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{\bf The Motion of Pluto}\\
Hiroshi Kinoshita\\
National Astronomical Observatory\\
2-21-1 Osawa, Mitaka, Tokyo 181 ,JAPAN\\
E-mail:Kinoshita@c1.mtk.nao.ac.jp
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Pluto's motion is said to be chaotic in the sense that the 
maximum Lyapunov exponent is positive.
The longest integration  over 845 million years (42 Pluto's Lyapunov times)
by Sussman and Wisdom(1988) does not show any indication of
 a gross instability in the motion of Pluto. 
We have carried out the numerical integration of Pluto over the age of 
the solar system (5.5 billion years 
both towards the past and the future ). This
integration also does not give any indication of chaotic evolution
of Pluto.
The divergences of Keplerian elements of a nearby trajectory
at first grow linearly with the time and then start to increase 
exponentially. The exponential divergences stop  at about 420 million years
and saturate.
  The exponential divergences are suppressed by the following three
 resonances that Pluto has:  \\
 1)Pluto is in the 3:2 mean motion resonance with Neptune.\\
 2)The argument of perihelion  librates
 around 90 degrees and its period is 3.8 Myr.
 The dominant periodic variations of the eccentricity and the inclination 
 are synchronized with the libration of the argument of perihelion.\\
3)Moreover the longitude of Pluto's node referred to the longitude
of Neptune's node circulates and the period of
this circulation is equal to the period of the libration of 
the argument of perihelion ( a secondary resonance).

Several possible scenarios how Pluto evolves to the present stable
state will be reviewed.


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