What is currently the closest known heavenly body, brown dwarf, rogue planet or other to our solar system? At one time it was Alpha Centauri.
The closest body we currently know to exist is Proxima Centauri which is part of the Alpha Centauri system at about 4.25 light years away.
There may be rogue planets that are closer but we haven't been able to detect any. Objects down to brown dwarf size that are closer than Alpha Centauri have not been found by extensive surveys.
Here is a list of close objects to the solar system: https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs