# Tag Info

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The outer parts of Neptune are mostly hydrogen and helium. There are small amounts of other gases such as methane, ammonia and water vapour. However, there is no oxygen at all. If you took some of Neptune's outer layer back to earth and mixed it with our air, it could burn. Even very cold hydrogen can burn (it soon heats up!) This couldn't happen on ...

19

Yes, metals and other elements and molecules can exist in gaseous form under the right conditions of temperature and pressure. A "gas" is simply one of the fundamental states of matter, as in solid, liquid, or gas (and a few other states outside the scope of this question). But as a gas, these substances exist entirely as either individual atoms, individual ...

17

Jupiter does not have a "surface" and nor is there anything but an arbitrary division between interplanetary space and where its atmosphere begins. The crushing pressure is its atmospheric pressure. The deeper into the atmosphere you go, the greater the column of gas that lies above you. It is the weight of this column of gas that is responsible for the ...

13

Doing a bit of reading up on this, I might have an answer, though credit where credit is due, the answer isn't really mine: https://www.reddit.com/r/askscience/comments/3wsy99/why_is_neon_so_rare_on_earth/ When the planets coalesced, it's likely that there was very little ices/gas around the inner planets when they formed and the Earth's atmosphere and ...

9

The scale height of gas in a disk (if it were in equilibrium) is roughly $kT/mg$, where $T$ is the temperature, $g$ is the gravitational field, $m$ the mean mass of agas particle, and $k$ the Boltzmann constant. If we assume most of the mass is in a thin disk, then Gauss's law for gravitation tells us that that $g = 2\pi G \sigma$, where $\sigma$ is the ...

9

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 trapped when planets are formed - and when they do get trapped they leak out easily. Argon is just heavy enough to not escape easily into space, so some ...

7

In astronomy, there is no formal definition of the threshold between gas and dust. Gas can be monoatomic, diatomic, or molecular (or made of photons, in principle). Molecules can be very large, and in principle, dust particles are just very large molecules. I've seen various authors use various definitions, ranging from $\sim100$ to $\sim1000$ atoms. This ...

6

It is only possible to detect gases in transiting Exoplanets. The spectrum of the star is taken when the Exoplanet is not in transit and again when in transit. The differences between the spectrums is due to a small amount of light from the parent star passing through the upper atmosphere of the Exoplanet and being absorbed by gases in the atmosphere. The ...

6

I am not sure what you mean by "thermal" pressure. Jupiter is supported by pressure, just like all objects that are in (approximate) hydrostatic equilibrium. That pressure is provided by your everyday, temperature-dependent Maxwell-Boltzmann ideal gas pressure in the outer parts, but the free electrons in the interior become degenerate and so in these ...

5

Mainzer et al. 2014 characterize the performance of the reactivated NEOWISE. Having run out of cryogenic coolant for the original WISE's 12 and 22 μm bands, it only detects in the 3.4 and 4.6 μm bands. The comet looks red in the false-color infrared image because, relative to the 4.6 μm "W2" band, it emits less in the 3.4 μm "W1" band than stars ...

5

Technically there isn't really a gas-liquid boundary because temperatures are well above the critical point of hydrogen (33K and about 18bar). It's a supercritical fluid. There are important changes at various depths though including the bottom of the circulating winds, the transition to metallic hydrogen and (it now appears) an increasing density of ...

4

Not really my area, but this question is probably related to the planetary migration in circumstellar disks. In this case, the migration is caused by gravitational interactions between the planet and the gas in the disk. There are two explanations for this effect Impulse approximation: consider a parcel of gas in the corrotating frame. If the gas is close ...

4

The "diffuse ionized gas" (DIG) is another term for the phase of the interstellar medium (ISM) usually called the warm ionized medium (WIM). With a temperature of the order $10^4\,\mathrm{K}$, but extenting to lower and higher temperatures, it is hot enough to keep hydrogen ionized, and various metals exist as low-ionization species, such as S II, N II, and ...

4

The clouds of gas and dust that form stars are usually what are called Molecular Clouds and Giant Molecular Clouds (GMCs). The "Molecular" means that most of the atoms are combined into molecules rather than being free atoms. So the hydrogen is mostly H2 and not H. This is really important, since a cloud comprised of molecules can radiate away the heat of ...

