The adaptability of organisms in different varieties of planets is described in the Brahma-saṁhitā as vibhūti-bhinnam, i.e., each and every one of the innumerable planets within the universes is endowed with a particular type of atmosphere, and the living beings there are advanced in science, psychology, etc., according to the superiority or inferiority of the atmosphere. Vibhūti means "specific power," and bhinnam means "variegated." Scientists who are attempting to explore outer space in an attempt to reach other planets by mechanical means must realize that organisms adapted to the atmosphere of the earth cannot exist in the atmospheres of other planets. As such, man's attempts to reach the moon, the sun, or Mars will be completely futile because of the different atmospheres prevailing on those planets. Individually, however, one can attempt to go to any planet he desires, but this is only possible by psychological changes in the mind. Mind is the nucleus of the material body. The gradual evolutionary progress of the material body depends on psychological changes within the mind. The change of the bodily construction of a worm into that of a butterfly and, in modern medical science, the conversion of a man's body into that of a woman (or vice versa) are more or less dependent on psychological changes.
In the Bhagavad-gītā it is said that if a man, at the time of death, concentrates his mind upon the form of the Personality of Godhead, Śrī Kṛṣṇa, and while so doing relinquishes his body, he at once enters the spiritual existence of the anti-material world. This means that anyone who trains the mind to turn from matter to the spiritual form of the Godhead by performance of the prescribed rules of devotional service can easily attain the kingdom of God, in the anti-material sky. And of this there is no doubt.
And in the same way, if one desires to enter into any other planet of the material sky, he can go there just after quitting the present body (i.e., after death). Thus if someone wants to go to the moon, the sun or Mars, he can do so simply by performing acts for that purpose. The Bhagavad-gītā confirms this statement in the following words:
That upon which a person meditates at the time of death, quitting his body absorbed in the thought thereof, that particular thing he attains after death.
Mahārāja Bharata, despite a life of severe penances, thought of a stag at the time of his death and thus became a stag after death. However, he did retain a clear consciousness of his past life and realized his mistake. It is important to realize that one's thoughts at the time of death are influenced by the actual deeds which one performs during his life.
In the Śrīmad-Bhāgavatam (Third Canto, Chapter Thirty-two), the process of entering the moon is described as follows:
Materialistic-minded men, who have no information of the kingdom of God, are always mad after material acquisition of wealth, fame and adoration. Such men are interested in the progressive weal of their particular family unit for their own self-satisfaction and so are also interested in the progress of social and national welfare. These men attain their desired objects by material activities. They are mechanically engaged in the ritualistic discharge of prescribed duties and are consequently inclined to satisfy the Pitās, or bygone forefathers, and controlling demigods by performance of sacrifices as prescribed by the revealed scriptures. Addicted to such acts of sacrifices and ceremonial observances, such souls enter into the moon after death. When one is thus promoted to the moon, he receives the capacity to enjoy the drinking of soma-rasa, a celestial beverage. The moon is a place where the demigod Candra is the predominating deity. The atmosphere and amenities of life there are far more comfortable and advantageous than those here on earth. After reaching the moon, if a soul does not utilize the opportunity for promotion to better planets, he is degraded and forced to return to earth or a similar planet. However, materialistic persons, although they may attain to the topmost planetary system, are certainly annihilated at the time of the cosmic manifestation's dissolution.
As far as the planetary system of the spiritual sky is concerned, there are unlimited Vaikuṇṭha planets in the para-vyoma. The Vaikuṇṭhas are spiritual planets which are manifestations of the internal potency of the Lord, and the ratio of these planets to the material planets (external energy) in the material sky is three to one. So the poor materialist is busy making political adjustments on a planet which is most insignificant in God's creation. To say nothing of this planet earth, the whole universe with innumerable planets throughout the galaxies is comparable to a grain of mustard seed in a bag full of mustard seeds. But the poor materialist makes plans to live comfortably here and thus wastes his valuable human energy in something which is doomed to frustration. Instead of wasting his time with business speculations, he might have sought the life of plain living and high spiritual thinking and thus saved himself from perpetual materialistic unrest.
