In August 2001 a formation appeared in a field beside the Chilbolton radio telescope in Hampshire. It copies the layout of the Arecibo message, the picture in binary that humanity sent towards the star cluster M13 in 1974. It changes key details as if answering it.
The reply adds silicon to the elements of life, gives the DNA an extra strand and shows a shorter figure with a larger head. Three planets are highlighted instead of one. The transmitting telescope is replaced by a device that had appeared in the same field a year earlier.
A few days before, a large face had appeared in the same field. Many see it as a portrait of the sender.
Read the full story in the Chilbolton formations and the Arecibo message. Each change is set out on the Arecibo response signal page.
