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 ...
Eric Jensen's user avatar
  • 4,864
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 ...
Connor Garcia's user avatar
  • 16.3k
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 ...
Connor Garcia's user avatar
  • 16.3k
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 ...
James K's user avatar
  • 122k
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 ...
David Hammen's user avatar
27 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 ...
David Hammen's user avatar
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. ...
James K's user avatar
  • 122k
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 ...
User123's user avatar
  • 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 ...
M. A. Golding's user avatar
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 ...
Steve Linton's user avatar
  • 10.3k
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 ...
David Hammen's user avatar
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, ...
called2voyage's user avatar
  • 6,322
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 ...
David Hammen's user avatar
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 ...
David Hammen's user avatar
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 ...
James K's user avatar
  • 122k
15 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 ...
James K's user avatar
  • 122k
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 ...
HDE 226868's user avatar
  • 36.6k
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 ...
Connor Garcia's user avatar
  • 16.3k
13 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 ...
David Hammen's user avatar
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 ...
Christopher James Huff's user avatar
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 ...
Luaan's user avatar
  • 498
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 ...
James K's user avatar
  • 122k
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 ...
Martin Kochanski's user avatar
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 ...
Sten's user avatar
  • 4,644
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 ...
ProfRob's user avatar
  • 152k
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}}...
David Hammen's user avatar
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 ...
James K's user avatar
  • 122k
8 votes
Accepted

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

Yes: It has a companion planet or an excessively large moon, with the two bodies orbiting their common center of mass (much like the Earth and the Moon). They could be tidally-locked to each other, ...
PMar's user avatar
  • 112
8 votes
Accepted

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 ...
James K's user avatar
  • 122k

Only top scored, non community-wiki answers of a minimum length are eligible