Directly observing the earliest stages of star and planet formation

Since I haven’t had much to write about recently (or, haven’t felt much like writing recently) I thought I would highlight one of my recent papers. It was lead by James Cadman, a PhD student who is been working with me, and is essentially an extension of some work done by Cassandra Hall, who worked with me while a PhD student in Edinburgh (and who is about to start a tenure-track position at the University of Georgia).

Spiral density waves in a simulation of a disc around a young protostar.

As I may have mentioned before, stars form from clouds of gas and dust that collapse under their own gravity. Conservation of angular momentum prevents most of the material from falling directly onto the young protostar in the centre; instead, most of the material forms a protostellar disc through which mass can then flow onto the central protostar.

When very young, these discs may be massive enough to be what we call self-gravitating, which could lead to them forming spiral density waves (left), much like what is seen in spiral galaxies (as an aside, these spiral waves may then play a role in driving mass onto the central protostar).

Recently, the latest astronomical instruments (ALMA) have become able to directly observe spiral density wavs in protostellar discs. These may be due to the disc self-gravity but they could also be due to some kind of interaction, with either an embedded planet, or a passing star.

In this latest work we wanted to better understand the properties of the systems that would most likely show evidence for these self-gravitating spiral density waves. The systems need to be young (less than 1 million years old) and they need to be reasonably strongly accreting. However, what we’ve shown in this recent paper is that it might be slightly easier to observe these spirals than previously thought, if some amount of grain grain has already occurred in the system.

The reason for this is related to some work I did about 15 years ago. It turns out that the interaction between dust grains and gas in a protostellar disc depends on the size of the dust grains. Very small grains are very strongly coupled to the gas, while very large grains are completely de-coupled. There’s an intermediate size (in the mm-cm range) where this interaction causes grains to drift towards pressure maxima. A consequence of this is that these grains will drift, and collect, in the spiral density waves.

Figure from Cadman et al. (2020) showing how grains collecting in the spirals can enhance the emission, making them easier to observe, and allowing us to probe grain growth.

Hence, if grain growth has occurred in these discs, and you observe at wavelengths that are sensitive to the emissions from these grains, the collection of these grains will enhance emission in these spirals, making them easier to observe. So, even when these spirals are quite weak, we may still be able to observe them.

The figure on the right illustrates how, if you take this grain enhancement effect into account, the spirals become more evident in synthetic observations. What’s more, you can potentially use these observations to constrain the growth of solid particles in these discs. When these discs form, the grains are pre-dominantly micron-sized, and don’t emit much at wavelengths longer than this. If you start to see emission at longer wavelengths (in, for example, the sub-millimeter and millimeter) then you can infer that some amount of grain growth must have occurred.

So, what we’ve shown in this recent paper is that it may be easier to observe these self-gravitating spirals than we had previously thought, and we’ve illustrated the optimal observations for doing so. The reason this is important is that these spiral waves may play an important role in driving mass onto the central protostar. Directly observing them may then allow us to probe a crucial part of the star formation process.

In addition, these observations could also help us to better understand grain growth in these very young systems. Grain growth is, of course, a key part of the planet formation process and there are indications that it starts very early in the star formation process. It’s still not clear how micron-sized dust grains grow to form the kilometre-sized planetesimals that then combine to form terrestrial planets, or the cores of the gas giants. Being able to probe grain growth during the earliest stages of star formation may help us to resolve this mystery.

Links:
The observational impact of dust trapping in self gravitating discs – Cadman et al. 2020.
Spiral density waves – a post about one of the first observations of spiral density waves in a protostellar disc.
Observing the earliest stages of star and planet formation – another one of my posts about this topic.

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42 Responses to Directly observing the earliest stages of star and planet formation

  1. I should probably have made clear that the lower figure in this post are synthetic images. We simulate the disc and the grain evolution (in this case semi-analytically) and then take the results from these simulations and run them through a radiative transfer code that will produce an emission map. We can then take this and put it through a simulator for the ALMA telescope that will produce synthetic images. We can then specify array configurations, water vapour in the atmosphere, and observing wavelength.

