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:

1. Allah is He Who created seven Firmaments and of the earth a similar number. Yusuf Ali
2. It is God who has created the seven heavens and a like number of earths. Sarwar
3. It is Allah who has created seven heavens, and of the earth [a number] similar to them. Qarai
4. It is Allah Who has created seven heavens and of the earth the like thereof (i.e. seven). Hilali & Khan
5. 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.

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:

1. Allah is He Who created seven Firmaments and of the earth a similar number. Yusuf Ali
2. It is God who has created the seven heavens and a like number of earths. Sarwar
3. It is Allah who has created seven heavens, and of the earth [a number] similar to them. Qarai
4. It is Allah Who has created seven heavens and of the earth the like thereof (i.e. seven). Hilali & Khan
5. 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.