<p>The discussion in that answer is slightly misleading. Here's the current picture, taking into account the <a href="http://adsabs.harvard.edu/abs/2019Natur.569...85B" rel="noreferrer"><em>Nature</em> paper by Bartos &amp; Marka referenced there</a>.</p>

<ol>
<li><p>Elements heavier than iron up through rubidium (atomic number 37) are produced by the <a href="https://en.wikipedia.org/wiki/R-process" rel="noreferrer">r-process</a> in supernovae.</p></li>
<li><p>Elements heaver than rubidium are produced by a combination of the <a href="https://en.wikipedia.org/wiki/S-process" rel="noreferrer">s-process</a> in the <a href="https://en.wikipedia.org/wiki/Asymptotic_giant_branch" rel="noreferrer">asymptotic giant branch stage</a> of intermediate-mass stars (i.e., masses of 2-10 solar masses) <em>and</em> the r-process in neutron-star mergers.[1] </p></li>
<li><p>The argument in the <em>Nature</em> paper is that when the solar system formed, a significant fraction of actinide metals <em>with short half-lives</em> (e.g., isotopes of curium and plutonium, with half lives <span class="math-container">$&lt; 100$</span> million years) came from one recent, nearby neutron-star merger. (These are the "fresh" r-process elements.)</p></li>
<li><p>Stable heavy elements produced by neutron-star mergers would have come from the cumulative contributions of hundreds (possibly a few thousand) NS mergers over the history of the Milky Way, mixed over hundreds of millions or billions of years into the Galaxy's interstellar gas (these are the "stale" r-process elements).</p></li>
<li><p>Unstable heavy elements with <em>long</em> half-lives -- e.g., U-238 (4.5 billion years) and Th-232 (14 billion years) -- would be mostly in the "stale" category, and so would <em>not</em> be significantly affected by the presence of said recent, nearby NS merger. In fact, the <em>Nature</em> paper estimates that their hypothesized nearby NS merger would account for only 0.3% of the solar system's initial Th-232. Even U-235, with a half-life of 700 million years, would probably only be moderately affected by that one NS merger.</p></li>
</ol>

<p>In general, then, the presence or absence of metals from a single nearby NS merger would have made very little difference to the formation of the solar system or to the evolution of life on Earth.</p>

<p>[1] See <a href="https://en.wikipedia.org/wiki/S-process#/media/File:Nucleosynthesis_periodic_table.svg" rel="noreferrer">this figure</a> for an approximate breakdown by element -- note that the "dying low-mass stars" label in the figure refers to the AGB stage of what I call intermediate-mass stars, which are "low mass" only in comparison to stars with masses <span class="math-container">$&gt; 10$</span> times that of the Sun.</p>

CC BY-SA 4.0
2019-05-23T12:56:56.613Z
I guess low mass short half-life isotopes like Al-26 came from a nearby collision of regular stars.
PM 2Ring
CC BY-SA 4.0
2019-05-23T13:19:24.707Z
@PM2Ring -- I believe Al-26 is supposed to be produced by core-collapse supernovae (which are a lot more common than neutron-star collisions).
Peter Erwin
CC BY-SA 4.0
2019-05-23T14:18:35.090Z
Ok, that's what Wikipedia says. OTOH, https://www.eso.org/public/australia/news/eso1826/ says "observations using ALMA find radioactive isotope aluminium-26 from the remnant CK Vulpeculae", which was produced by a collision of two relatively low mass stars, one being a red giant with a mass in the range of 0.8 to 2.5 $M_\odot$.
PM 2Ring
CC BY-SA 4.0
2019-05-23T15:36:20.283Z
That press release also says, "the team have concluded that the production of aluminium-26 by objects similar to CK Vulpeculae is unlikely to be the major source of aluminium-26 in the Milky Way".
Peter Erwin
CC BY-SA 4.0
2019-05-23T15:37:45.350Z
Ah, ok. Somehow I missed that bit.
PM 2Ring
CC BY-SA 4.0
2019-05-23T15:38:34.673Z
For what it's worth, the CK Vul paper says that Al-26 "is thought to be efficiently produced in a variety of stars, including: classical novae with O-Mg-Ne white dwarfs; Wolf-Rayet stars; core-collapse supernovae; and asymptotic-giant-branch (AGB) stars that experienced hot bottom burning". I gather the idea in this case is that the Al-26 wasn't *produced* by the stellar collision, but rather that pre-existing Al-26 inside one or both stars was *dispersed* by the collision.
Peter Erwin
CC BY-SA 4.0
2019-05-23T11:44:57.927Z
2019-05-23T12:53:16.290Z
2019-05-23T12:53:16.290Z
Peter Erwin
<p>In one of the answers to <a href="https://astronomy.stackexchange.com/questions/31962/is-it-plausible-for-a-planet-that-is-positioned-in-the-habitable-area-of-a-solar">this question</a> @MartinKochanski made the interesting point that the abundance of elements heavier than iron (r-process elements) in the solar system is probably due to a fairly recent and close (at the time) neutron star merger -- a relatively rare event on a galactic scale.  This means the early solar system was enriched with "fresh" r-process elements, as compared to the "stale" r-process elements that would be typical. For instance the early solar system is conjectured to have been rich in uranium and thorium compared to a "typical" system.</p>

<p>So my question is what differences might this have made to the formation and evolution of the solar system? Would it have had any bearing on the origins of life on Earth?</p>

CC BY-SA 4.0
2019-05-23T11:38:31.187Z
+1, but I’m wondering if your last paragraph is perhaps framed in the wrong direction. Are you asking what the evolution of the solar system would have been like (and the prospects for life on Earth) if we *hadn’t* had such a “high” level of fresh r-process elements?
Chappo Hasn't Forgotten
CC BY-SA 4.0
2019-05-23T11:44:01.963Z
@chappo yes, if you like
Steve Linton
<solar-system><solar-system-evolution>
How much difference did the supply of "fresh" r-process elements make to the Solar System.?
Steve Linton
# How much difference did the supply of "fresh" r-process elements make to the Solar System.?