  2. dikranmarsupial says:

    Very cool! Using computer models to help understand science – it’ll never catch on! ;o)

  3. What starts the grain process?

    Cohesive sediments?
    http://www.coastalwiki.org/wiki/Cohesive_sediment
    “Fine cohesive sediment deposit containing a high fraction (≥20%) of clay minerals. Fine sedimentary particles, consisting of clay minerals, but also other particles (silt, fine sand, organic matter), can be glued together by large organic molecules (extracellular polymeric substances, EPS) into large mud flocs. These flocs, with a diameter of 0.1-1 mm, settle much faster than the individual particles and can form a colloidal suspension on the seabed. This so-called fluid mud layer can move along the seabed (driven by pressure gradients at the interface, by flow entrainment or by bed slope effect) and be a major cause of harbor siltation. After consolidation, which is often a lengthy process, a mud bed can become highly resistant to erosion by currents.”

    Coastal/Civil Engineer here, go figure.

    Electromechanical/Electromagnetic charges? At the molecular or finer scales.

  4. EFS,
    The current idea is that for very small grains (micro-sized) they just stick together. They may even be a combination of rocky-material and ices, which will help them to stick. However, when they get to about a cm, or so, the collisions start to become desctructive (the relative velocity becomes too high for them to stick) and their interaction with the gas produces a fast inward drift. So, it’s never been clear how the solids grow beyong this barrier. We know they must (because we have asteroid and comets in the Solar System) but the exact mechanism is still not known.

    One possibility is a streaming instability. Essentially the inward drift can be such that particles at large radii catch up with those close in. If you can get a large enough build-up of particles, then the backreaction on the gas can reduce their relative motion, so that the solids stop drifting inwards, the local solid density builds up, and you have a region where grain growth becomes efficient.

    Something I’ve been working on for a while, is the possibility that collecting these grains in the spirals might also aid their growth. One reason this is attractive is because we think such spirals should be present when the system is very young, and we also think a lot of grain growth should be happening at this time (otherwise, you won’t have the planet building material present early enough to build the planets). So, maybe the presence of self-gravitating spiral density waves plays a role in both the formation of the star (through driving mass accretion through the disc) and planets (through providing a region where grains can collect and grow).

  5. David,
    That’s related, but is more to do with how the gas gets from the inner regions of the disc onto the star. It is probably funnelled – as they suggest – down the magnetic. You still need some of transporting the mass from the outer parts of the disc to the inner regions where it can then be funnelled down onto the star. When the system is very young, one possible way is to have these spiral density waves that act to transport angular momentum outwards and, consequently, mass inwards to the inner regions of the disc.

  6. Jon Kirwan says:

    I’m actually very interested in the topic. I’d love it if you had the time to teach me more and if I had the time to seriously engage that effort and pay it back, well. I’m sure that I’d really enjoy the applied mathematics and the insights (which I’d likely be able to apply elsewhere) I’d gain in the process. So close (we can talk here), and yet so far (we are both busy.) I shall look sadly upon my loss.

    That said, there’s some newly reported tentative results out (yeah, google told me) here:

    https://science.sciencemag.org/content/369/6507/1058

    In this, they examine a question about how Earth’s water may have arrived at Earth’s negative energy position around the sun. If I’m allowed for a moment to assume that the authors are smart enough to have already dealt with issues such as how the varying surface temperature of the sun over its life-cycle so far (which I’d like to assume isn’t a valid objection to their work as they dealt properly will all of the obvious details such as that), and that their results are strong in the sense that others should pay attention to this added examination, then I think it also may bear upon your work to some degree.

    When you are considering particulates, does any of it deal with the highly polar nature of water or it’s high surface tension (at Earthly temperatures and pressures, granted, which very likely were not the case where you deal with it?) In other words, how to you simplify (by the removal of complexities that would confound a solution but which, you believe, do not play a significant role and can therefore be ignored for analysis purposes?

