42 votes
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Can a tectonically inactive planet retain a long-term atmosphere?

Yes, a tectonically inactive planet can retain a long-term atmosphere. You make the connection that a lack of plate tectonics on a planet indicates a "dead" core and thus said planet has no ...
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39 votes

Can a planet with no atmosphere be orbited at extremely low altitudes?

Yes, but. Firstly the 400km orbits of the ISS are already extremely low, in comparison to the 6400km radius of the Earth. See https://what-if.xkcd.com/58/ for pictures of orbits. So if you rephrase ...
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  • 87.6k
36 votes
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Why is there so little nitrogen in the Martian and Venusian atmospheres?

Nitrogen, with a molecular mass of 28 atomic mass units, is too light to have remained in Mars's atmosphere. Carbon dioxide, with a molecular mass of 44 amu, could (and does) exist on Mars, but it is ...
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28 votes
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Why do gas giants have clearly delineated surfaces, whereas the Earth's atmosphere fades into space?

In an isothermal atmosphere, the exponential scale height of the atmosphere is $$ h \sim \frac{k_\mathrm B T}{\mu g},$$ where $g$ is the gravitational field, $\mu$ is the mean mass of a particle and $...
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  • 114k
25 votes
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How do we get to know the total mass of an atmosphere?

There is a simple$^*$ way to know the total mass of the atmosphere: measuring the pressure it exerts on the surface, which necessarily integrate all of the atmosphere above ground level. If you take ...
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22 votes
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Why doesn't Titan have a carbon dioxide atmosphere?

The chemistry of Titan's atmosphere is complex, with reactions occurring between carbon dioxide, oxygen, carbon monoxide, hydroxl, and other compounds. This means that carbon dioxide production and ...
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21 votes
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Why did Venus not lose its atmosphere without a magnetic field?

There is an interesting article on the magnetosphere of Venus on the ESA Science and Technology site. You can find the article here and it will probably answer your question. The article states, like ...
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  • 765
21 votes
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Is Earth unique in its fairly clear atmosphere?

Our atmosphere is only transparent to visible light, In most other wavelengths, some or all of the light is absorbed Image from Wikipedia, adapted from image by NASA Our eyes have evolved to take ...
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  • 87.6k
14 votes
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What does forward modeling mean?

There are different ways to model something. From what you're asking, there are two main types of modeling: forward modeling and inverse modeling. Forward Modeling In this type of modeling, you have ...
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14 votes
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Do brown dwarfs have stripes?

A number of brown dwarfs have had 'surface maps' created using the light from those stars. In 2013, observations of 2MASS J22282889–4310262, a brown dwarf 35 light years away, were published. These ...
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13 votes
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Why argon instead of another noble gas?

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/...
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13 votes

Why is there so little nitrogen in the Martian and Venusian atmospheres?

3.5% of all atmosphere in Venus still accounts for more partial pressure of nitrogen than on Earth. Venus has ~90bar pressure at the surface, 3.5% of them are ~3.2 bar nitrogen. Earth has only 0.8 bar ...
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  • 1,770
13 votes

Can a planet with no atmosphere be orbited at extremely low altitudes?

An example of a planetary mass object or planemo that is almost airless is the Moon. It does have an atmosphere, but very, very thin. The Moon has an atmosphere so tenuous as to be nearly vacuum, ...
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12 votes

How does Titan maintain its atmosphere?

You are right that it's surprising that Titan, being just a moon, has a thick atmosphere. Usually, the answer includes magnetism: Earth has an atmosphere because the liquid iron in the outer core ...
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  • 656
11 votes
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How does gravity affect pressure under water?

For a liquid, hydrostatic pressure is $\rho g h$ where $\rho$ is density (this is always the same for all water) g is gravitational acceleration and h is depth. The gravitational acceleration on ...
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  • 87.6k
11 votes
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Why do the upper-atmosphere clouds of Venus appear to have that V shape?

This is supplementary to antispinward's excellent answer and provides additional sources and a visualization from the JAXA spacecraft Atasuki. It has been shamelessly borrowed from Would it be ...
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10 votes

Why did Venus not lose its atmosphere without a magnetic field?

There are other ways to lose atmosphere. For example Jean's Escape. If average velocity of a gas molecule exceeds escape velocity, the planet will lose atmosphere. Venus' atmopshere is mostly $CO_2$ ...
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  • 1,332
10 votes
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At what depth on Mars would the atmosphere have equal pressure of that on Earth?

Nasa has a atmospheric model of mars: $$0.699 *e^{-0.00009 h} $$ A naive application of this model, solving for a pressure of 101 kPa, gives a depth of -55 km. The Armstrong limit depth (at which ...
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10 votes

How can clouds form in Jupiter's atmosphere of Hydrogen and Helium?

First, it's a great question. Mostly the answer is straight forward, so I can answer it, but it's still a great question. and I'll add a similar, but slightly more detailed picture to the one you ...
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10 votes

What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?

Torricelli, the inventor of the Mercury Barometer (~1644) argued that the height of the column of mercury was governed by atmospheric pressure (the "weight of the atmosphere" as he would have put it). ...
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10 votes

How do we get to know the total mass of an atmosphere?

Suppose the atmosphere has a density that decays exponentially with height. e.g. $$ \rho = \rho_0 \exp[-h/h_0]\ ,$$ where $\rho_0$ is the density at some surface and $h_0$ is a characteristic height ...
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  • 114k
9 votes

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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9 votes
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Why are Saturn bands much fainter than Jupiter's?

I'll give this one a shot. Correction is welcome. Upper atmosphere temperature. It's not just elements that give a planet color, but the temperature of elements. When we examine what a planet ...
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9 votes
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What is the underwater temperature of Europa?

No, nothing on Europa could possibly be photosynthesizing as we know it. Jupiter doesn't emit light, and what it reflects from the sun is not enough, plus there's no significant amount of carbon ...
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8 votes
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In the end what is the ultimate matter/element in the universe, due to fusion process in stars?

If we don't wait for too long, where we don't know for sure, whether protons or atomic nuclei stay stable forever, there won't be just one single element. The most abundant element in the universe ...
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8 votes
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Why is twilight longer in summer than winter and shortest at the equinox

See this diagram, Now, the slant appears to be the same for June and December Solstices, doesn't it? First thing, it is a wrong conception that Sun travels more "perpendicular" to horizon in the ...
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8 votes

Mountains are higher than the atmosphere?

This is a bit of a gray area, as an atmosphere doesn't have a clear boundary. That being said, Olympus Mons on Mars is so tall, the atmospheric pressure on top of it is only 12% the average pressure ...
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8 votes

Is Earth unique in its fairly clear atmosphere?

No, the clarity of the Earth's atmosphere cannot be considered unique. We don't have to speculate about exoplanets. You could argue the answer is no, because both the Moon and Mercury have (very, ...
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  • 114k
8 votes
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How do solar winds affect the atmospheric composition and density of planets?

Do these particles contribute to the planets' atmospheres? Or do they do more harm than good? (define: good = contribute). That depends on the size (mass/escape velocity) of the planet. See ...
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