Observations in 24 and 70 microns obtained by instrument MIPS (Multiband Imaging for 
Photometer Spitzer) have allowed to detect disk structures analogue to the Kuiper Belt in 
the Solar System in about 10 nearby-solar-type stars that harbor at least one extrasolar 
planet, detected by means of high precision radial velocity measurements. MIPS has also 
found Kuiper-Belt-like rings in another group of about 30 G-type stars not known to be 
associated with planets of the type detected by the Doppler technique, previously mentioned. 
In this contribution we present initial results of a statistical confrontation of the 
properties of the disks in both groups of stars. We try to identify the physical 
conditions that trigger or inhibit the process of planetary formation in each case.