    Their research brings up a whole bunch of questions in my mind about this. Partly, because gravity itself only becomes a force to be reckoned with at fairly large accumulations of mass. Long, long before that level, there are accumulated static charges (a back of envelope calculation using 4 pi e0 and G gives me something like 4.2×10^42 times as strong?) which must, due to solar winds, cause almost untold interesting effects — like an infinite number of pith balls touching and then reeling away. van der Waals forces, my experience, are for uncharged particles. But almost no particle would be uncharged. But gradually as accumulations take place I’d imagine that the mass of the particles would begin to mitigate the charge effects. But frankly I can’t even begin to imagine the useful math needed here. Not to mention the interesting behavior of water in all this.

    Oh, well. Perhaps someday you’ll write a suitably mathy blog and engage in a discussion or two over it. Might be fun. (Math, both applied and theoretical, are my life. And physics, too.)

  7. Jon Kirwan says:

    Crap. I think that means you need to add extensive Latex support. Nicht war?

  8. Willard says:

    It comes with a paid WP account, Jon.

    So no can do.

  9. Jon Kirwan says:

    Is that the USD8/month “premium” one?

  10. Jon Kirwan says:

    Geez. I’m seeing lots of WordPress sites offering Latex. JetPack, for example, and I think it is freely available as they say their site comes pre-configured for it and they offer free blogging. There’s also a free LaTeX2WP program (GPL’d) that I suppose I could try and see what happens here?

    I’m a little dizzy already just doing a google for “wordpress” and “latex”. Seems like there are lots of free options. (But, obviously, I know nothing until I go create a website and find out, directly, one way or another.) So should I think it is just about this particular wordpress.com site?

    Yours, still confused as before,
    Jon

  11. You can do Latex on a free wordpress account.

    \int x dx = \dfrac{x^2}{2} + C

    You just need to start with a dollar sign, then the word latex (no space) and then your latex, and then close with another dollar sign.

  12. Jon Kirwan says:

    Okay. Let’s test the idea.

    \begin{align*}   \begin{array}{c}       {V_1}\vphantom{\frac{V_1}{R_1}}\\\\{V_2}\vphantom{\frac{V_1}{R_1}}\\\\{V_3}\vphantom{\frac{V_1}{R_1}}   \end{array} && \overbrace{      \begin{array}{r}           \frac{V_1}{R_4} + \frac{V_1}{R_5} + \frac{V_1}{R_6}\\\\           \frac{V_2}{R_2} + \frac{V_2}{R_3} + \frac{V_2}{R_4}\\\\           \frac{V_3}{R_1} + \frac{V_3}{R_2} + \frac{V_3}{R_6}      \end{array}   }^{\text{outflowing currents}} &   \begin{array}{c}       &\quad{=}\vphantom{\frac{V_1}{R_1}}\\\\&\quad{=}\vphantom{\frac{V_1}{R_1}}\\\\&\quad{=}\vphantom{\frac{V_1}{R_1}}   \end{array} & \overbrace{      \begin{array}{l}           \frac{V_2}{R_4} + \frac{V_3}{R_6} + 2\:\text{A}\\\\           \frac{V_3}{R_2} + \frac{V_1}{R_4}\\\\           \frac{12\:\text{V}}{R_1} + \frac{V_2}{R_2} + \frac{V_1}{R_6} + 3\:\text{A}      \end{array}   }^{\text{inflowing currents}} \end{align*}

