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42 votes
Accepted

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 ...
zephyr's user avatar
  • 14.7k
41 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 ...
James K's user avatar
  • 107k
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 ...
David Hammen's user avatar
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32 votes
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Why is Venus's atmospheric pressure 75 times that of earth when carbon dioxide is only 1.5 times heavier than air?

Venus's atmosphere is very dense at the surface because Venus's atmosphere is very massive. The composition is nearly irrelevant. The pressure at Venus's surface is proportional to the mass of Venus's ...
David Hammen's user avatar
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29 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 $...
ProfRob's user avatar
  • 136k
29 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 ...
Jean-Marie Prival's user avatar
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 ...
HDE 226868's user avatar
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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 ...
James K's user avatar
  • 107k
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 ...
zephyr's user avatar
  • 14.7k
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 ...
Dave Gremlin's user avatar
14 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, ...
M. A. Golding's user avatar
13 votes
Accepted

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/...
userLTK's user avatar
  • 23.4k
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 ...
fraxinus's user avatar
  • 2,756
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 ...
James K's user avatar
  • 107k
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 ...
uhoh's user avatar
  • 30.8k
11 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 ...
ProfRob's user avatar
  • 136k
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 $CO_2$ ...
HopDavid's user avatar
  • 1,372
10 votes
Accepted

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 ...
James K's user avatar
  • 107k
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 ...
userLTK's user avatar
  • 23.4k
10 votes
Accepted

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 ...
Nathanael Vetters's user avatar
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). ...
JonesTheAstronomer's user avatar
9 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 ...
Florin Andrei's user avatar
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 ...
Florin Andrei's user avatar
9 votes
Accepted

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 ...
userLTK's user avatar
  • 23.4k
9 votes

Vacuum of space

Your assertion that our atmosphere doesn't escape is wrong. Helium and Hydrogen atoms have a low enough mass that they do have an escape velocity at the temperatures on the edge of our atmosphere. ...
UKMonkey's user avatar
  • 191
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, ...
ProfRob's user avatar
  • 136k
8 votes
Accepted

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 ...
userLTK's user avatar
  • 23.4k
8 votes

What does forward modeling mean?

Forward modeling is the use of a model in order to simulate an outcome. The problem of getting the model to produce data from the input is called the forward problem. The forward model takes certain ...
pablodf76's user avatar
  • 482
8 votes

Helium in terrestrial planet atmospheres?

Do you have any reputable estimates as to how much helium has been out gassed over the last 4 billion years Reputable estimates - no. Bad guesses, maybe. Short answer: only trace amounts. It's ...
userLTK's user avatar
  • 23.4k

Only top scored, non community-wiki answers of a minimum length are eligible