Cosmic-ray bath in a past supernova gives birth to Earth-like planets

Posted by toomuchtodo 22 hours ago

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Comment by phkahler 18 hours ago

Why is it said that it takes a supernova to make elements heavier than iron? You're not going to get iron-iron fusion, but what about proton-iron fusion or similar? Also, we can make reactors here on earth that convert Thorium into Uranium, and we can also make plutonium in a proper reactor. We mustn't confuse reactions useful for power production with reactions for element production right? Why can't a regular star produce some heavy elements?

Comment by bjelkeman-again 18 hours ago

“Elements heavier than iron, up to bismuth, are primarily produced via the s-process (slow neutron capture) in low to medium-mass stars during their later evolutionary stages.

The remaining and heaviest elements (beyond iron and bismuth) are formed through explosive events: core-collapse supernovae generate elements between neon and nickel, while the r-process (rapid neutron capture) in supernovae and, predominantly, neutron star mergers creates elements like uranium and thorium, dispersing them into the interstellar medium for planetary formation.”

From https://www.astronomy.com/science/the-universes-guide-to-cre...

Comment by largbae 18 hours ago

I think you're right that heavier elements can be made, it's just energy negative to do so. But without a nova they would never leave the inside of the star to find their way into a new planet.

Comment by pfdietz 17 hours ago

But they do leave. Stars not large enough to go supernova do still form planetary nebulas when the more gradually lose their outer layers to space. Only the core is left behind to form a white dwarf. This will be the Sun's eventual fate.

Comment by MattPalmer1086 16 hours ago

Wouldn't the heavier elements generally sink to the core and the outer layers be composed of the lighter ones?

Comment by pfdietz 16 hours ago

No, gravitational segregation like that is a very slow process and would be overwhelmed by any convection. In Earth's atmosphere, for example, it doesn't occur until very high altitude (80 km or so) where diffusion is fast enough to overcome mixing.

Comment by pfdietz 11 hours ago

See also "dredge-up".

https://en.wikipedia.org/wiki/Dredge-up

"By definition, during a dredge-up, a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion."

Comment by MattPalmer1086 5 hours ago

That seems to cover elements up to carbon. Not sure heavier elements would be convected?

Comment by pfdietz 3 hours ago

"The third dredge-up brings helium, carbon, and the s-process products to the surface," (emphasis added)

In the early universe, stars had so little in the way of "seeds" for the s-process to act on that the few seeds that were there absorbed large numbers of neutrons, eventually producing weird stars highly enriched in lead (the end point of the s-process). These stars have been detected from lead (and bismuth) in their spectra.

https://en.wikipedia.org/wiki/Lead_star

Comment by pixl97 16 hours ago

I mean it's not hard to do spectrometry on said nebula, and I don't think there is near enough heavier matter detected there.

Comment by pfdietz 16 hours ago

s-process elements (including radioactive ones like technetium) are detected in the spectra of the stars where the process occurs, which means they are right out at the "surface".

Comment by jmyeet 20 hours ago

The Universe coalesced into hydrogen and helium from a quark-gluon plasma soon after the Big Bang. It's kind of staggering the sequence of events that occurred afterwards to bring us here.

As many of us know, the fusion in stars produces elements as heavy as iron. It then takes explosions of those stars to scatter those elements into space, ultimately bringing them into the protoplanetary disc of a new star, such that it can form a planet in the right zone. That star then needs to live long enough and the system needs to be stable enough to produce complex life.

But it gets worse because we obviously have elements heavier than iron. So stars of a sufficient size need to form such that when the stars die they do so in an even more violent fashion. The core needs to collapse into neutronium and the resultant supernova can produce heavier elements. They also come from neutron star mergers.

So all the uranium we have on Earth came from such an event. Because of the nuclear decay chain we can estimate when this uranium was made and IIRC that's somewhere between 80 and 200 million years before the Earth formed.

So this all had to happen sufficiently close to the Sun and that material had to be captured in the Sun's protoplanetary disc. We needed the right combination of elements to form a protective magnetic field and produce enough but not too much heat.

