Arjuna, by the grace of Lord Sri Krsna, was able to reach the heavenly planet even with the selfsame body and was honored by the heavenly demigod Indradeva, being seated with him half-elevated. One can reach the heavenly planets by the pious acts recommended in the sastras in the category of fruitive activities. And as stated in the Bhagavad-gita (9.21), when the reactions of such pious acts are spent, the enjoyer is again degraded to this earthly planet. The moon is also on the level with the heavenly planets, and only persons who have performed virtues only — performing sacrifices, giving charity and undergoing severe austerities — can be allowed to enter into the heavenly planets after the duration of life of the body. Arjuna was allowed to enter into the heavenly planets in the selfsame body simply by the grace of the Lord, otherwise it is not possible to do so.
The present attempts to enter into the heavenly planets by the modern scientists will certainly prove futile because such scientists are not on the level of Arjuna. They are ordinary human beings, without any assets of sacrifice, charity or austerities. The material body is influenced by the three modes of material nature, namely goodness, passion and ignorance. The present population is more or less influenced by the modes of passion and ignorance, and the symptoms for such influence are exhibited in their becoming very lusty and greedy. Such degraded fellows can hardly approach the higher planetary systems. Above the heavenly planets there are many other planets also, which only those who are influenced by goodness can reach. In heavenly and other planets within the universe, the inhabitants are all highly intelligent, many more times than the human beings, and they
are all pious in the higher and highest mode of goodness. They are all devotees of the Lord, and although their goodness is not unadulterated, still they are known as demigods possessing the maximum amount of good qualities possible within the material world.

>>> Ref. VedaBase => SB 1.15.12