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Showing posts with label April. Show all posts
Showing posts with label April. Show all posts

2024-04-29

2024-04-28 (0) Slashdot posting before the editors mangle it.

As submitted, then edited.

Slashdot's editors often (daily, if not more often) get a slating for errors, and doing, esentially, nothing. Now, as a regular submitter (occasionally accepted - my count is approaching 130 stories ; whingers - get to that count yourself or stop whinging about the site's content) I know that's bullshit, but I'd never actually sat down to record the difference between what I submitted, and what the Ed. (EditorDavid, one of about a dozen) changed before posting the story to the "front page".

I forgot to mention that I fat-fingered the title in my submission : "shy" not "sky".

I should note that this is not my first brush with the editorial "blue pencil" - in the 1990s and 2000s I volunteered on a community (specifically, trade union) newsletter, supervised by a former newsroom (print and TV) editor, Bob Gibb (also a journalist for Lloyd's List, the shipping newspaper). Bob never seriously discouraged my over-wordy, excessive-detail style. It's easy for me to cut down your work, because I rarely need to add anything; just rearrange it, and clarify it. Far easier than writing it myself!

Vale, Bob.

I submitted my story in the wee sma' hoors of 2024-04-29, and it was accepted at 7:34 (time zone unsure ; I'm Zulu) by "EditorDavid", with these revisions : superseded text (deleted by Ed.) ; inserted text.

For clarification, I've no serious disputes with EditorDavid over this. I'm making notes to learn. No, as Bob would appreciate, "shome mishtake shurely"

The naked-eye sky will briefly host a "new" star.

By "star", I do not mean "comet", "meteorite" or "firefly", but genuine [star] photons arriving here after about 3000 years in flight, causing your eyes to see a bright point on the nighttime sky. When it happens, the star will go from needing a telescope ot good binoculars to see, to being the 50th (or even 30th) brightest star in the sky. PARA For a week or so.PARA

Of course, it could just go full-on supernova, and be visible in daylight for a few weeks, and dominate the night sky for months. But that's unlikely.

Named "T Corona Borealis" (meaning : because it is the 20th variable star studied in the constellation "Corona Borealis") is a variable star in the northern sky - circumpolar ( it's now visible all night, all year) for about 60% of the world's population which although normally you need binoculars to see it. PARA For over 150 years it has been known to vary in brightness, slightly. But in 1866, it suddenly brightened to become about the 35th brightest star in the sky. "Suddenly" meaning it was invisible one hour, and near full brightness an hour later. That made it a dramatic "nova" ("new star"), if not a "supernova", and people watched it like hungry haws as it faded over the next weeks, and months, and years.

And it faded back into it's previous obscurity, just wobbling a little, well below naked-eye visibility.

Until the late 1930s, when it started to change it's ESTABLISHED 280-day cyclic pattern. Then, in 1946 ... someone turned the switch back on, and again in less than an hour it brightened about 240 times, again becoming about the 50th brightest object in the sky. Which made it almost unique - a recurring nova. Today, only 10 of these are known, and they're extremely important for understanding the mechanisms underlying novae.

In 2016, "T CrB" (as it is known) started showing a similar pattern of changes to what were seen in the late 1930s. But RockDoctor writes that in 2016, "T CrB" (as it is known) has started showing "a similar pattern of changes" to what happened in the late 1930s when it became one of only 10 "recurring nova" known to science:

In 2023, the pattern continued and the match of details got better.PARA

The star is expected to undergo another "eruption" EN-dash EM-dash becoming one of the brightest few stars in the sky, within the next couple of months. Maybe the next couple of weeks. Maybe the next couple of hours. I'll check the databases before submitting the story, and advise the editors to check too. [I expected this to be deleted]

Last week, astrophysicist Dr Becky Smethurst posted on the expected event in her monthly "Night Sky News" video blog. If you prefer your information in text not video, the AAVSO (variable star observers) posted a news alert for it's observers a while ago. They also hosted a seminar on the star, and why it's eruption is expected Real Soon Now, which is also on YouTube. A small selection of recent papers on the subject are posted here, which also includes information on how to get the most up-to-date (unless you're a HST / JWST / Palomar / Hawai`i / Chile telescope operator) brightness readings. Yes, the "big guns" of astronomy have prepared their "TOO - Target Of Opportunity" plans, and will be dropping normal observations really quickly when the news breaks and slewing TOO the target.

You won't need your eclipse glasses for this (Dr Becky's video covers where you can send them for re-use), but you might want to photograph the appropriate part of the sky so you'll notice when the bomb goes off.

Bomb? Did I say that the best model for what is happening is a thermonuclear explosion like a H-bomb the size of the Earth detonating? Well, that's the best analogue. Understandably, taking a "close" (3000 light years - not close enough?) look at one seems like a good idea.

Preview, check for brightening/ detonation (JD 2460428.55208 = 2024 Apr. 28.05208 mag 9.905 ± 0.0052 - not "Gone" yet!), submit. This CNN article includes a nice animation from NASA illustrating the multi-star interaction that's causing the event:

The stars in the orbiting pair are close enough to each other that they interact violently. The red giant becomes increasingly unstable over time as it heats up, casting off its outer layers that land as matter on the white dwarf star. The exchange of matter causes the atmosphere of the white dwarf to gradually heat until it experiences a "runaway thermonuclear reaction," resulting in a nova [according to NASA]... The NASAUniverse account on X, formerly known as Twitter, will provide updates about the outburst and its appearance.

The BBC reiterates the key data points — that "The rare cosmic event is expected to take place sometime before September 2024. When it occurs it will likely be visible to the naked eye. No expensive telescope will be needed to witness this cosmic performance, says NASA."

Footnote

And, in the tradition I established while writing this post, I'll check the database : JD 2460429.6875, date/ time 2024 Apr. 29.18750, magnitude 10.0. No eruption yet!

2024-04-28

2024-04-08 Necessary Conditions for Earthly Life Floating in the Venusian Atmosphere

Reference : arXiv:2404.05356v1 [astro-ph.EP]. Published on 8 Apr 2024

https://arxiv.org/pdf/2404.05356

This is obviously a riposte to the claim, several years ago now, of phosphine in the radio spectrum of Venus' atmosphere. Which has been disputed, the instrument readings disputed, the noise profile challenged ... all the usual suspects.

Just from the title, it sounds like a discussion of the (theoretical) requirements, and potentially their observability, rather than actual new observations.

Now, here's weird - in some of the Blogger Preview modes, ":hover" doesn't work. Or is there something else going on? It's a problem with their preview system. I hadn't noticed that before.

Sections

Abstract
I. Introduction
II. LIFE CYCLE FOR VENUSIAN AERIAL MICROBES
III. REPLICATION RATES AND FALLOUT TIMES
IV. COSMIC RAY EFFECTS ON MICROBIAL LIFE
V. CONCLUSIONS
End of document

Abstract

Millimeter-waveband spectra of Venus from both the James Clerk Maxwell Telescope (JCMT) and the Atacama Large Millimeter/submillimeter Array (ALMA) provide conclusive evidence (signal-to-noise ratio of about 15σ) of a phosphine absorption-line profile against the thermal background from deeper, hotter layers of the atmosphere. Phosphine is an important biomarker; e.g., the trace of phosphine in the Earth’s atmosphere is uniquivocally associated with anthropogenic activity and microbial life (which produces this highly reducing gas even in an overall oxidizing environment). Motivated by the JCMT and ALMA tantalizing observations we reexamine whether Venus could accommodate Earthly life. More concretly, we hypothesize that the microorganisms populating the venusian atmosphere are not free floating but confined to the liquid environment inside cloud aerosols or droplets. Armed with this hypothesis, we generalize a study of airborne germ transmission to constrain the maximum size of droplets that could be floating in the venusian atmosphere and estimate whether their Stokes fallout times to reach moderately high temperatures are pronouncedly larger than the microbe’s replication time. We also comment on the effect of cosmic ray showers on the evolution of aerial microbial life.
Back to List.

So, one useful point - that airborne life is more likely in droplets, rather than actual free-floating microbes. Fair point. From which, settling velocities are an approachable topic, while the supply of minerals from the ground isn't so approachable - needs considerably more assumptions. The question of vertical mixing in the atmosphere should make an appearance too. Note: the Wiki atmosphere composition given below asserts significant ferric chloride as a component, which would be an important mineral.