We're going to keep discovering mechanisms like this and the importance of particular isotopes, events and things like how amino acids seem to form relatively easily (given the right elements are present), which itself is a consequence of CNO fusion.

But also why did the Sun form at all? It has to be in a nebula of largely hydrogen and helium and something had to trigger that like the shock wave from a nearby supernova or neutron star or black hole merger.

It's kind of why I think sentient life is incredibly rare.

Comment by zackmorris 18 hours ago

> It's kind of why I think sentient life is incredibly rare.

They just found the building blocks of life in asteroid Bennu:

https://science.nasa.gov/mission/osiris-rex/

https://physicsworld.com/a/components-of-rna-among-lifes-bui...

“So far we have not seen any evidence for a preferred chirality,” (Dan) Glavin says (important for understanding why amino acids on Earth seem to all be left-handed):

https://physicsworld.com/a/asteroid-bennu-contains-the-stuff...

Life is probably abundant everywhere in the universe. Also, evolution seems to spring up everywhere, in any system of sufficiently advanced complexity, regardless of what substrate it operates on. So I think that we'll start seeing life-like emergent behavior in computing, especially quantum computing, in the next 5-10 years.

So the question becomes: what great filter (in the sense of the Drake equation and Fermi's paradox) causes life as we know it to go dark or wipe itself out just after it achieves sentience?

Well, we're finding out the answer right now. Life probably merges with AI and moves into what could be thought of as another dimension. Where time moves, say, a million times faster than our wall clock time, so that it lives out lifetimes in a matter of seconds. Life everywhere that managed to survive probably ascended when it entered the matrix. So that by now, after billions of years since the first life did this and learned all of the answers, we're considered so primitive that Earth is just a zoo for aliens.

Or to rephrase, omnipotent consciousness probably gets bored and drops out of the matrix periodically to experience mortal life in places like Earth. So simulation theory probably isn't real, but divine intervention might be.

Comment by jmyeet 17 hours ago

> Life is probably abundant everywhere in the universe.

I'm not convinced of that. Yes it seems like the building blocks are abundant but there's so many steps beyond that to get to abundant life.

The first life we had in the Archeaen era was dependant on sulfur, which was concentrated around volcanic vents so this already presumes a lot, namely oceans and a geologically active planet. Oxygen leeched a bunch of minerals into the water.

And then came cyanobacteria who no longer needed volcano but had this annoying habit of producing a new waste product: oxygen. This both absolutely killed all the Archeaen life but also cleansed the oceans as ions like iron precipitated into ferric oxide and we can see the layers of these cycles in the rock.

So the Earth needed all these elements and the Sun and Solar System needed to be sufficiently stable for billions of years just to get to this point and there are so many steps beyond this.

I personally believe it's more likely than not that we are the only potentially spacefaring civilization in our entire galaxy.

Comment by estimator7292 13 hours ago

This all hinges on the presupposition that our solar system is unique in its configuration and location in the galaxy.

We haven't surveyed nearly enough other planetary systems to have any real idea if our system is unique. We barely have the ability to even see systems like ours in the first place. There's so little data available that it's not reasonable to draw a conclusion either way.

Comment by BurningFrog 18 hours ago

> But also why did the Sun form at all?

I don't understand the question. There must have been a cloud of gas big and dense enough to provide the mass for the solar system.

Once that exists gravity does the rest, right?

> all the uranium we have on Earth came from such an event

That must mean the Sun also has its fair share of that Uranium? Or maybe more of it, since the heavy elements were more drawn to the center of the solar system?

Comment by pixl97 16 hours ago

>That must mean the Sun also has its fair share of that Uranium?

That's a good question. I would assume the sun captured a whole pile of uranium around the time the earth was forming. And it likely sunk to the core. The question is what happened then. The core area is dense enough to fuse hydrogen into helium, without any calculation I'd guess a lot of this is now in much smaller elements as there are a lot of neutrons to break it apart.

Comment by lawlessone 15 hours ago

going on tangent here but Przybylskis Star might be relevant.

https://en.wikipedia.org/wiki/Przybylski%27s_Star#Chemically...

