7
We can never know how many planets there are in the entire universe.
Many astronomers, historians, regular people, and scientisis know about the planets in our Solar system.
There are 5 altogether.
No. We know what the stars are. They are not planets. They are distant suns, many of which do have undiscovered planets.
He knew about 6 planets. See the related link for further information.
one for now (at least publicly disclosed ;) )
Other than Earth, no planets have been confirmed to be habitable. We do know of planets in other star systems upon which liquid water could theoretically exist but we can't measure the composition of the planets atmospheres therefore we can't know for certain whether or not they are habitable.
They are gas planets
We don't know about any other other place, besides Earth, that harbors life. But many scientists think that there is life on other planets.
There are the inner, terrestrial planets, also know as the rocky planets. Earth is one of these. Then there are the outer planets, also know as the gas planets or gas giants.
Orbiting stars. We know of eight planets orbiting our Sun, and we know of over 300 planets orbiting other stars.
Planets compared to what? We will never know.