All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Allah Says (what means): {It is Allah Who has created seven heavens and of the earth the like thereof (i.e. seven). …} [Quran 65:12].
Allah further Says (interpretation of meaning): {And among His Ayât (proofs, evidences, lessons, signs, etc.) is the creation of the heavens and the earth, and whatever moving (living) creatures He has dispersed in them both. And He is All-Potent over their assembling (i.e. resurrecting them on the Day of Resurrection after their death, and dispersion of their bodies) whenever He will.} [Quran 42:29].
An-Nasai reported that the Prophet said: “If the seven heavens and whoever dwells in them apart from Me, and the seven Earths were put in one scale and La Ilaha Illah Allah in another scale, La Ilaha Illa Allah will outweigh them”.
It is concluded from the above verses and other texts, that the seven Earths are planets like planet Earth, one above the other.
Creatures live on each one of these Earths, but nobody knows the reality of these creatures except Allah.
Al-Qurtubi said in his Tafseer (Interpretation of the meaning of the Holy Quran): ‘The view of the majority of scholars is that it refers to seven Earth one above the other, and the distance between one Earth to the other is like the distance between the sky and the Earth. And there are creatures of Allah on each Earth'.
The probability of Mars being one of these Earths that the Qur'an has mentioned is not certain, Allah Says (interpretation of meaning): {We will show them Our Signs in the universe, and in their own selves, until it becomes manifest to them that this (the Quran) is the truth….} [Quran 41:53].
Allah knows best.