Phosphine (PH3) has recently been identified (but only tentatively) in the
circumstellar shell of IRC +10216 by
Agúndez et al, but there is also evidence that is a
constituent of the atmospheres of both
early detections have been confirmed by later observations, including
measurements made by the
Composite Infrared Spectrometer (CIRS)
on the Cassini probe.
Phosphine is the next-heavier periodic
cousin of ammonia. Like ammonia, phosphine
also has a pungent aroma, but it is toxic as well.