48
votes
Accepted
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 ...
- 4,854
47
votes
Accepted
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 ...
- 15.9k
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 ...
- 15.9k
45
votes
Why, since Earth is in free fall towards Sun, are tides affected by Sun's gravity? Why aren't the oceans "weightless" like astronauts?
Yes, the sun does raise tides in just the same way that moon raises tides. It is the difference in gravity that causes the tide. So it is your point 1 and 2. The rotation of the earth causes the ...
- 112k
34
votes
Accepted
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 ...
- 33.3k
26
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 ...
- 33.3k
26
votes
Accepted
Would the Earth and Moon still have tides after the Earth tidally locks to the Moon?
There won't be significant lunar tides. The moon will become fixed at one location above the Earth. The tidal forces that drive the resonant water flows that we call "tides" will be fixed. ...
- 112k
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 ...
- 1,004
23
votes
Accepted
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-...
- 1,070
22
votes
Accepted
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 ...
- 2,879
21
votes
Under which conditions could a planet's massive moon's orbit get closer to the planet?
Yes, it is possible for a moon of a planet to move closer to the planet. If a moon moves close enough to the planet, the moon will eventually reach its Roche limit and shatter or else collide with ...
- 7,233
20
votes
Accepted
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 ...
- 10.1k
20
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 ...
- 33.3k
19
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, ...
- 6,234
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 ...
- 33.3k
16
votes
How would ocean tides work on a tidally-locked planet?
Since the tidal bulge is always in the same place, how would that affect ocean tides?
The concept of tidal bulge is a useful fiction, but fiction nonetheless. For an object in an eccentric orbit, the ...
- 33.3k
15
votes
Accepted
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 ...
- 112k
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 ...
- 35.8k
14
votes
Accepted
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 ...
- 15.9k
13
votes
Accepted
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 ...
13
votes
Accepted
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 ...
- 112k
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 ...
- 498
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 ...
- 33.3k
12
votes
Do tidal forces on moons cause them to emit gravitational waves?
Yes, but the effect is tiny
Tim Rias (in a comment below) calculates it to be $10^{-18}$ Watts. (see a paper about doing a similar calculation for neutron stars)
Bodies that have spherically ...
- 112k
10
votes
Why, since Earth is in free fall towards Sun, are tides affected by Sun's gravity? Why aren't the oceans "weightless" like astronauts?
Yes, it is the minor effects. The Sun’s gravitational pull as such is not what raises tides. What raises tides is, as you suggest, the difference between the Sun’s pull on the near, “midday” side and ...
- 1,349
10
votes
Under which conditions could a planet's massive moon's orbit get closer to the planet?
Under which conditions could a planet's massive moon's orbit get closer to the planet?
I'll give the most straightforward condition:
The tidal interaction tends to accelerate the orbiting moon in the ...
- 4,261
9
votes
Accepted
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 ...
- 140k
9
votes
Accepted
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}}...
- 33.3k
9
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 ...
- 112k
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