I had this idea for a terrestrial planet-ice giant binary system. Both planets had their origin inside the outer solar system but were moved into the habitable zone by a passers-by black hole.
The terrestrial planet, an object around the mass of Earth but with a larger radius(around 1.2 times Earth's radius), became a water world, and began to host bacterial life. However this fledgling world immediately faced a crisis caused by its larger neighbor.
The ice giant companion is around 9 earth masses and around 3.2 Earth radii, ad its composition is similar to Neptune. However, since it migrated into the habitable zone, it is no longer able to maintain its hydrogen gas. The gas escapes in sudden bursts, some expelling as much mass as Pluto from the giant. These hydrogen bursts slam into the giants companion, and are sterilizing its atmosphere.
Now, my question is, is this setup plausible? Could a terrestrial-ice giant duo even form, would these sudden hydrogen bursts be the result, and is it even possible for the water world to develop life?