"Small but very dense" sounds like the description of a neutron star or "collapsed matter star". Theoretically, a black hole (the only thing more dense) has no physical size at all.
So, "neutron star". If the neutron star is spinning rapidly, they are called "pulsars" for the radio-wave pulses that they generate.
There is no "small dense object" that orbits between Mars and Jupiter. There are however numerous asteroids which are rocky objects up to a few hundred miles in diameter that orbit in this region making up what is called the asteroid belt.
a planet like our own
In a way that's what dense means. If something is dense then a small volume of it will have lots of mass. Something that has lots of mass will be subject to considerable gravitational force, which is weight.
a satellite
Neutron stars
Small agranulocytes that have a dense nucleus and very little cytoplasm are called Lymphocytes.
The dense area of the nucleus is called the nucleolus. The nucleolus consists of nucleic acids and proteins and takes part in the formation of ribosomes.
malta
It is called a forest.
epicycles
Particles.
A black hole ofcourse