    \begin{align*}   \begin{array}{c}       {V_1}\vphantom{\frac{V_1}{R_1}}\\\\{V_2}\vphantom{\frac{V_1}{R_1}}\\\\{V_3}\vphantom{\frac{V_1}{R_1}}   \end{array}  \overbrace{      \begin{array}{r}           \frac{V_1}{R_4} + \frac{V_1}{R_5} + \frac{V_1}{R_6}\\\\           \frac{V_2}{R_2} + \frac{V_2}{R_3} + \frac{V_2}{R_4}\\\\           \frac{V_3}{R_1} + \frac{V_3}{R_2} + \frac{V_3}{R_6}      \end{array}   }^{\text{outflowing currents}}    \begin{array}{c}       &\quad{=}\vphantom{\frac{V_1}{R_1}}\\\\&\quad{=}\vphantom{\frac{V_1}{R_1}}\\\\&\quad{=}\vphantom{\frac{V_1}{R_1}}   \end{array}  \overbrace{      \begin{array}{l}           \frac{V_2}{R_4} + \frac{V_3}{R_6} + 2\:\text{A}\\\\           \frac{V_3}{R_2} + \frac{V_1}{R_4}\\\\           \frac{12\:\text{V}}{R_1} + \frac{V_2}{R_2} + \frac{V_1}{R_6} + 3\:\text{A}      \end{array}   }^{\text{inflowing currents}} \end{align*}

  13. Jon Kirwan says:

    I just ran my code through this web site:

    https://quicklatex.com/

    And it worked fine! See below:

    So it does NOT appear to work well.

    Can you show me how to write it so that what I provided will work correctly here?

    I’m at a loss.

  14. Jon Kirwan says:

    Well, that example isn’t perfect. (The equals aren’t lined up correctly by the phantoms I added.) But at least it represents something semi-readable. I can’t seem to produce that here, though.

    I guess I need an education, still.

  15. Jon Kirwan says:

    Let’s try another one:

    \begin{align*}I_{L\left(t\right)}=\left\{\begin{array}{l}V_{\left(0\right)}\ne 0\:\text{V},&&I_{L\left(0\right)}+\frac{V_{\left(0\right)}}{L}\left[\frac{\alpha+\eta\:\omega_d-e^{-\alpha\:t}\big[\left(\alpha+\eta\:\omega_d\right)\operatorname{cos}\left(\omega_d\:t\right)+\left(\eta\:\alpha-\omega_d\right)\operatorname{sin}\left(\omega_d\:t\right)\big]}{\alpha^2+\omega_d^2}\right]\\&&I_{L\left(0\right)}+\frac{V_{\left(0\right)}}{L}\left[\frac{\alpha+\eta\:\omega_d}{\alpha^2+w_d^2}-e^{-\alpha\:t}\sqrt{1+\eta^2}\frac{\operatorname{sin}\left(\omega_d\:t+\operatorname{tan}^{-1}\left[\frac{\alpha+\eta\:\omega_d}{\eta\:\alpha-\omega_d}\right]\right)}{\sqrt{\alpha^2+w_d^2}}\right]\\\\V_{\left(0\right)}= 0\:\text{V},&&I_{L\left(0\right)}+\frac{B_2}{L}\left[\frac{\omega_d-e^{-\alpha\:t}\big[\omega_d\operatorname{cos}\left(\omega_d\:t\right)+\alpha\operatorname{sin}\left(\omega_d\:t\right)\big]}{\alpha^2+\omega_d^2}\right]\\&&I_{L\left(0\right)}+\frac{B_2}{L}\left[\frac{\omega_d}{\alpha^2+w_d^2}-e^{-\alpha\:t}\frac{\operatorname{sin}\left(\omega_d\:t+\operatorname{tan}^{-1}\left[\frac{\omega_d}{\alpha}\right]\right)}{\sqrt{\alpha^2+w_d^2}}\right]\end{array}\right.\end{align*}

