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Freshly made plutonium from outer space found on ocean floor (npr.org)
218 points by aerophilic 32 days ago | hide | past | favorite | 78 comments

The scale of time in fields like astrophysics and geology never ceases to amaze me. When I saw freshly made, I thought it was recently created. Turns out it dropped on earth some time in the last 10 million years.

Astronomy is a somewhat weird field in this in other respects. For example, astronomers frequently consider everything that isn't helium or hydrogen a "metal."

They just have a very different take on some things, because their way of looking at the universe is different from how we look at earth.

Even more bizarre is the idea of metallic hydrogen: https://astronomy.com/magazine/ask-astro/2018/06/metallic-hy...

Is this the reason Hydrogen is grouped with the alkali metals on the periodic table?

The most immediate reason is that hydrogen is a group 1 element, meaning its outer (in this case, only) shell contains just a single electron, in its s (spherically symmetric) orbital.

The electronic structure of an element greatly influences its chemical behavior, so elements in the same group tend to be chemically similar. However, hydrogen is a bit of an odd-ball as group 1 elements go.

That strikes me as sbsurd.

Sure, the table has mostly metals but there are a lot of gases.

In Astronomy STP is the exception not the rule. Not much is a gas at 3 kelvin in deep space, the other common option is stars where everything is a plasma. And that’s ignoring white dwarf’s which are mostly electron-degenerate matter, neutron stars which don’t have chemical elements, and black holes which are even stranger.

So, really hydrogen, helium, and everything else is a perfectly reasonable classification as everything else acts the same outside of fusion.

What is the typical state of matter at 3 kelvin in deep space?

Most matter in deep space is individual ions, atoms, or molecules, so has no well-defined phase. Then there's solid dust particles which are made of all sorts of stuff including silicates, organic compounds, and ices of different elements.

Solid. Everything except hydrogen and helium would be in a solid state I think.

That’s not obvious because of the ultra low pressure.

Agreed. I haven’t thought about this stuff since taking gen chem in college, so I went and looked up the phase diagram for Neon, as an example.

At low pressures, it looks like as little as 15 Kelvin is enough to make Neon a gas.

However, deep space is 2.7 Kelvin. Though of course it gets much hotter near stars and even simply being inside a galaxy is enough to hit 10-20 Kelvin.

Does this include the noble gases?

Yes, though noble gases can actually form molecules in space. https://phys.org/news/2013-12-noble-gas-molecules-space.html

The reason astronomers use “metallicity” this way is largely historical: (chemical) metals are not as prevalent in stars as non-metallic elements like carbon and nitrogen, but they are much easier to detect in spectral analysis. So historically the “metallicity” of a star really did refer to the heavy metal content (generally Fe), and considering the physical processes involved it’s not unreasonable to extend this to all non-H/He elements in the star.

I think it would be “absurd” for astronomers to change this because people who aren’t scientists get confused.

The way it was explained to me, astronomers considered them metals because they’re much more rare than H and He. They’re not made in the core of fusing stars. That might seem trivial, but a huge amount of the universe is H/He compared to the rest of the periodic table.

> nicklecompte 1 hour ago | parent [–] | on: Freshly made plutonium from outer space found on o...

The reason astronomers use “metallicity” this way is largely historical: (chemical) metals are not as prevalent in stars as non-metallic elements like carbon and nitrogen, but they are much easier to detect in spectral analysis. So historically the “metallicity” of a star really did refer to the heavy metal content (generally Fe), and considering the physical processes involved it’s not unreasonable to extend this to all non-H/He elements in the star. I think it would be “absurd” for astronomers to change this because people who aren’t scientists get confused.

My bad yo. Please accept my humble apology in not knowing the historical signifacance of something. I'll be doing my masters in 2022/23, biochemistry/microbiology.

I really should have been a bird watcher instead.

Who cares about plant proteins anyway? That's not science at all.

