dougettinger wrote:Why cannot astrophysists be certain about the capture of the iregular moons of Mars ? And more than likely they came from the Asteroid Belt. What other mechanism exists for the reason for these Martian moons ?
The moons may have coalesced in place, during or shortly after the formation of Mars. They may also be the product of a collision between a large body and Mars- something like the way the Moon was formed, but on a smaller scale. The problem is that from a material standpoint, the Martian moons don't seem very much like asteroids.
Likewise, the highly inclined, sometimes retrograde, irregular moons of the outer planets have to be captured bodies. What other option exists ?
I don't know of any theories other than that they are captured bodies. But they were probably captured when these planets still had protolunar discs (the source of their inner moons). These discs provided environments where passing asteroids/planetoids could shed energy, allowing them to be captured. Captures in today's Solar System environment are much more difficult.
I read about the Yarkovsky effect and the YORP effect . Thank you for these references. Spin-up that you mentioned where some asteroids would break apart was only suggested for smaller objects and objects within 1 AU of the Sun.
Not at all. The effect is size dependent, and it is the apparent cause of otherwise high rotation rates for most asteroids (in the asteroid belt). The effect is very strong at that distance for objects smaller than a few kilometers. As I noted, this YORP spin-up is currently the favored theory for the production of a large amount of small debris that eventually produces sporadic meteors.
It seems that the Yarkovsky effect was utilized more so to explain why some asteriods could move away from their stable orbits into other orbits and then be possibly perturbed by other asteroids. There is a strong need to explain why asteroids have so many different orbits other than those inside the Asteroid Belt. And then there is a pressing need to know how some of the asteroids gained extra energy to be kicked into the outer solar system and be captured by the outer planets.
YORP helps explain a lot of dynamics. I don't think there is any mystery surrounding the observed orbits of asteroids outside the belt. And asteroids are not being sent to the outer system and captured by planets. Those captures occurred billions of years ago, when the entire environment of the Solar System was very different from today.
[quote="dougettinger"]Why cannot astrophysists be certain about the capture of the iregular moons of Mars ? And more than likely they came from the Asteroid Belt. What other mechanism exists for the reason for these Martian moons ?[/quote]
The moons may have coalesced in place, during or shortly after the formation of Mars. They may also be the product of a collision between a large body and Mars- something like the way the Moon was formed, but on a smaller scale. The problem is that from a material standpoint, the Martian moons don't seem very much like asteroids.
[quote]Likewise, the highly inclined, sometimes retrograde, irregular moons of the outer planets have to be captured bodies. What other option exists ?[/quote]
I don't know of any theories other than that they are captured bodies. But they were probably captured when these planets still had protolunar discs (the source of their inner moons). These discs provided environments where passing asteroids/planetoids could shed energy, allowing them to be captured. Captures in today's Solar System environment are much more difficult.
[quote]I read about the Yarkovsky effect and the YORP effect . Thank you for these references. Spin-up that you mentioned where some asteroids would break apart was only suggested for smaller objects and objects within 1 AU of the Sun.[/quote]
Not at all. The effect is size dependent, and it is the apparent cause of otherwise high rotation rates for most asteroids (in the asteroid belt). The effect is very strong at that distance for objects smaller than a few kilometers. As I noted, this YORP spin-up is currently the favored theory for the production of a large amount of small debris that eventually produces sporadic meteors.
[quote]It seems that the Yarkovsky effect was utilized more so to explain why some asteriods could move away from their stable orbits into other orbits and then be possibly perturbed by other asteroids. There is a strong need to explain why asteroids have so many different orbits other than those inside the Asteroid Belt. And then there is a pressing need to know how some of the asteroids gained extra energy to be kicked into the outer solar system and be captured by the outer planets.[/quote]
YORP helps explain a lot of dynamics. I don't think there is any mystery surrounding the observed orbits of asteroids outside the belt. And asteroids are not being sent to the outer system and captured by planets. Those captures occurred billions of years ago, when the entire environment of the Solar System was very different from today.