M22 is one of the nearest globular clusters
to our sun. Its stars stretch some 200 light years across and
its collective brightness ranks it third among the 150 known Milky
Way globulars. It is outshined visually only by the two bright
southern globulars, Omega Centauri and 47 Tucanae. M22 is considered
an old globular cluster having its beginning some 12 billion years
ago not long after the formation of the Milky Way. Recent excitement
was generated when astronomers observed the possibility of free
floating planets within M22. Although controversial planet sized
masses were evoked to explain a micolensing effect on stars in
the galactic bulge far behind M22. An alternative explanation
is that the planets may not be within M22 but could be located
somewhere in the line of sight between earth and the cluster.
M22 is one of only 4 globular clusters known to harbor a planetary
nebula.