SB 10.3.27

martyo mṛtyu-vyāla-bhītaḥ palāyan
 lokān sarvān nirbhayaṁ nādhyagacchat
tvat pādābjaṁ prāpya yadṛcchayādya
 susthaḥ śete mṛtyur asmād apaiti
Synonyms: 
martyaḥ — the living entities who are sure to die; mṛtyu-vyāla-bhītaḥ — afraid of the serpent of death; palāyan — running (as soon as a serpent is seen, everyone runs away, fearing immediate death); lokān — to the different planets; sarvān — all; nirbhayam — fearlessness; na adhyagacchat — do not obtain; tvat-pāda-abjam — of Your lotus feet; prāpya — obtaining the shelter; yadṛcchayā — by chance, by the mercy of Your Lordship and Your representative, the spiritual master (guru-kṛpā, kṛṣṇa-kṛpā); adya — presently; su-sthaḥ — being undisturbed and mentally composed; śete — are sleeping; mṛtyuḥ — death; asmāt — from those persons; apaiti — flees.
Translation: 
No one in this material world has become free from the four principles birth, death, old age and disease, even by fleeing to various planets. But now that You have appeared, My Lord, death is fleeing in fear of You, and the living entities, having obtained shelter at Your lotus feet by Your mercy, are sleeping in full mental peace.
Purport: 

There are different categories of living entities, but everyone is afraid of death. The highest aim of the karmīs is to be promoted to the higher, heavenly planets, where the duration of life is very long. As stated in Bhagavad-gītā (8.17), sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ: one day of Brahmā equals 1,000 yugas, and each yuga consists of 4,300,000 years. Similarly, Brahmā has a night of 1,000 times 4,300,000 years. In this way, we may calculate Brahmā’s month and year, but even Brahmā, who lives for millions and millions of years (dvi-parārdha-kāla), also must die. According to Vedic śāstra, the inhabitants of the higher planetary systems live for 10,000 years, and just as Brahmā’s day is calculated to equal 4,300,000,000 of our years, one day in the higher planetary systems equals six of our months. Karmīs, therefore, try for promotion to the higher planetary systems, but this cannot free them from death. In this material world, everyone from Brahmā to the insignificant ant must die. Therefore this world is called martya-loka. As Kṛṣṇa says in Bhagavad-gītā (8.16), ābrahma-bhuvanāl lokāḥ punar āvartino ’rjuna: as long as one is within this material world, either on Brahmaloka or on any other loka within this universe, one must undergo the kāla-cakra of one life after another (bhūtvā bhūtvā pralīyate). But if one returns to the Supreme Personality of Godhead (yad gatvā na nivartante), one need not reenter the limits of time. Therefore, devotees who have taken shelter of the lotus feet of the Supreme Lord can sleep very peacefully with this assurance from the Supreme Personality of Godhead. As confirmed in Bhagavad-gītā (4.9), tyaktvā dehaṁ punar janma naiti: after giving up the present body, a devotee who has understood Kṛṣṇa as He is need not return to this material world.

The constitutional position for the living entity is eternity (na hanyate hanyamāne śarīre, nityaḥ śāśvato ’yam). Every living entity is eternal. But because of having fallen into this material world, one wanders within the universe, continually changing from one body to another. Caitanya Mahāprabhu says:

brahmāṇḍa bhramite kona bhāgyavān jīva
 guru-kṛṣṇa-prasāde pāya bhakti-latā-bīja

(Cc. Madhya 19.151)

Everyone is wandering up and down within this universe, but one who is sufficiently fortunate comes in contact with Kṛṣṇa consciousness, by the mercy of the spiritual master, and takes to the path of devotional service. Then one is assured of eternal life, with no fear of death. When Kṛṣṇa appears, everyone is freed from fear of death, yet Devakī felt, “We are still afraid of Kaṁsa, although You have appeared as our son.” She was more or less bewildered as to why this should be so, and she appealed to the Lord to free her and Vasudeva from this fear.

In this connection, it may be noted that the moon is one of the heavenly planets. From the Vedic literature we understand that one who goes to the moon receives a life with a duration of ten thousand years in which to enjoy the fruits of pious activities. If our so-called scientists are going to the moon, why should they come back here? We must conclude without a doubt that they have never gone to the moon. To go to the moon, one must have the qualification of pious activities. Then one may go there and live. If one has gone to the moon, why should he return to this planet, where life is of a very short duration?