Jupiter's Four Galilean Moons--Io, Europa, Ganymede, and Callisto
The European Space Agency Launches the Jupiter Icy Moons Explorer (
On April 14th, the European Space Agency (ESA) launched the "Jupiter Icy Moons Explorer" (JUICE) spacecraft on its way to Jupiter to explore three of the major moons of Jupiter--Europa, Ganymede, and Callisto--including a prolonged orbit around Ganymede, the largest moon in the solar system. Because Jupiter is so far away from the Earth, and because of the need for gravity assist flybys of the Sun, Earth, and Venus, the spacecraft will not reach Jupiter until July of 2031. In the fall of 2024, NASA will launch the Europa Clipper to explore Jupiter's Europa. Clipper will launch on a SpaceX Falcon Heavy rocket, which is a more powerful launch vehicle than ESA's, and consequently Clipper will actually reach Jupiter in April 2030, a year ahead of JUICE.
One of the primary reasons for these exploratory missions to the moons of Jupiter--and particularly, Europa and Ganymede--is to look for signs of extraterrestrial life. We might wonder why human beings want to search for extraterrestrial life. Is this a foolish pursuit? What difference would it make for us if life were discovered on these moons?
Can Christians accept this? Or must Christians insist that we know from the Bible that the only form of extraterrestrial life is angels (supernatural spirits without bodies), and so extraterrestrial embodied life is impossible? Or could the discovery of extraterrestrial material life beyond the Earth be understood as compatible with the central doctrines of Christianity?
The four largest moons of Jupiter were first discovered in January of 1610 by Galileo when he turned his newly invented telescope towards the night sky. In March of that year, he published his discoveries in The Starry Messenger. For many reasons, this was one of the most important discoveries in the history of science. One reason was that it seemed to be clear evidence against the geocentric model of the universe and for the heliocentric Copernican model, because Jupiter's moons were orbiting around Jupiter and not around the Earth. Another reason for the importance of this discovery is that some people saw it as suggesting the possibility of extraterrestrial life. Johannes Kepler published a letter to Galileo, which included his claim that Galileo's discovery of the four moons made it probable that there was life on Jupiter. After all, if Jupiter with four moons is so similar to the Earth with one moon, then why shouldn't Jupiter have living inhabitants just as the Earth does? Galileo himself, however, cautiously resisted Kepler's suggestion.
But despite Galileo's caution on this point, the telescopic discoveries in astronomy, beginning in the 17th century, renewed a debate over the possibility of extraterrestrial life that had begun in ancient Greece and then reappeared in the late 13th century as a debate among Christians over whether extraterrestrial life was compatible with Christianity. The documents in this debate have been conveniently collected in one volume by Michael J. Crowe in The Extraterrestrial Life Debate, Antiquity to 1915: A Source Book (University of Notre Dame Press, 2008).
An assessment of this debate from the perspective of a conservative Catholic has been
written by Benjamin Wiker--"Alien Ideas: Christianity and the Search for Extraterrestrial Life" (
Crisis Magazine, November 4, 2002). Wiker argues that the search for extraterrestrial life is an anti-Christian attack on religion rooted in the atomistic materialism of Epicureans like Lucretius. I have already challenged Wiker's stance in a series of
posts.
Against Wiker are those Jesuit astronomers who work for the Vatican Observatory, who see no conflict between the possibility of extraterrestrial life and Christianity. Some years ago, Jack Hitt wrote a
long article on how these Catholic scientists think about this debate--"Would You Baptize an Extraterrestrial?" (
The New York Times Magazine, May 29, 1994).
In his didactic philosophical poem--On the Nature of Things--Lucretius defends the Epicurean understanding of nature as arising from the spontaneous, random, and purposeless motions of atoms, without any need for intelligent design by the gods. From this atomistic conception of nature, he infers that "it is in the highest degree unlikely that this earth and sky is the only one to have been created and that all those particles of matter outside are accomplishing nothing," and that we are bound "to acknowledge that in other regions there are other earths and various tribes of men and breeds of beasts" (2.1056, 2.1078). He thus affirmed the plurality of worlds and extraterrestrial life.
