[Question] Orbital velocities of bodies

[fullarmor2]

I don't understand something. I read that Titan completes one orbit around Saturn in about 15 days. And its altitude is over 1.1 million km. Now, our Moon is only 300 and something thousand km, and it takes over 27 days to orbit Earth? How in the hell does Titan get all the way around at that altitude! Quicker than our Moon does aroun Earth? Titan would have to go many many times farther at that altitude also!

 

[Loru]

Well - Saturn creates much stronger gravity well so Titan has to move really quickly not to fall back to Saturn.

m2 is here mass of Saturn so you can see it's pretty high number.

 

[Urwumpe]

For comparison: Io is 420,000 km away from Jupiter, but needs only 42.5 hours for one Orbit. 17 km/s velocity relative to Jupiter.

 

[fullarmor2]

Thanks for the response. What you said gave me an idea. I went on orbiter and brought up orbit mfd in my ship. And I can reference any planet and then target a moon. I did this to find out the orbital information, and as you alluded to, Titan is orbiting Saturn at over 5 km per second, compared to our Moon's speed of barely over 1 km per second. That explains it. But, I have another question. I read that if you could stand on Saturn, you would only experience 91% of Earth's gravity. Because although its large, its not dense. So then why would its gravity well be so strong as to require Titan's orbital speed? Maybe the shear size of Saturn has something to do with it. Perhaps closer to the core there is much stronger gravity.
For anyone interested I found this cool article on gravity wells!
http://www.explainxkcd.com/wiki/index.php?title=681:_Gravity_Wells

 

[Loru]

Well - if you bloat Earth to Saturn's density, still moon won't change it's orbit as gravity well of the earh wil be roughly the same at moons distance. If you squeze Saturn to Earth's density Titan will be largely unaffected. Total mass counts not density, assuming you're far enough from center of gravity.

 

[Urwumpe]

I read that if you could stand on Saturn, you would only experience 91% of Earth's gravity. Because although its large, its not dense. So then why would its gravity well be so strong as to require Titan's orbital speed?

Remember that you are also much further away from the center of Saturn, if you would stand at its "reference surface" (Saturn has no surface, it goes without any surface from gaseous over fluid to metallic, the surface gravity and surface diameter are defined at the 1 bar pressure altitude by scientists to have ANY reference to work with). Saturn is about ten times as large as Earth... ten times the distance means hundred times less gravity at this point.

Relative to the surface, Titan is 20 times further away and gets thus 400 times less gravity by Saturn.

Our own moon is 63 times further away than our surface from the center of Earth.