Some scholars understand from the following verse that there exist seven earths as well:
اللَّـهُ الَّذِي خَلَقَ سَبْعَ سَمَاوَاتٍ وَمِنَ الْأَرْضِ مِثْلَهُنَّ
It is God who created the seven heavens and the same number of earths. 65:12
Other similar translations are:
- Allah is He Who created seven Firmaments and of the earth a similar
number. Yusuf Ali
- It is God who has created the seven heavens and a like number of
- It is Allah who has created seven heavens, and of the earth [a
number] similar to them. Qarai
- It is Allah Who has created seven heavens and of the earth the like
thereof (i.e. seven). Hilali & Khan
- It is Allah Who has created the seven heavens, and seven earthly
worlds like them. Ahmed Raza Khan
مِثْلَهُنَّ literally means like them but since سَمَاوَاتٍ are not similar to الْأَرْضِ in their make as we know it, the translators were compelled to believe that the Quran is equating their number.
This, however, does not explicitly endorse the existence of aliens there. We can only argue like this: Since the most distinguishing feature of earth is life, other earths may have some form of life too.