Back to List.

I. Introduction

Their citations for early discussion of Venus-life as cloud-life starts with "H. Morowitz and C. Sagan, Life in the clouds of Venus?, Nature 215, 1259 (1967) doi:10.1038/2151259a0" - which shouldn't really be a surprise. Sagan gets everywhere.

And they go straight into modelling a "sHigo" (spherical Hydrogen isopyenic gasbag organism) and, with reasonably conservative assumptions get a minimum buoyant size of ~4cm (diameter). That's not insane for a multicellular organism, but a bit much from terrestrial experience of microbes. It also sort of (to me) implies an origin on the ground, getting lofted (evolving into buoyancy) as the environment went from Hadean era (with solar illumination ~20% down on today) to triggering the runaway greenhouse and boiling the oceans. But I'll leave that aside for the time being.

RETURN TO THIS

Refereences [4] through [12] cover the controversy about the original detection claim, and raised concerns about the calibration and interpretation of the signals. Clearly these authors feel that the issues raised have bene answered, and the phosphine detection can be treated as valid.

Back to List.

II. LIFE CYCLE FOR VENUSIAN AERIAL MICROBES

This seems to be a re-hash and expansion of :

[14] S.Seager, J.J.Petkowski, P.Gao, W.Bains, N.C.Bryan, S.Ranjan, and J.Greaves, "The venusian lower atmosphere haze as a depot for desiccated microbial life: A proposed cycle persistence of the venusian aerial biosphere." Astrobiology 21, 1206 (2021) doi:10.1089/ast.2020.2244 [arXiv: 2009.06474]

This modle life cycle is predicated on the atmosphere of Venus. Only two references are given, but the structure of the atmosphere has been probed by multiple landers and tested by various combinations of radar from Earth and from (Venus) orbit, so it's not much in dispute.

I'm in the habit of collecting such bits of data on the expectation that I'll need them again. So ... I'll do exactly that, and put the information below. Wait - what's this - from Wiki : Additionally, the clouds consist of approximately 1% ferric chloride. Other possible constituents of the cloud particles are ferric sulfate, aluminium chloride and

Atmospheric Pressure and Temperature of Venus, against altitude. From Wiki, citing Blumenthal, Kay, Palen, Smith (2012). Understanding Our Universe. New York: W.W. Norton & Company. p. 167. ISBN 9780393912104.
Altitude (km) Temperature (K) Pressure (Pa)
0 735.16 9332032.5
5 697.16 6753311.25
10 658.16 4801791.75
15 621.16 3347778
20 579.16 2281839
25 537.16 1512782.25
30 495.16 998152.575
35 453.16 599540.025
40 416.16 354738.825
45 383.16 200522.175
50 348.16 108012.45
55 300.16 53844.105
60 263.16 23882.3025
65 243.16 9894.38625
70 230.16 3738.8925
80 197.16 482.307
90 169.16 37.85502
100 161.16 2.695245
phosphoric anhydride. Well, that's a thing I hadn't considered when making my "supply of minerals" comment above. Hmmm.

Well, let's find some pressure-temperature-altitude data. Ah, good, Wiki has done the searching for me. But ... it seems difficult to generate a chart (in LibreOffice) with multiple ranges for the X-axis, and a common factor for the Y axis. So - subterfuge. Including "tweaking" the drawing in LO.Draw. Not perfect, but it'll do for the moment.

Clearly, I've forgotten the details of Blogger's floating of elements. I'm trying to put the data table beside the graph, but that's not working. I thought I'd figured that out a while ago, but I'll have to work on it again.

Updating on 2024-05-19.

The figures in the "Temperature" column have spurious accuracy. Originally they were temperatures in °ree; Celsius at , but I've conmverted them to Kelvin, which produces about 3 seemingly significant digits.

Maybe I'll do better plotting this with GnuPlot? A project.

I need to add a line for "Earth sea level" pressure (100.0e+03 Pa) and temperature (288.16 K, like I said, "spurious accuracy"). I also need to annotate my diagram with the cloud levels and temperatures for the cycling. Or should I just copy the paper's Fig 1?

I seem to have borked the blog style. That approach at setting up "previous" and next" post-links. I knew I'd regret it.

Lower limit ~45km altitude / pressure ~1.2 bar (~120kPa) / 100°ree;C (~370 K) ; upper limit 60km / 0.2 bar (20 kPa) / 0°ree;C (~270 K). Temperatures and presures well within the range of biological activity on Earth. The visible cloud top moves through this region at different levels at different latitudes. Aerosol droplet sizes vary between around 0.1µm near the lower boundary to up to 4µm towards the upper parts of that range - reasonably realistic for bacteria.

Low in the atmosphere (within the range of the topography) is a low level "haze", with temperatures and pressures rising rapidly out of the (terrestrial) biological window.

A 5-stage life cycle is envisaged :

Proposed life cycle
Stage Description
1 The cycle begins with dormant desiccated spores (black blobs in Fig. 1) which partially populate the lower haze layer of the atmosphere.
2 Updraft of spores transports them up to the habitable layer.
3 Shortly after reaching the (middle and lower cloud) habitable layer, the spores act as cloud condensation nuclei, and once surrounded by liquid (with necessary chemicals dissolved) germinate and become metabolically active.
4 Metabolically active microbes (dashed blobs in Fig. 1) grow and divide within liquid droplets (shown as solid circles in the figure). The liquid droplets grow by coagulation.
5 The droplets reach a size large enough to gravitationally settle down out of the atmosphere; higher temperatures and droplet evaporation trigger cell division and sporulation. The spores are small enough to withstand further downward sedimentation, remaining suspended in the lower haze layer (a depot of hibernating microbial life) to restart the cycle.

The authors are using "spore" to designate a resistant, inactive life stage specifically light enough to be suspended in the atmosphere in the upper parts of the lower atmosphere. They're also using "hibernate" where "estivate" (resting through the "summer" might be more appropriate.

One thing I don't see is consideration of suunlight intensity. With about twice terrestrial illumination intensity at the cloud tops (Venus orbits at about 0.723 AU, so has an irradience of 1.912 that of Earth) that should be good, but 15km depth of cloud around terrestrial troposphere pressure will make for a lot of light absorbtion by the time you get to the lower clouds.

The Venera probes took photos. Someone knows what the illumination at the surface level is. From Wiki, although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface, resulting in average daytime levels of illumination at the surface of 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds".[68] although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface,[67] resulting in average daytime levels of illumination at the surface of 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds". OK, that will have an effect on photosynthetic yields, but not a show-stopper.

Back to List.

III. REPLICATION RATES AND FALLOUT TIMES

Wrapped up in some entropic justification, and a list of quite variable "generation times" for various bacteria - they choose the old standby of a 20 minute generation time. Yeah, that might be true in aerobic, comfotable temperature, well-fed nutrient broth. It seems optimistic to me for something floating in a gas, depending on meeting aerosol droplets for most of it's chemical inventroy. They go for a 12 hour settling time, giving a potential 2(3×12) growth factor in that settling time. I distrust that 20min fuigure as being representative. Achievable, certainly, but as an average?

OK - I did the calculations, The mean of their cited dataset is 163 minutes. But the harmonic mean is 25-3 minutes. Maybe it's not such a bad extimate after all - but it's throwing away a lot of variability.

Various calculations ensue about the terminal velocity of these drops. The come to the conclusion that it's not a big problem - which we knew already because there is a cloud layer.

My thoughts

I think they're being a bit optimistic about their growth rates. The rates they're assuming are some of the fastest - not just that I've heard of, but also of their own examples. In reality, only a short part of each cycle will be spent near "optimum conditions" (whatever they are), so the average growth rates will be considerably lower.

Their calculation of fallout speeds takes no account of the "gasbag" part of their organism's name. Even a fairly modest "gasbag", supporting only half the organism's mass , would halve the settling force, while approximately doubling the drag forces. The buoyancy would be unbalanced though - sinking slightly below optimum pressure level would compress the "gasbag", accelerating the drift down, while rising above the optimum level would increase the lifting forces and accelerate the drift from optimum. The situation will be familiar to anyone who has tried scuba diving with a buoyancy compensator or "ABLJ" - maintaining your level in the water column - particularly at a decompression stop depth - can be really tricky. But it can be done. For example, fish (teleosts, those with a swim bladder) use two buoyancy systems - a major one using liquids of different density to the water, and a smaller one using gases with a much greater pressure- volume feedback as described above. That works for fishes in water - it's harder for "gasbags in gas". But not being a balloonist, I can't talk to that from experience.

