A team of astronomers at the California Institute of Technology has found strong evidence of a massive gaseous planet – informally named Planet Nine – tracing an extremely elongated orbit in the outer Solar System. Planet Nine is thought to be gaseous, similar to Uranus and Neptune; hypothetical lightning lights up the night side. Image credit: R. Hurt, IPAC / Caltech. Planet Nine is likely a gas giant about 10 times more massive than Earth,...