# Superheavy Elements

There are currently 118 known chemical elements. The most recent, 118 Oganesson (chemical symbol Og), was first synthesized in 2002 . Its only known isotope, $\mathbf{\frac{294}{118}\textrm{\textbf{Og}}}$ (118 protons + 176 neutrons = 294 nucleons), has a half-life of just 0.0007 seconds, and to date only five oganesson atoms have been produced.

It is possible, given our current knowledge of nuclear physics, that there is at least one island of nuclear stability where stable or quasi-stable isotopes of superheavy elements exist. One such island might exist around Z = 164, that is an element having 164 protons and something like 246 neutrons.

Are any superheavy elements stable enough to be found in nature? Is there any astrophysical process that could produce them? If superheavy elements exist, we would expect such matter to have a mass density in excess of the densest-known stable element, osmium (element 76), 22.59 g/cm3. Superheavy elements around Z = 164 are expected to have a mass density between 36.0 and 68.4 g/cm3.

Researchers at the University of Arizona in Tucson explain that superheavy elements might exist in nature, either in the exotic form of extremely dense alpha matter — nuclear matter composed of alpha particles in a Bose-Einstein condensate-like configuration — or as standard matter. Though a long shot, they suggest looking at asteroids (and other objects) possibly having anomalously high densities, which they call Compact Ultradense Objects (CUDOs).

In order to calculate the density of an asteroid, you need to measure its volume and its mass. The volume can be calculated if you know the size and shape of the asteroid, and the mass can best be calculated if the asteroid has a satellite (either natural or artificial), or from a spacecraft flyby. A less certain mass can be calculated by measuring how an asteroid gravitationally perturbs a neighboring asteroid as they both orbit around the Sun. We must keep in mind that any asteroids that presently appear to have an unusually high density may later be found to have a more normal density upon better estimates of the size and shape of the asteroid, and especially its mass.

The most recent available table of asteroid bulk densities can be found on the SiMDA (Size, Mass, and Density of Asteroids) web site. In that table, a bulk density accuracy rank of A (most accurate) to E (least accurate), and X (unrealistic) for each object is given. Among the A-rank densities, we find that 16 Psyche is listed as having the highest bulk density of 3.90 ± 0.29 g/cm3. NASA’s Psyche robotic spacecraft was launched on October 13, 2023 and is expected to begin orbiting 16 Psyche in August 2029.

Among the B-rank densities, two asteroids have nominal bulk densities higher than 16 Psyche’s: 135 Hertha at 4.45 ± 0.63 g/cm3 and 192 Nausikaa at 4.10 ± 0.70 g/cm3.

Among the C-rank densities, 21 asteroids have nominal bulk densities higher than 16 Psyche’s:

### Rank "C" Asteroid Densities (> 16 Psyche)

 206 Hersilia 6.08 ± 2.55 181 Eucharis 5.46 ± 2.43 410 Chloris 4.96 ± 2.41 679 Pax 4.95 ± 1.45 110 Lydia 4.88 ± 1.75 97 Klotho 4.80 ± 1.01 124 Alkeste 4.74 ± 2.22 275 Sapientia 4.69 ± 1.12 92 Undina 4.64 ± 1.75 34 Circe 4.63 ± 1.21 56 Melete 4.57 ± 1.07 102 Miriam 4.46 ± 1.88 680 Genoveva 4.37 ± 2.06 129 Antigone 4.35 ± 2.14 69 Hesperia 4.33 ± 1.11 709 Fringilla 4.12 ± 1.98 89 Julia 4.01 ± 1.61 675 Ludmilla 3.99 ± 1.94 201 Penelope 3.99 ± 1.97 455 Bruchsalia 3.93 ± 1.29 354 Eleonora 3.93 ± 1.84

Among the D-rank densities, 16 asteroids have nominal bulk densities higher than 16 Psyche’s:

### Rank "D" Asteroid Densities (> 16 Psyche)

 250 Bettina 7.84 ± 5.42 138 Tolosa 7.69 ± 4.39 360 Carlova 6.62 ± 4.51 388 Charybdis 5.80 ± 3.66 43 Ariadne 5.54 ± 2.84 536 Merapi 5.39 ± 4.77 172 Baucis 5.34 ± 3.31 420 Bertholda 4.94 ± 4.44 103 Hera 4.78 ± 2.87 491 Carina 4.58 ± 3.11 683 Lanzia 4.49 ± 2.69 849 Ara 4.29 ± 2.18 506 Marion 4.16 ± 2.29 363 Padua 4.10 ± 2.25 705 Erminia 4.02 ± 2.39 786 Bredichina 3.91 ± 2.28

Among the E-rank densities, 7 asteroids have nominal bulk densities higher than 16 Psyche’s:

### Rank "E" Asteroid Densities (> 16 Psyche)

 2004 PB108 6.74 ± 7.23 1013 Tombecka 6.39 ± 53.43 306 Unitas 6.23 ± 6.77 132 Aethra 5.09 ± 7.72 445 Edna 4.60 ± 4.91 147 Protogeneia 4.18 ± 5.03 769 Tatjana 4.09 ± 4.38

Among the X-rank densities, 14 asteroids have nominal bulk densities higher than 16 Psyche’s:

### Rank "X" Asteroid Densities (> 16 Psyche)

 1686 De Sitter 430.61 ± 213.19 33 Polyhymnia 75.32 ± 9.72 1428 Mombasa 43.03 ± 14.78 152 Atala 42.29 ± 10.80 949 Hel 12.31 ± 5.14 582 Olympia 9.98 ± 27.31 61 Danae 9.74 ± 9.45 665 Sabine 9.05 ± 5.19 217 Eudora 8.94 ± 0.64 204 Kallisto 8.89 ± 26.79 234 Barbara 8.89 ± 29.30 202 Chryseis 8.66 ± 1.63 126 Velleda 8.64 ± 106.21 67 Asia 8.59 ± 1.23

Obviously, most—if not all—of the asteroids listed above will eventually be found to have bulk densities less than that of 16 Psyche as more accurate masses and volumes are determined. Presently, only the following asteroids have minimum bulk densities greater than that of 16 Psyche, assuming the mean error listed is correct:

### Asteroid Densities > 16 Psyche (within error)

 1686 De Sitter 430.61 ± 213.19 33 Polyhymnia 75.32 ± 9.72 1428 Mombasa 43.03 ± 14.78 152 Atala 42.29 ± 10.80 949 Hel 12.31 ± 5.14 217 Eudora 8.94 ± 0.64 202 Chryseis 8.66 ± 1.63 67 Asia 8.59 ± 1.23

LaForge, Price, and Rafelski choose 33 Polyhymnia as the current best candidate to search for superheavy elements. Even a small amount of superheavy elements (especially in the alpha matter state) could significantly raise the bulk density of the asteroid as a whole. Kretlow lists the mass of 33 Polyhymnia as (6.20 ± 0.74) × 1018 kg and its volume-equivalent diameter as 54.0 ± 0.9 km, giving a bulk density around 75 g/cm3.

This finding is not without controversy, however. See the following discussion:

https://groups.io/g/mpml/topic/33_polyhymnia/101917502

References
Kretlow, M. Size, Mass and Density of Asteroids (SiMDA) – A Web Based Archive and Data Service” (2020). https://astro.kretlow.de/?SiMDA

LaForge, E., Price, W. & Rafelski, J. Superheavy elements and ultradense matter. Eur. Phys. J. Plus 138, 812 (2023). https://arxiv.org/abs/2306.11989
https://doi.org/10.1140/epjp/s13360-023-04454-8