Planet Rotation Speeds

[Spoo]

MasterChiToes said:
The Terrestrial planets can be expected to turn slower due to 'tidal forces' dissipating their rotational angular momentum. If you check out the length of a day on ancient earth, it was much shorter than the Jovian planets.

In general, for a stable climate, I would agree that smaller planets better turn slower.

I think you would have to make a number of assumptions about the event that formed the Moon to know what Earth's original rotation rate was. Although, I agree that it must have slowed since then.

Also, tidal forces would have little effect on Mars (two very small moons), and none on Venus (no moons) - although something must have happened to Venus to make it rotate "backwards". It's generally thought that terrestrial planets with a satellite as large as the Moon are very rare. However, Mercury's rotation is very strongly determined by tidal forces from the Sun.

[Baron Munchausen]

Spoo said:

I think you would have to make a number of assumptions about the event that formed the Moon to know what Earth's original rotation rate was. Although, I agree that it must have slowed since then.

Also, tidal forces would have little effect on Mars (two very small moons), and none on Venus (no moons) - although something must have happened to Venus to make it rotate "backwards". It's generally thought that terrestrial planets with a satellite as large as the Moon are very rare. However, Mercury's rotation is very strongly determined by tidal forces from the Sun.

Venus's odd rotation (very slow retrograde) combined with the entire surface being only ~500 million years old (evenly random distribution of craters over entire planet = same age for entire surface, the number of craters gives the rough age estimate) adds up to one known cause: a huge farking impact event.

[dmm]

As a longtime reader/viewer of SF, I can tell you that your analysis is messed up. Up until the 1950s, Venus was inhabited by a technologically-advanced humanoid race consisting entirely of extremely hot babes. Then something happened, and now the place is a wasteland. Perhaps their cycles all synched up.

[Renegade 13]

Spoo said:
I think you would have to make a number of assumptions about the event that formed the Moon to know what Earth's original rotation rate was.

From everything I've read over the past several years, the general consensus is that a roughly Mars-sized planetoid ran head-on into the proto-Earth, hitting with sufficient force to liquify, well, pretty much everything. The impact blasted up sufficient material into orbit that eventually coalesced into the Moon. This theory is supported by the fact that all the Moon material they've ever studied is the same as the material the Earth's crust is composed of, but nothing deeper than the crust, suggesting a massive impact origin.

[Spoo]

Renegade 13 said:
From everything I've read over the past several years, the general consensus is that a roughly Mars-sized planetoid ran head-on into the proto-Earth, hitting with sufficient force to liquify, well, pretty much everything. The impact blasted up sufficient material into orbit that eventually coalesced into the Moon. This theory is supported by the fact that all the Moon material they've ever studied is the same as the material the Earth's crust is composed of, but nothing deeper than the crust, suggesting a massive impact origin.

Of course. What I meant is, we don't know things like the relative velocities or the angle of impact. Thus, we don't know what Earth's original rotation rate was.