It is impossible to tell since the number grows every day.
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.
The Gaseous Planets The Planets That Are So Far Away That We Don't Even Know If Life Could Exist There (TPTASFATWDEKILCET) :) ;)
Currently there are 353 known extrasolar planets (that is to say, outside of our solar system), but it is unknown how many planets exist in the universe.
Difficult to say, as we do not know (1) how many planets exist that could support life like that on our Earth or (2) of those, how many developed plants such as bananas.
Currently it is not known. With current technology, we are not able to detect the presence of life on other planets even if it does exist. However, we now know that planets are relatively commonplace, which many scientists believe strongly suggests that life must exist elsewhere in the universe.
We can never know how many planets there are in the entire universe.
We know now that planets are a fairly common occurrence in the universe. This discovery provides many potential opportunities for life to exist beyond Earth.
Not yet, but, as we have discovered water on various planets and moon, the possibility of life - as we know it - does exist.
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Many astronomers, historians, regular people, and scientisis know about the planets in our Solar system.
As far as what we know today, there is no life on any planet anywhere, except the Earth.
A star is a ball of plasma : life as we know it cannot exist there.