What is the difference between a planet-satellite system as we have with the Earth and moon, versus a binary planet—two planets orbiting each other in a cosmic do-si-do?
![](https://scx1.b-cdn.net/csz/news/tmb/2019/whatmoonsino.jpg)
Source:
https://phys.org/news/2019-10-moons-stellar-reveal-planets-neptune.html