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Laser irradiation experiments have been performed on
powdered silicates (othopyroxene, clinopyroxene, and olivine) using a
nanosecond pulse UV excimer laser (193 and 248 nm) to simulate the effects
of space weathering induced on minor bodies of the Solar System by
micrometeorite bombardment.
We have used different fluences (from 0.05 J/cm2
to 2 J/cm2) to weather the
samples, experimenting below and above the ablation threshold. All the
irradiated materials have shown reddening and darkening of their UV-Vis-NIR
reflectance spectra.
 In addition we have found that:
(1) below ablation threshold,
weathering effects increase with increasing number of laser pulses, and with
increasing fluence, confirming that a thermal process is active;
(2) above ablation threshold,
weathering is much stronger and efficient than in the previous case, and is
independent on the number of pulses.
We show that astrophysical time-scales,
i.e. times necessary to obtain similar effects on planetary objects, are of
about 108 yr for both olivine
and pyroxene in the case of ablation. The time grows up to 1010
yr in the case of thermal effects.
We infer that micrometeorite
bombardment can be rightly simulated by laserirradiation only considering
congruent laser ablation. |