(Asked by: username_0 on 2019-05-23)

In one of the answers to [this question](https://astronomy.stackexchange.com/questions/31962/is-it-plausible-for-a-planet-that-is-positioned-in-the-habitable-area-of-a-solar) @MartinKochanski made the interesting point that the abundance of elements heavier than iron (r-process elements) in the solar system is probably due to a fairly recent and close (at the time) neutron star merger -- a relatively rare event on a galactic scale. This means the early solar system was enriched with "fresh" r-process elements, as compared to the "stale" r-process elements that would be typical. For instance the early solar system is conjectured to have been rich in uranium and thorium compared to a "typical" system.

So my question is what differences might this have made to the formation and evolution of the solar system? Would it have had any bearing on the origins of life on Earth?

**Tags:** solar-system, solar-system-evolution

> **Comments:**
> **username_1**: +1, but I’m wondering if your last paragraph is perhaps framed in the wrong direction. Are you asking what the evolution of the solar system would have been like (and the prospects for life on Earth) if we *hadn’t* had such a “high” level of fresh r-process elements?  
> **username_0**: @username_1 yes, if you like  

---

## 1 answers

### Answer by username_2 on 2019-05-23. Score: 6 | Accepted answer

The discussion in that answer is slightly misleading. Here's the current picture, taking into account the [*Nature* paper by Bartos & Marka referenced there](http://adsabs.harvard.edu/abs/2019Natur.569...85B).

1. Elements heavier than iron up through rubidium (atomic number 37) are produced by the [r-process](https://en.wikipedia.org/wiki/R-process) in supernovae.
2. Elements heaver than rubidium are produced by a combination of the [s-process](https://en.wikipedia.org/wiki/S-process) in the [asymptotic giant branch stage](https://en.wikipedia.org/wiki/Asymptotic_giant_branch) of intermediate-mass stars (i.e., masses of 2-10 solar masses) *and* the r-process in neutron-star mergers.[1]
3. The argument in the *Nature* paper is that when the solar system formed, a significant fraction of actinide metals *with short half-lives* (e.g., isotopes of curium and plutonium, with half lives $< 100$ million years) came from one recent, nearby neutron-star merger. (These are the "fresh" r-process elements.)
4. Stable heavy elements produced by neutron-star mergers would have come from the cumulative contributions of hundreds (possibly a few thousand) NS mergers over the history of the Milky Way, mixed over hundreds of millions or billions of years into the Galaxy's interstellar gas (these are the "stale" r-process elements).
5. Unstable heavy elements with *long* half-lives -- e.g., U-238 (4.5 billion years) and Th-232 (14 billion years) -- would be mostly in the "stale" category, and so would *not* be significantly affected by the presence of said recent, nearby NS merger. In fact, the *Nature* paper estimates that their hypothesized nearby NS merger would account for only 0.3% of the solar system's initial Th-232. Even U-235, with a half-life of 700 million years, would probably only be moderately affected by that one NS merger.

In general, then, the presence or absence of metals from a single nearby NS merger would have made very little difference to the formation of the solar system or to the evolution of life on Earth.

[1] See [this figure](https://en.wikipedia.org/wiki/S-process#/media/File:Nucleosynthesis_periodic_table.svg) for an approximate breakdown by element -- note that the "dying low-mass stars" label in the figure refers to the AGB stage of what I call intermediate-mass stars, which are "low mass" only in comparison to stars with masses $> 10$ times that of the Sun.

> **Comments:**
> **username_3**: I guess low mass short half-life isotopes like Al-26 came from a nearby collision of regular stars.  
> **username_2**: @username_3 -- I believe Al-26 is supposed to be produced by core-collapse supernovae (which are a lot more common than neutron-star collisions).  
> **username_3**: Ok, that's what Wikipedia says. OTOH, https://www.eso.org/public/australia/news/eso1826/ says "observations using ALMA find radioactive isotope aluminium-26 from the remnant CK Vulpeculae", which was produced by a collision of two relatively low mass stars, one being a red giant with a mass in the range of 0.8 to 2.5 $M_\odot$.  
> **username_2**: That press release also says, "the team have concluded that the production of aluminium-26 by objects similar to CK Vulpeculae is unlikely to be the major source of aluminium-26 in the Milky Way".  
> **username_3**: Ah, ok. Somehow I missed that bit.  
> **username_2**: For what it's worth, the CK Vul paper says that Al-26 "is thought to be efficiently produced in a variety of stars, including: classical novae with O-Mg-Ne white dwarfs; Wolf-Rayet stars; core-collapse supernovae; and asymptotic-giant-branch (AGB) stars that experienced hot bottom burning". I gather the idea in this case is that the Al-26 wasn't *produced* by the stellar collision, but rather that pre-existing Al-26 inside one or both stars was *dispersed* by the collision.  

---

