There are lots of stars in clusters, so why are most of the planets found orbiting single stars? It looks as though the planets are there, but are faint and very hard to detect. A group of astronomers studied 88 stars in the cluster Messier 67 over a period of six years. They found three planets, including one around a star that's practically the Sun's identical twin. Even using one of the world's most sensitive instruments, they found these planets at the limits of what was detectable.
Artist's impression of Sun's twin with planet