| Left over from April Renumbering Of The Antikythera Mechanism Saros Cells, Resulting From The Saros Spiral Mechanical Apokatastasis |
| Diurnal variation of the surface temperature of Mars with the Emirates Mars Mission: A comparison with Curiosity and Perseverance rover measurements |
| The origin of Earth’s mantle nitrogen: primordial or early biogeochemical cycling |
| A numerical approach using a finite element model to constrain the possible interior layout of (16) Psyche |
| The possible formation of Jupiter from supersolar gas |
| End of document |
May science readings.
And that's the backlog sort-of addressed.
Renumbering Of The Antikythera Mechanism Saros Cells, Resulting From The Saros Spiral Mechanical Apokatastasis
Mediterranean Archaeology and Archaeometry Vol. 21, No 2, (2021), pp. 107-128The Antikythera mechanism has substantially deformed in it's time under the ocean (original density of the bronze (about 8.87 g/cc ; current density about 3.4 g/cc ; sides aren't straight ; the mechanism disintegrated after eing brought to the surface and drying out - this is why marine archaeology puts finds straight into salt-water tanks on surfacing, and takes years to clean them). Pins, straps and machined-out grooves further complicate the stiffness of the structure, throwing direct measuremnts of the structure into some doubt. The authors propose that considerations of symmetry in the external and internal design of the mechanism might help resolve or resuce ambiguities in the mechanical analysis, to try to work out which Saros cycle the mechanism was intended to start predicting eclipses at. Unfortunately they don't give a specific date- but do add the constraint that the readout spiral starts with a month which includes a solar eclipse and the second half Saros starts with a lunar eclipse
. Which probably means a series of possible start dates, 223 synodic months apart. How much ofan advance that is, I'm not sure.
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Diurnal variation of the surface temperature of Mars with the Emirates Mars Mission: A comparison with Curiosity and Perseverance rover measurements
arXiv, for MNRASA fairly simple one this one - there are several thermometers in various places on Mars. Having a radiation thermometer ("EMIRS", one of the less strained astronomical acronyms) in space, in a simpler environment, allows comparison between these multiple measures, for a more global picture (exactly like the effect Earth Observation Satellites (EOS) have on terrestrial environmental measurements.
Any surprises? There is a small difference between the temperatures seen by EMIRS (from high, covering a large area around the rover) and the MEDA instrument package on Mars 2020 (viewing the immediate proximity of the rover), during night time observations. The difference varies between 10 and 20 Kelvin (compared to instrument precisions of 1-3 K). The proposed explanation of this diffference is that the rover's drivers choose a less rocky, less rough route for it to travel along, while the satellite observes a wider area, including the rockier areas, with slightly less heat retention than the area around the rover. Well, maybe, maybe not. Time and argument will tell.
The paper introduces - to me - the Mars Climate Database (MCD) - which are at http://www-mars.lmd.jussieu.fr/, and allow you to get time- or location- constrained sets of up to 4 of about 50 parameters. Worth noting. Here is the weather (at time of writing) on Olympus Mons.
"Fun", for a very specific type of "fun".
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The origin of Earth’s mantle nitrogen: primordial or early biogeochemical cycling
linkHmmm. Interesting. So, the Earth has a lot of nitrogen in it's atmosphere, and it is an essential, often a limiting nutrient. But there is about as much nitrogen in dissolved in the mantle as in the atmosphere, and nitrogen doesn't have a high solubility in magmas (from experimental data) ... so how did the nitrogen get into the mantle? Two options are examined - that the nitrogen is primordial - pre-dating the current arrangement of Earth and atmosphere - or that the nitrogen has been introduced by subdction of nitrogenous sediments. Which needs the nitrogen to be in mineralised forms, as a likely product of biological nitrogen cycling. Very early biological cycling.
Plain Language Summary
Nitrogen (N) is the main component of Earth’s atmosphere, and essential for life. The atmospheric N content influences Earth’s climate and capability to retain its surface water. Primary biological production is limited by bio-available N as well as phosphorous on modern Earth. It has been recently recognized that Earth’s interior contains N comparable to that found in its atmosphere, and thus its origin is important for our understanding of Earth-life co-evolution. We modeled N partitioning in Earth’s molten stage and long-term cycling after Earth’s solidification. Two scenarios are proposed from our modeling. One is that Earth’s mantle acquired its modern N content in the earlier stage due to an excess amount of N Earth accreted, which was later lost to space following asteroid impacts. Another is that Earth’s mantle acquired N via subduction of N-rich sediments, which requires the sedimentary N burial rate on early Earth comparable to the modern value sustained by biological activity. The two scenarios can be tested with future analysis of the geochemical record of surface and mantle N.
Good plain language summary. More journals should try something like that (like PNAS's "Significance" statement).
How much nitrogen is in the early mantle will influence - a lot - the nitrogen levels in the atmosphere, and with it the degree of greenhouse warming (di-nitrogen, N2 itself is not a greenhouse gas, but by bulking up the atmosphere it broadens the IR absorbtion bands of other gasses, enhancing their greenhouse potentials. That holds for water vapour as much as CO2.) subducting N on modern Earth has δ15N ∼ +6‰ [...] Thus, efficient subduction should lead to 15N enrichment in the mantle. Carbon-bearing deep mantle diamonds have been found to host N with almost exclusively positive δ15N values, which might be consistent with an origin from subducted oceanic sediments.
