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We present the results of numerical integrations of motion of an asteroid due to solar graviation and Yarkovsky diurnal effect. Thermal properties of different types of materials come in Table 1.

type of material -> | bare basalt |
iron rich |
regolith covered |

bulk density rho [kg · m^{-3}] |
3500 | 8000 | 3500 |

surface density rho [kg · m_{s}^{-3}] |
3500 | 8000 | 1500 |

thermal conductivity K [W · kg^{-1} · K^{-1}] |
2.65 | 40 | 0.0015 |

specific heat C [J · kg^{-1} · K^{-1}] |
680 | 500 | 680 |

Other relevant physical properties common for all three types are surface
albedo *A* = 0, surface infrared emissivity *epsilon* = 1, **obliquity**
*dzeta* = 0°. Radii of fragments vary **from 0.1 m upto 1 km**.
You could see a summary of all **linear drift rates** d*a*/d*t*,
d*e*/d*t*, d*i*/d*t* in Table 2.

Integration time was **0.1 Myr**, integration step **36.525 day** using
SWIFT_RMVSY program.

Three graphs show drifts of **semimajor axis** for three
types of fragments and three different
initial semimajor axes: 1 AU, 2 AU and 3 AU. All other orbital elements are zeros.
Compare these results with seasonal drift rates

Very little **eccentricity** increase could be seen in the d*e*/d*t*(*R*)
graph for the regolith covered bodies. Consequently this effect could be important
only for orbits with low semimajor axes (not in the main belt) and only on long
timescales in order of 100 Myr.
In general, diurnal variant of Yarkovsky effect is most effective for bodies with
low thermal conductivty.

**Inclination** does not show any variations on timescale 0.1 Myr. See next section
for inclined orbits.

We repeated all calculations for eccentric and inclined orbit. Initial conditions of 39 test particles were

The most interesting features, which are visible in values of rates are that d*a*/d*t*
has not changed a lot, because eccentricty increase is balanced by the change of inclination
and consequently obliquity of spin axis. The eccentricity changes are 10 or even more times
greater than for circular orbits. The rate for bodies larger than 100 m in diameter is greater
for base basalt ones.

Inclination rates d*i*/d*t* has changed dramatically - now they seem to be
very important, e. g. in surroundigs of nu_6 secular resonance, which is dependent
strongly on inclination. However these high rates will be supressed by perturbations
coming from planets (through precession of nodes) and precession of spin axis itself.

Miroslav Broz: miroslav.broz@usa.net, last updated Mar 19th 1999