53

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 W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III) The radio emissions of the gas giants have well-defined ...


31

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 differently on the rotating planet in the up/downwelling bands. Spots on stars originate due to very different physics. At the temperatures which are prevalent on ...


29

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 altitude. Gas at this altitudes will usually sit deep enough in the gravitational well and be of a near-uniform density and temperature, as to not be influenced by ...


28

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 $T$ is the temperature (in kelvin). i.e. The pressure/density of the atmosphere falls exponentially, with an e-folding height given by the above expression. I ...


19

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 planets and does not make the case for any other planets. The paper doesn't indicate that more planets could exist, but does remark that there are large error bars on ...


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 ...


17

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 Sun won't change the mass of Jupiter. Jupiter will continue to orbit the Sun as it evolves into a red giant. Although the solar wind will be much much more ...


14

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 with what would be found in a cometary nucleus. Those heavy elements are consistent with the comet being at least being partially composed of rock. So Jupiter is ...


13

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 gravity - and Jupiter has 317x Earth mass.


12

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 which produces a stronger Coriolis effect and thus more cells. This is the reason why there are so many different coloured bands on Jupiter (see image below). ...


12

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 planetesimals all have their orbit and spin axes closely aligned with that of the proto-Sun. And while a planetesimal continues to grow by attracting nearby material ...


10

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 outliers a bit above that. They may have significant quantities of hydrogen and helium in their atmospheres, as well as water, in liquid or vapor form. The latter ...


10

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 posted. Source You're right that there is a clear difference between Earth's surface where liquid water can exist, evaporate, make clouds, rain and repeat. ...


9

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. However I differ with some on the answer to the headline title question. We simply do not know whether Jupiter has a rocky core. A popular theory for the formation ...


9

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 not dead) the only gravity comes from the layers that are closer to the centre. So the gravitational pull is always down. If fact, the pressure increases as ...


8

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 preference for some reactions (and resulting compounds) over others. See the references below. The giant planets are all mostly hydrogen and helium, but Uranus and ...


8

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 field acting on everything else. So if, for example, the mass is $M=2\times 10^{27}\rm kg$ (i.e. one Jovian mass), then the gravity field outside the planet ...


7

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 divided the $M \sin i$ by the sine of the measured inclination angle (this is required to avoid using masses that have been estimated using an assumed mass-radius ...


7

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 than if it were closer to the Sun. Eventually, conditions become cold enough for volatiles to condense into grains. These volatiles make it possible for large-...


7

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 occupied in a completely degenerate fermion gas. It is given by (for non-relativistic conditions) $$ E_F = \frac{h^2}{2m}\left(\frac{3}{8\pi}\right)^{2/3} n^{2/3},$$...


7

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 end of the red giant phase the sun will grow more than 1,000 times brighter, and occasionally release pulses of energy reaching 6,000 times current ...


7

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 is that, unless I make the effort to point the apples in the same direction they will point in random directions. The planets were formed independently, (...


7

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 it is wallowing in its own muck. Red giants form when the fusion is no longer taking place in the centre of the star, but instead in a shell around the centre....


7

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 quickly via attracting gas from the surrounding nebula via the core’s gravitational pull, a process called “runaway accretion.” As this summary shows, you can ...


7

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 initial masses of few to tens of percent of their stellar host masses, are relatively cold (T<150K in about 95% or more of their mass, which is outside the ...


6

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 anything in the core would be liquefied, and you could be right. Many models predict that Jupiter's core is rocky, but others predict that it is liquid. Still ...


6

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 that gas giants are really just planets that are massive enough to accrete substantially large atmospheres (because deep down, they have a rocky core - although ...


6

"At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium" (Wikipedia). No significant abundancy of free oxygen to react with. A source of oxygen could easily made burn on Neptune, like a source of hydrogen on Earth. Or take a sample of Neptun's atmosphere. It would easily burn in Earth's atmosphere. Hydrogen oxygen combustion is sufficiently ...


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