Glancing impacts on Earth

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

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

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

On a Possible Giant Impact Origin for the Colorado Plateau

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

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

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

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

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

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

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

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

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

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

November Slashdottery

Some new interesting things on Arxiv.

Avi Loeb doing his "'Oumuamua is an Alien Spaceship" thang, again.

Astronomical gadfly Avi Loeb has summarised his arguments why he thinks interstellar object 1I/2017U1 'Oumuamua is an artefact, and since we didn't make it (or did we? That'll get the conspiracy nuts foaming at the mouth.) then it proves the existence of alien civilisations, and probably a lot of them.

Well, there aren't many other serious astronomers who'd go that far, but 'Oumuamua remains a very peculiar object. 2I/Borisov in contrast was a very much more normal cometary object. And everyone in the asteroid-hunting game is looking to put their own handle on 3I/YourNameHere.

There's nothing particularly new here - 'Oumuamua has disappeared into the dark depths of space and we're never going to see it again or acquire more data on it (unless a Star Trek scriptwriter decides to take a plunge, V'ger style). But if you're looking for a quick summary of why it's considered weird, this is as good as any half-dozen of the 130-odd other papers on the subject hosted on Arxiv. 

Planet and asteroid formation histories

A couple of Russian astronomers have contributed an appendix for a forthcoming book on the Chelyabinsk meterorite of 2013. One would hope that such a chapter would be a reasonably even-handed description of modern theories (note : plural) of how the medium to large bodies in the inner Solar system accreted, but really the authors have beaten their own drum for a minority position and have paid short shrift to the majority opinion. (They dislike the "giant impact" scenarios, and prefer forming a debris disc from multiple small impacts, then assembling a Moon from that ; moons of various asteroids are proposed to form by analogous events.) Well, it's a position, but I'd hope they at least put in another appendix on the Giant Impact family of theories, since they're considerably the more popular. If they want this to become a textbook, they're doing their readership a disservice.

I didn't read this closely. In the introduction they make several significant errors (they assert that the asteroid belt has about the same mass as the Moon - it's about 4% of the mass of the Moon ; they question "where did the 99.9% of the original matter of the asteroid belt go to", when again the majority opinion within mainstream planetary science is that it was scattered by early migrations of Jupiter (and Saturn) in the "Grand Tack" model). With these problems, I didn't think it worth more than a cursory read. As a model for the formation of asteroid satellites and/ or double asteroids, their ideas have some merit, but as an appendix to what aspires to be a textbook, this chapter has some serious problems.

Was Venus Ever Habitable?

In popular science, Venus is often described as "Earth's twin", with an implicit subtext about "why isn't it habitable like Earth?" In reality, it is much more dubious if Venus was ever habitable, and this paper describes some quite detailed modelling of the evolution of the planet's mantle chemistry and atmosphere to arrive at the current situation, from an inferred formation of chondritic composition (with several Earth-oceans of water). They find there is a significant chance of the planet going directly from a magma ocean state to a runaway greenhouse without any appreciable period of habitability.

Dull stuff, but it's important to remember when people are getting excited about terraforming planets. Venus remains potentially easier to terraform than Mars (there aren't enough volatiles on Mars to make a useful atmosphere - you'd have to move essentially all the volatiles of the asteroid belt onto the surface of Mars - which is going to take millennia during which the surface is going to be a very dangerous place to be. Stick that in your Musk and smoke it.), but it is quite dubious whether it has ever been habitable.

This was making me think last night. 

The Faint Young Sun paradox has always been a challenge over why Earth has remained habitable for so long. I wondered, how much geological evidence would be left by a close approach (not an impact!) by, say, Mercury migrating inwards at (say) 2Gyr, to move Earth (and potentially Venus too) out by, say, a tenth of an AU. I don't think I've seen any work trying to address early rearrangements of the inner solar systems, while there have been a number of studies projecting the Solar system forwards to the Sun's red giant stage, which produce a few percent chance of Mercury and Venus interacting to eject Mercury from the system - potentially even to impact the Earth! If that could happen in the future, then I don't see a clear reason why it couldn't have happened in the past.

That's some special pleading to try to resolve the FYS paradox : might be completely unnecessary ; might be a part of the "Rare Earth" question.

Could Mercury be the core of whatever hit Mars to make the "hemispheric dichotomy"? Not seriously - Mercury is half Mar's mass, but the hypothesised "Borealis Impactor" is, IIRC, a few % of the mass of Mars. (Off to check - SETI talks, Martian Dichotomy, Margarita Marinova. Paper : Nature v453 p1216, 2008 ; where they look at impactors 1600-2700km diameter. Mars is 6792km (nominal diameter), so diameter ratio 0.23 to 0.4 and volume ratio to 1.3 to 6%. It's not so simple to go to masses, because there is compression in the cores, but it's not a huge effect at these small masses.) 

Nice idea. Doesn't even begin to work.

Comets can be active a LONG way out.