In math, I was taught to always be mindful of the definitions-particularly because they change on context. When studying certain systems different conventions make sense than in other studies. It’s not a judgement call as to what matters absolutely, just what helps the area of study the most. Further, the better flexible you are with working across contexts the better a grasp on the topic you have. (So further, the more ways you can explain a concept or prove a theorem the better you understand the concept.)

Universe is more than 98% hydrogen and helium by mass, with all other being less than 2%.

Maybe metal was not the best word for that, but having word for "all elements except hydrogen and helium" is useful in astronomy

see https://en.wikipedia.org/wiki/Metallicity

Ok, so, maybe they could have, you know, invented a new word? Or picked another one which isn't putting them at odds with the chemists?

Astrophysics was probably a thing before chemistry, so maybe the chemists ought to have picked a different word!

True, but at that time nobody knew about hydrogen and helium in stars.

If it works for them.

Metal vs gas is a poor choice of dichotomy: every element is a gas at the right temperature and pressure.

I would guess that they aren’t distinguishing on the basis of phase state, but rather atomic number.

Astronomers presumably mostly think about matter in the form of a star, in which presumably all the hydrogen and helium would be in some sort of plasma state, and perhaps all the “metals” would be too.

Everything's pretty much a plasma when it's burning at millions of degrees.

Sometimes it is perfectly adequate to model cows as spheres :)

This was my initial thoughts on reading the title as well. First thoughts were "what craft re-entered with that material" went to "oh, cosmologically recent".

Oceanic plates are indeed quite young compared to the continental plates. Oceanic plates are made from heavier materials and subduct below the lighter continental plates, so they only live millions of years while the material making up continental plates lives billions.

I think this is a bit misleading. It's true that the average density of oceanic crust is greater than that of continental crust, making it less buoyant, but also continental crust is way thicker and overall more massive, which is a huge factor in causing oceanic crust to subduct in addition to the buoyancy factor.

I sometimes wonder about interesting fossils and lifeforms we'll never know of, because they were subducted away before we ever had a chance to discover them.

Not just subduction but also erosion. Outside of dedicated digging efforts like deep mines or such, the fossils we find today are the ones close to the surface that are almost eroded and will be gone soon (on geologic timescales).

There is a nice curious droid video on the topic whether a humans if they went extinct tomorrow, wouldn't create a fossil record similar to dinosaurs, simply because we've been on planet earth for a too short period. https://youtu.be/8xDK2LgSeyk

> What we have to remember is that they existed for over 165 million years, 3300 times longer than modern humans have been around and the number of creatures that lived in that time frame alone, not including very small insect-sized ones must be in the trillions. However, only a tiny number of those would have been in the right conditions to be quickly covered in sediment and then fossilized. Then millions of years later they happen to be exposed on the surface at just the right time before they are eroded away for us to find them. The latest estimate is that the total number of modern humans to have ever existed over the 50,000 years we have been around is about 107 billion. But 50,000 years is a very small slice of geological time and all of our 5000 years of recorded history would be a fraction of that, and the last 200 years or so since the industrial revolution, a tiny fraction of that again, maybe a razor-thin sliver of a darkened layer somewhere in the dozens of kilometers of limestone, siltstone, and shale of the future earth's crust. Depending on where we look, there are gaps covering millions of years in the fossil records, if we were to slip into one of those, we too would be lost in time.

I sometimes wonder if life evolved on exoplanets, complete with its own billions of years of fossil record, only to be obliterated when their star reaches the red giant phase.

Or even on earth:


Granted it is just a hypothesis but it is an interesting idea.

Hell, I'm worried about fossils on Venus buried under kilometers of lava. That's actually pretty likely IMO.

Maybe not just lifeforms, civilizations?


What's awe inspiring to me is the fact that life on Earth was single celled for around 3.5 Billion years.

Yeah, I read "10" and my brain automatically filled in "days" until I read "millions of years"

Haha, exactly me!

Astrophysics should invent their own terminology instead of repurposing ours.

