  We present Spitzer IRAC and MIPS 24um imaging of members of the 27+/-5Myr old
open cluster IC 4665. Models for the assembly of terrestrial planets through
planetesimal collisions and mergers predict episodic dust debris discs at this
epoch. We determine that 42(+18-13)% of the solar-type (F5-K5) cluster members
have excess emission at 24um indicative of these debris discs, the highest
frequency of the clusters studied with Spitzer to date. The majority of these
discs have intermediate levels of excess (F_24/F_phot < 2), and no source is
found to have extreme levels of excess indicative of a recent transient event
as opposed to steady-state collisional evolution. We find no evidence of a link
between multiplicity and 24um excess in this cluster sample. Only the
early-type star TYC424-473-1 (T_eff~8420K) has significant near-infrared excess
from 4.5um as measured with IRAC. Two solar-type targets have low significance
8um excess but no significant 24um excess. All other targets show no evidence
for near-infrared excess which could indicate the presence of an optically
thick primordial disc, demonstrating that the observed 24um excess arises from
a debris disc.