  16. Jon Kirwan says:

    One final try:

    \begin{align*} I_{L\left(t\right)} = \left\{      \begin{array}{ll} 		        V_{\left(0\right)}\ne 0\:\text{V}, 						&  						\quad I_{L\left(0\right)}+\frac{V_{\left(0\right)}}{L} 						    \left[ 								   \frac{\alpha+\eta\:\omega_d-e^{-\alpha\:t}\big[\left(\alpha+\eta\:\omega_d\right)\operatorname{cos}\left(\omega_d\:t\right)+\left(\eta\:\alpha-\omega_d\right)\operatorname{sin}\left(\omega_d\:t\right)\big]}{\alpha^2+\omega_d^2} 								\right]\\ 						& 						\quad I_{L\left(0\right)}+\frac{V_{\left(0\right)}}{L}\left[\frac{\alpha+\eta\:\omega_d}{\alpha^2+w_d^2}-e^{-\alpha\:t}\sqrt{1+\eta^2}\frac{\operatorname{sin}\left(\omega_d\:t+\operatorname{tan}^{-1}\left[\frac{\alpha+\eta\:\omega_d}{\eta\:\alpha-\omega_d}\right]\right)}{\sqrt{\alpha^2+w_d^2}}\right]\\\\ 						V_{\left(0\right)}= 0\:\text{V}, 						& 						\quad I_{L\left(0\right)}+\frac{B_2}{L} 						    \left[ 						    \frac{\omega_d-e^{-\alpha\:t}\big[\omega_d\operatorname{cos}\left(\omega_d\:t\right)+\alpha\operatorname{sin}\left(\omega_d\:t\right)\big]}{\alpha^2+\omega_d^2}\right]\\ 						& 						\quad I_{L\left(0\right)}+\frac{B_2}{L}\left[\frac{\omega_d}{\alpha^2+w_d^2}-e^{-\alpha\:t}\frac{\operatorname{sin}\left(\omega_d\:t+\operatorname{tan}^{-1}\left[\frac{\omega_d}{\alpha}\right]\right)}{\sqrt{\alpha^2+w_d^2}} 				   \right] 		    \end{array} 		\right. \end{align*}

    It should render as:

    If not, that’s the last I will try, for now. It would only prove I’ve some education yet before I can use Latex with wordpress with any confidence.

  17. Jon,
    You’re trying to do something much more complicated than I would normally try to do in a blog comment. If I get a chance, I’ll see if I can get it to work. It does seem that things like \text and the ampersands, don’t always work as expected.

  18. It’s the arrays that are messing it up. I’ll try to see if I can fix it. Meeting in 10 minutes 🙂

  19. Jon Kirwan says:

    Thanks for any effort towards solutions allowing fine-grained use of Latex. I can verify the Latex I use at a web link elsewhere to make sure that what I post *should* work okay, once you have things in hand.

    There’s two issues: (1) any blog you might write which is highly technical in nature (which I would very much look forward to) would need to be able to write equations, cleanly and clearly; and, (2) any comments you get in reply should be equally capable of the same. Otherwise, the communication breaks down because the comments, if in an inferior position using Latex, can’t really then well deal with issues or thoughts that are clearest when expressed in mathematical form.

    Theory itself is broad in scope and isn’t necessarily any particular mathematics, per se. Theory is the idea space out of which we think about problems. But in order to test our abilities to apply it well, we take specific questions which make specific assumptions and then deduce from theory, as applied to some case in hand, a detailed mathematical treatment which predicts quantities that can then be tested, or used to suggest the kinds of things we might looked for. For that bit, we need mathematics as the clearest expression allowing for quantities to be computed.

    How we deduce theory into specifics also needs to be examined by others so that mistakes we may make, through ignorance of other theory that should also be applied for example or through some failure of logic in developing them, can be found and corrected. This requires mathematics for communication, because it is always crystal clear and allows anyone to identify terms or factors that may be missing, incorrectly combined, etc.

    Of course, I honestly don’t know if you’d ever entertain such discussion on your blog. So that’s another question. But should you feel like it, I’d really enjoy learning more about what you do. Published papers are, unfortunately for me, too sterile and assume too much background that I do not yet have. So I’m a student, a beginning student more or less, and published papers fall a little short of being a helping hand and a tutorial for self-education on some topic when I’m trying to gain a more comprehensive view starting from almost total ignorance.

