Life on Other Planets?

As many know, C.S. Lewis, author of a space trilogy known as the Ransom series, speculated on the possibility of life on other planets in his essay "Religion and Rocketry," published in The World's Last Night: And Other Essays. Moreover, the Vatican in the last few years has an expressed an openness to the possibility that extraterrestial beings do exist. So what have Reformed theologians in the past had to say about this? I have found a few who have written on the topic with surprising willingness to allow for the possibility.

Richard Baxter, The Reasons of the Christian Religion, in The Practical Works of Richard Baxter, Vol. 21, pp. 324-327:

8. To recite what I said, and speak it more plainly, I confess it greatly quieteth my mind against this great objection of the numbers that are damned and cast off for ever, to consider how small a part of this earth is of God's creation, as well as how sinful and impentitent. Ask any astronomer that hath considered the innumerable numbers of the fixed stars and planets, with their distances, and magnitude, and glory, and the uncertainty that we have whether there be not as many more, or an hundred or thousand times as many, unseen to man, as all those which we see, (considering the defectiveness of man's sight,) and the planets about Jupiter, with the innumerable stars in the milky way, which the tube hath lately discovered, which man's eyes without it could not see: I say, ask any man who knoweth these things, whether all this earth be any more in comparison of the whole creation than one prison is to a kingdom or empire, or the paring of one nail, or a little mole, or wart, or a hair, in comparison of the whole body. And if God should cast off all this earth, and use all the sinners in it as they deserve, it is no more sign of a want of benignity, or mercy, in him, than it is for a king to cast one subject of a million into a gaol, and to hang him for his murder, or treason, or rebellion; or for a man to kill one louse, which is but a molestation to the body which beareth it; or than it is to pare a man's nails, or cut off a wart, or a hair, or to pull out a rotten, aching tooth. I know it is a thing uncertain and unrevealed to us, whether all these globes be inhabited or not. But he that considereth, that there is scarce any uninhabitable place on earth, or in the water, or air; but men, or beasts, or birds, or fishes, or flies, or worms, and moles, do take up almost all; will think it a probability, so near a certainty as not to be much doubted of, that the vaster and more glorious parts of the creation are not uninhabited; but that they have inhabitants answerable to their magnitude and glory, as palaces have other inhabitants than cottages; and there is a connaturality and agreeableness there as well as here, between the region, or globe, and the inhabitants.. But whether it be the globes themselves, or only the inter-spaces, or other parts, that are thus inhabited, no reason can doubt, but that those more vast and glorious spaces are proportionably possessed. And whether they are to be called angels, or spirits, or by what other name, is unrevealed to us: but whatever they are called, I make no question but our number, to theirs, is not one to a million at the most.
...
4. Yet, after all this, I am neither asserting that all this is so, nor bound to prove it; I only argue, that you, who are offended at the numbers that sin and perish, do wrangle in the dark, and speak against you know not what.

Cotton Mather, The Christian Philosopher, p. 59:

For Mr. Derham has confuted Hugenius with his own Glasses, and has demonstrated, that there are great Collections of Waters in the Moon, and by consequence Rivers, and Vapours, and Air; and in a word, a considerable Apparatus for Habitation.

But by what Creatures inhabited? A Difficulty this, that cannot be solved without Revelation.

John Dick, Lectures in Theology, Vol. 1, pp. 381-382:

The discoveries of modern science make no part of Theology; but they are worthy of attention, because they exalt our ideas of the might and beneficence of our Creator. As the planets are removed from us by many millions of miles, they could not be visible unless their magnitude was great. How much greater is the magnitude of the fixed stars, the distance of which from the earth is such, that it seems but a step to the utmost planet which revolves around the sun! It is natural to ask, for what purpose they were placed in the heavens? It was not surely to give light to the earth; for all their light is of little account, and more would be furnished by a single satellite of a size far less than the moon. It is not to mark the revolution of the year, and the progress of the seasons; for this is ascertained by the motion of the sun, and the changes which take place upon the surface of the earth. Shall we then suppose that they were created in vain? Shall we suppose that a Being of infinite wisdom, who made the little ball which we inhabit for great purposes, and made that star which we call the sun, to give it light, has lavished his power in the production of thousands and millions of suns for no assignable end? Why are such vast bodies so situated as to appear to us only as points? Was their surpassing splendour, which attracts, indeed, the eye of a spectator upon earth, but darts upon it only a faint and ineffectual ray, bestowed to be wasted on the barren fields of ether? We cannot for a moment admit a conclusion which seems to charge the Lord of nature with folly, and is at variance with the proofs of intelligence and design which are so amply supplied by his other works. The opinion, that around those suns planets revolve, the inhabitants of which rejoice in their light, and are cheered by their influences, is something more than a flight of fancy. It rests upon strong grounds of belief; and while it vindicates the wisdom of God in replenishing with so many bodies the wide regions of space which would be otherwise useless, it fills us with admiration of his inexhaustible goodness, which has diffused life and happiness far beyond the reach of the eye, and the more extended range of imagination. It may be mentioned as a corroboration of this theory, that in the heavenly bodies which lie nearer to us, we observer certain phenomena, which indicate that they are destined for some other purpose than to give light to the earth. The surface of the moon, like that of our globe, is diversified by hills and vallies, which we cannot conceive to be of any use, if the moon is a solitude. In three of the planets, we observe a provision similar to what is made for us, to alleviate the darkness of the night, in the satellites which move around them, in different times, and at different distances. Why are they accompanied with moons, if there are no inhabitants to whom their light would be grateful in the absence of the sun? To us they can be of no use, because they are invisible to the unassisted eye. There is another wonderful fact, from which, however, we cannot reason so certainly, the ring of Saturn, because we are unacquainted with its use; but we may be confident that it was not placed there in vain. If it was intended for ornament, there must be some spectators nearer than the inhabitants of this globe, to whom it was unknown till modern times, and of whom scarcely one in a hundred thousand has ever seen it, and then very imperfectly through a telescope: if it was intended for accomodation, it was the not of the planet itself, which no more needed this appendage than Jupiter or Mars, but of the beings who reside upon its surface. Upon the whole, it is highly probable, that as the fixed stars are luminous bodies of an immense size, or in other words, suns, they are surrounded, like our sun, with planets, which are not deserts, but the seats of life, and activity, and enjoyment. Thus, the universe opens upon us in all its magnificence and extent; and lifting up our thoughts to Him, at whose fiat it arose out of nothing, we feel ourselves constrained to express our admiration and praise in the words of the Psalmist, "How manifold, O Lord, are thy works! in wisdom has thou made them all; the earth is full of thy riches."

Charles H. Spurgeon, "The Love of Jonathan and the Love of Jesus" (Sermon No. 2336 - intended for reading on Nov. 26, 1893, delivered by Spurgeon on Sept. 29, 1889), Metropolitan Tabernacle Pulpit, Vol. 39 (1893)

I have told you before what I sometimes dream shall be my lot in Glory—to stand not here and preach to a handful of people, though it is truly a large handful—but to stand upon some starry orb and preach of Christ to whole constellations at once and thunder out my remembrances of His sweet love to myriads of beings who have never heard of Him as yet, for they have never sinned, but who will drink in all the tidings of what Jesus did for sinful men! And each of you, according to your training for it, shall make known to angels, principalities and powers, the manifold wisdom of God! There is plenty of room for you all, for God’s universe will need millions upon millions of messengers to go through it all and tell out the story of redeeming love. And we, I believe, are here in training for that eternal work of making known to illimitable regions of space and countless myriads of intelligent beings whom God has created, but who have never fallen, the story of this little planet and of the God who loved it so that He came here and died that He might save His people from their sins.