Comment by marcus_holmes 12 hours ago

great rabbit hole, thanks :)

Comment by mr_toad 14 hours ago

> I don't understand the question. There must have been a cloud of gas big and dense enough to provide the mass for the solar system. Once that exists gravity does the rest, right?

Very large clouds of gas can exist with gravitation attraction balanced by gas pressure. This delicate balance can be disturbed by passing stars, supernovae, galactic mergers and other events.

Comment by kldavis4 19 hours ago

> So this all had to happen sufficiently close to the Sun and that material had to be captured in the Sun's protoplanetary disc. We needed the right combination of elements to form a protective magnetic field and produce enough but not too much heat.

any idea how close? like 10s of light years or what?

Comment by pfdietz 15 hours ago

Not just captured; some of the isotopes were formed in situ by bombardment of the protoplanetary disk by ~GeV range protons formed in the supernova shock by the Fermi mechanism (basically, bounce particles back and forth between moving magnetic mirrors and their energy gradually but exponentially increases.)

Comment by MarkusQ 19 hours ago

According to the article, ~1 parsec, or something like 1-10 light years (further, less effect; closer, you disrupt the protoplanetary disk).

Comment by 01100011 18 hours ago

Surely someone has proposed the existence of a civilization forming from <=iron and making the heavier elements themselves? Seems far fetched but you have quite a bit of time to play with there.

Comment by mcswell 11 hours ago

Obviously this doesn't answer your question, but there are scifi stories about alien civilizations that arise on planets without heavy metals. Usually the plot revolves around their not getting past the stone age.

Comment by jmyeet 10 hours ago

So here's a fun experiment for you. Look at a periodic table and start with Cobalt (the first element after Iron) and look at what its uses are. Wikipedia is fine. And then ask if there are alternatives for that metal. In some cases we won't know but in other cases, the situation would be dire.

The first few include Nickel, Copper and Zinc. Think of all those alloys and direct uses, particularly copper as an electrical conductor. Or all the rare earths for magnets and semiconductors. Or gold or lead even.

Then there's Iodine, which is actually essential for human life. Zinc, selenium and others are used too, possibly others.

The scarier question is what happens when the universe runs out of hydrogen in vast quantities? It will only be around for stars to burn for so long. Most are in the billions of years. A handful are in the trillions. But eventually they will run out too.

Comment by jcims 19 hours ago

>It's kind of why I think sentient life is incredibly rare.

Agreed. The universe is big, but combinatorics are bigger.

I'd be disappointed but ultimately unsurprised if an all-knowing oracle said it has only happened once in the history of the universe. My follow up question, of course, would be whether or not it happened on Earth.

Comment by buu700 19 hours ago

Turns out "God" was just a convenient shorthand for "alien AI", and Genesis was about terraforming and seeding life on Earth.

Comment by jcims 17 hours ago

Eden would be a great name for a sterile yet fertile planet waiting for a visitor.

Comment by moktonar 20 hours ago

And yet, inevitable. That’s why a simulation of the universe would be a secure way of creating AGI in the true sense. All depends on: can you find an algorithm that simulates quantum physics efficiently, or, can you make a quantum computer with sufficiently many qbits?

Comment by lanyard-textile 19 hours ago

... huh, wow.

Talk about sublimity.

Comment by kakacik 19 hours ago

Incredibly rare X maybe a trillion planets(oids) in our galaxy X maybe a trillion galaxies in whole universe may change the outcome a bit.

Of course if speed of light is the hard unavoidable limit it doesnt matter now or for next few trillions of years. Eventually though, if it will keep expanding, the only important thing in universe will be energy. Species that will grok that first may decide to not share and take it all for themselves. Although sustainability of some empire over 10^10^10^10 years and further... its something even my otherwide vivid imagination can't concieve.

Comment by dhosek 19 hours ago

If I was going to design a universe where multiple intelligences would evolve but never interact, this one would meet the requirements quite well.

Comment by mr_mitm 19 hours ago

Not if incredibly rare is something like 10^-30