Alien Anomalies

Eaol · Veteran Member

RE: Tidal locking and the frontiers of Physics

Eaol · Veteran Member

Interesting stuff.

Eaol · Veteran Member

http://en.wikipedia.org/wiki/Tidal_locking

fruitnut1 · Dedicated to the truth

When I was a kid I remember I read about our Moon being locked to the earth because of the interaction with water in its big ocens. That's where the "tidal" part in "tidal locking" came to play.

Ever since lots of other satellites have been discovered also tidally locked to their mother planets.

Well here's the most interesting thing, those planets aren't supposed to have oceans!

So I guess in the future that "tidal" part of this ides will be disappearing without anybody noticing smile

-- Frutty

fruitnut1 · Dedicated to the truth

According to wikipedia

Tidal Locking occurs when the gravitational gradient makes one side of an astronomical body always face another; for example, one side of the Earth's Moon always faces the Earth. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. This synchronous rotation causes one hemisphere constantly to face the partner body. Usually, only the satellite becomes tidally locked around the larger body, but if the difference in mass between the two bodies and their physical separation is small, both may become tidally locked to the other, as is the case between Pluto and Charon. This effect is employed to stabilize some artificial satellites. Also

An estimate of the time for a body to become tidally locked can be obtained using the following formula:

$t_{\textrm{lock}} \approx \frac{w a^6 I Q}{3 G m_p^2 k_2 R^5}$

where

$w\,$ is the initial spin rate (radians per second)
$a\,$ is the semi-major axis of the motion of the satellite around the planet
$I\approx 0.4 m_s R^2$ is the moment of inertia of the satellite.
$Q\,$ is the dissipation function of the satellite.
$G\,$ is the gravitational constant
$m_p\,$ is the mass of the planet
$m_s\,$ is the mass of the satellite
$k_2\,$ is the tidal Love number of the satellite
$R\,$ is the radius of the satellite.

As can be seen, even knowing the size and density of the satellite leaves many parameters that must be estimated (especially w, Q, and mu), so that any calculated locking times obtained are expected to be inaccurate, to even factors of ten.

Further, during the tidal locking phase the orbital radius a may have been significantly different from that observed nowadays due to subsequent tidal acceleration, and the locking time is extremely sensitive to this value. Since the uncertainty is so high, the above formulas can be simplified to give a somewhat less cumbersome one. By assuming that the satellite is spherical, k_2\ll1\,, Q = 100, and it is sensible to guess one revolution every 12 hours in the initial non-locked state (most asteroids have rotational periods between about 2 hours and about 2 days)

-- So this formula is not enough to explain why "tidal locking occurs" as it's parameters are as ambiguous as those of the Drake equation.

When science starts speculating it can't hardly be held as Science anymore.

Source

-- Frutty

PS Tidally Locked celestial Objects