Jewitt and Bouziani study the observation that comet C/2017 K2 had visible gas emission while out beyond Uranus. Who ordered that !? That's not the normal story. But yeah, it happened. They make a model of heat conduction into the body of a comet after perihelion, and it's effect on CO pressure, suggesting that as the warming front propagates into the body (but it is already past perihelion) then pressure can build up under the surface crusts and migrate to the surface producing outgassing potentially out as far as 150AU. That's ... a lot further out than expected - for example C1/Halley could be outgassing all the way to aphelion.

Nautilus coven.

Allegedly 876 (a suspicious number) ft - a bit less than 300m - down in the Pacific near Palau.

Lighting is suspiciously bright. 

Original pic

My reading.

Slashdot Aug-Sept 21

Slashdot Submissions – Aug 2021

It has been a while since I posted anything, and the potential submissions have been piling up. 

Arxiv Ref	Title	Comments
2108.09868	The Orbit of Planet Nine	Probably the most interesting to the general reader.
2108.07207	(216) Kleopatra, a low density critically rotating M-type asteroid	Partly the “M-class” (no, not Star Trek), but in itself interesting because quite large asteroids can get spun up to the point of shedding matter from their extremities.
2108.03343	On the Need for a Classification System for Consistent Characterization of the Composition of Planetary Bodies	An actual planet classification.
2108.03323	Warm terrestrial planet with half the mass of Venus transiting a nearby star	New competitor for lightest planet known – check on Exoplanets.org
2108.05321	Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project	Its the citizen science that is most interesting.
2108.01422	The interior of hairy black holes in standard model physics	Funny phrase – save it for next time someone is whinging about Uranus.
2108.01471	What’s inside a hairy black hole in massive gravity	ditto
2108.01783	Comment on “Observation of a Neutrino Burst from the Supernova SN1987A”	There was a 7.3 second gap during the records of neutrinos from SN1987A at Kamiokande. This is suggested to be a hardware eror, when the tape staging recorder experiences a write error and performs a rewind-reset, which takes about this period of time.

1 - Planet Nine

Ever since the demotion of Jupiter, any mention of "Planet Nine" invariably attracts a swarm of comments about how, for some people, "Planet Nine will always be 134340 Pluto. Well, that battle has been fought and lost, and @plutokiller (Professor Mike Brown of Caltech, USA) himself has moved on to trying to find a new Planet Nine. In 2016 an analysis of the orbits of the largest, most distant "minor bodies" of the Solar system suggested that there may be a large planet "out there", controlling the distribution of these (relatively) large, distant bodies orbits, and from that inferring where they think their suggested planet would be seen on the sky.

Such efforts have a patchy history. Certainly LeVerrier is famous for predicting the position of Neptune from irregularities in the orbit of Uranus (cue whooping from the peanut gallery), but equally certainly he was working with an inaccurate data for the masses of solar system bodies (Uranus, particularly), and his result was correct by luck, not judgement. Similarly, the calculations which led to the discovery of 134340 Pluto were also based on inaccurate mass data leaving the mass of 134340 Pluto uncertain between the mass of Earth and "very small". The fly-by of a spacecraft - Voyager 2 - greatly improved the measurement of Uranus's mass, which is crucial to understanding the motions of the rest of the Solar system.

Since Brown (and others) started discovering multiple bodies of mass comparable to that of 134340 Pluto, orbiting in the same region of space, the identity of 134340 Pluto as a planet has been challenged, resulting in it's demotion to a "dwarf planet" in 2006. But since then, the discovery of more, and more distant, dwarf planets (including by Brown) has led to suggestions that they may hint at the presence of something big, "out there". Which Brown and colleagues have been looking for for several years, securing observing time on very large telescopes to carry out this work.

Their current best estimate of properties for Planet Nine is mass 6.2 (average: spread 8.4 - 4.9) Earth masses ; semi-major axis 380 (520- 300) AU ;  inclination 16 (21 - 11) degrees and an argument of perihelion of 300 (440 - 240) degrees (centred on Capricorn, but with a wide spread).

Hopefully they'll find it soon, because not finding it would only prove that they were looking in the wrong place at the wrong times, not that it doesn't exist.

This one posted 2021-09-02

2 - Kleopatra and planet classification.

3 – Ross 19b – a relatively nearby planet discovered by a Citizen Science project.

Slashdot posting, 1950 astronomical transient

"Exploring nine simultaneously occurring transients on April 12th 1950"

A new (potential) Slashdot submission. This is my working copy.

Working Title : Did you see that?

Paper : https://arxiv.org/pdf/2106.11780.pdf

9 authors, including one un-person (Geoff Marcy) from 10 institutions from the USA, via Spain (Gran Canaria), Sweden and the Ukraine, and ending up in India. In other words, the usual international football team.

A paper just published on Arxiv, the astronomy/ physics/ computing/ mathematics preprint service, describes studies into old astronomical data sets, to prepare the ground for the "transient" phenomena which will be discovered by new "repeated survey" telescopes. These will photograph the whole sky every few days, capturing novae and supernovae, many new Solar system bodies, the new "mega-constellations" of thousands of satellites, and other, more surprising "transient" phenomena.

