LEAD ARTICLE by Hugh Ross, PhD
UpdateUpdate onon thethe QuestQuest forfor anan Earth-LikeEarth-Like PlanetPlanet uring the Middle Ages and especially in DArthurian legend, the quest for the Holy Grail, the cup from which Jesus drank at the Last Supper, became the consuming passion of nobles. They were driven by belief that the cup possessed miraculous healing powers. Today, many astronomers passionately pursue a different Holy Grail. Their quest—to find a planet sufficiently like Earth to support life, perhaps even advanced life. The discovery of such a planet could, some believe, hold the power to deliver humanity from our cosmic loneliness, from our isolated existence on this pale blue dot.
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Many of these modern-day Galahads and Lancelots, been able to measure the characteristics of nearly 700 aware that life arose as soon as the late heavy confirmed planets (at the date of this publication).6 bombardment subsided enough for liquid water to remain, assume that wherever liquid water exists, Of these confirmed and measured planets, 373 are life exists also. Such reasoning explains astronomer at least as massive as Jupiter or more so (Jupiter = Steven Vogt’s excitement at a recent news conference 317.4 Earth masses); 239 are less massive than Jupiter announcing the (presumed) discovery of Gliese 581g, but more massive than Uranus (Uranus =14.5 Earth a planet with a predicted surface temperature (at two masses); 77 are “super Earths,” more massive than Earth longitudes only) that would allow for the presence of but less massive than Uranus. Only one is less massive liquid water. Vogt exclaimed, “[G]iven the ubiquity and than Earth (by fifty times), and it orbits a pulsar. Six of propensity of life to flourish wherever it can, my own the planets have yet undetermined mass. personal feeling is that the chances of life on this planet Holy Grail pursuers fix their gaze on the super-Earths. are 100 percent.”1 The three smallest are HD 20794c, Kepler-11f, and Since that announcement, Bayesian analysis (application Gliese 581e, which range from two to two-and-a-half of a statistical technique) has negated the existence times Earth’s mass. All three are hot planets orbiting too of Gliese 581g.2 And, at the same time, two noted close to their host stars to permit the presence of liquid astronomers have challenged the familiar ubiquity- or frozen water. Two larger super-Earth planets, Gliese of-life hypothesis.3 It’s one thing, they note, for life 581d and HD 85512b, may possibly be more favorable to to arise just as soon as conditions would allow for its water’s presence. survivability, but it’s another for that initial, relatively While Gliese 581d is at least seven times more massive simple life to give rise to a species (in just 3.8 billion than Earth, it orbits a star much less massive than years) sufficiently advanced to research and the Sun at a distance of about 20 million miles and recognize its (first life’s) early emergence. receives only 35% of the energy Mars receives Using the same Bayesian analysis technique, from the Sun. Given its mass, Gliese these astronomers concluded that life must 581d likely possesses a thick be “arbitrarily rare in the universe.”4 atmosphere. Two How do astronomers go about their quest of finding and determining the features of other planets? They use one of these two methods: the radial velocity method and the transit method. The radial velocity method calibrates the degree to which a distant planet’s gravity alters the position of its host star as it orbits that star. This method works best in detection of huge planets positioned relatively close to their host stars. The transit method, on the other hand, measures the degree to which a planet dims our view of its host star’s light when passing in front of that star. This method works only if the plane of the planet’s orbit is aligned with the telescope’s line of sight. But this method can detect both large and small planets.5 Figure 1: Artist’s Conception of a Distant Planetary System To date, researchers have identified about 1,800 planet credit: NASA/G. Bacon (STScI), candidates outside our own solar system and have iStockphoto.com
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different research teams have calculated that if Gliese This conclusion is consistent with the Bible’s message 581d contains the expected level of carbon dioxide in that God supernaturally designed the Sun, the Earth,
