“Water, water everywhere, nor any drop to drink.” This famous verse from “The Rime of the Ancient Mariner” by Samuel Taylor Coleridge describes a thirsty man surrounded by water as far as the eye can see and yet not a single drop of the water is safe to drink. Astronomers have discovered many planets beyond our solar system that are far richer in water than Earth. However, as it was for Coleridge’s ancient mariner, astronomers are finding that all this water may be deadly—not only for extraterrestrial mariners, but also for virtually all forms of life.

Astronomers have discovered hundreds of exoplanets (planets beyond the solar system) displaying a wide range of mass densities, from 0.09 grams per cubic centimeter to >23 grams per cubic centimeter.1 This mass density spread indicates that exoplanets range from possessing no water at all to being very rich in water, where 50 percent or more of the planet’s mass is water. Earth, with a little less than 0.03 percent of its mass as water, is technically classified as a water-poor planet.

Water-Rich Planets
Water-rich planets are explained by small planets forming beyond their host stars’ snow lines (the distance from the host star where it is cold enough for water, ammonia, methane, carbon dioxide, and carbon monoxide to freeze into solid ice grains) and later migrate inward toward their host stars. Low-mass (≤2 Earth masses) water-rich planets that migrate close enough to their host stars to lose light-weight gases from their atmospheres will possess as their outermost condensed layer a globally extensive deep (>1,000 kilometers) liquid water ocean.

Where the planet’s water mass fraction is a few percent or more, the pressure at the bottom of the surface ocean will be so great as to form a frozen ice layer that permanently separates the liquid water from the planet’s rocky interior.2 That is, there will be no chemical exchange between the liquid water and the rocky material (see figure 1.)

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Figure 1: Waterworld Cross Section

Two astronomers, Amit Levi and Dimitar Sasselov at Harvard University, produced detailed models of these water worlds where the surface ocean is separated from crust and core by a frozen ice barrier.3 They demonstrated that the pH of the such oceans would range from 2 to 4. Solutions with a pH less than 7 are acidic. A pH measure of 2.0 is akin to the acidity of pure lemon juice. A pH of 4.5 is akin to the acidity of pure tomato juice. Earth’s sea water is slightly basic with a pH range = 7.5–8.4.

Acidic Waterworld Problem
There are extremophile microbes on Earth that are able to survive in acidic environments where the pH is as low as 2–4. However, life cannot originate under such acidic conditions.4 Thus, waterworlds where a permanent ice layer separates the surface liquid water ocean from the rocky interior must be permanently lifeless (unless an intelligent Agent creates and delivers extremophiles to such planets).

This habitability limitation applies not just to the planets considered by Levi and Sasselov, but also to the cold moons in our solar system and other planetary systems.

Over the past two decades, there has been much speculation about the possibility of subterranean life on such icy solar system moons as Ganymede, Europa, Callisto, and Titan. For many reasons, astronomers are convinced that these moons possess more than 30 percent of their mass as water.5 Given these planets’ cold space environments, their surfaces must be frozen. Tidal heating exerted by the host planet’s gravity or interior heat released from radioisotopes conceivably could create a layer of liquid water below the surface ice layer. However, as with the planets modeled by Levi and Sasselov, there would be a permanent ice layer separating the subterranean ocean from the rock interior (see figure 2). Thus, the icy solar system moons must be lifeless. And I’d argue there are better space exploration missions for NASA to fund than, for example, its current proposal to send a spacecraft to Europa, punch a borehole through its 26+ kilometer surface ice layer, and send a movie camera through the hole to swim through the possibly existing subterranean ocean and photograph hypothesized existing microbes.

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Figure 2: Internal Structure of Jupiter’s Largest Moon, Ganymede. Image credit: Kelvinsong

Origin of Life on Earth
Earth likely began with a deep-surface ocean like the worlds investigated by Levi and Sasselov. However, the moon-forming event and other events in Earth’s early history stripped the original liquid water surface layer down to its present thin layer. Earth’s liquid water layer is so thin that there is inadequate pressure for an ice layer to form at the bottom. Therefore, Earth’s oceans have remained in contact with the planet’s crust.

Also, at the time of life’s origin on Earth 3.8 billion years ago, a few volcanic islands and cratons (ancient mini-continents) pierced above sea level. Thus, the early marine environment experienced mineral exchange from two sources: (1) the rocky ocean floors and (2) the volcanic islands and mini-continents. This mineral exchange kept Earth’s oceans from becoming either too acidic or too basic. Thanks to how radically different Earth’s features and formation history was from all other known planets, a wide diversity of life has been able to thrive here for the past 3.8 billion years. Because of the diversity, abundance, and longevity of this life, it is possible for billions of humans to simultaneously live on Earth and develop the technology where those billions of humans can hear and respond to the Creator’s offer of redemption from their evil and gain an eternal loving relationship with him. In my book Improbable Planet, I describe how Earth’s unique features and its 3.8-billion-year history of diverse life makes possible the redemption of billions of human beings.6 Thanks to Levi and Sasselov, we have yet more reasons to thank God for how wonderfully he designed Earth and its life.