I'm pretty dubious of their estimated "dry" density for E.coli (and by extension, other organic materials) 300 kg/cu.m is quite low. But I haven't read ahead yet to see where they're going with that.

They come out concluding that settling velocities are usefully long for droplets/ gasbags below about 0.1mm ... which we knew already from the overved persistence of water droplet clouds.

So what was the point of that digression?


IV. COSMIC RAY EFFECTS ON MICROBIAL LIFE

Again, I struggle to see the importance of this section. By definition, we're talking about organisms spending most of their life cycle at pressures similar to on the Earth's surfce. So, above the putative organism is a similar mass of atmosphere ("shielding") to an organism on Earth. Yes, radiation is important, but also, yes terrestrial organisms exhibit over a thousand-fold difference in radiation resistance (e.g. Deinococcus radiodurans) … so, again, wile it's important to state your assumptions, we already know the cosmic ray conditions at the appropriate levels on Venus aren't going to be wildly exclusionary.

They do make an interesting point about the conductive (UV-ionised) ionosphere providing a local magnetic field via generation of eddy currents, mitigating to a degree the absence of a geomagnetic (veneromagnetic?) field. But only up to a few hundred keV particle energy - and only (obviously) for charged particles. Which isn't as much protection as Earth's magnetic field provides, but helps to reduce the aparrent differences between Earth's surface and the Venusian cloud layers.

Back to List.

Adding these effects together,

numerical simulations show that cosmic radiation would not have had any hazardous effect on putative microorganisms within the potentially temperate zone (51 to 62 km)

Which is where I started in my consideration of this section. Good to see that we agree, by rather different route.

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V. CONCLUSIONS

we can conclude that if updraughts exist, a stable population of microorganisms that in the early history of Venus emigrated from the surface to the atmospheric clouds and now remain confined to aerosols may be possible.

P …

The caveat about "if updraughts exist" is important. The surface topography of Venus varies by 5-8 km, while the Earth-comparable zones are 30~50km above this agitation, so it's not clear from first principles that there would be much topographically-induced vertical updraughts.

P …

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Blockquote 2
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-->

Well, I've got a backlog to try to work my way through. Thick end of 100 days, which would be pushing 10,000 papers, if I looked at everything. But I've already blindly thrown about 90% of that over the side. Probably including some tatties. Oh well. Modify the default template with the "fonty" stuff.

Nothing attractive in the first part of the pile. But I should go back to the previous post and add anything I see in the archives for T.CrB.

Did the T CrB (see - even i'm not consistent in the abbreviation used!) submission to Slashdot - with a Tyop in the title. Quick look through another day's worth of IArχiv, then bedtime. Bit of a collection post.

Article List.

Articles read and things studied this month, April 2024.
Link Description
HTML Recent HTML Learnings - 2024-04
T CorBor Article submitted to Slashdot
Quadruple massive star system Arχiv, non-planar system (decided against it)
NGC 708 A 10-billion solar mass black hole in a low dispersion galaxy with a Kroupa IMF (decided against it)

Recent HTML Learnings - 2024-04

I learned a little about using external fonts, specifically from Google, but I should be able to generalise it, if it's worthwhile. (I'm dubious enough about Google's committment to keeping these fonts generally available, or any of their self-interested "philanthropy", but that'll be another thing to work on.)

This block should be in a silly font. "Google Monoton ". Nope, I'm borked again. Forgotten how to make it work. [...]

Fixed it now. Different funny font, "Jacquard 12 Charted" at 30 pix.

Back to RTFM, and improve my notes.

Where did I (initially) go wrong? I've got (1) the link in the HEAD section, then (2) the font family chosen in the (CSS)STYLE section. (I use PRE for demonstration. Meh.)

The example given encloses the URL for the stylesheet link in only one set of quotes - which is problematic when there are spaces in the font name. Let's get rid of that (and put single-quotes on the outside) for starters.

Yep, that did it. So, names with spaces now.

That looks a bit odd. (Note the different quote marks.) rel="stylesheet" href='https://fonts.googleapis.com/css?family=Monoton|Major Mono Display' works, but I'm sure there were warnings about mixing names with spaces in there. Oh well. Lesson learned, into the default header it goes.

I've also done a little paragraph-level formatting with p style="font-size:30px ; font-family:'Jacquard 12 Charted'" above. Note the arrangement of different quotes in there.

Back to Article List.

T Corona Borealis - submitted

The naked-eye shy will (briefly) host a new star. Fuck - check the BODY and you'll have a tyop in the title!

Well, I do hope the editors do catch that. At least I'm a lot more polite about them than the average Slashdotter.

Back to Article List.

A Quadruple System with A Massive Star

Arχiv 2403.12771

Looks moderately interesting. Total system mass ~25 M, of considerably differing sizes, thus MS-durations. Not co-planar (now that's surprising - worse then Pluto-Sun-Jupiter, without the tail-wags-doggery). There's a chain of logic implied from the distribution of system masses to the range of bound NS-NS and NS-BH potential future systems, and a difference between expected [NS] and [BH] occurrence rates seen in GW mergers. Which will need more brain cell than I have tonight. This morning, even.

Abstract

Hierarchical massive quadruple systems are ideal laboratories for examining the theories of star formation, dynamical evolution, and stellar evolution. The successive mergers of hierarchical quadruple systems might explain the mass gap between neutron stars and black holes. Looking for light curves of O-type binaries identified by LAMOST, we find a (2+2) quadruple system: TYC 3340-2437-1, located in the stellar bow-shock nebula (SBN). It has a probability of over 99.99\% being a quadruple system derived from the surface density of the vicinity stars. Its inner orbital periods are 3.390602(89) days and 2.4378(16) days, respectively, and the total mass is about (11.47 + 5.79) + (5.2 + 2.02) = 24.48 M. The line-of-sight inclinations of the inner binaries, B$_1$ and B$_2$, are 55.94 and 78.2 degrees, respectively, indicating that they are not co-planar. Based on observations spanning 34 months and the significance of the astrometric excess noise ($D>2$) in Gaia DR3 data, we guess that its outer orbital period might be a few years. If it were true, the quadruple system might form through the disk fragmentation mechanism with outer eccentric greater than zero. This eccentricity could be the cause of both the arc-like feature of the SBN and the noncoplanarity of the inner orbit. The outer orbital period and outer eccentric could be determined with the release of future epoch astrometric data of Gaia.

Looks worth a read.

Back to Article List.

Triaxial Schwarzschild Models of NGC 708: a 10-billion solar mass black hole in a low dispersion galaxy with a Kroupa IMF

2403.12144

I met Kroupa IMFs last week - oit's the 4-class IMF, with different power laws indices for each successive mass class.

Look at this one too. Might help me modelling the IMF (and other models).

That's enough for tonight.

Got up to the start of March (mostly by throwing lists away un-examined). I need to thin down (or increasingly specialise) IArχiv for the weighted list. No more work here, just separate posts tomorrow on the "interesting" stuff.

Back to Article List.

End of Document
Back to List.

2024-04-27 (Update -06-05) T CorB - a recurrent nova.

Articles studied this April - some of which might go to Slashdot.
'T' Corona Borealis (T CrB) - A recurrent nova in Corona Borealis likely to erupt Real Soon Now
T CrB - Recent papers in Arχiv.
T CrB - Distance and position on the sky.
T CrB - When ? The $64.000.00 question.
update Are We There Yet?
update 2Are We There Either?
End of document

'T' Corona Borealis (T CrB) - a Recurrent Nova, about to recur.

This came off DrBecky's YT channel, which is good fun and well worth the effort. Another useful link is a seminar held for the AAVSO (American Association of Variable Star Observers - don't worry, unlike most Americans, they acknowledge there is a Rest Of the World) on the subject last year. Essentially, if you're a variable star observer, in the Northern hemisphere, they want you to be checking it as a regular part of your sweeps (news announcement). If you've got a spectroscopic rig on your telescope, particularly calibrated for UV spectroscopy that can detect neon lines (see seminar video), then your observations are particularly encouraged.

