There may be hundreds of small seed planets - or planetesimals - which grow in the disk of matter around a star.
We now know that stars which are abundant in heavy metals are five times more likely to harbor orbiting planets than are stars deficient in metals.
Whether a star has planetary companions or not is a condition of its birth. Those with a larger initial allotment of metals have an advantage over those without.
Naturally, we think that finding another Earth-like planet is identifying a site that's at least friendly here for the evolution of life. The primary goal of the Kepler mission is to statistically assess the occurrence of these small terrestrial worlds.