4

In short, No. Side detail: Uranus and Neptune consist likely of 20% gas and 80% rock, coming from simple density considerations. They have large inner cores with masses around $\rm 12-14 \; m_{earth}$, and something like $\rm 2-3 \; m_{earth}$ of gas on top of them. Jupiter and Saturn are true gas giants. They both have $\rm 5-20 \; m_{earth}$ of solids ...

4

I may just add to the excellent answer by Robert that interstellar dust particles, very much like cigarette smoke in air, hangs in the interstellar gas and interacts with it both kinematically (is dragged along with it depending on the particle size) and energetically (exchanges heat, which can result in significant cooling of the gas). Dust particles also ...

3

Schindler et al. 1999: Morphology of the Virgo Cluster: Gas versus Galaxies has details for $\beta$ model fits for Virgo and its subclusters.

3

Two techniques immediately spring to mind. For the stars you detect, you can compare their colours and luminosities (Gaia provides photometric colours and distances) with what you expect for a star of that type at that distance. The difference between what you expect and what you observe tells you the reddening and extinction caused by interstellar dust, ...

3

Most of my information is sourced from here: https://apod.nasa.gov/apod/ap990511.html To summarize the source, Bok globules are extremely cold because of their composition -- they're generally just clouds of pre-stellar material which block out all light. This makes the interior of Bok globules "shielded" from interstellar radiation that would otherwise ...

3

They know there's molecular gas because they observed emission from the CO molecule in two of the previously identified (atomic-hydrogen-emitting) gas clouds. From the paper: ... we targeted two objects (hereafter, MW-C1 and MW-C2), highlighted by red boxes in Fig. 1, in the 12CO(2 → 1) emission line at 230.538 GHz with the 12-m Atacama Pathfinder ...

3

Yes, a blueshift here would mean relative to the systemic velocity of the galaxy - which means that, relative to the galaxy, the material is moving at least partly in the direction of Earth. In many cases the outflow may be a pair of jets being ejected in opposite directions out of the nucleus of the galaxy, but we are less likely to see absorption lines ...

2

The light that we receive from space contains a lot of information. Specifically, because of quantum nature of molecules and atoms, theses small species absorb light at very specific wavelengths.Each molecule, atom or ion has a unique set of absorption features. Think of it as the molecule own fingerprint. Hence, if we look at a star or a hot gas, we can ...

2

A gravitating object in a disk creates a wake on the inner edge of its orbit as well on the outer edge of its orbit. The inner wake is the leading wake, while the outer wake is trailing. The torques created by these two wakes would cancel, if the disk had no shear. Yet disks in astrophysical contexts are subject to Keplerian shear - and thus the torques ...

2

Yes. It's certainly feasible to obtain a sample from Jupiter or Saturn, effectively getting gas from the planet, but it's not easy. Massive planets, as a byproduct of their high mass, create large gravity wells which require a lot of fuel to fly close enough to get a sample from and return with it to where it's needed. It would take perhaps a ton of ...

2

Your equations seem correct. Note, you can also get $v$ without having to differentiate, from $E=\gamma mc^2$ and $p=\gamma mv$. Here are some notes on relativistic fluids as related to stellar interiors, including derivation of these equations and their solutions in the non- and ultra-relavistic limits http://www.jb.man.ac.uk/~smao/starHtml/equationState....

2

Weight is a property of mass which you can experience only when on the solid surface of a gravitating body - but not when you are in free fall. Yet even in free fall you retain your mass. Weight is the force the mass exerts on a scale (in the presence of and proportional to the strenght of a gravity field which pushes the mass onto that scale - which ...

1

This is fairly standard bookwork that I am not going to reproduce and you should understand that the lines on your diagram are "fuzzy" in the sense that they mark the loci where you can neither use one approximation or another. So first, the division between a classical gas and a quantum gas (note that all the gases in your plot are ideal - the term ideal ...

1

This particular object I tracked down by comparing the visual with the infrared image of the sky. It was a little tricky because no very bright star appears at that location. But after making comparisons, the star in the original image is HD 155161, also known as V* AH Sco, indicating that it is a variable. In fact, Simbad lists it as a red supergiant at ...

1

There is no hard and fast answer. To be treated as an idea gas (your title question), the particles in your gas should be point-like and they should be non-interacting if you are to use the ideal gas approximation. This means you can take the mean separation ($\sim n^{-1/3}$) and compare that with the size of the particles - it should be much bigger. You ...

1

From this book it seems you can have $\epsilon_{core}$ values raging from ~$30\%$ (a low value) up to $70\%$ (which is more "usual", i.e., requested by theories). More information can be found here and here.

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