The last two times (or maybe 4, or 5 - there are interesting hints of pre-1800 CE observations) this star went into "eruption", it passed from well below naked-eye visibility (good binocular visibility though - it doesn't need a big scope) to about the 50th-brightest star in the sky in a matter of (at most) a couple of hours. (That's from two events, involving 4 observers - 2 discoverers, and two who were too early ; so it's a good bet for this time around too.) Thus, even if you don't catch it in eruption, yours could be the last pre-eruption brightness record - which itself is a very valuable datum.

Dr Becky and the seminar provide the details on the star ; no point in me repeating their statements here. There's a small chance of the eruption this time being a supernova (type 1-SN, even - the ones used as "standard candles" for distance measurement across the universe), which adds to the importance of understanding it as well as possible. In theory, the system could go through many of these eruptions before eventually triggering the SN - but how many ... theory doesn't have a good answer for that.

It's not hard to find - follow the full length of the handle of the Plough asterism ("Big Dipper" in America - as if "dippers" were more common implements than ploughs ; odd that) from the Plough-share, through the "wedge" of Boötes (with red Aldebaran at the tip of the wedge) but not as far as the "Square of Hercules" ; Corona Borealis is the semi-circle of stars between Boötes and Hercules. Get to know what the area looks like. When the system "goes", there will be a new star there. (At the time of writing (2024 Apr. 27.55056), the AAVSO reported a brightness of 10.034 - which means it hasn't "gone" yet. When it goes, it'll make it to about magnitude 2. THe AAVSO website above lets you interrogate their database (but please don't melt their servers if you hear of the eruption having started - scientists and actual contributors will need it - unmelted!)

T.CrB finder chartHere is a "finder chart" of the area (astronomical convention : bigger blobs = brighter stars). The field of view is 15 degrees square, so your fist at arms-length will approximately cover the arc of stars comprising the Corona Borealis and the target a finger's width to the south (away from the Pole Star !? ) from the semicircle of the "Northern Crown".

Get used to what this part of the sky looks like. Some time this year, for a week to 10 days, it's going to look visibly different. Just maybe, you'll be able to see it by daylight. The constellation is about circumpolar from the UK, so you should be able to see what is happening without checking your clock first. Which includes the state of the clouds.

I missed an important point. Going on past events, the eruption will last between a week and 10 days.


Recent papers in Arχiv.

Obviously, I should look at what has recently been published on Arχiv about T.CrB. And, to my surprise, it's already in my search history. What do we have ?

I should note that the naming is a little lax. The "T CrB" ("identifier" in "constellation") code is variably capitalised. The star has different names in various catalogues as well, but "T CrB" is concerned with the variable star. The HD catalog name (for example) might be used if you were working specifically on the (relatively) normal star, not the variable in the system. But if you were looking at the position (does it wobble?), you might look at the GAIA catalogue entry.

Arχiv references encode the year, month and sequence-within-month as "YYmm.sequence". So you've got the date in the reference.

Recent additions to Arχiv concerning the recurrent nova T.CrB
Code Title Comment
https://en.wikipedia.org/wiki/Nova#Recurrent_novae Nova Wiki article on recurrent novæ.
Includes a list of the known recurrent novæ.
https://en.wikipedia.org/wiki/T_Coronae_Borealis T CrB Wiki article on T CrB
https://arxiv.org/search/?query=T+CRB&searchtype=all&source=header Arχiv search Returns a list of 128 results (today ; this will change).
arXiv:2312.04342 Accretion in the recurrent nova T CrB: Linking the superactive state to the predicted outburst The 1946 had a dip then a brightening of about 1mag in the years before the 1946 eruption, and similar trends have been seen in 2023, leading to the current expectations.
arXiv:2308.13668 The recurrent nova T CrB had prior eruptions observed near December 1787 and October 1217 AD Discussed in the "webinar" referreed to above.
arXiv:2307.00255 The "super-active" accretion phase of T CrB has ended More discussion of the recent changes.
arXiv:2207.14743 Stringent limits on 28SiO maser emission from the recurrent nova T Coronae Borealis Looking for signs of "mineral dust" being cooked by the variable star.
arXiv:2009.11902 Increasing activity in T CrB suggests nova eruption is impending This event has been expected for some time!

The blue entry above adds context in the Abstract, with my [annotations] :

T CrB is known to display the SiO [basic unit of silicate minerals] fundamental vibrational feature at 8μm. [microwave radio signal] When the anticipated eruption occurs, it is possible [possible!] that the shock produced when the ejected material runs into the wind of the red giant in the system may be traced using SiO maser emission.

So ... they're measuring the "quiet" state signal (nothing much visible) so they can compare any "eruption" state signal to the measurements already "in the can". "We find no evidence for such emission." is useful "negative" science.


T CrB - position on the sky and range.

Up in the main message, I described how to find the object "on the sky" :
- follow the full length of the handle of the Plough asterism ("Big Dipper" in America - as if "dippers" were more common implements than ploughs ; odd that) from the Plough-share, through the "wedge" of Boötes (with red Aldebaran at the tip of the wedge) but not as far as the "Square of Hercules" ; Corona Borealis is the semi-circle of stars between Boötes and Hercules. And don't forget - on previous "eruptions", the star became about the 50th (to 30th) brightest on the sky, for a week and a bit.

That's not quite the complete story. For fullness you'd normally also want to know the range. People tend to get (unduly) worried about potential big explosions in our backyard.

The Wikipedia page (link above) cites a report from the GAIA team of a parallax of 1.2127 ± 0.0488 mas, which equates to a distance of 802 parsecs (± 30 parsecs) or 2598.48 (± 97) light years.

Which is close enough for me to think it interesting, even if it's not quite far enough to be convincingly safe. But a strongly beamed explosion ... could be interesting. The results of the eruption could be very interesting.

Back to Article List.

When ? The $64.000.00 question.

When making predictions, the "when" bit of the prediction isa always important. When the star entered it's "active" phase (as seen about 1938 to 1946) in 2016, fingers were pointed at 2024. When the star entered the brightness dip (see the "seminar" in the man section) phase, the date was revised to 2024, May, with a ± of about 0.5 years (6 months). We're currently nearing the mid-point of that range, but no updates on the expected time. So ... weeks to months, possibly days to hours. I'll check the figures again when I submit this to Slashdot. (Checked for brightening on JD 2460428.55208 = 2024 Apr. 28.05208 mag 9.905 ± 0.0052 - not Gone yet!). Saved submission in this blog, to see how the editors mangle it. The "check for brightening" string should be pretty unique.

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UPDATE Are We There Yet?.

So, has it gone yet?

I check the AAVSO site every so often. (And I deliberately don't provide a direct link, to avoid melting their servers.)

2024-05-10 22:25 +000 (my clock)

  Star 	JD 	Calendar Date 	Magnitude 	Error 	Filter 	Observer 	Collapse All Expand All
	T CRB 	2460440.933050 	2024 May. 10.43305 	9.976 	0.003 	V 	CSEB 	Details...
	T CRB 	2460440.931128 	2024 May. 10.43113 	9.969 	0.003 	V 	CSEB 	Details...

It hasn't gone yet. Does it's light curve show any interesting features (in the last couple of days)? (I only ask for the last couple of week's worth, and just the commonest bands. Server melting, plus response time.

There were a few reports of enhanced brightness (visible magnitude up to about 8, R band up to about 7) a few days ago, but that looks like noise. Not "Gone", yet.


End of Document
Back to List.

UPDATE Are We There Yet?.

It hasn't gone - YET

But today's check of the AAVSO site was interesting.

2024-06-05 14∶25∶09 BST (my clock)

Time series of brightness of T CrB in Visible (brightest, most erratic), Red, Green and Blue bands over several hundred days showing increasing amplitude and frequency of oscillation.

It hasn't gone yet. But ... I'm sure that the brightness oscillation is increasing in both frequency, and amplitude. Which is a pretty good sign of something that can't go on much longer without something breaking. That's a "model-free prediction" - whatever the forces involved are, something is going to break at some point.

Are we approaching a turning point in the B luminosity (blue curve above, representing usig a blue-transmitting filter when estimating the magnitude ; "visible" is no flter (apart from the inherent slight colour of the glass) ; red and green as obvious, but with specified standard filter ranges)? And if so ... will the star "go at the turn around in the B curve? Or at the maximum slope of the B? Or will the B just never start to slow in it's brightening?

