Are transuranic elements found naturally in stars?

Also, are they found naturally on other planets, like gas giants?


In first generation stars… no (those are stars made out of elemental hydrogen from the big bang)
in second generation stars, yes, but in very very small amounts (those are stars that formed out of the products of supernovae from first generation stars - these would have some “impurities” from across the periodic table, inculduing the actinides

Planets of second generation stars would also have about the same level of “impurities”


Cosmologists, please feel free to correct my aged learning

Full Metal Lotus is about right. I can expand on this a little.

There are three major groups of stars:

Population III - The oldest stars composed mainly of hydrogen, with very small amounts of helium and lithium (I think).

Population II - Stars dating back to about 1 billion years after the BB. Some metals and heavy elements from the early supernovae. Whether any of these are transuranic I don’t know. If there are any the abundances will be very low (See below).

Population I - Third generation stars with relatively high metal contents (compared to the early stars).

The chemical composition of our sun shows that 0.04% by mass are composed of elements heavier than sulphur. Some of these might be transuranic, but the amounts are likely to very low if not unmeasurable. It may be possible to measure them spectroscopically, but I don’t know if anyone has attempted this.

Hopefuly someone will have access to more accurate information soon.

What about metals heavier than plutonium?


BTW: remember that “metal” means “lithium or heavier” in this context.

That is why I said “heavier than plutonium”.


That was in response to Stryfe using the term “metal”, to fill in the blank that another reader might not have known.

Not in significant amounts, owing to the fact that transuranic elements have pretty short half-lives, at the most on the scale of millions of years, in the case of [sup]244[/sup]Pu[/sup], and more generally on the scale of minutes or less. Elements above nickel are formed exclusively via explosive nucleosynthesis in exploding supernovas, which then decay down to lighter elements. [sup]238[/sup]U and [sup]232[/sup]Th are commonly found in the Earth’s crust because they have such extraordinarily long half-lives.

There is actually a large subfield of stellar astronomy associated with measuring the heavy metals composition of stars based upon spectral analysis (most of it in the X ray and gamma ray regions which ground based instruments can’t measure) which permits a very accurate estimate of age based upon the composition and decay rates of various unstable isotopes.


Do you find significant amounts in supernovae themselves? How long do supernovae last anyway?


Thanks for the correction. Sorry to get off track a little, but isn’t there an isotope of some kind that was used to estimate the age of the solar system? Can’t find a reference, but I seem to remember something from some Uni lectures. Don’t think it was transuranic, but it did have a long half life.

A supernova just a large star in the final stages of fusion, going through the neon, oxygen, and silicon burning processes. How long these stages last depends on the mass of the star and its original composition (as well as external effects, like feed from a companion star) but as a general range a star will go through these stages in a few years or months. (Silicon burning will actually only last a few hours.) After this the star matter becomes so dense that it exceeds electron degeneracy pressure and undergoes core collapse, which last spare seconds, basically limited only by propagation speed of the escaping neutrinos and high energy photons pushing the heavier elements outward. The remnant that survives will continue to radiate for thousands or millions of years (or even longer in the case of pulsars, for reasons that are not fully understood) as the planetary nebula expands and eventually blends into the interstellar medium.

The ratio of [sup]60[/sup]Ni (a daughter product of [sup]60[/sup]Fe[/sup]) to stable isotopes of iron gives good estimations as to the age of the material composition of the solar system, and its distribution offers clues about formation. The primary measure of the age of the Sun, however, is the ratio of H to He and a few other spectral lines.


The only natural process capable of forming elements heavier than nickel (usually “heavier than iron” but two isotopes of nickel, marginally heavier than iron, are so near the bottom of the curve of binding energy that they are the real upper limit) is the endothermic reaction at the silicon/iron core of supernovas just as they explode. There’s some evidence in the spectra of supernovas for the presence of transuranic elements, notably californium. But clearly from the presence of lead, gold, mercury, thorium, iridium, etc. in nature, albeit in fairly low proportions, they are in fact created, and almost certainly in supernovas. There’s no reason to believe that the process somehow stops short at what’s metastable; transuranics certainly can reasonably be argued to be formed – but to decay at their normal rapid rates.

Contrary to popular supposition, plutonium and neptunium do occur in nature, but in the most minuscule of trace amounts – the occasional U-238 atom in pitchblende or uraninite absorbing a neutron (from a nearby uranium atom) to become U-239, beta decaying to Neptunium 239 and Plutonium 239 sequentially in short order. Quantities are on the order of a few grams, though, for the entire planetary crust.

Pop III stars are actually presumed to have a fair amount of helium. Most of the helium in the Universe is primordial, that is, formed in the Big Bang. A large proportion of the Universe’s lithium is primordial, too, but it’s not nearly as common as helium, and I think there’s expected to be some trace amount of primordial beryllium.

On the question of dating, uranium-238 (with a half-life of about 4.5 billion years) and thorium-232 (14 billion years) are also useful for dating things on the scale of the Solar System.