43
votes
Why is Uranus called a "green planet"?
I think your issue is linguistic not astronomical. The way a language cuts up the space of colours into discrete names is varies strongly from one language to another, and even from one dialect to ...
- 115k
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 ...
- 14.9k
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 ...
- 115k
36
votes
Accepted
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 ...
- 33.4k
32
votes
Accepted
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 ...
- 33.4k
30
votes
Accepted
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 ...
- 1,732
30
votes
Accepted
why is it impossible to infer the surface temperature of Venus by spectroscopy observation from earth？
The important difference is that the word "surface" has a different meaning depending on whether we're talking about the Sun or Venus.
When we say "the surface of the Sun," we ...
- 418
29
votes
Accepted
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 $...
- 146k
22
votes
Accepted
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 ...
- 36k
21
votes
Accepted
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 ...
- 115k
18
votes
why is it impossible to infer the surface temperature of Venus by spectroscopy observation from earth？
I think the problem is that spectroscopy at visible and infrared wavelengths simply can't penetrate the thick atmosphere of Venus. Thus the information comes from much higher in the atmosphere and not ...
- 146k
17
votes
Why is Uranus called a "green planet"?
This answer looks into why Uranus is "green" or at least greener compared with Neptune's blue.
Both planets have similar atmospheric compositions and would ordinarily be expected to show ...
- 1,055
14
votes
Accepted
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 ...
- 14.9k
14
votes
Accepted
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 ...
- 1,051
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, ...
- 7,411
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/...
- 23.9k
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 ...
- 2,776
11
votes
Accepted
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 ...
- 115k
11
votes
How does the Earth not lose its atmosphere to 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. ...
- 211
11
votes
Accepted
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 ...
- 31.4k
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 ...
- 146k
11
votes
Accepted
Is there a formula for calculating surface temperature of a rocky world based on atmosphere and solar input?
Guillot et al. 2010 give a comparatively simple solution (their Eqn. 27) for a double-gray purely radiative atmosphere. It reproduces the equilibrium temperature in the optically thin limit.
Robinson &...
- 9,757
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 ...
- 115k
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 ...
- 23.9k
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 ...
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). ...
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 ...
- 23.9k
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 ...
- 18.1k
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 ...
- 18.1k
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