🚀 go-pugleaf

ref@CS.CMU.EDU (Robert Frederking) writes:

>> WHY PLANETS SPIN 
>> A report in today's issue of the journal SCIENCE describes a new study
>> of why planets spin. Luke Dones and Scott Tremaine conclude that
>> Mercury, Venus, Earth, and Mars all spin the way they do not because of
>> some orderly influence during their formation, but instead because of
>> random collisions with massive objects. They're not sure, however, how
>> the giant outer planets were set spinning so fast. 

>Is this really right?  Does anyone have more details, in particular,
>why the traditional explanation involving the angular momentum of the
>particles they were formed from isn't right?

Especially: why do Earth and Mars then both spin "regularly", i.e. in
the same sense as Jupiter, Saturn, and Neptune and with only slightly longer 
periods ? (on the other hand, the "irregular" rotation of Mercury seems to
have a rather "natural" explanation from tidal deformation by the Sun
so that only Venus (and perhaps the eq. inclination of Uranus' equator)
need for exceptional explanation in the "standard model". Also: what
happened to the "initial" angular momentum in the Dones-Tremaine model ?
 Hartmut Frommert                 <phfrom@nyx.uni-konstanz.de>
 Dept of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                           -- Eat whale killers, not whales --