Super dense asteroids

[Moontanman]

Do super dense asteroids point to the possibility of heavy elements not found on Earth? 33 Polyhymnia is thought to be 3 times as dense as the densest element on the earth Osmium. Osmium is 22.59 grams per cubic centimeter with an atomic number of 76 but 33 Polyhymnia seems to be made of something close to three times as dense as Osmium. This would correspond to an element that has an atomic number of around 164. 

 https://earthsky.org/space/ultradense-asteroids-polyhymnia-cudos-superheavy

Quote

osmium, the densest stable element on the period table? Osmium has a density of 22.59 grams per centimeter cubed (g/cm³). Scientists think Polyhymnia has a density of around 75 g/cm³. So the team was looking for stable, superheavy, ultradense elements that could explain Polyhymnia’s suspected composition.

Their calculations confirmed the prediction that atoms with around 164 protons in their nuclei (elements with atomic numbers of around 164) were likely to be stable. They also found that a stable element with atomic number 164 would have a density between 36.0 and 68.4 g/cm³. While not a slam dunk, the range does approach the suspected density of Polyhymnia.

Should we be thinking of visiting this asteroid to see if we can obtain samples of this unknown element? 

[TheVat]

I was taught that all elements with atomic number above 92 are radioactive, making me think visitors may want to pack their lead undies.  But if there is a way an element with 163 AN is stable, I would be interested to hear how that happens.  

[Anirudh Dabas]

 

37 minutes ago, Moontanman said:

Should we be thinking of visiting this asteroid to see if we can obtain samples of this unknown element? 

It's a teeny-tiny rock, only about 100 kilometers in diameter. Landing a spacecraft on that celestial pebble is like trying to parallel park a spaceship in rush-hour traffic – not for the faint of heart.

And let's not forget the interplanetary travel challenges. You're looking at a journey sandwiched between the red and the giant.

 Maybe it's a bit of space FOMO

[exchemist]

48 minutes ago, Moontanman said:

Do super dense asteroids point to the possibility of heavy elements not found on Earth? 33 Polyhymnia is thought to be 3 times as dense as the densest element on the earth Osmium. Osmium is 22.59 grams per cubic centimeter with an atomic number of 76 but 33 Polyhymnia seems to be made of something close to three times as dense as Osmium. This would correspond to an element that has an atomic number of around 164. 

 https://earthsky.org/space/ultradense-asteroids-polyhymnia-cudos-superheavy

Should we be thinking of visiting this asteroid to see if we can obtain samples of this unknown element? 

According to Wiki, the only estimate of its mass was by Benoit Carry, whose results are thought to be most likely wrong, by a factor of 10 or more. The technique depends on the perturbations 33 Polyhymnia causes to other bodies, and this is subject to large uncertainties due to its small size.

My money is on nuclear physics being right and these results being wrong.

 

[Ken Fabian]

I am very doubtful. It would be WOW if true but our solar system's Asteroid materials underwent a lot of violent mixing during their formation so traces of those superheavy elements should appear in at least some (maybe most?) of the 10's of thousands of meteorite specimens that exist on Earth. Or within Earth based rocks.

Or are people suggesting these particular (poorly observed) asteroids are truly outsiders, that didn't originate within the solar system and have always remained separate?

My money is on these results being wrong.

 

 

Edited November 13, 2023 by Ken Fabian

[swansont]

4 hours ago, exchemist said:

According to Wiki, the only estimate of its mass was by Benoit Carry, whose results are thought to be most likely wrong, by a factor of 10 or more. The technique depends on the perturbations 33 Polyhymnia causes to other bodies, and this is subject to large uncertainties due to its small size.

My money is on nuclear physics being right and these results being wrong.

 

Agree. This is all extrapolating from a value that’s got a very large uncertainty 

https://en.m.wikipedia.org/wiki/33_Polyhymnia

“For example, the 68 km (42 mi)-diameter asteroid 675 Ludmilla was originally measured to have a density of 73.99±15.05 g/cm3 in Carry's study,[5] but improved orbit calculations in 2019 showed that it had a much lower density of 3.99±1.94 g/cm3”

If it’s right, someone needs to explain how superheavy elements are found on an asteroid but not elsewhere, as Ken points out.

[mistermack]

I don't know what the accepted theory is regarding dense asteroids, but off the top of my head, the most likely way they would form, is from a collision of two planet-size bodies, like the one that is theorised to have formed the Moon. 

If the collision was big enough, the material at the very centre of one or both could be spilt into space, so you would get a lot of fairly pure iron, and some materials that are denser still. 

