "Figure 1", but placed on P 52. That's an artefact of publishing conventions (let the journal arrange the figures into the text ; the author supplies them after the text) - annoying but not the author's fault. There's no legend on the map, which I think only shows volcanic rocks at surfaces versus "other" - which looks very single minded from a geologist's PoV.

Now, this is where the author departs from conventional cratering theory (to put it politely). Given the dimensions of the area considered "anomalous", and an estimate for how deeply the anomalies are incised into the Earth (estimate : 16km, but this seems to be derived from conventional cratering scaling laws, which this paper is rejecting for this "feature" - that point needs justification) then the author derives a simple geometrical estimate for the size of the "grazing" impactor as "Mars size". Actually, "3208km". The calculation used is the inverse of the well-known one for "distance to horizon from ships mast/ cliff, whatever". An allowance is made for drag changing the travel vector of the impactor by several degrees. But that's just about bonkers.

At this sort of scale, planets don't have significant strength. Their spherical shaoe is because the strength of the rocks is negligible compared to the hydrostatic forces due to their weight. Essentially, planets behave as strengthless drops of liquid. A contact like that would leave both objects with surfaces vibrating up and down by hundreds if not thousands of km until the energy is dissipated through most of the mass of the bodies.

It's also a very improbable contact. Even a small degree closer to head on, and the bodies would have merged, or generated so much ejecta that there would have been global secondary impacts, if not forming a moon of orbiting ejecta. And if the alignment had been 16km in the other direction (0.5% of impactor diameter) then it would have been a near miss.

It seems the geological data the astronomer is tieing onto is reporting of apparent horizontally directed shear at high levels in the crust of the Colorado plateau, combined with the Plateau's elevation. He's also relying on there being some great mystery about the so-called "Great Unconformity" observed in the Neoproterozoic of the Grand Canyon. (We have a "Great Unconformity" covering about the same Interval here in Scotland, but we don't blame it on wildly unusual events.)

The author ascribes the appreciable NW-SE elongation of the "Plateau" to the motion of the "impactor" ("grazer"?), but makes very little mention of the Sudbury structure in the Canadian Shield, which is generally accepted as being an impact structure that has been compressed on a NW-SE axis to have about twice the NE-SW dimension compared to the NW-SE dimension. The deformation of Sudbury is generally ascribed to continent-scale compression during the Grenville orogeny shortly after the impact. The more modest non-circularity of the posited Colorado Plateau structure is as easily explained by distortion since it's formation - regardless of intrinsic (e.g. mantle plume) or extrinsic (impact, the FSM's paintbrush) origin. (I emphasised elongation versus compression to avoid people thinking there was some stress field similarity - the elongation is similar, but the direction is opposite.)

Memo to astronomical dynamicists : you leave the geology alone, and I'll leave stirring the pot of star alone. OK?