In the early 1950s the then-new "200 inch" Hale telescope at Mt Palomar was employed in performing a sky survey. They would take a plate (literally, a glass plate ; this was long before electronic image capture) with a blue-sensitive emulsion, then a plate with a red-sensitive emulsion ; six days later, another red plate covered the same area (by planned overlap). The middle red plate showed a cluster of 9 objects, covering about a tenth of the full Moon's apparent size, which weren't visible in the previous blue plate, nor in the subsequent red plate. The simplest astronomical explanation is that 9 objects of red colour appeared and disappeared in that time interval.

As astronomers get more short-interval surveying of the sky, they get a better idea of how often such "transients" occur. Individual transients (novae, unidentified Solar system bodies, etc) are not, themselves, rare. But nine, in such a small area, in such a short time period - that is rare.

A sceptic's first question would be - is the data good? Photographic plates are a mature technology - and were around a century old at the time of taking. Nobody knows of a similar "contamination" process. Millions of plates have been scanned into computers after the glassware was replaced with CCD detectors - again, nobody has found a similar set of contamination marks. Ideas such as grains of dust from the Alamagordo atomic tests getting onto the plates (and being washed off in the processing) were considered, but it is very unlikely that no other plates for the same manufacturer show similar defects. Human events (matches producing "flares" in spectroscopic observations ; the infamous "Fast Radio Burst" microwave oven) were considered, such as an astronomer with hayfever spraying the plate with snot droplets. But again, why haven't comparable artefacts been found on other plates - and people have looked, digitally, for them! Water drops and processing chemical streaks have characteristic sizes, which these images don't. 

A fragmenting asteroid ("small body") was considered. But that would leave images substantially elongated by the Earth's motion - and only one of the 9 "transients" showed signs of elongation. Some astronomers used to refer to asteroids as "the vermin of the skies" referring to their common occurrence on the sky - invariably through the middle of what you were really trying to photograph. The term is being re-purposed for satellite megaconstellations.

What about a meteor fragmenting in the atmosphere above the telescope? They take too long, and produce even longer streaks than asteroids. They are photographed often enough to be well understood, and this image isn't one of those.

A satellite might produce a short enough "glint" of reflected sunlight. But ... the first satellite was launched 7 years after this image. Unless the launch records from Area 51 say differently.

One event, with 8 reflections from some nearby objects, could work. But with the plate exposure being 50 minutes, the maximum spacing of the reflecting objects is about 30 light minutes, and the size of the spread means the object is about 0.02 light years away. Comfortably beyond the Voyager probes, launched over 20 years later. Unless the launch records from Area 51 say differently.

 

The obvious next step is to look at existing images of the area taken with newer technology. That has been done. The Pan-STARRS survey (2010 to "continuing" ; to 3.4 magnitudes dimmer than the plates managed - a factor of about 23-fold in brightness) saw nothing there. The Sloan Digital Sky Survey (SDSS, 2000 to "continuing"), to 16-fold dimmer than the plates, saw nothing there.  

To mis-quote Capt.Brody [no, Quint!], "We're gonna need a bigger telescope!" And that is what this report is about. Using the GTC (Gran Telescopio Canaria, 10.4m, ~409in) they photographed the region to a brightness (dimness) of 250-fold compared to the original plates. And they found a number of matches. That's not unexpected : the astronomers estimate the odds of getting such matches by chance as about 17% - far from impossible, but not terribly likely. 

Still, nobody knows what there objects were (or even if the 1950 observation was real)

 (The authors also consider the possibility that in the 70 years between observations, the original objects have drifted out of the field of study - in itself, that would mark them as likely outer Kuiper Belt objects, or Oort Cloud objects. In which case, the question of the simultaneous movement of 9 close objects remains a question. Cue the "I'm not saying it was aliens, but ..." video clip.)

 

This is a first draft. I'll post it to Slashdot after editing it down a bit.

Two planets around Kapteyn’s star

 G. Anglada-Escud ́e et al, https://arxiv.org/pdf/1406.0818.pdf with a small football team of co-authors.

I noticed the paper while searching for something else on Arxiv ; the title hooked me, but on second reading I'm realising it's old (2014) work.

Kapteyn's Star is one of the closest stars to the Solar system (well known) ; it's a red dwarf with a parallax of 0.25 arcsec (4 parsecs). It is considered a halo star - a star passing through the Milky Way's disc, but generally residing in the galaxy's halo). Proper motion just under 9 mas/year. Discovered about 1897 in compilation of the Cape photographic Durchmusterung. It has a low spectroscopic rotational speed (v.sin(i) <~3km/s) and low metallicity. It is considered a pretty ancient star, and possibly derived from the Omega Centaurus galaxy's halo into the Milky Way's halo, stripped off during the collision.

Located in Pictor, southern hemisphere. It moves, relatively quickly.

Between 1999 and 2013, using several devices, a sequence of spectra were taken and yield a periodic drift with two period peaks of 121 and 48.6 days.

With a low-mass primary, and relatively large planets (4.8 and 7.0  Msin(i)_earth) the orbits seem stable on the 10 Gyr timescale (appropriate for a merger star).

This work has been challenged several times, but seems to survive it reasonably well.