How can rogue planets form?

"A groundbreaking study suggests rogue planets form in a dramatic way — through violent disk collisions in young star clusters, not failed star formation. Credit: SciTechDaily.com" (ScitechDaily, Scientists Just Discovered a Violent New Way Rogue Planets Are Made)

The rogue planets can form when two forming planets' planetary disks impact together. When those material disks impact each other, and they rotate opposite sides that can form the material whirl that travels out from the star's gravity field. In that case, impacting material whirls act like catapults and throw those planets into interstellar space. Those planets can someday travel to another solar system and cause chaotic situations like impacts. 

Another thing that can form rogue planets is supernova or nova eruptions. The post-stellar planets that form in nova and supernova debris can also turn rogue planets. When neutron stars or white dwarfs pull some other planet to them, that detonation can throw other planets away from that star remnant orbital. 

The ultimate fast winds and very hot conditions in exoplanets' atmosphere can cause a situation in there is an explosion in the planet's atmosphere. If there is some eruption or asteroid impact that kind of situation can throw lots of atmosphere from around the planet. That thing can cause a very powerful punch to the planet or its moon. 

If that object travels to its star at a certain angle or goes a little bit past the star, gravity can push it into a half-elliptical trajectory. The light and small moon maybe the size of Earth's Moon or Saturn's Enceladus can travel out of the solar system and then start to collect material on it. 

"Illustration of LTT 9779 b, the only known ultra-hot Neptune. This planet orbits so close to its star that its atmosphere is scorching hot, glowing from its own heat while also reflecting starlight. Because it is tidally locked — always showing the same side to its star — one half is permanently in daylight while the other remains in darkness. New JWST observations with NIRISS reveal a dynamic atmosphere: powerful winds sweep around the planet, shaping mineral clouds as they condense into a bright, white arc on the slightly cooler western side of the dayside. As these clouds move eastward, they evaporate under the intense heat, leaving the eastern dayside with clear skies. Credit: Benoit Gougeon, Université de Montréal" (ScitechDaily, A 2,000°C Inferno That Still Shimmers: An Ultra-Hot Neptune’s Mystery)

There is the possibility that some other planet pushes exoplanets away from their trajectory to their star. And then the explosion in the star causes a situation in the atmosphere and seas on that planet to boil or explode. And that effect can push small planets to interstellar space. The strong winds on the planet can also make an eruption that can push the planet away from its trajectory. That kind of situation can happen when an icy planet suddenly starts to travel to its own star. 

Suddenly vaporizing hydrocarbon or maybe helium and hydrogen ice can push the atmosphere away and cause the rocket effect. It's possible. The remarkable mass of the planet is frozen gas. And that vaporization can decrease its size and mass remarkably. 

Also in that kind of case the star's own gravity can act as a gravity sling that pushes the planet away from its trajectory and accelerates it into interstellar space. 

The planet can also form when some asteroid travels in the middle of the cosmic molecular nebula. That gravity center can pull material around it, and form even a large-size planet. That kind of thing can cause the form of icy super Jupiter that travels in interstellar space. 

https://scitechdaily.com/a-2000c-inferno-that-still-shimmers-an-ultra-hot-neptunes-mystery/

https://scitechdaily.com/scientists-just-discovered-a-violent-new-way-rogue-planets-are-made/

 https://scitechdaily.com/red-dwarf-fury-how-wolf-359s-radiation-may-fry-alien-atmospheres/

https://scitechdaily.com/33000-km-h-winds-scientists-just-found-the-fastest-jetstream-on-an-alien-world/