Even if a materialist wants to enjoy developed material facilities, he can transfer himself to planets where he can experience material pleasures much more advanced than those available on the earth planet. But the best plan is to prepare oneself to return to the spiritual sky after leaving the body. However, if one is intent on enjoying material facilities, one can transfer himself to other planets in the material sky by utilizing yogic powers. The playful spaceships of the astronauts are but childish entertainments and are of no use for this purpose.
The aṣṭāṅga-yoga system is also materialistic, inasmuch as it teaches one to control the movements of air within the material body. The spiritual spark, the soul, is floating on air within the body, and inhalation and exhalation are the waves of that air containing the soul. Therefore the yoga system is a materialistic art of controlling this air by transferring it from the stomach to the navel, from the chest to the collarbone and from there to the eyeballs and from there to the cerebellum and from there to any desired planet. The velocities of air and light are taken into consideration by the material scientist, but he has no information of the velocity of the mind and intelligence. We have some limited experience of the velocity of the mind, because in a moment we can transfer our minds to places hundreds of thousands of miles away. Intelligence is even finer. Finer than intelligence is the soul, which is not matter like mind and intelligence but is spirit, or antimatter. The soul is hundreds of thousands of times finer and more powerful than intelligence. We can thus only imagine the velocity of the soul in its traveling from one planet to another. Needless to say, the soul travels by its own strength and not with the help of any kind of material vehicle.
The bestial civilization of eating, sleeping, fearing and sense-gratifying has misled modern man into forgetting how powerful a soul he has. As we have already described, the soul is a spiritual spark which is many, many times more illuminating, dazzling and powerful than sun, moon or electricity. Human life is spoiled when man does not realize his real identity with his soul. Lord Caitanya appeared with His disciple Nityānanda to save man from this type of misleading civilization.
Śrīmad-Bhāgavatam also describes how yogīs can travel to all the planets in the universe. When the vital force is lifted to the cerebellum, there is every chance of this force bursting out from the eyes, nose, ears, etc., as these are places which are known as the seventh orbit of the vital force. But the yogīs can block out these holes by complete suspension of air. The yogī then concentrates the vital force in the middle position, that is, between the eyebrows. At this position, the yogī can think of the planet into which he wants to enter after leaving the body. He can then decide whether he wants to go to the abode of Kṛṣṇa in the transcendental Vaikuṇṭhas from which he will not be required to descend into the material world, or to travel to higher planets in the material universe. The perfect yogī is at liberty to do either.
For the perfect yogī who has attained success in the method of leaving his body in perfect consciousness, transferring from one planet to another is as easy as an ordinary man's walking to the grocery store. As already discussed, the material body is just a covering of the spiritual soul. Mind and intelligence are the undercoverings, and the gross body of earth, water, air, etc., is the overcoating of the soul. As such, any advanced soul who has realized himself by the yogic process, who knows the relationship between matter and spirit, can leave the gross dress of the soul in perfect order and as he desires. By the grace of God, we have complete freedom. Because the Lord is kind to us, we can live anywhere—either in the spiritual sky or in the material sky, upon whichever planet we desire. However, misuse of this freedom causes one to fall down into the material world and suffer the threefold miseries of conditioned life. The living of a miserable life in the material world by dint of the soul's choice is nicely illustrated by Milton in Paradise Lost. Similarly, by choice the soul can regain paradise and return home, back to Godhead.
At the critical time of death, one can place the vital force between the two eyebrows and decide where he wants to go. If he is reluctant to maintain any connection with the material world, he can, in less than a second, reach the transcendental Vaikuṇṭha and appear there completely in his spiritual body which will be suitable for him in the spiritual atmosphere. He has simply to desire to leave the material world in both finer and grosser forms and then move the vital force to the topmost part of the skull and leave the body from the hole in the skull called the brahma-randhra. This is the highest perfection in the practice of yoga.