WHAT IS THl3 COSPiOGONIC MEANING OF THE ASTEROID
DIAMETER ~dd-125 km?
D.F,Lupishko a nd F.P,Velichko, Astronomical
Observatory of Kharkov University, U,S.S.R.
One can expect t h a t sense of r o t a t i o n i s t h e most s t a b l e
r o t a t i o n c h a r a c t e r i s t i c of a s t e r o i d s i n process of t h e i r dynamic evolution, That i s why studying r e l a t i o n s h i p of t h i s and
o t h e r c h a r a c t e r i s t i c s of a s t e r o i d s i s of considerable cosmogonic interest.
Analysing a v a i l a b l e d a t a on a s t e r o i d sense of r o t a t i o n we
have a l r e a d y noted /I/t h a t : ( i ) t h e l a r g e s t a s t e r o i d s have
prograde r o t a t i o n , ( i i ) t h e predominance of prograde r o t a t i o n
over r e t r o g r a d e one t a k e s p l a c e , and ( i i i ) d i s p e r s i o n of mean
r o t a t i o n r a t e of a s t e r o i d s with r e t r o g r a d e r o t a t i o n i s much more t h a n f o r a s t e r o i d s with prograde one.
A t p r e s e n t t h e sense of r o t a t i o n has been determined f o r
about 56 a s t e r o i d s . The i n c r e a s e of t h e s e d a t a p u t s a question
t . ~what l i m i t i n g &Lameter t h e predominance of prograde r o t a t i o n
t a k e s p l a c e o r , i n o t h e r words, whether an equal p r o b a b i l i t y of
prograde and r e t r o g r a d e r o t a t i o n s e x i s t s and with what diameters.
Fig, a) p r e s e n t s t h e p a r t of a s t e r o i d s with r e t r o g r a d e rov e r s u s a s t e r o i d diameters. The value n
t a t i o n n=Nret/Nret+Npr
was c a l c u l a t e d i n t h e i n t e r v a l hD=lddkm, which was successivl y s h i f t e d by a q u a r t e r of i t s value (25km) to smooth t h e funct i o n n(D). I n t h i s a n a l y s i s t h e f o u r t h a s t e r o i d i n s i z e I d Hyg i e a was not used because i t s sense of r o t a t i o n i s not determined unambiguously.
A s one can s e e
from Fig. a) t h e cham
t
r a c t e r of n(D).&ependence i s complicated
and i n t r i g u i n g . A t
D=36dkm t h e dependence has a r u p t u r e which
separates the largest
z
a s t e r o i d s Ceres, Pal+
l a s and Vesta with
primordial prograde
zL0.1 I
I.
,,o CI
r o t a t i o n from astero\
+
idswith D=266+366km
e
f
o r which n ~ 6 , 5 . The
z
,+'
b)
equal p r o b a b i l i t y of
0.6-,
,
both r o t a t i o n s , i n
C
-b
main belt
our opinion, must be
43ashrolds
c h a r a c t e r i s t i c of an
0.4- ;,
,Z1
evolved s t a t e of colall
l
i s i o n a l evolution.
--'
48astemids
And
the fact that t h i s
Q2 I
I
I
p r o b a b i l i t y proved t o
0
100200300400Soo
be c h a r a c t e r i s t i c of
D, km
l a r g e a s t e r o i d s agrees
with view of Binzel
e t a1./2/ t h a t t h e s e
l a r g e a s t e r o i d s , probably, reached t h e evolved s t a t e of c o l l i s i o n a l e v o l u t i o n having t h e s u r v i v a l l i f e t i m e ( a g a i n s t c a t a s t I
t
4
0)
I
I
I
I
,$I
I
I
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-
-.
I
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.
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O Lunar and Planetary Institute
Provided by the NASA Astrophysics Data System
838
LPSC X X I I
WHAT IS THE COSHOGONIC M3ANING OF THE ASTEROID ::,
D,F.Lupishko
and F.P,Velichko
rophic d i s r u p t i o n ) compared t o t h e a ge of S o l a r System,
Q u i t unexpected i s t h e minimum n e a r D=125km. A s it is
known, t h e minimum i n t h e s i z e range Ibb-I25km i s a l s o p r e s e n t
i n t h e dependences of mean r o t a t i o n r a t e and l i g h t c u r v e amplikude v e r s u s a s t e r o i d diameter /2/, And t h e f a c t t h a t minimum
i s d i s p l a y e d s o c l e a r l y i n a s t e r o i d sense of r o t a t i o n , indicat e s s t a b i l i t y of t h i s p e c u l i a r i t y and i t s cosmogonic n a t u r e .
If t h i s ncosmogonic diameterw r e a l l y d i v i d e s t h e p r i m o r d i a l
a s t e r o i d s and t h e i r c o l l i s i o n a l fragments, t h e n an i n c r e a s e of
t h e p a r t of r e t r o g r a d e r o t a t i o n i n t h e s i z e r e g i o n D ~ 1 2 5 k m
becomes c l e a r : with decrease of fragment s i z e t h e p r o b a b i l i t y
t h a t it w i l l ac u i r e prograde o r r e t r o g r a d e r o t a t i o n w i l l be
equal ( t h a t is 8.5).
The o t h e r , descending branch of minimum ( 2 d d a ~ > 1 2 5 k m )
a p p a r e n t l y r e f l e c t s a g r a d u a l f a l l of equilibrium ( t h a t i s
evolved) s t a t e of c o l l i s i o n s because w i t h decrease of a s t e r o i d
s i z e t h e p r o b a b i l i t y of c a t a s t r o p h i c d i s r u p t i o n before t h e i r
reaching evolved c o l l i s i o n a l i n t e r a c t i o n s i s i n c r e a s e d ,
This q u a l i t a t i v e i n t e r p r e t a t i o n i s undoubtedly not exhaus t i v e . Here t h e c h a r a c t e r of dependence n(D) and t h e presence
of min5mum i n t h e s i z e r e g i o n 166-125km a r e of more importance.
Fig. b) confirms t h e e x i s t e n c e of t h i s minimum. The curve h a s
been obtained by c a l c u l a t i n g n i n t h e i n t e r v a l s AD=5dkm an&
without: smoothing, t h a t i s a l l p o i n t s i n t h i s f i g u r e a r e independent of each o t h e r , Though t h i s curve i s more rough, becaus e of s c a r c e d a t a , it shows t h e minimum n e a r ~=ldd-I25kmwith
confidence.
There i s no doubt t h a t e x p l a n a t i o n of t h e n a t u r e of "cosmogonic diameterN phenomenon w i l l provide important information on t h e p r o c e s s e s of dynamic e v o l u t i o n i n a s t e r o i d b e l t ,
References :
1. Lupishko D,F. and Velichko FOP., 1987, Cinemat. Phys*
C e l e s t . Bodies, 3, 57-65.
2. Binzel ~ , P , , ~ a r i E e l lP.,Zappala
a
V. and C e l l i n o A.,1989,
In: trAsteroids II", Eds.R.Binze1 e t al. ,Arizona Univ.
P r e s s , Tucson.
O Lunar and Planetary Institute
Provided by the NASA Astrophysics Data System