In this way, he was opposed to Plato (particularly in the
Timaeus) and Aristotle (particularly in
On the Heavens and the
Metaphysics), who argued that the cosmos was governed by a divine mind (Plato's Demiurge, Aristotle's Prime Mover) according to a divinely purposeful design. They inferred from this that there was no plurality of worlds. As Aristotle said: "the unmovable first mover is one both in definition and in number; so too, therefore, is that which is moved always and continuously; therefore, there is one heaven alone" (
Metaphysics 1074a37-39). (I have written some posts contesting these popular interpretations of
Plato and
Aristotle as proponents of cosmic divine teleology as opposed to the natural immanent teleology of Darwinian natural right.)
From the beginning of Christianity, many Christian theologians have embraced Christian versions of this popular interpretation of this Platonic and Aristotelian theological cosmology as opposed to Epicurean atomism, and this has led them to deny a plurality of worlds with extraterrestrial embodied life. But beginning in the late 13th century, some Christians have seen a plurality of life-worlds in one cosmos as compatible with Christianity.
The debate here is over whether the plurality of worlds can be reconciled with the central doctrines of Christianity--particularly, the Story of Creation and the Story of Salvation.
THE STORY OF CREATION
The key Biblical text for the Story of Creation is the opening chapters of Genesis with its account of the six days of creation.
"In the beginning, God created the heavens and the earth" (Genesis 1:1). On the first day, God created light and separated it from darkness.
On the second day, God created the vault that He called "sky" to separate the water above the vault from the water below the vault.
On the third day, God gathered the water under the sky to one place, so that the dry ground appeared. He called the dry ground "land," and the gathered waters "seas." He then allowed the land to produce vegetation--seed-bearing plants and trees.
On the fourth day, God let there be two great lights in the sky to separate day from night on the Earth. The greater light (the Sun) would govern the day. The lesser light (the Moon) would govern the night. He also made the stars in the vault of the sky to give light on the Earth.
On the fifth day, God allowed the seas to teem with marine animals, and he allowed birds to fly above the Earth across the vault of the sky.
On the sixth day, God allowed the Earth to produce the land animals. And then, God said, "Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the Earth, and over every creeping thing that creepeth upon the Earth" (Genesis 1:26).
The first problem for any reader of this first chapter of Genesis is deciding how much of this was intended to be interpreted as literal history and how much of it is figurative poetry. Deciding that question is crucial for determining whether this Biblical account of Creation can be compatible with the natural sciences of cosmology, astronomy, geology, and evolutionary biology. As I have indicated in
previous posts, Christians cannot reach any agreement on this issue, which is most evident in how revelation through the Holy Spirit has failed to resolve the creation/evolution debate among Christians.
Consider what a literal reading of this first chapter would teach us. God created everything in the Universe in six days. The Universe is geocentric in that the Earth is at the center. (Wiker observes that "early Christians held to a geocentric universe.") Above the Earth, the sky is a solid vault that separates the waters above from the waters below, which is the boundary between heaven and earth. This cosmic geography saw the sky as having a form and function similar to what was found in the ancient Near East. Most people believed that the sky was solid.
In that solid sky, there were the Sun, the Moon, and the stars. The Earth was the only planet in the Universe. And the Moon was the only moon in the Universe. The stars did not have any planets orbiting around them.
All life was found on or a little above the Earth. So, there was no extraterrestrial life. There were, however, divinities or spiritual beings (angels?) who lived in the heavens. Notice that when God speaks of creating human beings, He speaks in the plural ("Let us make man in our image"). The Bible often has God speaking in the plural (for example, Gen. 3:22; 11:7; Deut. 32:8; Job 1:6; 2:1; Isa. 6:8. Sometimes, God sits on a throne and meets in a council with "all the multitudes of heaven standing around Him" (1 Kings 22:19-23; Job 1:6; 2:1). So, there was no extraterrestrial bodily life beyond the Earth. Christians who believe this will have to say that the search for extraterrestrial life is foolish and anti-Christian.
Notice that if we accept the literal reading of the Bible's cosmology, we will have to say that modern science has shown that the Bible's teaching is false. So, for example, if we think the Bible is teaching that the universe is geocentric, then this is denied by modern astronomy.
