Dark Comets are objects that look like asteroids (rocky, with absolutely no sign of cometary activity) but whose orbit show a non-gravitational

acceleration (typical of ice sublimation pushing the object). One of the most famous one is 1I/`Oumuamua; we now know over a dozen of these

objects. Understanding their nature -and what pushes them- has a series of consequences, ranging from helping (maybe) finding the origin of

Earth's water to planetary defence. We just caught one of them in the act: SH2 is releasing a very, very tenuous amount of very, very large dust grains.