its atmosphere, CO2 would trap enough heat from the our planetary partners, and Earth’s earlier life-forms host star to sustain a temperature above water’s freezing to provide a suitable (though temporary) home for point.7 However, Gliese 581d is tidally locked to its host humanity. And, if we consider the angels, humans are star; therefore a liquid-water-permitting temperature, not really alone in the universe. Better yet, the Creator if it exists anywhere on the planet’s surface, would be Himself of this wondrous habitat has personally visited, present at only two tiny locations. in human form, bearing the name Immanuel,11 which means “God with us.” And He made a promise to those The possibility of an extremely heavy atmosphere who worship Him: “I will never leave you or forsake around Gliese 581d seems reasonable. Heavy you.”12 atmospheres appear to be the norm for super-Earths. Even planets orbiting so close to their host stars as to endnote reach temperatures of 2,000+°K (and thus drive off 1. Steven Vogt as quoted by Terrence Aym in “Alien Life on New Planet most of their atmospheric constituents) would possess Gliese 581g 100 Percent Certain,” Helium (October 4, 2010). atmospheres exponentially thicker than Earth’s.8 2. Philip C. Gregory, “Bayesian Re-Analysis of the Gliese 581 Exoplanet System,” Monthly Notices of the Royal Astronomical Society 415 (August 2011): 2523–45; Mikko Tuomi, “Bayesian Re-Analysis of the Radial (As one research team observed, super-Earths, because Velocities of Gliese 581. Evidence in Favour of Only Four Planetary of their very thick atmospheres, would be more Companions,” Astronomy & Astrophysics 528 (April 2011): L5. appropriately termed “mini-Neptunes.”9) 3. David S. Spiegel and Edwin L. Turner, “Life Might Be Rare Despite Its Early Emergence on Earth: A Bayesian Analysis of the Probability of Abiogenesis,” arXiv:1107.3835v1 (July 19, 2011), submitted to Ultra-thick atmospheres do not necessarily rule out Proceedings of the National Academy of Sciences, USA. the existence of archaea or bacteria on a planet’s 4. Spiegel and Turner, 1. surface, but they certainly rule out advanced life. Lungs 5. Jean Schneider, an astronomer at the Paris Observatory, maintains an cannot function for very long in atmospheric pressures interactive extra-solar planet catalog. exceeding Earth’s by even just three times. Furthermore, 6. Lisa Kaltenegger, Antígona Segura, and Subhanjoy Mohanty, “Model Spectra of the First Potentially Habitable Super-Earth—Gl581d,” thick atmospheres imply lots of water, far too much Astrophysical Journal 733 (May 20, 2011): 35; Robin D. Wordsworth et water for continents and oceans to coexist. Then there is al., “Gliese 581d Is the First Discovered Terrestrial-Mass Exoplanet in the matter of partner planets. The existence of advanced the Habitable Zone,” Astrophysical Journal Letters 733 (June 1, 2011): L48. life requires more than an exact Earth twin. It requires a 7. Bryce Croll et al., “Broadband Transmission Spectroscopy of the Super- planet accompanied by nearly exact analogues of Earth’s Earth GJ 1214b Suggests a Low Mean Molecular Weight Atmosphere,” seven planetary partners.10 Astrophysical Journal 736 (August 1, 2011): 78; Joshua N. Winn et al., “A Super-Earth Transiting a Naked-Eye Star,” Astrophysical Journal Letters 737 (August 10, 2011): L18. Planets roughly the size, mass, and distance from their 8. Lisa Kaltenegger, S. Udry, and F. Pepe, “A Habitable Planet around HD host stars as Earth may eventually be found and may 85512b?” August 17, 2011), arXiv:1108.3561. even prove abundant. However, Earth-like planets with 9. Hugh Ross, “Elemental Evidence of Earth’s Divine Design,” New Reasons the same atmospheric conditions, ocean-to-continent to Believe, vol. 2, no. 2 (2010): 6–8. ratios, and elemental abundances as Earth, with a star as 10. Hugh Ross, “The Remarkable Design of the Solar System’s Turbulent Youth, Parts 1-5,” Today’s New Reason To Believe (May 30–June 27, luminous and stable as the Sun, and with the necessary 2011). suite of planetary partners, are either extremely rare or, 11. Isaiah 7:14, 8:8, Matthew 1:23 (NIV). more likely, altogether nonexistent (unless specifically 12. Hebrews 13:5 (NIV). designed by the Creator).
Listen to Jeff Zweerink talk more about the Gliese 581g discovery on the Science News Flash podcast (Oct. 14, 2010).
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