But then Christian scientists (like Francis Collins and Deborah Haarsma) will say that much of the Bible uses figurative stories of the sort that would have been comprehensible to the people of the ancient Near East that were not intended to be taken as literal history. The Bible, therefore, is not a science textbook but rather a book that tells us what we need to know about salvation. Or, as Galileo put it, the Bible tells us "not how the heavens go," but "how to get to heaven." The scientific study of the Book of Nature must be separated from the religious study of the Book of Scripture, although the two books should ultimately be compatible. Many scientists (like Galileo and Darwin) and many Christian theologians (like Pope John Paul II) agree on this conception of God speaking through two books.
Moreover, Christians need not read the Book of Scripture as denying the possibility of extraterrestrial life. For example, Thomas Chalmers was one of the leaders of Scottish evangelical Christianity in the 19th century; and he wrote extensively about how the Christian Revelation could be harmonized with the enlarged cosmos of modern astronomy that might include extraterrestrial life in many worlds beyond the Earth. In one text, he began by quoting from the book of Psalms:
"When I consider thy heavens, the work of thy fingers, the moon and the stars, which thou has ordained; What is man, that thou art mindful of him, and the son of man, that thou visitest him?" (Psalm 8:3-4)
Chalmers saw here a suggestion that God's universe is so vast and varied, extending far beyond what is visible to the naked eye, that we should see the Earth as only "one paltry and insignificant portion of it," and "how minute is the place, and how secondary is the importance of our world, amid the glories of such a surrounding magnificence." And so, "to an eye which could spread itself over the whole, the mansion which accommodates our species might be so small as to lie wrapped in microscopical concealment; and, in reference to the only Being who possesses this universal eye, well might we say, 'What is man that thou art mindful of him, or the son of man that thou shouldest deign to visit him'" (Crowe, 245, 250, 253, 268-69).
Chalmers suggests that we can see this expansiveness of God's universe confirmed by what modern astronomy tells us about the many stars that are suns with planets orbiting around them just as our Earth orbits around its star. And we can imagine that "worlds roll in these distant regions; and these worlds must be the mansions of life and of intelligence." In the remote future, we can foresee that our Sun will die or the Earth will fall into it, and then our world will disappear. But the many other worlds of life and intelligence orbiting other stars will survive. This shows that what God did in the first chapter of Genesis to create the human world on Earth, He has done for other distant planets to create other worlds of intelligent life. The Bible does not explicitly recognize these other worlds, but we should not assume that the Bible's silence is a denial of their existence.
THE STORY OF SALVATION
If the purpose of the Bible is to teach us "how to get to heaven"--rather than "how the heavens go"--then we must consider whether the Bible's story of salvation--based on the doctrines of Adam's Fall, the Incarnation of Christ, and the redemption of humanity through Christ's sacrifice--is compatible with extraterrestrial life. Nicholas of Cusa in 1440 seems to have been the first thinker in Latin Christianity to affirm a plurality of inhabited worlds in space. Remarkably, despite his radical views, the Church made him a cardinal in 1448 (Crowe, 27-34). But then a few years later, the Franciscan philosopher and theologian William Vorilong became the first Christian author to raise the question of whether the idea of a plurality of worlds could be reconciled with the Christian doctrines of divine incarnation and redemption.
Did the people who live on other worlds beyond the Earth sin just as Adam sinned? If they did, would Christ have to be incarnated in each world and then die in that world to redeem them? Or would the redemptive life of Christ on Earth be enough to universally redeem those sinners in the other worlds? Or is it possible that the people on those other worlds did not make Adam's mistake, and so they were sinless and did not need redemption? Chalmers implied that he could not decide between these alternatives (Crowe, 26-27, 37, 220-21, 224, 229, 242, 256-58, 325-332).
Jack Hitt reports interviewing some of the Jesuit astronomers affiliated with the Vatican Observatory and asking them about the theological implications of discovering extraterrestrial intelligent life. Would you baptize an extraterrestrial? One priest answered, "only if he asked for it."
The Rev. George Coyne, S.J., identified himself as a Jesuit astrophysicist. He was a close associate of Pope John Paul II and the director of the Vatican Observatory. Hitt reports Coyne's answer to the question: "'O.K., so I meet this 'person.' I would ask him: 'Are you intelligent? Self-reflexive? In the traditional sense do you have what we can call a soul?' Good. 'Nice to meet you.'" He says he would then find out if their civilization sinned, then if it was redeemed, then if the redeemer was a man named Jesus, and then: 'If they say, Oh yes, now you have a theological problem. How could Jesus Christ be our redeemer on earth and of another planet and still be the one Son of God? Could he have had several incarnations? That's a pretty ticklish theological problem, and I don't know the answer.'"