"Isn't it Exci-e-ting ... to lose a little weight!?"

(stolen from Flanders & Swann)


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Edited for some tyops, and putting links to the Arχiv papers.

2023-04-02

2023-04 April Science Readings

2023-04 April Science Readings

Well, I'm still ploughing through the backlog. But progress …

Articles studied this April - some of which might go to Slashdot.
The backlog of old stuff
A quick "Funny"
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The Backlog

I get a daily mailing of new papers, and open ones that grab my attention by the title. I've got to speed up that pipeline to get through the backlog.

What have I got open on the tab list?

The Event Horizon Telescope Image of the Quasar NRAO 530 link This isn't "new" observation with the EHT, but calibration observations made back in 2017 as part of the initial runs of the radio interferomenter. "Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. " - Intensity, polarisation and position of features changes. Further observations. I think I can leave this one pending.

Machine learning detects multiplicity of the first stars in stellar archaeology data link Complex study on Population-III stars, trying to work out their multiplicty from the fine details of the metallicity of thes Milky Way's "EMP" (Extremely Metal-Poor) stars. Yes, there were probably a lot of multiple, within the same range as today. Worth testing - because these stars supernovae are likely to end up beig the oldest probes into the universe since the CMB, and we need to know (or at least, test) that the stars then were similar to those we see "today" to calibrate our models on.

The Venus’ Cloud Discontinuity in 2022 link There's some weird stuff going on in Venus' atmosphere - it rotates faster (at some altitudes - than the ground. Which is ... odd. Continuing observation campaign.

Limits on Neutrino Emission from GRB 221009A from MeV to PeV using the IceCube Neutrino Observatory link In last month's GRB221009A Slashdot posting I predicted more papers. I think this was posted to ArXiv a couple of days later than that one, and there will be more in the backlog. I commented on /. that this was a (relatively rare) negative report - "we looked for Y, which we expected to see, but didn't". Valuable, but as sexy as the Ann Widdicombe range at Ann Summers.
See also : The first JWST spectrum of a GRB afterglow: No bright supernova in observations of the brightest GRB of all time, GRB 221009A, "The host galaxy appears rather typical amongst long-GRB hosts and suggests that the extreme properties of GRB 221009A are not directly tied to its galaxy-scale environment." ; The power of the rings: the GRB 221009A soft X-ray emission from its dust-scattering halo (What formed those ring-like structures presented in the composite paper, and what we can deduce from them.) ; Implication of GRB 221009A: Can TeV Emission Come from the GRB Prompt Phase? The highest-energy particles from the source probably "probe" deepest into the central "engine" of the event, and thus the whole class of events. ; GRB 221009A THE BOAT Studies the brightness of the GRB, and justifies calling it at least the "Brightest since human civilisation began."

Galaxy Zoo stuff : Galaxy Zoo: Kinematics of strongly and weakly barred galaxies ; Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies I know "Galaxy Zoo" - do you? (Seriously - answers in a comment below, please!) It's one of the early examples of "Citizen Science", using the bulk observations of (lightly) trained amateur observers to classify (previously-made survey) images of galaxies using the human eye-brain abilities for pattern recognition. No dpoubt it'll be replaced by AI models ... uhhh, trained on Galaxy Zoo results. That's counting "angels dancing angel-counting dances on pinheads" territory. Recursion, potentially to a worrying level.
Anyway, two papers here. The first reports a moderate, neither expected nor unexpected relationship between bar strength (contrast) and rotation speed). Peculiar, but not exactly Earth shattering.
The second is just odd. Peculiar. As determined by GZ observers, presumably not interacting, the spin direction of galaxies is fairly strongly non-random (sigma 2.33~3.97). Which ... might be some larege scale structure of the universe. Or some unexpected aspect of GZ viewers, users, or ... something. What it means I have no idea, but it's definitely not expected. Watching brief.

And that's got my "Feburary pile" cleared (with a couple of exceptions). Things to do tomorrow, but maybe get March cleared over the next couple of days.

And now it's May 11th, and I haven't touched this for nearly a month.

Back to List.

Redshift calculator https://wellsite-geologist.blogspot.com/2023/02/2023-february-posting-commentary.html#Redshift Something is borked, but I didn't note what.

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Funny diving.

DiverNet job advert for people to work diving in the "storage ponds" at Sellafield.

This looks like a really fun job. I wonder if the Slashdoterati will find it as amusing?

Actually, it's probably going to be a really tedious job, with masses of paperwork and endless waiting around, taking radiation readings. But the pay would be good. Maybe. [May update : the /. editors didn't bite.]

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End of Document
Back to List.

And that's as much as I got last month.


2022-04-09

April Arxivery

Articles studied this month - some of which might go to Slashdot.
The Origin and Evolution of Multiple Star Systems
Martian meteorites reflectance and implications for rover missions
Chemical Habitability: Supply and Retention of Life’s Essential Elements During Planet Formation
Why tyrannosaurid forelimbs were so short? An integrative hypothesis.
Weak versus Strong Chaos (in planetary orbits, particularly outer Solar system ones
Freeze-thaw cycles enable a prebiotically plausible and continuous pathway from nucleotide activation to nonenzymatic RNA copying

April science readings.

I guess I should look for Acta Primae Aprila, but I can't say I'm really bothered. See this post for a trip down April Fool Road.

The Origin and Evolution of Multiple Star Systems

https://arxiv.org/pdf/2203.10066.pdf
FTFA : Most stars are born in multiple stellar systems.
Is this true? I knew it was getting close, but was it over the 50% line? I guess, it's easier to disrupt a multiple star system to form a single and a (lower-)multiple, or two singles, while it's much harder to form two singles into a double, or a single and a multiple into a (higher-) multiple, so the multiple:single ratio should decrease over time. Even in a relatively densely packed molecular cloud, it's still going to be harder.

Corollary, and this is my own thought, hence date - when disrupting a multiple star system to form a multiple and a single, wouldn't most of the Oort cloud and Kuiper belt stay with the larger star, potentially giving a way to distinguish single which were born as singles from singles which were ejected from multiples? So, finding a Sun-like star with a much smaller Oort cloud (and/ or Kuiper Belt) than the Sun's, might be a flag that this newly-characterised system is an ejectee? Do we have observational techniques which could survey to this depth? (2022-04-09 13:22)

OK, back from that rabbit hole.

RoTFA : In this review, we compile the results of observational and theoretical studies of stellar multiplicity. We summarize the population statistics spanning system evolution from the protostellar phase through the main-sequence phase and evaluate the influence of the local environment.

[See, I did notice the impact of nearby (proto-)stars above!]

We describe current models for the origin of stellar multiplicity and review the landscape of numerical simulations and assess their consistency with observations. We review the properties of disks and discuss the impact of multiplicity on planet formation and system architectures. Finally, we summarize open questions and discuss the technical requirements for future observational and theoretical progress.

Those last sections sound like a useful review.

Introduction Observational data is catching up with theoretical models.

Observed Stellar Multiplicity- Multiplicity changes a lot during formation and early evolution of systems. A significant increase in multiplicity happens at star (system?) masses greater than 0.5 M⊙ (see figure 4). That bears a lot on the question I pose above. Does that represent a mass at which collapsing molecular clouds become more likely to have complex turbulance that can fragment the cloud? The decline in multiplicity continues down towards and possibly into the brown dwarf regime, but detectability biases become challenging. (Table 1, in Astronomy notebook, 13columns, does not render well.) "Moving toward earlier spectral types, we find that the trend of an increasing MF with primary mass continues" and that trend continues to O-type stars - the biggest and brightest, where 90% are multiples, and most are triples or higher (companion frequency (CF) is 2.1 ± 0.3 for O-B stars)
Definitions : MF, CF
My question above remains in play when the authors say "The multiplicity fraction increases monotonically with primary mass from MF ≈ 20% for [brown dwarves] and late-M dwarfs to ≈ 50% for solar-type stars to MF > 90% for OB stars. The triple fraction increases even more dramatically from THF ≈ 2% for late-M dwarfs to 14% for FGK dwarfs to nearly 70% for O-type stars." because more than half of all stars are in the M class. There are also moderate (but significant) trends in metallicity, separation of stars within a system, and the ratio of star masses between primary and subsidiary stars in a system. For M stars, there doesn't seem to be much reduction in multiplicity in the first few hundred million years of life (which bears on my corollary above).