    All I have is that I’m familiar with a lot of mathematics and can “think in that universe” with some fluency. So I’d use that skill as my segue into gaining better understanding and eventually the larger pictures, while at the same time trying to take the larger theoretical ideas and break them down using specifics. By combining both, I work towards fitting everything at the middle zone. If I am successful doing that, then I am relatively assured that I’ve mastered both the larger theoretical parts that lead towards the specifics, as well as the important specifics that you and others choose and why you choose just those and ignore the rest.

    Okay. I know I’m asking way way too much. And I know you’ve not promised anything, either. But if it should come to pass that you find yourself in a position where you could consider even the tiniest fraction of my over-eager hopes, even if only this much:

    \frac{ \textrm{d} hope }{ hope }

    at learning more, then I think Latex may be as important as words.

  20. Delighted to learn that spiral density wave optical contrast is a real phenomenon– I thought I was seeing things in 1997, because the dust-spouting visual magnitude -1 Hale-Bopp nucleus looked for all the world like a Catharine Wheel as viewed through a 25cm refractor

  21. Jon Kirwan says:

    Hmm. I guess my prior comment (admittedly long) is still quarantined. (Or lost, entirely.) It is as it is.

  22. Jon,
    Not sure why it got caught by the moderation filter, but is out now.

  23. Jon Kirwan says:

    Noted and thanks.

    But I am gathering your moderation AI must be pretty smart.

    Clearly, it knows a lack of relevance when it sees it!

  24. Dave_Geologist says:

    Apropos of imperfect greenhouse analogies, I’m reading Katie Mack’s excellent (for my level 🙂 ) The End of Everything. Evaporating black holes and virtual particles:

    Hawking made use of the quantum weirdness of virtual particles—pairs of positive- and negative-energy particles popping into and out of existence from the vacuum of space itself. The idea is that this spacetime popcorn is happening all the time, everywhere, but usually it has no effect on anything because the two particles will appear and immediately annihilate against one another, both going back to being nothing again. But, Hawking said, near a black hole, you could have a situation where the negative-energy virtual particle falls past the horizon, leaving the positive-energy virtual particle so bereft that it becomes real and wanders away. The mass of the black hole would reduce a little as it absorbs that bit of negative energy, and the same amount of positive energy would appear to radiate off the black hole’s horizon. Because these virtual particles are always popping up everywhere in space, any black hole that’s not actively pulling in matter from its environment should be gradually bleeding off mass through this evaporation process all the time.

    As complicated as this might sound, it’s still a vastly simplified picture, meant to capture just the basic idea without getting too technical, and it’s an explanation that’s used all the time. But it has never been particularly satisfying to me, since it seems to require the negative-energy particles to preferentially fall toward the hole, and the positive-energy ones to be traveling away from the black hole with enough energy to escape. It turns out that despite talking in these terms for popular audiences, Hawking never really wanted this explanation to be taken literally, and the real explanation involves calculating wave functions and the scattering that the waves experience in the vicinity of a black hole. I can’t really get into it without a massive amount of math and a level of physics exposition that would probably require weekly lectures for two or three semesters, but I’m telling you about it because if it bugged me, it might bug you too, and I wanted to assure you that despite the inadequacy of the popular analogy the full calculation does make sense if you do it all rigorously, using general relativity and quantum field theory.

    Dangnabbit! Why can’t those pesky simplified analogies fully represent the physics? It’s not like everyone can’t calculate wave functions in their heads, is it?

  25. Dave_Geologist says:

    I’m a bit annoyed I didn’t see the flaw in that analogy myself. “How does the negative-energy one know to fall inwards?” is a close cousin to the misconception that “Heat flows from a warmer to a colder object so how can cold atmospheric CO2 molecules radiate heat to the warmer ground?” Applying 19th-century physics to quantum mechanics never ends well. The counter is of course “How does the CO2 molecule know up from down? And how does it know that the ground is warmer than itself and the CMB colder?”. Although the kinetic theory of gases also answers that one. “How does the molecule know how warm it is if temperature is an ensemble property of a bunch of molecules: the average molecular kinetic energy is proportional to the ideal gas law’s absolute temperature?”.

