Specifically, a planet that is small but rich which cannot be expanded in size (neither QSE nor rift)
There are two ways this can be done.
1. an artifact(probably limited) that can only be used on a VL or smaller planet that reduce the planet size by 2 while increasing all production by 20.
2. Randomly occurring planet of average or smaller size, with production of 30x mega or above in primary and 15x or above in other types.

I think it might be interesting to make players balance the defensive power and production power of a smaller planet. Right now players mostly defend their bigger ones and leave the smaller ones in ruins. except a few exotics, there is really no small planets worth keeping and even those exotics are rarely of extensive value.

I guess something related to making the planet's mass more dense (by making it smaller) would be best

Ive got mixed feelings about this, but we need something new so +0.5

So if i were to use this on an tiny or smaller what planet size would i end up with?

It would revert to a nebula.

It would still take up an planet slot, but not make or produce anything,

good point... maybe it'll explode(implode?) and turn into a bundle of resource....

your very own black hole?? lol

that has a random chance to gives you random amount of artifacts every 2 hours ??
or you can make it deliver random amount of research or minerals
found in planetary list, 2 per person,

even thou only a sun can only make a black hole but myeh

actually im going to work on this....

using it on a tiny planet would get you either

A neutron star
or
A black hole

(technically a planet does not have enough mass at all for any of this...but meh)
Making a planet smaller does not cause it revert to a dust cloud.

I'm not sure how Dan would counter their extremely small size to make them "viable" and desirable.
Special events? A stupidly high output (200x)?

If it were a black hole all you could get from it would be research anyways. By lurking near the event horizon and studying.

The neutron star would be very very small, and very very hot, and very very dense. However they emit so much X-ray radiation it makes shielding all but impossible at short distances. Also their escape velocity is about 1/3rd the speed of light.

Seems generally wierd , needs rework and more thinking. +0.25