Astronomers Search For Giant Planet On Outer Edges Of Solar System NPR | By Joe Palca Published September 25, 2017 at 4:31 PM EDT Facebook Twitter Bluesky LinkedIn Email Listen • 2:19 Caltech/R. Hurt (IPAC)An artist's depiction of Planet Nine. The object is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Copyright 2017 NPR