48 votes
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Why don't the inner moons of Jupiter have tidally-induced volcanism?

It’s because they are much smaller than Io. Tidal forces are differential forces, that is, they result from the difference in gravitational pull on one side of a body compared to the other. When an ...
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47 votes
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A moon in eccentric orbit dipping below Roche limit

Comet Shoemaker-Levy 9 (SL9 for short) is a great example of a moon in a highly eccentric orbit that passes through the Roche limit at periapsis. SL9 was discovered in 1993, but is thought to have ...
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47 votes

If we replaced the Moon with Ceres, how close would Ceres have to orbit to cause the same tides?

Tidal forces generated are proportional to $m/r^3$, where $m$ is the mass of the Earth satellite and $r$ is the semi-major axis (we assume circular orbits for simplicity). The derivation of this ...
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34 votes
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How can Io be tidally heated while it is in tidal lock?

How can Io be tidally heated while it is in tidal lock? It is tidally locked in a mean motion sense of "tidally locked". That Io is in an eccentric orbit rather than a circular orbit means ...
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25 votes

What causes the antipodal bulge?

That is because the moon attracts both the water and the earth. The gravity of the moon reduces with distance (by the inverse square law). So, the moon's gravity is Greatest at the point nearest to ...
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  • 974
23 votes
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How did Mars come to have a 24 hour 39 minute day?

"It's believed that the Earth was rotating about once every 5 hours before the theorized collision with a Mars sized coorbiting object referred to as Theia." Almost. Theia did not have to be co-...
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  • 1,060
22 votes

Why there are no terrestrial planets with a subsurface ocean?

Some hypothesize that the Earth did have a subsurface ocean during the Cryogenian period, which lasted from 720 to 635 million years ago. The Cryogenian saw the two greatest known ice ages in the ...
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22 votes
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If we replaced the Moon with Ceres, how close would Ceres have to orbit to cause the same tides?

As is nicely put on the Wikipedia page about tidal forces, the tidal force is given by $$T=Gm\frac{2r}{d^3}$$ where $T$ is the tidal force (see below), $G=6.67\cdot 10^{-11}\rm\,\frac{m^3}{kg s^2}$ is ...
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  • 2,660
19 votes
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How does the Moon's gravity affect Earth's oceans despite Earth's stronger gravitational pull?

Everything in the universe has a gravitational influence on everything else in the universe. It isn't a question of the strongest gravitational pull winning out and all the others doing nothing. The ...
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  • 9,893
19 votes

How does the Moon's gravity affect Earth's oceans despite Earth's stronger gravitational pull?

The following diagram from the wikipedia article on the tidal force shows the tidal force that results from a moon. Note that the tidal force is directed away from the center of the planet when the ...
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17 votes

Will the Earth ever be tidally locked to the Moon?

As the moon orbits Earth, tidal forces slow down the Earth's rotation by 2 milliseconds per century. Eventually, in tens of billions of years, the Earth and Moon would achieve a double tidal lock, ...
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  • 6,084
17 votes

Why don't the inner moons of Jupiter have tidally-induced volcanism?

There are four moons that are closer to Jupiter than Io with higher eccentricities, yet they don't seem to have any volcanism at their surface. Only one of those innermost moons (Thebe) has an ...
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14 votes
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Why do Earth and moon move apart but binary black holes move closer?

Here is how the tides move the moon away from the Earth: The moon orbits the earth, and there is a difference in gravitational force between the the side of the Earth nearest the moon, and the side ...
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14 votes

Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

Leconte et al. (2015) suggested that the presence of an atmosphere could prevent or at least slow tidal locking. The star should exert two separate torques: one on the atmosphere and one on the solid ...
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14 votes
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Is there any difference between tidal locking and synchronous rotation?

Synchronous rotation is when the orbit of a body has the same period as its spin. If the inclination and obliquity are the same, then the same face of the body will always point towards the ...
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13 votes
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Can you create an orbit in a space station using balls?

As PM 2Ring mentioned, you seem to have a misunderstanding that spin is involved in creating an orbit. What matters for gravitational attraction is the mass of the bodies and their distance, the ...
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13 votes

How can Io be tidally heated while it is in tidal lock?

That sentence on wikipedia continues "from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean moons". There's an orbital resonance (with the other ...
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  • 478
12 votes

Why do Earth and moon move apart but binary black holes move closer?

A belated answer, but neither of the existing answers properly explain this. The proper explanation is simple. In Newtonian mechanics, tidal influences make all objects in retrograde orbits and those ...
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10 votes
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Why there are no terrestrial planets with a subsurface ocean?

The terrestrial planets are Mercury, Venus, Earth and Mars. Mercury and Venus are too hot for liquid water to exist at any level, Mars has lost nearly all its water and Earth has a surface ocean, not ...
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9 votes
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Are there any known objects in a "dual" tidally locked orbit?

Pluto and its largest moon Charon are tidally locked to each other. Charon and Pluto revolve about each other every 6.387 days. The two objects are both gravitationally locked to the other, so each ...
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9 votes
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Tidal influences of planets on the sun

The basic tidal acceleration felt by a test mass near the surface of the Sun, due to a body of mass $m$ at a distance $r$ is given by $$a_{\rm tidal} = 2\frac{Gm R}{r^3},$$ where $R$ is the radius of ...
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9 votes
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How strong are the tides raised by Io on Jupiter relative to the ones raised by the Moon on Earth?

Both expressions are incorrect. The first should be $$\frac{GM_{\text{moon}}}{(R_{\text{moon}}-r_{\text{planet}})^2} - \frac{GM_{\text{moon}}}{{R_{\text{moon}}}^2}\tag{1b}$$ or $$\frac{GM_{\text{moon}}...
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8 votes

What causes the antipodal bulge?

I am probably going to get slammed for this, because it violates everything we were taught about tidal forces, but the antipodal tide is caused by the centrifugal force created by the Earth's rotation ...
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  • 1,351
8 votes
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Why are tides high only on a full moon day?

There are two main gravitational causes of tides: the Moon, and to a lesser extent the Sun. When the moon is full or the moon is new, the Earth, Moon and Sun are roughly aligned, and the Lunar tide ...
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  • 87.6k
8 votes

Do tides occur on planets like Neptune, having water?

There will be tides, but they will be not very large. It's pretty easy to get a good estimate of their size. There are two things that control tides on Earth and both will be present anywhere else: ...
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  • 7,370
8 votes

Is there any difference between tidal locking and synchronous rotation?

Mercury has a 3:2 spin-orbit resonance, that has evolved as a form of tidal lock, but not synchronous rotation (a 1:1 resonance) "Tidal lock" could be used strictly to mean only the 1:1 ...
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8 votes
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If Earth was a moon of Jupiter orbiting at the same distance as Metis (Jupiter's innermost moon), then how much lighter would a 100 kg person feel?

TL; DR Around $8$ kg. You can calculate the tidal force using Newton's law of gravitation, $$F = G\frac{m_1m_2}{r^2}$$ where $G$ is the universal gravitational constant, $m_1$ and $m_2$ are the ...
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  • 8,862
7 votes
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What causes objects to become tidally locked?

Tidal locking occurs because the planet deforms the satellite into an oval, with long axis pointing towards the planet. If the satellite is rotating the long axis will move away from being pointing ...
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  • 87.6k
7 votes

Does the Sun impose back it's tidal forces onto the Earth (such as the Earth's to the Moon)?

Yes - the earth and sun do have tidal forces like the moon and earth. There are two main reasons this is happening. The sun is always losing mass due to nuclear reactions, the sun is always ...
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