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60 votes
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Is oxygen really the most abundant element on the surface of the Moon?

Yes, that's correct; it's also true for the Earth's crust. The reason is that "rocks" are typically made up of components containing combinations of silicon or one or more metals (e.g., ...
Peter Erwin's user avatar
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27 votes

What are the chances of finding an element in the outer solar system that otherwise can't be found on earth?

New elements might be found in the crusts of neutron stars, new isotopes of known elements certainly will be. But they can't be brought to the Solar System. Under conditions of extreme pressure and ...
ProfRob's user avatar
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25 votes

Why is there a zig-zag in elemental abundances?

TL;DR: Nature favors packing nucleons in pairs of anti-parallel spins. (electrons as well!) The zig-zag is a nucleosynthesis artifact. H, He and Li are "primordial" (made out of the abundant ...
fraxinus's user avatar
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23 votes

Is oxygen really the most abundant element on the surface of the Moon?

Note this fact is unsurprising. Oxygen is the third most abundant element in the solar system (by mass and by number) after hydrogen and helium. Planets/moons with the size and escape velocities of ...
ProfRob's user avatar
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23 votes

What are the chances of finding an element in the outer solar system that otherwise can't be found on earth?

This question is probably better suited to Worldbuilding SE, but here are some suggestions. Some element from a superheavy Island of Stability. There once were claims for the natural occurrence of ...
David Bailey's user avatar
14 votes
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Why do we want to normalize the solar abundance of elements to Si?

The abundances for many elements are judged or estimated from rocky material. i.e. Material that often contains silicon, but not that much hydrogen, or the hydrogen has been heavily modified. For ...
ProfRob's user avatar
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12 votes
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Within the Milky Way, how much helium is made each second?

I think this is really hard for the Milky Way because we are in it and have no accurate evaluation of how many stars it contains or its overall luminosity. Some sort of answer would be to assume that ...
ProfRob's user avatar
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11 votes

What is the composition of the Solar Wind?

We have very good data on the heavy metals in the solar wind from the Charge, Element, Isotope Analysis System (CELIAS) on SOHO: Some of these elements were previously known; others were observed for ...
HDE 226868's user avatar
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11 votes

What are the chances of finding an element in the outer solar system that otherwise can't be found on earth?

New elements on the outer Solar System? Not so much. But different types of molecules are commonplace on lots of places other than Earth. Just a few examples: Perchlorates on Mars On Earth, we jump ...
Oscar Lanzi's user avatar
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10 votes
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How are heavier elements such as carbon and silicon distributed within the Sun?

A page from the Institute for Advanced Study links to data from various modifications to the Standard Solar Model. The newest given there is from Bahcall1 et al. (2005), which I'll use as an example. ...
HDE 226868's user avatar
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10 votes
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Is the Sun "chemically peculiar", and if not why is HD 222925?

No, the Sun is not "chemically peculiar". (I'm not sure most astronomers would call HD 222925 chemically peculiar, either, certainly not in any of the ways discussed on the Wikipedia page.) ...
Peter Erwin's user avatar
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9 votes

Why is there a zig-zag in elemental abundances?

A very informative, short, You Tube video discusses this - see the 4:20 mark. Apart from hydrogen, helium, lithium and beryllium, all the elements were formed as the products of fusion in stars. If ...
Fred's user avatar
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6 votes

Using the "Lithium test" to distinguish low-mass stars and brown dwarfs

The "lithium test" for a brown dwarf involves measuring two things - the lithium content and the spectral type (a proxy for surface temperature) or luminosity. But you may also need to know (...
ProfRob's user avatar
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6 votes

What are the chances of finding an element in the outer solar system that otherwise can't be found on earth?

The question is whether you look for element or for isotope or molecule or material. In both former cases, the answer is "you can find any naturally occurring element or isotope on Earth". ...
planetmaker's user avatar
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5 votes
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Why are certain elements so common?

