In 1976 mercury 's mercury spacecraft sent back an image of Mars with blue skies . the claimed image had yet to be calibrated with right colour balance . Some conspiracy theorists have criticized Nasa 's calibration methods . it admits it is n't an exact science and often uses different methods .
In 1976 Nasa 's Viking 1 sent back an image of Mars with blue skies . Nasa claimed image had yet to be calibrated with right colour balance . Some conspiracy theorists have questioned Nasa 's calibration methods . Nasa admits it is n't an exact science and often uses different versions .