Discovered by Philippe Loys de Chéseaux in 1746.

Located in the constellation of Scorpius and at an estimated distance of 7200 light-years, M4 is one of the closest globular clusters to the Earth.  Under very dark sky conditions, M4 can be detected by naked eye observation.  It is easily seen with the aid of binoculars and is very impressive in even small telescopes.  M4 would be a very striking object except for interstellar dust and gas between our location and it.  This interstellar matter "reddens" and obscures some of the brightness of the cluster and gives it a definite "orange" tint in images.  In 1987 a "millisecond" pulsar was discovered in M4.  It rotates at an incredible rate of over 300 times per second.  The Hubble Space Telescope has identified many white dwarf stars in the cluster.  An exoplanet orbiting one of these white dwarfs has been discovered.  The age of the planet is estimated to be approximately the same as the stars that make up the cluster. This places the planet's age to be over 12 billion years old.   This makes it the oldest known planet yet discovered.

¹http://www.messier.seds.org/m/m004.html