Featured image: Artist’s Rendition of a Waterworld Planet. Image credit: Luciano Mendez

Endnotes
  1. “The Catalog,” The Extrasolar Planets Encyclopaedia (website), Exoplanet TEAM, last updated May 2, 2018, http://exoplanet.eu/catalog/; Joshua Pepper et al., “KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396,” Astronomical Journal 153 (May 2017): id. 215, doi:10.3847/1538-3881/aa6572; “List of Exoplanet Extremes,” Wikipedia, last modified April 29, 2018, https://en.wikipedia.org/wiki/List_of_exoplanet_extremes.
  2. A. Levi, D. Sasselov, and M. Podolak, “Structure and Dynamics of Cold Water Super-Earths: The Case of Occluded CH4 and Its Outgassing,” Astrophysical Journal 792 (September 10, 2014): id. 125, doi:10.1088/0004-637X/792/2/125.
  3. A. Levi and D. Sasselov, “A New Desalination Pump Helps Define the pH of Ocean Worlds,” Astrophysical Journal 857 (April 10, 2018): id. 65, doi:10.3847/1538-4357/aab715.
  4. H. James Cleaves and John H. Chalmers, “Extremophiles May Be Irrelevant to the Origin of Life,” Astrobiology 4 (March 2004): 1–9, doi:10.1089/153110704773600195; Fazale Rana and Hugh Ross, Origins of Life: Biblical and Evolutionary Models Face Off (Covina, CA: RTB Press, 2014), 175–85.
  5. Rana and Ross, Origins of Life, 200–206.
  6. Hugh Ross, Improbable Planet: How Earth Became Humanity’s Home (Grand Rapids: Baker, 2016).

Check out more from Dr. Hugh Ross @Reasons.org

 

About The Author

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. I also am eager to equip Christians to engage, rather than withdraw from or attack, educated non-Christians. One of the approaches I’ve developed, with the help of my RTB colleagues, is a biblical creation model that is testable, falsifiable, and predictive. I enjoy constructively integrating all 66 books of the Bible with all the science disciplines as a way to discover and apply deeper truths. 1 Peter 3:15–16 sets my ministry goal, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience." Hugh Ross launched his career at age seven when he went to the library to find out why stars are hot. Physics and astronomy captured his curiosity and never let go. At age seventeen he became the youngest person ever to serve as director of observations for Vancouver's Royal Astronomical Society. With the help of a provincial scholarship and a National Research Council (NRC) of Canada fellowship, he completed his undergraduate degree in physics (University of British Columbia) and graduate degrees in astronomy (University of Toronto). The NRC also sent him to the United States for postdoctoral studies. At Caltech he researched quasi-stellar objects, or "quasars," some of the most distant and ancient objects in the universe. Not all of Hugh's discoveries involved astrophysics. Prompted by curiosity, he studied the world’s religions and "holy books" and found only one book that proved scientifically and historically accurate: the Bible. Hugh started at religious "ground zero" and through scientific and historical reality-testing became convinced that the Bible is truly the Word of God! When he went on to describe for others his journey to faith in Jesus Christ, he was surprised to discover how many people believed or disbelieved without checking the evidence. Hugh's unshakable confidence that God's revelations in Scripture and nature do not, will not, and cannot contradict became his unique message. Wholeheartedly encouraged by family and friends, communicating that message as broadly and clearly as possible became his mission. Thus, in 1986, he founded science-faith think tank Reasons to Believe (RTB). He and his colleagues at RTB keep tabs on the frontiers of research to share with scientists and nonscientists alike the thrilling news of what's being discovered and how it connects with biblical theology. In this realm, he has written many books, including: The Fingerprint of God, The Creator and the Cosmos, Beyond the Cosmos, A Matter of Days, Creation as Science, Why the Universe Is the Way It Is, and More Than a Theory. Between writing books and articles, recording podcasts, and taking interviews, Hugh travels the world challenging students and faculty, churches and professional groups, to consider what they believe and why. He presents a persuasive case for Christianity without applying pressure. Because he treats people's questions and comments with respect, he is in great demand as a speaker and as a talk-radio and television guest. Having grown up amid the splendor of Canada's mountains, wildlife, and waterways, Hugh loves the outdoors. Hiking, trail running, and photography are among his favorite recreational pursuits - in addition to stargazing. Hugh lives in Southern California with his wife, Kathy, and two sons.



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