Models For Multiple Star Formation - Well, I didn't know that Fred Hoyle had his finger in the pie of star formation processes. "Hoyle F., 1953 ApJ, 118, 513. On the Fragmentation of Gas Clouds Into Galaxies and Stars" Hoyle studied the radiation of heat from contracting (self-gravitating) gas clouds and showed that they were unstable to separation into smaller, denser, faster-contracting clumps. Which leads naturally to a hierarchical system of collapse. More recent treatments add in the effects of turbulence and magnetic fields, for a fuller but inherently stochastic model (due to the turbulence, if nothing else).

Current ideas for multiple formation can be divided into three main categories: theories in which multiples form via fragmentation of a core or filament (§3.1), via fragmentation of a massive accretion disk (§3.2) or through dynamical interactions (§3.3). This third mode can also rearrange the hierarchy and multiplicity of systems formed via the prior fragmentation channels.[...] Due to their wide initial separations, multiples formed from turbulent fragmentation accrete gas with different net angular momentum. This frequently produces misaligned stellar spins, accretion disks and protostellar outflows.

There's a lot more, but it boils down to we/ve got several ways which could lead to the story of star system formation that we do see, and distinguishing between them is unlikley to be clear statisitcally. It's not a recipe for "this model works, and no other", more likely "this that and the other model all work, and any could have formed this system". That's for systems which have settled into Main Sequence tedium for a few tens to hundreds of million years. High mass, bright stars don't live long enough for the evidence of their birth environment to have dissipated, but that doesn't necessarily reflect the conditions under which low mass stars form.

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Martian meteorites reflectance and implications for rover missions

https://arxiv.org/pdf/2203.10051.pdf

Obviously you need to do the legwork before trying to interpret what you see with your rover/ helicopter/ Musk-0-nought. So you look at what samples of Mars you do have using instruments as similar as possible to the ones being flown. If that means putting a Martian meteorite into a sock and beating Musk round the head with it, well, it's a dirty job, but someone's got to do it. Please remember that Musk wants to "die on Mars, but not on impact". Maybe hit him about the torso and limbs instead?

The problem (FTFA) is

the current spectral database available for these [Martian meteorite] samples does not represent their diversity and consists primarily of spectra acquired on finely crushed samples, albeit grain size is known to greatly affect spectral features.

Yeah, legwork definitely needed.

The spectrometers in question are VNIR (Visible and Near-Infrared) instruments. So while some classroom/ Mark-1 Eyeball experience is helpful, you do need to characterise the behaviour of real minerals and mineral mixtures (rocks) to have confidence in their interpretation.

the physical state of the sample, and especially its grain size, have been shown to significantly influence both the absolute reflectance and the shape of the absorption bands

Geologists know this from thier thousands of hours in the laboratory and field. (No lab-work? Not a geologist.) Non-geologists may need to be reminded of it. In theory you can do it from a book. But in theory there is no difference between theory and practice, whereas in practice there is. (Ref : "Oldies but Goodies", Chthulhu & Ugg, Gobekli Tepe Publications, 10000 BCE

In addition, in situ measurements by the SuperCam instrument [on the Mars 2020 rover, currently on Mars as "Perseverance"] will be achieved remotely and without any sample grinding

I wasn't paying close attention, but I had noticed repeated references to "pew-pew-pew"-ing various rock surfaces before drilling a hole, then later collecting the rock dust, or "pew-pew-pew"-ing the dust pile after drilling. I'd been taking that as getting spot measures versus a bulk-rock, but it would also address the grains size issue above. The rock dust pile would represent the mixed (to some degree) minerals of the rock interior, while the surface readings would be measuring the oxidised, UV+cosmic-ray-blasted surface minerals - which are not necessarily the same. Then there is the fact that soft minerals (interstitial carbonates, weathering clays ("phyllosilicates")) would express different surface area in the powder than in the bulk rock. It may be hard to differentiate these effects from the data collected in each drilling procedure, but if you didn't collect the data, then it would be impossible to differentiate these effects.

11 Martian meteorite had previously been IR-sperctrogrammed (mostly as powders, e.g. cutting debris) ; this study add 16 more meteorites in IR, and 11 of these were also studied with hyperspectral imaging.

Petrology

Most of the samples were mafic to ultramafic rocks, often showing cumulate textures. One polymict breccia (NWA 7034, explosive or sedimentary?) and several basalts and phenocrystic lavas were also in the suite examined. The shergottites in general yeild three ages : cosmic-ray exposure ages (indicating duration of interplanetary flight before a relatively recent impact on Earth) of 0-5 to 20 Ma ; mineral separates show Rb-Sr, Sm-Nd, Lu-Hf and U-Pb ages of 175-475 Ma (possibly a metamorphism age, or a re-melting?) and whole-rock Pb-Pb and Rb-Sr ages of about 4.1 Ga (original intrusion, or a protolith later re-melted?). That's a nice example that will go into the isotope geochemistry text books - if it's not there already.

Contamination of the meteorite samples by weathering on Earth's surface (or possibly during interplanetary transport) is quite common. It is more reported in finds from hot deserts than from cold deserts - Antarctica - but that 40-60 °ree;C storage temperature difference is sufficient to account for that. Carbonate mineals in Martian meteorites are mostly in vein-fills, and typically interpreted as terrestrial weathering products. (The presence of carbonates in distinct "rosette" concentric discs in specimen ALH84001 is one of the arguments for this feature having been formed on Mars.)

The zoning in the cpx in some of the shergottites looks really nice. But I doubt I'd ever afford a big enough sample for a thin section. Is there a sample in the BGS files? (No, but a reasonable number elsewhere. and some of them are pretty!)

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Chemical Habitability: Supply and Retention of Life’s Essential Elements During Planet Formation

https://arxiv.org/pdf/2203.10056.pdf

This paper is part of the proceedings of conference "Protostars and Planets VII".

Which elements ? Well, they're sticking with "life as we know it" (Star Trek quote?), so CHONPS - Carbon Hydrogen, Oxygen, Nitorgen, Phosphorus, Sulphur. Some terrestrial lifeforms require a bit of other elements (humans a few ppb of molybdenum, IIRC), but for the structures of living things, you need that lot, in about that order. It's a choice, which could be challenged, but in itself it's a perfectly reasonable choice.

The fact that they're most of the commonest elements in the universe, is also probably part of the reason that life uses them. My data bucket (taken from http://www.kayelaby.npl.co.uk/chemistry/3_1/3_1_3.html, but you'll probably have to drill through the site to get to the table) tells me the commonest elements in the Sun are (in descending order) H, He, O, C, N, Ne, Mg, Si, Fe, S, Ar, Al, Ca, Na, Ni, Cr, Cl, and eventually P. Removing the nobel gasses, chlorine, silicon and the metallic elements (which are mostly combined with oxygen), the list is H, O, C, N, S, and P. And that, in itself is ample justification for choosing to concentrate on these elements.

From a physiological/ metabolism point of view, they're the elements used to make carbohydrates, amino acids, and energy-labile phosphates - the major structural components of biochemistry. (Sulphur is most important in cross-linking proteins into meshes as chains are folded and bring sulphur-containing amino acids into proximity, when they can cross-link.

Why is this a question? Well, it's reasonably easy to model the accumulation of high-melting point materials (metal oxides, silicate minerals) into planets, and to model the accumulation of hydrogen and helium onto a body in a condensing stellar nebula. But it's not so easy to understand how moderately volatile (boiling point a few hundred Kelvin) compounds (carbon oxides, ammonia, sulphur hydrides and oxides) accumulated onto a planetaty core, since the accumulation of the planet probably heated materials to lava-like temperatures - around a thousand (Kelvin or Centigrade). (Phosphates compounds are the least troublesome in this respect - magmas can directly crystallise phosphate minerals such as apatite from the melt, as anyone who has studied mineralogy under the polarizing microscope will remember it as one of the first minerals you are taught to diagnose (rounded crystals, moderate relief, low birefringence, optically negative, uniaxial if you can get an indicatrix). The substantially different volatire inventories of the Solar "rocky" planets, and the range of properties inferred for exoplanets show that the volatile content of planets is something that varies, a lot, even within one system, so might be a distinguishing factor etween which planets develop life and which don't.

