Chris Peterson wrote:neufer wrote:
While it takes only a small deflection to nullify an Oort cloud object's angular momentum...
how does the angular momentum get canceled out almost completely?
How are you figuring that the (orbital) angular momentum of the comet has changed significantly?
My figuring was wrong on that matter but it has taken me this long to figure it all out.
At the Oort cloud distance of 50,000 AU the escape velocity ~188m/s
and the circular orbital velocity ~133m/s.
The (
phase space) 3D Oort cloud
velocity distribution at 50,000 AU basically fills a sphere of radius 133m/s with a 8.6m/s wide cylindrical axial hole down the center depleted due to interactions with the solar system at perihelion (= ~32AU at 4.3m/s radius).
However, for Comet ISON to reach a perihelion as close as 0.01244AU it must have started within only about 8.6
centimeters per second of the center of that 8.6m/s wide cylindrical axial hole.
While this narrow cylinder represents only about 6 x 10
-7 of the volume of the entire Oort cloud phase space a velocity change of 5 to 10 m/s at ~50,000AU is really all that would have been required.
Presumably this (5 to 10 m/s) perturbation was provided by a well positioned
passing red dwarf about 2 million years (= 0.5*(25,000)
3/2) ago.
(Note: Alpha Centauri is currently in the process of inducing a ~1 m/s velocity perturbation on the Oort cloud but it is inducing a similar ~1 m/s velocity perturbation upon
the whole solar system. Hence, the
effective [quadrupole] Oort cloud perturbation [vis-a-vis the solar system] amounts to only about a ~0.1 m/s velocity perturbation.)
Chris Peterson wrote:neufer wrote:
This will be the first pass of Comet ISON (
C/2012 S1) and it has an eccentricity ~ 1.0000021.
To be clear, it is likely this body remains in a closed solar orbit.
Your figuring is wrong on that matter.
An Oort comet which starts at an aphelion of ~50,000AU needs
very little extra energy to escape the solar system.
At perihelion Comet ISON will be traveling ~377 km/s or ~2,000 V where V = ~188 m/s (the escape velocity at 50,000AU).
If Comet ISON's velocity at perihelion could be
slightly increased to just (2,000 + ϵ)V [where ϵ = 1/4,000]
then Comet ISON would have gained enough energy to reach escape velocity.
Hence, a perihelion velocity increase of just 47 millimeters per second (= 188 m/s/4000)
is all that is required to reach escape velocity
In the case of a sungrazer this tiny (47mm/s) perihelion velocity increase could come either from:
- 1) strong cometary (tail) jets near perihelion from a rotating cometary nucleus and/or
2) a gravitational assist near perihelion from a Sun moving at ~13m/s in the anti-Jupiter direction.