Wiker, however, thinks the answer is clear: "we find no evidence of speculation about extraterrestrials among the early Christians. Not only did such speculation run directly against the central doctrinal claims of Christianity, but it also smacked of Epicureanism (which entailed, among other things, the denial of the immortal, immaterial soul, heaven, and hell). Small wonder the early Christians tossed the Epicurean package, extraterrestrials and all, into the abyss of doctrinal errors."
Furthermore, Wiker insists, not only is extraterrestrial life a doctrinal error, there is no scientific evidence for it despite many years of scientific searching for it. But is that correct?
ABSENCE OF EVIDENCE? EVIDENCE OF ABSENCE?
Wiker argues:
"By the end of the 20th century, scientists had demonstrated to all but the most zealously intransigent that--humble Earth excepted--our solar system was devoid of intelligent life and most likely devoid of any life. Further, as biologists discovered the ever-greater complexity of living organisms and the delicate balance of conditions that make them possible, it became clearer and clearer that fewer and fewer places in the universe could meet the conditions required for even the most rudimentary forms of life."
"Yet the dismal result of the high-tech search for extraterrestrials only stirred advocates all the more, resulting in the optimistic but defensive battle cry: 'The absence of evidence is not evidence of absence.' While this might warm the dwindling fires in the enthusiast's heart, it pays little service to reason. To be blunt, since it was the negative result of a century-long search for aliens, the absence of evidence is the evidence for absence. What else could it be?"
But it's not quite right to speak of "the negative result of a century-long search for aliens" for three reasons. First, it ignores the fact that the first evidence for exoplanets (planets outside the solar system) appeared only in 1996; but now, as of today, there are 5,346 confirmed exoplanets in 3,943 planetary systems with 855 having more than one planet. There are now some estimates that there are at least 20 billion Earth-like habitable planets in the Milky Way Galaxy alone. So, the search for extraterrestrial life on those planets has just begun within the last 25 years.
The second problem with Wiker's dismissal of the search for extraterrestrial life as a failure is that he ignores the recent intensity in the exploration of the solar system, which began in the 1970s with the first robotic exploration spacecraft, starting with the Pioneer 10 mission to Jupiter. For example, there is plenty of evidence that the icy moons of Jupiter have liquid water oceans on them, and some of them could have geothermal and water-rock interactions on the bottom. Europa is an ocean world entirely covered by sea ice. Europa actually has more liquid water than does Earth! In the 1980s, oceanographers discovered deep-sea life with a food chain based not on photosynthesis but on chemosynthesis linked to hot vents on the seafloor. The subsurface ocean on Europa is kept liquid by heating due to tidal interaction with Jupiter. Everywhere on Earth that has these conditions gets colonized by microbial life. Wiker says nothing about this.
That points to the third problem for Wiker. Even though he is right that the exploration of the solar system has not found any clear evidence of extraterrestrial intelligent life, there is growing evidence for the likelihood of finding extraterrestrial microbial life (or perhaps fossil evidence of its past existence). Increasingly, astrobiologists are concluding that microbes are the most likely forms of extraterrestrial life because the necessary conditions for such life are so much more common in the universe than the necessary conditions for intelligent life.
Wiker's insistence that we are unlikely to ever find any evidence for "even the most rudimentary forms of life" beyond the Earth is implausible, because he is silent about the growing evidence for likely conditions favorable to microbial life in places like the oceans of Europa. Does Wiker believe that if we were to find microbes on one of the icy moons of Jupiter, that would deny the central doctrines of Christianity?
Finding microbes in the Solar System beyond the Earth or on exoplanets might not seem spectacular. But consider the implications. This would show that the processes that lead to the origin of life are not peculiar to the Earth, and they might be common in the Universe. The history of life on Earth has been one of continual development from the simplest forms of life to the most complex, with every increasing degrees of living sensitivity and intelligence. If life is a general phenomenon in the cosmos, then so is intelligence.
And with the evolutionary development of symbolic intelligence, there will be minds capable of asking questions about the intellectual and spiritual meaning of it all, and about whether their extraterrestrial souls need to be saved.
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