However, MORBs (Mid-Ocean Ridge Basalts - in the slim chance that anyone other than me reads this.) on the other hand have less positive δ15N values (typically, ~-5‰) which is generally taken to imply that the mantle contains a significantly negatively enriched N reservoir. But the authiors seem to blow hot then cold on this question. A little later they say (my emphasis): The N isotopic ratio of initial mantle is from −40 to 0‰ as found in enstatite chondrites. We note that such low δ15N values have been reported for some rare diamonds from Earth’s mantle, which possibly record the signature of Earth’s N source (Palot et al., 2012).
To my mind, that implies that they don't think that the typical mantle composition is as negatively enriched as that. Which is odd.
So, did the Earth's mantle get it's nitrogen inventory by primordial inheritance, or through biogenic nitrogen cycling? That's not clear.
One useful point is their discussion of how N solubility is related to oxidation state. Neutral N (as dinitrogen, N2) behaves similarly to Ar, an inert gas but in a reduced magma (reduced below the QFM buffer?) the N is present as NH4+, and can substitute for K+ in mineral lattices.
It's a modelling result, so highly prone to one's premises. That question about the reduction state of the Earth's mantle before the Great Oxidation Event of roughly 3.2 ~ 2.0 Gyr BP. and how soluble nitrogen was then. But without that, doe the nitrogen content of the mantle require a highly biogenic source of subducted N, very early in the Earth's history. Which isn't without precedent (the alleged carbon enrichment in Akilia's near-Hadean metasediments, for example), but is nibbling away at the fairly hard limit on the origin of life, as some time between the formation of the Earth, and the oldest fossils (trating Akilia's apatite-encased graphite as a fossil). You might stretch a point and look at the Moon-forming impact as the early bound, ut that only shifts borders by around 0.1 Gyr of a ~0.8 Gyr window.
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A numerical approach using a finite element model to constrain the possible interior layout of (16) Psyche
arXiv, no indication which journal it's intended for, or if it has been accepted.So, why did this grab my attention? Probably it's that an awful lot of Musk-o-philes think it's an almost archaetypal asteroid - made of metal, big, lumpy, ideal for mining for "Precious Metals Measurless to Man" (to mis-quote Coleridge). It's what people want to hear, so it's what people hear. They don't want to hear that it comprises about 1% of the mass of the asteroid belt, which is reasonably consistent with other estimates of the abundance of metal-rich ("M-type" ; nothing to do with Star Trek) asteroids.
The paper is about modelling efforts to try to constrain the internal structure of Psyche, given the observations. It has metal on it's surface (spectroscopy tells us this, but radar reflectance also tells us that the surface is not entirely metals) ; it is not pure metal (iron meteorites have density typically ~7.5 g/cc (7500kg/m3 ; Psyche has overall density ~4.0).
The density data could be achieved by a rubble-pile structure with porosity of about 50% - but it would have remained malleable (temperature >~800K) until well after the bombardment intensity decreased below what would be needed to make so much porosity. Therefore the mixed composition (metals plus silicates) is the likely route to follow. That in itself raises a question - if the body is large enough and hot enough to be soft, why didn't large metal masses sink into the core? At which point, "ferrovolcanism" - the eruption of metal-rich magmas to the surface becomes a logical necessity.
We don't know the interior structure of Psyche - that's why there is an investigation mission somewhere between the drawing board and the assembly room - but people are working on models of it so that when more data comes in, the options can be rapidly narrowed down. Standard science - incremental advance, testing hypotheses against reality and discarding those that are wrong- Feynman would be proud.
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The possible formation of Jupiter from supersolar gas
arXiv, accepted for Planetary.Sci JournalFTFA, More than two decades ago, the Galileo probe performed in situ measurements of the composition of Jupiter’s atmosphere and found that the abundances of C, N, S, P, Ar, Kr and Xe were all enriched by factors of 1.5–5.4 times their protosolar value. Juno’s measurements recently confirmed the supersolar N abundance and also found that the O abundance was enriched by a factor 1–5 compared to its protosolar value.
So ... if Jupiter was formed from the smae gas as the Solar nebula, then 1 to [several] Jupiter-masses (MJ) of [H, He] material has been lost from Jupiter. Or, it was formed from a [H, He]-depleted region of the Solar nebula. But that "region of the Solar nebula" was probably most of the nebula, which is somewhat challenging.
Note that the abundances have been confirmed by two sets of measurements - from Galileo and from Juno - so it would take religious/ Trumpian levels of mendacity to claim the results are "fake news".
The results of modelling the inflow of dusts (and vapours when the dusts comes in too close to the Sun) from the "proto-solar nebula" (PSN) with the majority of the PSN (H, He) staying out in the vasty deep, but the condensed materials (dusts, then their vapours) settling towards the Sun by dynamic friction.
Their modelling shows that the right sort of composition of material occurs between the H2O and CO2 "ice-lines" (about 4AU from the Sun) between about 100 kyr and 300 kyr after solar ignition. Which is pretty early - compared to "planetesimal accretion models for the formation of the "terrestrial" planets, but people have always thought that most of the accretion of the gas giants took place very early, with the terrestrial planets (and "small bodies") forming as the giants exhibit their pas de deux of orbital evolution as the last of the nebula dissipates.
On the other hand, the necessary accretion timescales and rates are compatible with both core-accretion and gravitational-instability models for building a gas giant. This model doesn't help us decide which mechanism (or possibly, a third, but they're the two lead contenders by a considerable margin) occurred - or possibly both, in close sequence - but it does suggest that both are plausible.
Real Life &tm; intruded.