The availability of these volatile materials influences whether a planet is considered in the "habitable zone", as the presence of "greenhouse gases" in a planets atmosphere can considerably alter the surface properties. If the Earth didn't have a lot of water available on it's surface - and therefore in the atmosphere in amounts approaching a percent - it's surface temperature would be sitting near the freezing point of water. The FUD around anthropogenic global warming is about whether people want to live on a planet with 15 degrees (Kelvin or centigrade) of global warming, or 16, 17, even 20 degrees of warming. Geologically, that experiment has been done, recently : algal blooms in the Arctic Ocean, Scandinavian crocodile-infested swamps, unbearale tropics.

The authors define "chemically habitability" in terms of

  • 1) a supply of carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur (”CHONPS”), and other bio-essential elements that are accessible to prebiotic chemistry, and
  • 2) is capable of maintaining the availability of the CHNOPS elements over relevant geologic timescales.

As observational techniques improve, and the planetary examples and systems which need to be explained increase and diversify, the range under which models of chemical habitability will be tested also increases.

Section 2. Tracing The Earth’s Ingredients Back Through Time The main constraint on this is understanding when life originated on Earth. From the (body) fossil record, we know it originated before the oldest fossils at 3.5 Gyr ago, but more controversial arguments (for example, Moizjies Akilia graphite-in-apatite at 3.9 Gyr and Bell's graphite in a Jack hills zircon of 4.1 Gyr) interpret negative carbon-13 isotope ratios as evidence of a functioning biosphere consideraly before then. This is only a few hundred Myr after the Moon-forming impact, and well into the period of the Late Heavy Bombardment (if that happened, and isn't an artefact of the distribution of rocks around the Imbrium crater). If (again, a real "if") the Moon-forming impact stripped Earth's preimordial atmosphere off (alternative : formed a synestia) then the final accretion of the Earth included the volatiles for the atmosphere/ hydrosphere in it's (relatively) undifferentiated (i.e. unheated) components. With the exception of P, and the special case of O, the CHONPS are fairly uniformly distributed in the Earth's various zones (core, lower & upper mantle, lithosphere, crust, hydrosphere, atmosphere, biosphere) and can affect the systems at part per million levels (e.g. CO2 in the atmosphere). Generally, they don't form distinct minerals (though #TeamIce keep having that argument in the annual #MineralCup on @Twitter, and winning it.) and mostly are fluids. There is a lot of cycling of CHONPS between the Earth's lithosphere, hydrosphere, atmosphere and biosphere, a lot of it mediated (on Earth) by plate tectonic activities. On other worlds, that may be different - cases of "Waterworld" and "Stagnant Lid" worlds (example Venus) are considered. (Venus, being a neighbour, is obviously a prime example for examining the variations in CHONPS behaviour and other aspects of planetary science). Via it's role in reducing fault friction and enabling (or enhancing) plate tectonics, the presence of water may be very inportant in altering fluxes of other CHONPS components. But further, the role of plate tectonics-mediated heat flux in mantle may be an important point in altering the convection in the liquid core which is responsible (most likely) for producing the Earth's magnetic field, which itself is a part of the system reducing water loss from the upper atmosphere by solar wind fluxes. That may (or may not) be a general condition for habitability.

Carbon Through it's role as a greenhouse gas, even at ppm levels, the cycling of C as CO and/or CO2 between atmosphere and crust/ lithosphere/ hydrosphere has whole-planet consequences, but remember that H2O is also a significant greenhouse gas at surface temperatures above about 250K. These effects probably also constrain the levels of N (as NH3, NOx), though P and S are thought to be less effected. At high (core) pressures, C is a siderophile element, and most of Earth's C inventory is thought to reside in the core (about 4 times the amount in the atmosphere, hydrosphere and biosphere). If Earth's crustal and mantle inventories of C were to be put into the atmosphere as CO2, the resultant atmosphere would be broadly comparable to that of Venus.

Hydrogen is more evenly distributed between Earth's surface and deep interior, with an uncertain amount in the core, several "oceans" worth in the mantle (as mineral defects, which has a considerable effect o nmineral viscosity, and of course one ocean on the surface. Hydrogen that makes it ot the upper atmosphere is prone to loss via photodissociation to form monatomic hydrogen. However the current structure of the atmosphere is such that there is a "cold trap" in the stratosphere which effectively prevents water from getting above the UV-absorbing tri-oxygen layer.

Oxygen is the commonest element in the Earth - but almost all as oxide and silicate minerals, not di-oxygen gas (let alone tri-oxygen - ozone - and hypothetical higher allotropes of interest to the explosives chemists). The oxidation state of the whole Earth is dominated by the metallic oron in the core, ut that is effectively isolated from the mantle by it's density contrast. The oxidation state of the mantle is more managed by the QFM - quartz-fayalite-magnetite - reaction system than interaction with the metallic iron of the core. A similar interaction barrier exists between the mantle (and crust) and the atmosphere, with the atmosphere having a thermodynamically delicate store of 21% di-oxygen which is maintained by photosynthesis. This state has only existed since (approximately) the second to third Gyr of the Earth's existance, when the development of life, and then of photosynthesis, led to surface reservoirs of reducing power (e.g. Fe2+ minerals) being oxidised before di-oxygen started to accumulate in the atmosphere in the "Great Oxidation Event" (GOE). There is some debate over whether the GOE is due mainly to biological events, or to changes in mantle properties or circulation leading to less reducing power at the surface. This is considered problematic for the development of biological (or proto-biological) chemistry, which mostly reacts to di-oxygen by falling apart. Only small parts of biochemistry can tolerate the presence of di-oxygen, and there are considerable biochemical complications to keep it in it's place (in mitochondria and chloroplasts, for eukaryotes; prokaryotes are more variable). In a more general situation than just Earth, it is not at all clear if a "GOE" is necessary. Compared to other planets (where there is evidence), the Earth's mantle seems to be relatively oxidised (have a low free iron content) - whether this is a cause or an effect of habitability is unclear.

Nitrogen distribution between the atmosphere and the body of the Earth is strongly influenced by the oxygen fugacity of the atmosphere. As such it is then dependent on the details of the early atmosphere in contact with a post-formation magma ocean, or synestia if that was the path taken. The pressure of the Earth's atmosphere at different stages in it's history is an open question.

Phosphorus Tyrrell (1999 Nature, v400, p525, "The relative influences of nitrogen and phosphorus on oceanic primary production") considers P to be the ultimate limiting nutrient on Earth. Since there is no significant gaseous reservoir of phosphorus, it is primarily available through aqueous solution replenished by rock weathering. Currently, phosphorus is mostly released from granite/ granitoid rocks into which it is significantly segregated in igneous differentiation. However on Early Earth, there probably wasn't as much granite/ granitoid rocks at surface today and smaller amounts of phosphorus would have been released from basaltic/ mafic rocks. Very early, schreibersite ((Fe, Ni)3P), a mineral found in some meteorites may also have been a source. (The discovery of 4-4.3 Gyr zircons from the Jack Hills (Australia) and Acasta (Canada) gneisses challenges ideas of an early paucity of granite/ granitoid rocks in the very early Earth.)

Sulphur is degassed from the mantle as SO2 and H2S, but rapidly converts to sulphate and rains out into the hydrosphere. Sulphur cycles back inot the mantle via subduction, primarily as sulphide minerals (which are often processed biologically). In surface ultramafic rocks - and presumably in the mantle too - separate liquid sulphide phases (a "matte")can separate out and segregate core-wards due to it's density, taking chalcophilic elements with it. Other elements don't seem to have an effective sink to the core operating to this day. This matte process probably also operated during the Earth's assembly and after the Moon-forming impact. After the GOE, cycling between sulphide and sulphate minerals happened near the surface, which can lead to some very high degrees of isotopic differentiation.