[Ken Fabian]

57 minutes ago, mistermack said:

I don't know what the accepted theory is regarding dense asteroids, but off the top of my head, the most likely way they would form, is from a collision of two planet-size bodies, like the one that is theorised to have formed the Moon. 

If the collision was big enough, the material at the very centre of one or both could be spilt into space, so you would get a lot of fairly pure iron, and some materials that are denser still. 

All that nickel-iron (never pure iron going by meteorites) is material that was the core of planetoids that got smashed and reformed and smashed and scattered. I don't see how any superheavy elements could remain strongly differentiated (as specific asteroids) yet leave no traces anywhere else. Not if these asteroids (if they actually have such densities) were formed within the solar system.

I am thinking it would have to have origins very different to what occurred in this solar system - supernova remnants or something exotic? - and somehow it never got smashed together with the rest. Yet if such elements were tossed out by supernova - and our solar system includes supernova produced elements - we should find traces everywhere.

Edited November 13, 2023 by Ken Fabian

[mistermack]

I'm not clear on what happens at the core of a planet. The effective pull of gravity must be decreasing as you travel towards the centre, as the mass of material above you increases, and the mass below you decreases. So right at the centre, the pull would be equal in all directions, so I suppose the tendency to separate the higher density metals won't be great at the core. It might happen to some degree, but over a very long time.

[exchemist]

15 hours ago, Ken Fabian said:

All that nickel-iron (never pure iron going by meteorites) is material that was the core of planetoids that got smashed and reformed and smashed and scattered. I don't see how any superheavy elements could remain strongly differentiated (as specific asteroids) yet leave no traces anywhere else. Not if these asteroids (if they actually have such densities) were formed within the solar system.

I am thinking it would have to have origins very different to what occurred in this solar system - supernova remnants or something exotic? - and somehow it never got smashed together with the rest. Yet if such elements were tossed out by supernova - and our solar system includes supernova produced elements - we should find traces everywhere.

Quite so. 

But I've been looking at the paper that prompted this pop-sci article and I think it is really about something else: https://link.springer.com/epdf/10.1140/epjp/s13360-023-04454-8?sharing_token=mpXkcFl6UFuZEgh4DYZK0YsPkCdkOxEKPl2JoxdvwqHW9N-hyrzP0f-_h1nqnhXLsBVT4-pBXuVn0gcP16CLQEc-ew_UOQdLD1nth6S52AHTdX0rhTFNttiC-j8pe1CuBqagSArD56jvpd9SuXeiQAMMgZtdthJYevFjXzWBsh0=

The real interest of these researchers seems to be modelling superheavy metals to see what densities they might have. Their key point seems to be that densities are expected to be high for 2 reasons: (i) as Z increases, the ratio of neutrons to protons in the nucleus goes up, as the Coulomb repulsion between protons has to stay within certain bounds if the nucleus  is not to fly apart, and more neutrons help to "dilute" the proton concentration. As a result, the nuclear mass goes up more than linearly with increasing Z. However (ii), the electrons, which determine the effective atomic radius, i.e. the volume the atom occupies, can be accommodated within a greater variety of degenerate orbitals of high angular momentum (f and I suppose maybe even g in some cases) as the principal quantum number goes up, so the atomic radius does not need to expand as fast as Z increases. I suppose what they must have in mind here is overcoming the constraints imposed by the Pauli exclusion principle, rather than electrostatic repulsion between electrons.

I don't see anything stating that a nucleus with a Z of 164 is expected to be actually stable, in fact they admit they don't know. My understanding is that the islands of stability are only relative, i.e. the nuclei are less likely to fly apart than those that are not on or near the island.  But they do refer to something called "CUDOs" (Compact Ultradense Objects) which they seem to think are a thing in astronomy. I tried to look these up but only got a handful of arxiv references, so I wonder if their existence is established or if they are just hypothetical exotica. Perhaps someone like @Janus would know.  

They also introduce another idea for a dense form of matter called "alpha matter". In this, they hypothesise a dense nuclear "gas" of alpha particles, bound (somehow?) in a Bose-Einstein condensate, permeated sufficiently by the electron cloud to reduce the Coulomb repulsions. Not being a nuclear physicist I have no idea whether this can really work or whether they are just playing with the idea.

So quite interesting, but this is about nuclear modelling not astronomy. It looks to me as if they have thrown in the references to CUDOs and 33 Polyhymnia to make their research look as if it could have some practical applications. 