The same can (and has) been applied to every profession out there. Daemons, bugs, etc.

Jargon will always exist.

An international scientific seafloor drilling project has drilled over 1500 deep holes in the past half century. The oldest seafloor sediments go to 220 million years. Anything older has been consumed by plate tectonics subduction.

Scientists could count Pu244 in these cores to see how many nearby supernovae there were.

I'm amazed by how we can now detect an element with only several hundreds of atoms in a large chunk of rock.

I had a chemistry practical class just a couple of hours ago in which I asked about the sensitivity of mass spectrometry. I was amazed when I was told that it is sensitive enough to detect individual atoms. Modern analytical techniques really are amazing!

(A book recommendation along these lines: Echoes of Life: What Fossil Molecules Reveal about Earth History, by Susan M. Gaines, Geoffrey Eglinton and Jurgen Rullkotter. If you already know a bit of chemistry, it’s a wonderful introduction to the techniques used to analyse rocks in organic geochemistry.)

Some classes of (mostly older) neutrino-detection experiments detect single radionuclides in many tons of material.

https://en.wikipedia.org/wiki/Homestake_experiment is perhaps the most-famous, but GALLEX and SAGE use a similar approach.


Funny, I had a similar re-adjustment of my idea of what mass spectrometry is capable off a few weeks ago and I remember being totally amazed. That has come a very long way in the last decades.

The tech behind it is fascinating too.

So does this mean we can move plutonium into the natural element category?

Actually plutonium belongs to the so-called primordial elements, which existed in the matter from which the Earth and the rest of the Solar System were made.

Among the primordial element isotopes, a large number are radioactive, including e.g. certain isotopes of the potassium and calcium of our body.

All the radioactive primordial element isotopes have partially decayed since the formation of the Earth, so they can be found now in smaller quantities than in the beginning.

Among the isotopes that can still be found in large quantities, U235 has the smallest half-life and it has decreased about one hundred times.

The next isotopes with the longest half-life, but lower than U235 are plutonium 244 and one isotope of samarium, which have half-time close to one hundred million years.

So these 2 have decreased about 2^45 times. This is a lot so you would not be able to extract a visible quantity of plutonium from a terrestrial rock, but due to the huge number of atoms that existed in the entire Earth, there are still a few atoms of plutonium 244 that have survived from the formation of the Earth.

A few years ago, it was announced that a team succeeded to detect some atoms of primordial plutonium 244 in some rocks, so the primordiality of plutonium can be considered as proven, even if that does not matter from a practical point of view, as there is too little primordial plutonium left, to be useful.

On the other hand, during the formation of the planets, in the early Solar System, plutonium 244 and many other short-lived isotopes, with half-lives of a few million years, could have played a non-negligible role, because they were a significant source of internal heat.

It already was in that category: natural plutonium has previously been found in Oklo, Gabon (https://en.wikipedia.org/wiki/Oklo).

Has anybody detected any actual plutonium there, rather than its fission byproducts? It 'reactor' event itself took place nearly 2 billion years ago, a long time for most of us, including isotopes of plutonium.

That would be interesting, I wonder what other elements will eventually join it. Also, I'm sure they know what they are doing, but it came out of the ocean floor off the coast of Japan, how did they rule out Fukushima? Is the way it was incorporated into the rock make it certain?

They said a Japanese oil exploration company, not that it was near Japan. It could have been anywhere in the pacific, and it was as gifted to researchers in Australia not Japan.

Radionucleotide contamination is an issue though. Apparently carbon dating will be useless to date anything since the 1950s in the future due to carbon isotope emissions from nuclear testing. So they must have taken care to ensure they were examining clean samples.

The Fukushima disaster was only 10 years ago, which is an eye blink in geology.

Pretty sure it was not an isotope producible in an Earth fission reactor. A stable plutonium you could date back to only 10 million years old would be a different animal.

Wikipedia lists it as such, at least.

This may explain why that fish walked out of the water so long ago.

