There may be hundreds of small seed planets - or planetesimals - which grow in the disk of matter around a star.
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.
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.
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.
