Are there any solar systems that have only one planet in them?

I imagine it would be a rarity

Especially f they all formed from a collapsing cloud, like ours did

Nope as there is only one Solar system the one we live in . Our star is called Sol.

Stellar systems with a single planet are possible but should be very rare.

Since there is only one Solar System, ours, as there is only one Sol, the technical answer is "no"

Other systems with a sun and planets are called "planetary systems" Picky, aren't I

We have discovered about 3500 planets and more than 2600 planetary systems. Therefore, most of the planetary systems discovered so far have only ONE planet that we have discovered at this time. I would not be surprised if there were many planetary systems that actually have only one planet ... though these same systems might also have the sort of objects that we characterize as dwarf planets, asteroids, comets, etc.

The earth has only one moon, right? But of course we now have loads and loads of orbiting objects such as defunct weather satellites and abandoned launch-vehicle stages.

Unknown at present, as our ability to detect planets around the nearby stars is limited.

There are systems that only have one planet that has been discovered, but that does not prove that there are not other planets.

Cheers!

There are quite a few solar systems where we've only *seen* one planet - but, that doesn't mean it's the only one... I would bet there are a few out there, but I'd also bet there aren't very many.

Probably not usually more then one sometimes their might be no exoplanets at all.

We don't have the faintest idea. There are billions of stars in the Milky Way, and billions of galaxies in the observable universe. According to the accepted view of the evolution of planetary systems, it is unlikely that any star would have only one planet. But not inconceivable that somewhere or other a "rogue" system may not, through some cosmic accident, somehow end up with a single planet. But we would never know about it.

Astronomers detect planets by either noting the slight dimming of the star's light as the planet passes in front of it, or by measuring the slight wobble of the star. Whatever method they use, it takes three orbits of the planet to detect and to confirm the planet's presence.

Some of the the planets further out from the star can take tens or even hundreds of years to complete one orbit. Using the current methods, it will take us many decades, or even many centuries to discover these planets.

the small one