53 votes
Accepted

Why does the Sun have different day lengths, but not the gas giants?

It's a matter of how "day" is defined. Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following: The equations for ...
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  • 2,958
33 votes
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Why can't stars be multicolored like gas giants?

Just rotation is the wrong tree to bark up on. You see color variations on gas giants due to differences in composition, i.e. ammonia vs. sulfuric acid clouds on Jupiter, which are transported ...
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29 votes
Accepted

Where do we define the "surface" of a gas planet?

There are two common definitions in use for the surface of gas planets: The 1-bar surface: As pressure increases, the deeper in we go into the gas planet, we will hit a pressure of 1 bar at some ...
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28 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 $...
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  • 115k
19 votes
Accepted

Is there a gas giant orbiting TRAPPIST-1?

No such planet has been announced as having been discovered. The paper only shows evidence for the 7 (really 6 because the 7th can't be officially confirmed with only 1 observation) terrestrial ...
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  • 14.4k
17 votes
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What will happen when landing on Jupiter?

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. ...
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  • 115k
17 votes
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Fate of Jupiter when our sun dies

Jupiter won't evolve into a star, it is not big enough. A body would have to have about 80 times the mass of Jupiter for there to be significant fusion occurring in the core. The end of life of the ...
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  • 88.7k
14 votes

Is Jupiter made entirely out of gas?

Comet Shoemaker–Levy 9 crashed into Jupiter a few years back. As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with abundances consistent ...
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13 votes

Is Jupiter made entirely out of gas?

It doesn't matter if the body is made of gas, rocks, liquid or plasma, the four states of matter all have mass. So, as we know, mass create a gravitational field, and the more mass the stronger the ...
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12 votes
Accepted

Why don't storms on gas giants move to the poles, like hurricanes on Earth do?

The answer is the Coriolis effect, on Earth this produces cells within which storms move, converging towards the cell boundaries as you can see below. Jupiter however spins much faster that the Earth ...
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  • 1,471
12 votes
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Why does each and every planet of our solar system have an unique axial tilt angle?

In the early stages of the formation of the solar system, planetesimals start condensing and everything rotates with angular momentum inherited from the collapsing cloud of gas and dust, so the ...
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  • 9,260
10 votes
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Why don't we have in-between planets?

Super-Earths and Mini-Neptunes are the "in-between" types of exoplanets you're looking for. A sweeping generalization would put most in the range of $\sim1$-$10M_{\oplus}$ (Earth masses), with some ...
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  • 33.8k
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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  • 22.9k
9 votes

Is Jupiter made entirely out of gas?

I concur with everyone else here (of course) that the gravity at the "surface" of Jupiter is entirely determined by the mass contained within that surface. The composition makes no difference. ...
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  • 115k
9 votes
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How is the diameter of a gas giant calculated?

I won't argue with the wikipedia definition (although the NASA Jupiter fact sheet lists it as the radius at 1 bar), but just to point out that the scale height of the atmosphere of Jupiter is given by,...
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  • 115k
9 votes

Can a gas giant be hollow?

Newton's shell theorem proves that inside a gas giant, any layers that are further than you from the centre have a zero gravitational effect on you. So if you are inside a gas giant (and by some magic ...
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  • 88.7k
8 votes
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Why do Uranus and Neptune have more methane than Jupiter and Saturn?

Why does Uranus and Neptune have more methane than Jupiter and Saturn? It's a combination of equations of state (EOS), serpentinization, and mixing (rotational and convective) that favors a ...
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  • 2,517
8 votes
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Gravity of a gaseous planet without a core

The gravitational force on a small mass on the outside of a planet is always the Newtonian $$F_{G}=-\frac{GM}{r^2},$$ so any planet, and particularly, any mass in the universe produces a gravitational ...
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7 votes
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Maximum and minimum gas giant & ice giant densities

Here is a plot I generated in 5 minutes at the site exoplanets.org To construct this I took planets discovered by the transit method and which had a $M \sin i$ measured using radial velocities. I ...
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  • 115k
7 votes

Why do the gas giants in the Solar System have comparatively large orbits compared to the inner planets?

The current explanation for this is something called the frost line (which changes over time). At greater distances from the Sun, a body will receive less and less radiation, and so it will be colder ...
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7 votes
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Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?

The test to see whether degeneracy pressure is going to be significant is to compare $kT$ with the Fermi energy $E_F$ The Fermi energy is the energy level up to which all energy states would be ...
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  • 115k
7 votes

Fate of Jupiter when our sun dies

How will the atmosphere deal with the extreme heat? Using this article as a guide During most of the red giant lifetime, the sun will be only 30 times brighter than its current state. Toward the ...
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  • 22.9k
7 votes

Why does each and every planet of our solar system have an unique axial tilt angle?

You could also ask: Why is each planet a different size. or Why is each planet a different colour. or even Why are the apples in my fruit bowl pointing in different directions. The reason ...
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  • 88.7k
7 votes

Can a dying, swelling, star be rejuvinated by enveloping orbiting gas giants?

Stars turn into Red Giants not because they're running out of fuel, but because they're accumulating material they can't use for fusion (yet) in the core. The star isn't so much dying of starvation as ...
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  • 3,928
7 votes
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What's the critical mass of a rocky planet before its gravity traps enough gas in its atmosphere to start becoming a gassy planet

In most planet formation theories, the boundary is around 10 Earth masses - the build up of the core mass before that is relatively slow, but once it crosses that threshold, the planet gains mass ...
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  • 4,259
7 votes
Accepted

Why do the solar system planets go rock-gas-ice instead of rock-ice-gas when moving away from the sun?

Prelude It is now generally accepted in the planet formation community that planets form as a side-product of the star formation process in so-called protoplanetary discs. Protoplanetary discs have ...
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6 votes
Accepted

Planetary gas giants

Short answer: 1) Yes and no; 2) Yes, there is a supercritical fluid, of hydrogen. Long answer: It's fairly hot deep down in Jupiter; estimates range from 10,000 K to 24,000 K. You would think that ...
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  • 33.8k
6 votes

Why are the natural satellites (moons) of all planets solid?

To answer this, we have to consider the definition of an atmosphere. A popular way of looking at it is to think of an atmosphere as a layer of gases surrounding a body. by that definition, we can say ...
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