  26. Dave_Geologist says:

    Oops, they were meant for the previous thread 😦

  27. Dave_Geologist says:

    Jon, I haven’t had time to read the Earth’s water one, but based on recent geological publications I’d lean towards both an early and a late delivery. Recent work has upgraded both the amount of water in the mantle and the amount which can stably be retained there and in the core. That water doesn’t solve the where-did-the-oceans-come-from problem, because that water is still down there and not in the oceans. Some comes out of volcanoes, but we’ve had oceans ever since we cooled enough for liquid water which is too soon, and since plate tectonics started, more than half an Earth-lifetime ago, we’ve also been recycling water back into the mantle in the form of hydrous minerals.

    For the early water there’s a way to solve the carbonaceous-chondrites-are-wrong problem, because some very old, undifferentiated and unmixed mantle (or something interpreted as such) has been found which can be paired with carbonaceous chondrites to give the right Earth-average isotopic composition. Assuming the right proportions, which is a free variable and pretty much unconstrained given the few observations.

  28. Jon Kirwan says:

    I’ve got another message in quarantine for Dave the Geologist.

    I’m growing to enjoy my prison.

    Or not.

  29. mrkenfabian says:

    In note that Richard Muller is another that likes arguing that we should be skeptical of climate science because of people saying “alarmist” stuff about hurricanes/cyclones. To me it looks like choosing to focus on an area of climate research and prediction that has a lot of uncertainty and different (professional scientist) opinions that aren’t resolved to the exclusion of those that are – because they are uncertain and unresolved. Seems to me more about Doubt, Deny, Delay politicking keeping the focus on uncertainty and on “Alarmists” – including blaming them for the existence of climate science denial itself (after hearing Al Gore or xxxx say something wrong how could they ever take an IPCC report seriously again?) – rather than the terrifying abundance of real world evidence of global warming and the potential for harms from current trends going unchecked.

  30. Jon,
    I can’t see any other comments of yours, in moderation or in spam.

  31. Jon Kirwan says:

    That’s bad. It was a rather long one, responding to all three of his posts. I posted the comment, saw the button go into a “posting” mode for a moment, but when the page refreshed it wasn’t there to see. No idea what happened, then.

    Oh, well. If I get the energy to post that again, I’ll get at it.

    Thanks for the note.

  32. Dave_Geologist says:

    Jon, hope it’s not me 😉

    I save long posts in a text editor just in case.

    I’ve found three responses:

    1) The browser hangs for a few seconds then refreshes with the post.

    2) The same but it appears with a message that it’s in moderation.

    3) It disappears instantly and the page instantly refreshes sans post.

    Sometimes (1) looks like (3), but with a delay before refreshing sans post. Presumably because the delay is long enough for a browser auto-refresh, perhaps because the server is particularly busy. But I always take instant disappearance as a sign it’s gone for good.

    I’ve interpreted that as Akismet intervening upstream of ATTP or Willard. It seems to happen with very long posts, post with lots of links, or posts with certain links. And probably with certain keywords popular with spammers. I tested once and found the spoof Daily Mail headline generator was a trigger. It is a bot, but a funbot not a spambot. But it outputs masses of machine generated text each day on demand so looks like the latter.

    I’ve not noticed it here but on other sites successive rapid posting is also a flag. I’ve been caught by that when splitting long texts so wait a bit between parts; and I’ve even been caught out by rapid, successive typing (I can touch-type on a keyboard) in contexts where unlike here I’m not posting technical stuff which requires attention and proof-reading.

  33. Dave_Geologist says:

    Having now read the Science paper Jon, it seems consistent with my (recent) understanding. There’s more water in the mantle (and perhaps core) than we used to think, but it’s not the primary source of the oceans because it’s still down there and the isotopic composition is wrong. It could have come from CM carbonaceous chondrites because that’s a diverse group with a large isotopic range, but you’d have to explain why only a subset of compositions was incorporated into the early Earth. Since original distance and degree of alteration are potential mechanisms for that diversity, I could perhaps bring it on-topic by speculating that the path from the spiral arms to Earth’s orbit either tapped a particular source region or, per your comment, that the degree of aqueous alteration played into how hydrogen bonds influenced the growth of grains into bodies and their migration rate and position within the system.

