# Tag Info

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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., ...
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### 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 ...
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### 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 ...
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### Is any consensus forming on the solution to the "Lithium Problem"?

There is no absolute consensus and nothing proven beyond doubt, but there are favourite explanations. The discrepancy between the predicted big bang nucleosynthetic abundance of Lithium 7 and the ...
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### Why is carbon so rare on the Moon and on Mars?

There is not much doubt that the abundance of carbon in the protosolar nebula was not abnormal. We can tell that by looking at the carbon abundance in the atmosphere of the Sun - it has an abundance ...
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### Why argon instead of another noble gas?

why Argon specifically? Both helium and neon are pretty lightweight, tend to vaporize easily even at low temperatures, and are chemically inert. For all these reasons combined, they tend to not get ...
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### 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 ...
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### 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 ...
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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. ...
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### 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 (...
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### Why is carbon so rare on the Moon and on Mars?

Although carbon is highly abundant in the universe, it is not homogeneously distributed. Some regions of the interstellar medium could be rich in carbon and others rich in silicon or oxygen, ...
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I think it's an interesting question. The trick would be a sustained fission reaction, faster than half life, but slower than a chain reaction. A chain reaction could hardly be considered "star ...
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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 ...
• 113k
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### How are the element abundances calculated for a meteorite in the Hydrogen log10 scale?

Meteorite abundances are referenced to their silicon abundance and then that is bootstrapped onto the hydrogen scale by assuming that the silicon abundance of meteorites is the same as that in the Sun....
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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 ...
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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 ...
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### 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 ...
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### 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 ...
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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 ...
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### 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 ...
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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-...
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### 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 ...
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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 ...

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

Just to add, while I think Rob Jeffries answer covers it. Now is it expected that in future more stars will be made of more heavy elements or are there causes/laws which prohibit stars forming ...
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### How to determine atomic number density of an element in a star based on equivalent width measurements

The measurement of a chemical abundance is not a question of using a simple equation. The simplest it gets is using a "curve of growth", which relates equivalent width to abundance and assumes you ...
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