During the accretion of the Earth (or any other planet under consideration) there were several phases, with differing processes and rates of CHONPS loss or segregation. The earliest event that can be clearly dated in the Solar system was the formation of Calcium-Aluminium Inclusions (CAIs) which are now found in chondrittic meteorites. That dates quite precisely to the memorable 4.567 Gyr ago. Rapidly, about 4~5 Myr, the gaseous component of the nebula dispersed, by which time Jupiter and Saturn had of necessity formed, and probably the cores of the terrestrial planets had reached considerable size - maybe half their current masses - which were capable of holding their own primordial atmospheres. Addition of material to the terrestrial planets continued, possibly stimulated by rearrangements of the gas giants and ice giants accreting the last of the gaseous nebula, with the hierarchical accretion of nearly similar-size bodies including the "Moon forming impact" (roughly dated to 50-150 Myr after the formation of CAIs). It remains somewhat unclear how much accretion was driven by interaction with Jupiter (including bringing in outer Solar system material to the terrestrial planets), and from where the Earth's volatile inventory came. The stable isotope ratios of meteorites (and their parent bodies) suggest formation in different parts of the Solar nebula, at different times, but the story seems complex and mixed up. Possibly by the Jovian "Grand Tack", if that happened. Possibly by the (relatively) long distance movement of "protoplanets" before their mutual collision to form "planets". It is still unclear if the Solar nebular disc remained effectively segregated by isotopic composition. One of the recent discoveries is how highly siderophile elements on Earth, which should have gone into the core during the core-forming event, and the Moon-forming impact, remain accessible on the Earth's surface, where they shouldn't be. Hence ideas of a late "veneer" on the Earth's surface.

Is this a situation that numerical scientists would describe as "ill-conditioned"? Where the models are looking for the crossing points of relationships whith very low closing angles (if you plotted them graphically), so that unavoidable noise leads to numerical results which are outside the range of the possible.

There's a huge amount more in this. Which I don't have time to go into in the necessary depth. We have a good understanding of the processes involved, but which processes are important isn't clear, and may be different in different places. And our data sources are not of the best - unavoidable because of distance and the contrast ratio between stars and planets. Frankly, "more data!" - which means visiting more planetary systems as soon as possible.

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Why tyrannosaurid forelimbs were so short: An integrative hypothesis

Acta Palaeontologica Polonica

A change from astronomy. APP has been a trail-blazer for Open Access publication in the field of palaeontology for a long time (well over a decade?) The journal has a tendency towards publishing material from Eastern European researchers, but it is global in it's spread. (Follow the link for the abstract ; the PDF is linked from that page.

Padian is a well-known palaeontologist, aprticularly in the cretaceous dinosaurs of Canada and their close relatives in Mongolia.

So waht's his big idea? People have puzzled over why the forelimbs of Tyrannosaurus species (rex, and others) are so relatively small since the species was recognised in the early years of the 20th century, and has been a staple of popular (vertebrate) palaeontology ever since. What is less well known outside the field, is that similar developments happen in multiple other types of large dinosaurian carnivores through both Jurassic and Cretaceous (tyrannosaurids, albertosaurids, abelisaurids, carcharodontosaurids). Something repeatedly propelled large dinosaurian carnivores towards relative reduction in the size of their arms.

Padian's proposal is that this is a passive but recurrent process. The genera which develop the small-arms feature have previously adapted their hunting and feeding strategies to using only the mouth (and it's scary set of teeth) to catch, kill, and consume their prey. This leaves the arms with, literally, nothing to do, so energy conservation tends to reduce their size. So much isn't particularly new, but Padian adds that many of these species show evidence of group or cooperative hunting (aligned trackways, mass mortality assemblages), and proposes that the presence of these arms dangling uselessly where multiple carnivores are tearing apart a prey item is an invitation to inadvertent biting, bleeding and infection, which provides an amplification to the passive drift to reducing arm size.

Padian adds a lot more detail to the argument, but that's the basic argument. Interesting idea, and Padian discusses the ways it could be falsified, which is a good sign. We'll never know witout a time machine, so we'll never know.

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Weak versus Strong Chaos

PNAS QnAs with Renu Malhotra

Does any reader (not me) need introduction to Renu Malhotra? A celestial dynamicist, she studies the variation and interrelationship of the orbits of bodies in the Solar system. That PNAS chose to do a Q'n'A with her affirms her status in the field.

What struck me here was the distinction between "weak" and "strong" chaos. Many people falsely think that "chaotic" means "anything can happen" ; what it actually means is more like that "future events can't be accurately predicted far into the future".

Also, as people did more accurate computer simulations of the orbits of the planets over the age of the Solar System, they learned that Pluto’s orbit is chaotic on the long time scale. Interestingly, it’s chaotic in a mathematical sense only; it doesn’t actually translate into any dramatic consequences for Pluto’s orbit. Pluto still remains more or less very close to its current orbit, the resonance with Neptune is preserved, and nothing terrible happens to Pluto over billions of years. So, there was this understanding that Pluto’s orbit is chaotic, but only weakly so. [...] We now understand that with the orbital arrangement of Jupiter, Saturn, and Uranus, there’s only a small range of their effective quadrupole moment over which Pluto-like orbits are stable for billions of years. If that quadrupole moment were not in that narrow range, then Pluto would be very strongly chaotic. So, Pluto is much closer to strong chaos than had been previously understood.

What is the distinction between "weak" chaos and "strong" chaos?

Google Is My Friend. But I use DDG, so here are the search results. A number of discussing systems that move between weak and strong chaos, which aren't very likely to discuss the meaning of the phrase, which one would be expected to know if you're in the field. A lot of this work is done in electronics type labs - relatively easy to do experimentally, I guess.
"We start by reminding the reader of fundamental chaos quantities (https://webspace.maths.qmul.ac.uk/r.klages/papers/klages_wchaos.pdf)" ... [Contents] "2.3 A generalized hierarchy of chaos" Sounds useful. It does help, by bringing in a thing called the Lyapunov exponent λ but there's a lot more background. "The Lyapunov time mirrors the limits of the predictability of the system. By convention, it is defined as the time for the distance between nearby trajectories of the system to increase by a factor of e." (https://en.wikipedia.org/wiki/Lyapunov_time) Which isn't terribly helpful, since the time varies over many orders of magnitude. There are hints that people use the time-behaviour of Lyupanov exponents - if they're increasing, the chaos is strong (gets worse with time ; if they're decreasing, the chaos is weak. But otherwise, I don't find anything resembling a simple measure of chaotic-ness.

Aha! Malhotra and colleagues seem to be using the Lyupanov exponent as a discriminant. It's in the paper that prompted the Q'n'A - Doh! "Sussman & Wisdom (6) propagated the orbital motion of the outer four giant planets and Pluto for 845 million years, and found that its nearby trajectories diverge exponentially with an e-folding time of only about 20 million years" What numbers they attach to "Strong" or "Weak" chaos though ... Or maybe not? "The detection of positive Lyapunov exponents notwithstanding, Pluto’s and the planets’ perihelion and aphelion distances and their latitudinal variations remain well bounded on multi-gigayear timescales, indicating that the chaos detected in the above investigations is very weak indeed." This still isn't well defined. They use the J2 parameter as a probe for examining the influence of the guiant (and inner) planets on the outer bodies, and at values of J2 somewhat less than what we actually have, the evolution of eccentricity * cos(argument of perihelion) changes from attaining all values (circling the Sun) to having values restricted to one quadrant (only a partial arc) That may be what she means by "strong" versus "weak" chaos, but I wish it was clearer.

I think that's enough on this question. If I ever meeet her, I'll ask.

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Freeze-thaw cycles enable a prebiotically plausible and continuous pathway from nucleotide activation to nonenzymatic RNA copying

https://www.pnas.org/doi/10.1073/pnas.2116429119

Another sideline from the usual arXivery.

The Faint Young Sun Paradox (or Problem) is the problem that the steady accumulation of helium in the core of the Sun leads (via the increasing mean particle mass) to higher fusion pressures, temperatures and so power outputs. Power increases at something like 5% per gigayear, or about 22% increase from the origin of the Solar systems to today. That implies that the surface of the Earth would have been frozen regularly and repeatedly during the Hadean and Archean. This is very sympathetic to the "Smowball Earth" hypothesis, but also suggests that Darwin's "warm little pond" may actually have had ice crusting it and sometimes covering it at frequent intervals during the O(s)OL period.

That's not necessarily a bad thing. Growing ice crystals in a pond of dilute organic soup is a good way of getting round the "concentration problem" - a growing ice crystal would have had a far higher concentration of "soup" on it's growing surface than the bulk liquid. So there are good justifications for looking at the influnece of ice crystals, even if it's not necessarily the perfect soilution. Of course, ice-crusted pools in one place are not incompatible with the products flowing down hill to ice-free pools, nor to the pools having hydrothermal heating X days in Y, and ice the other Y-X days.

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Ooops, end of the month, and time to start the next batch.

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