Writing in 1826, Amos Pettengill affirmed, based, in part, on the biblical witness, that other planets have been, and are, inhabited, albeit, by people who were not in a rebellious state:
Lesson XV
The Inhabitants of the Worlds Innumerable
Dominion and fear are with him; he maketh peace in his places. Is there any number of his armies?—Job xxv. 2.
The Planets are evidently calculated and designed to accommodate rational beings. They are all like this Earth, and some of them vastly larger. They have day and night, summer and winter. Three of them at least have moons to attend them. Many circumstances constrain us to believe that they are filled with inhabitants; and that every Fixed Star illuminates worlds peopled with creatures like ourselves, but not involved with us in rebellion against the Creator—that there is pace in all his high places.*
He informs us that the morning stars sang together, and all the sons of God shouted for joy, when he laid the foundations of this earth (Job xxxviii. 7). Hence intelligent creatures, and perhaps systems of worlds, previously existed. The declaration seems to intimate that the holy inhabitants of these early created worlds, as well as the innumerable company of angels rejoiced to see the new displays of power, wisdom, and goodness, their creator made in bringing this world into existence. At least, there is reason to think, that such inhabitants are included in his numberless armies among the principalities and powers in heavenly places.
The descendants of Adam are numerous beyond our conception. But they probably bear no greater proportion in this respect, to the other subjects of God’s moral government, than a drop does to the ocean, or the smallest particle of dust to the whole earth. Were the Solar System with all its inhabitants struck out of existence, the loss would be comparatively no greater, than that of a single leaf in a boundless forest.
Every intelligent creature separately considered, is inconceivably valuable, in that he possesses immortal powers, and must exist in endlessly increasing bliss or woe, according to the character he forms while on trial. How immensely valuable then is the aggregate of the intelligent creation! But all are vanity when contrasted with the Creator. His powers, glory and happiness transcend theirs, as infinite space does a single point. The Lord is high above all nations, and his glory above the Heavens:--Who humbleth himself to behold the things that are in the heaven and in the earth (Psalm cxiii). All nations before him are as nothing; and they are counted to him less than nothing, and vanity (Isaiah xl. 17). Yea, the heavens are not clean in his sight. He put no trust in his servants, and his angels are charged with folly (Job xv. 15 and iv. 13).
* Jehovah intimates that it would have been inconsistent for him to create the Earth, had he not designed it to be inhabited. He created it not in vain, he formed it to be inhabited. Isaiah xlv. 18. As he shows us a number of other worlds, and gives us reason to believe that a far greater number are enlightened by the myriads of suns, greater, presented to our view, must we not infer from his perfections that he acted consistently in creating them, that he created them not in vain, but to be inhabited? (Amos Pettengill, A View of the Heavens, or Familiar Lessons on Astronomy: With a Celestial Map, by which the constellations can be easily found Adapted to the Use of Schools [New Haven: Nathan Writing, 1826], 64-66)
What is interesting is that Pettengill affirms the existence of other peopled planets based on the same reasoning Latter-day Saints use, based on Moses 1:33:
And worlds without number have I created; and I also created them for mine own purpose; and by the Son I created them, which is mine Only Begotten.
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