This is a very broad question: its answer involves the full details of stellar evolution, Galactic chemical evolution and nuclear physics. I'll limit myself to the following observations: The ...
ProfRob's user avatar
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5 votes
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Why are O III lines so prominent in the spectra of emission nebulae when the amount of oxygen relative to hydrogen is a million times smaller?

This is an excellent question. Think about the way in which emission happens. $\text{H}\alpha$ emission happens when an electron makes a transition from the third energy level to the second, emitting ...
HDE 226868's user avatar
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5 votes
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What is the elemental composition of the Sun overall, rather than at the photosphere?

Both your estimate and @ProfRob's answer are roughly in the right area. I've done the integration on an older standard solar model, Model S (Christensen-Dalsgaard J., et al., 1996, Sci, 272, 1286) and ...
Warrick's user avatar
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4 votes
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How early could life supporting planets been formed?

You can get relatively high metallicity rather quickly in parts of the early universe -- especially some globular clusters and the centers of massive galaxies -- because star formation rates in those ...
Peter Erwin's user avatar
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4 votes

Is the composition of stars in future made of more and more heavy elements?

The initial stars were made of hydrogen and helium. These enriched the interstellar medium (ISM) with some chemical elements right across the periodic table, when massive primordial stars ended their ...
ProfRob's user avatar
  • 155k
4 votes

What is the elemental composition of the Sun overall, rather than at the photosphere?

I think you are right. Metals are not produced in the Sun (though lithium is destroyed), so will be distributed throughout. To first order you can ignore radiative diffusion and chemical ...
ProfRob's user avatar
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4 votes

Stellar classification spectral lines: chemical abundance vs temperature

Both explanations are right. The strength of an absorption line does depend on the abundance of a chemical element in the photosphere. But it also does depend on the temperature of the photosphere. ...
ProfRob's user avatar
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3 votes

Are there any naked-eye visible stars in our Milky Way that are particularly rich in calcium? (I'm just curious)

Stars that are rich in metals tend to be younger stars, and they tend to be richer in all of the elements above Helium. Moreover, you should note that any star is still mostly Hydrogen and Helium. ...
James K's user avatar
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3 votes
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Why is the carbon/oxygen ratio at low metallicities important to study?

I think I can in part answer your questions. The [CII] ($\lambda=158\,\mu m$) and [OIII] ($\lambda=88\,\mu m$) are the most brightest IR emission lines in the local Universe Stacey et al. (1991). The ...
Michele Bianco's user avatar
3 votes
Accepted

Can you recommend a book about big bang nucleosynthesis and chemical abundances?

I highly recommend Nucleosynthesis and Chemical Evolution of Galaxies by Bernard Pagel. It contains the basics of nuclear reactions andstellar evolution, chapters on big bang nucleosynthesis and light ...
ProfRob's user avatar
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3 votes

Difference in stellar abundance numbers

According to Lodders (2003, https://arxiv.org/pdf/1010.2746 ) the relative abundance of helium to hydrogen is $A({\rm He})=10.925$, on a logarithmic scale where the hydrogen number abundance is 12. So ...
ProfRob's user avatar
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3 votes
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How many times can iron be detected for the first time in an exoplanetary atmosphere?

Neither of these, interestingly enough, is the first time iron has been detected in an exoplanetary atmosphere. Other groups (Hoeijmakers et al. 2018, cited by both papers) have detected absorption ...
HDE 226868's user avatar
  • 36.6k
3 votes

What is a "differential chemical abundance"?

If the line emission is optically thin, then the measured line flux is proportional to the abundance $F_{\nu} \sim n$ of a species along the line of sight (if it's only one species). The problem here ...
AtmosphericPrisonEscape's user avatar
3 votes
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Will the detection of colliding neutron stars by LIGO help answer the question of where heavy elements came from?

I just found out the answer to my question from a live press release on You Tube that has been covered by blogs like this: http://news.nationalgeographic.com/2017/10/gravitational-waves-discovered-...
Jack R. Woods's user avatar

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