 

 

 

Edited November 14, 2023 by exchemist

[mistermack]

Maybe there are conditions at times that increase the conditions where denser metals can be separated from less dense. You could have a planet that orbits it's star very closely, making conditions far hotter than we usually observe. Maybe that raises the centrifugal forces within the planet to very high levels, causing more separation. Or you could have a pair of planets close to a star, rotating about each other very rapidly. Or other setups that we don't observe here in the Solar System. 

[exchemist]

11 minutes ago, mistermack said:

Maybe there are conditions at times that increase the conditions where denser metals can be separated from less dense. You could have a planet that orbits it's star very closely, making conditions far hotter than we usually observe. Maybe that raises the centrifugal forces within the planet to very high levels, causing more separation. Or you could have a pair of planets close to a star, rotating about each other very rapidly. Or other setups that we don't observe here in the Solar System. 

Conceivably. But you still need some credible process for creating one or more elements with an atomic number way beyond anything found in the solar system to date and moreover, they have to be stable isotopes, which seems highly doubtful for theoretical reasons. 

Edited November 14, 2023 by exchemist

[Ken Fabian]

Rather than exciting speculation about exotic super heavy elements in super dense asteroids what is needed is dull and ordinary astronomical observations to get more accurate estimates of their density. As well better observations of everything else that can be determined about them - which should be standard practice, to add to the inventory of known asteroids and their characteristics. Confirmation of unusual characteristics would give cause to investigate further, including with probes. If very unusual it would be very good cause.

But without that confirmation it is like an anomalous experimental result - worth finding out why but it seems much more likely to be mistake than breakthrough.

[Moontanman]

18 hours ago, Ken Fabian said:

Rather than exciting speculation about exotic super heavy elements in super dense asteroids what is needed is dull and ordinary astronomical observations to get more accurate estimates of their density. As well better observations of everything else that can be determined about them - which should be standard practice, to add to the inventory of known asteroids and their characteristics. Confirmation of unusual characteristics would give cause to investigate further, including with probes. If very unusual it would be very good cause.

But without that confirmation it is like an anomalous experimental result - worth finding out why but it seems much more likely to be mistake than breakthrough.

Yes, I have my doubts about a stable element at atomic number 164, in fact I was under the impression that the so called island of stability was supposed to be around element 124 and the stability was somewhat less than... stable. 

More important than simply speculating is getting an accurate measurement. However, the margin of error is so great on this one it makes you wonder how such a extreme error could be taken seriously at all. Even if the asteroid was 100% Osmium the density is far and away from anything you would expect from a reasonable measurement. A pure Iron Nickel asteroid should have a density of around 7.8 grams per CC  even a pure Osmium asteroid, 22.59 grams per CC, which is wildly unlikely, wouldn't come close to the claimed measurement of 75 grams per CC.

Lots of unknowns in science, various readings, findings, measurements that do not comport with reality was we think we know it. I think it's important to investigate these things when possible, remeasure when possible, but we shouldn't fall into the trap of assuming something is impossible because we can't explain it.  

Is there some other possibility which would make this measurement a bit closer to reality? 

 

[exchemist]

29 minutes ago, Moontanman said:

Yes, I have my doubts about a stable element at atomic number 164, in fact I was under the impression that the so called island of stability was supposed to be around element 124 and the stability was somewhat less than... stable. 

More important than simply speculating is getting an accurate measurement. However, the margin of error is so great on this one it makes you wonder how such a extreme error could be taken seriously at all. Even if the asteroid was 100% Osmium the density is far and away from anything you would expect from a reasonable measurement. A pure Iron Nickel asteroid should have a density of around 7.8 grams per CC  even a pure Osmium asteroid, 22.59 grams per CC, which is wildly unlikely, wouldn't come close to the claimed measurement of 75 grams per CC.

Lots of unknowns in science, various readings, findings, measurements that do not comport with reality was we think we know it. I think it's important to investigate these things when possible, remeasure when possible, but we shouldn't fall into the trap of assuming something is impossible because we can't explain it.  

Is there some other possibility which would make this measurement a bit closer to reality? 

 

In the circumstances it is reasonable to assume the results are more likely than not wrong. After all, the whole point of science is to be able to predict what we should expect to observe. So the first thing to do when results are far away from that is to try to reproduce them, in order to check them, before devoting a lot of time to exotic speculation. It seems this was done for another asteroid that this experimenter had applied his technique to - and lo and behold it was found he was off by more than a factor of 10.  

To make matter denser than the forces of electromagnetism and the nuclear strong force support, one has to resort to gravitation, in bodies containing enough matter to enable it to outweigh them, e.g as in stars.