In terrestrial aeronomy, remote sensing and active probing of the upper atmosphere are accomplished using both optical and radio techniques. For passive optical systems-imagers, spectrographs and interferometers- applications to studies of planetary atmospheres often involve the innovative use of standard methods. Here we describe three such passive methods recently applied to studies of the moon’s exosphere, Mercury’s surface, and the atmospheres of Jupiter’s moon Io and comet Hale-Bopp. The active probing of a non-terrestrial atmosphere has not yet been attempted. Here we describe the challenges and potential science yield from light detection and ranging (LIDAR) probing of the lunar atmosphere and incoherent scatter radar (ISR) sounding of Venus’ ionosphere.