Earth may have been a cooling tank for spent fuel rods used by an alien civilization. Ocean water levels depleted as a result of the cooling process which exposed the land masses. Radiation from the spent rods did radiating things to the surrounding organisms.

IPSO FACTO, we're a result of the super powers bestowed to our watery ancestors.

*edit /fiction ... because some people took this as super serious

Sorry. This is my head canon now and I will spread it far and wide.

As an exercise in creative writing, I think a fun story could be made.

also explains where godzilla comes from

It's honestly amazing that we can identify distinct supernovae that happened millions of years ago and find debris from them.

Considering that we are just self-aware debris from one such supernovae...

Somebody probably just ordered some highly radioactive isotopes from Advanced Space Civilization Amazon, and told them to leave it at the doorstep.

Either that, or the dolphins are done putting up with our shit.

> Somebody probably just ordered some highly radioactive isotopes from Advanced Space Civilization Amazon, and told them to leave it at the doorstep.

You mean United Nuclear, which brokers[1] radio isotopes to the general public? https://unitednuclear.com/index.php?main_page=index&cPath=2_... I don't see any Plutonium for sale, but that's not as interesting or useful as Cesium-137 or Polonium-210. They also sell Uranium ore, and do so directly, not brokered, so they have to be careful to vent Radon from their storage room.

[1] IIRC, the Polonium-210 I received was sent directly from Oak Ridge National Laboratory.

EDIT: The sample was actually sent by Spectrum Techniques (https://www.spectrumtechniques.com/). They must be ORNL adjacent or something.

United Nuclear hasn't changed in decades. I remember buying thermite and other fun mixtures from them for my high school chemistry class experiments 15 or so years ago. Nowadays, you can probably find some of their products much cheaper elsewhere, but they've been selling these cool things for hobbyists for so many years, I like to support them.

And by them, I mean Bob Lazar,.. United Nuclear is his operation. (UFO guy who is likely viewed in a polarized fashion here, I myself am not into the conspiracies)

Wow, that is way more affordable and easier than anything I found twenty years ago when I was looking! (Then again, back then things like this may very well have existed, but discovering them was a huge part of the problem.)

That is massively cool! I wonder if you can get depleted uranium. Would love to grab a cube of it for discussions on density.

Turns out you can! But it's $750 for a one-centimeter cube, because the US government limits commercial sales of DU to 15kg per year.

I thought they used DU as counterweight in some civilian airliners? But maybe the manufacturers have some special license to procure more DU..?

Depleted uranium has indeed been used in airplanes. Some models of 747 have a ton or so of depleted uranium, though I believe this practice was phased out in later models.

It's not just planes though. Some sailboats have been made with DU keels. Usually lead is used, but DU would presumably allow for a smaller (thinner?) keel.

Or a a nearby supernova happened to deposit plutonium and other heavy elements in a fine mist over the planet within the last 10 million years...

I'm somewhat curious if modern human civilization happened to emerge in the last ~10ky simply because all other time periods since modern humans evolved were too unstable to support civilization.

Well it was raining plutonium until now

"The Pacific Ocean is a major repository of plutonium released from atmospheric tests of nuclear weapons. Both global fallout from plutonium released to the stratosphere as well as close-in fallout from the troposphere contributed to the present levels of plutonium in seawater and sediment of the Pacific Ocean." [2001: https://www.sciencedirect.com/science/article/pii/S156948600...]

Now that is fresh. NPR's article fails to tell us how we can tell 'space' Pu from 'test' Pu. It further confounds the issue by calling it 'freshly Made Plutonium From Outer Space' then stating that fresh means 'arrived on Earth within the last 10 million years'. Bad science article.

The isotope in question is plutonium 244 which isn't known to be produced in appreciable quantities by nuclear weapons testing or nuclear reactors.

Could an alien ship have landed and the ship is decayed and plutonium is what remains?

Or it turns out Bertrand Russell's teapot was made of Plutonium and de-orbited.


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