    The recent paper provides a mechanism for making the solid Earth from enstatite chondrites, and challenges earlier scepticism that they wouldn’t bring enough water, scepticism which had been increased by the view that they had to bring even more water than we used to think.

    I found the one that was at the back of my mind: Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. They looked at Ru isotopes and found relict early mantle which is s-process-enriched relative to average mantle, implying a contribution from objects formed inboard of Earth’s current orbit. Average mantle is intermediate between s-enriched and EC but closer to EC, so you’d still need a large EC contribution. Carbonaceous chondrites are on the other side of EC so for a single isotope you have three (five with CC, CM and CI) mixing components so a wide possibility of mixing models. They argue for a small (0.3%) late veneer of carbonaceous chondrites (but early enough to mix into the mantle so not the ocean-water delivery ones because these ones have to melt or mix into a magma ocean). If you assume, per the Science paper, that EC’s have about a thirtieth the water content of carbonaceous chondrites that’s not too inconsistent with their 24(0,32)% carbonaceous chondrite contribution. This is the sort of early, developing work with limited samples and a lot unconstrained where a factor of two or three counts a a hit and an order of magnitude a near miss.

    These are exciting times if you’re interested in the origin and development of the early Earth. My money would still be on a giant planet disturbance even if there are alternative delivery mechanisms from the outer Solar System, because you also have to deliver material from the innermost Solar System. But there’s someone on here far more knowledgeable on such matters 🙂 . The dog that didn’t bark would then be why the bulk Earth is so close in terms of its major contributors to what you’d expect from its orbital radius. Why didn’t we get thrown inwards and outwards, picking up that veneer of debris as we veered around the Solar System? And if we did, why did we end up back in the same place? I’ll carefully avoid any hypotheses involving large, invisible hands with our future welfare in mind 😉 .

  34. izen says:

    @-DG
    “I’ll carefully avoid any hypotheses involving large, invisible hands with our future welfare in mind 😉 .

    AFAIK the preferred explanation is an infinite number of large invisible hands, all supremely indifferent to the outcome.

  35. Dave_Geologist says:

    Actually, isn’t an infinite number of large invisible hands acting through gravity (which grew out of tiny invisible hands), all supremely indifferent to the outcome, kinda the standard model as per ATTP? A self-organising Solar System.

    I was thinking more of the one that comes attached to someone with a long white beard (invisible beard, of course; and inscrutable, and ineffable) 😉 .

  36. Ben McMillan says:

    The particle concentration mechanism is interesting (pressure gradients don’t affect big dense particles much). I foolishly thought there was going to be something fancy like ionisation or radiation pressure doing the work…

  37. Ben,
    Radiation pressure can be important when the systems are slightly older, most of the gas has gone, but there are still remnant solids. The dust, which can be primoridal or for collisions between larger bodies, can then the be influenced by radiation pressure. In fact, for small dust grains (micron to millimetre size) the effect of radiation is actually to cause them to lose angular momentum and spiral inwards. It’s called Poynting-Robertson drag.

  38. izen says:

    @-DG
    I was also referencing, perhaps wrongly, the Kurt Vonnegut invention.

    https://vonnegut.fandom.com/wiki/The_Church_of_God_the_Utterly_Indifferent.

  39. Dave_Geologist says:

    Ah – I assumed you were referencing that other religion izen, the one invented by Adam Smith 😉 .

    I don’t recall TCOGTUI, although I’ve definitely read The Sirens Of Titan. And of course the chrono-synclastic infundibulum is an earthworm I’ve never been able to get out of my head!

  40. Dave_Geologist says:

    an earworm 😦

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