Ever since 1995, when the first planet outside the solar system orbiting a hydrogen-burning star was discovered,1 astronomers have been on a holy grail search to find a planet sufficiently like Earth that it could possibly host life. A quarter of a century and 4,255 discovered exoplanets2 later, some people think scientists have found an Earth twin. A team of twelve astronomers led by Andrew Vanderburg published a paper in Astrophysical Journal Letters in which they announced their discovery of an Earth-sized planetcalled Kepler 1649c, orbiting its star in the “habitable zone.”3

What Earth-Like Means
This paper caught the attention of science journalists around the world. Writing for USA Today, Doyle Rice quoted a NASA spokesperson, stating “This world is most similar to Earth both in size and estimated temperature.”4 The Financial Express wrote about Kepler 1649c’s “proximity to the life conditions on the Earth”5 and that “there is no exoplanet that is closer to Earth in size and temperature and which also lies in the habitable zone”6

As typically occurs with discoveries of this nature, the peer-reviewed paper on which the popular web articles were based was much more subdued and qualified in its claims. It is true that Kepler 1649c is the most Earth-like discovered to date. The planet is only 6% larger in diameter than Earth (see figure 1) and the amount of light and heat it receives from its host star is 74% of what Earth receives from the Sun. Thus, Kepler 1649c could be in the habitable zone—the distance range from its host star where liquid water could conceivably reside on its surface.

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Figure 1: Artist’s Rendition Comparing Kepler 1649c to Earth. Image credit: NASA/Ames Research Center/Daniel Rutter

Receiving 74% of the light and heat Earth receives from the Sun implies that its average surface temperature with no heat-trapping atmosphere (no greenhouse gases) would be -39°C (-38°F). This temperature compares with -18°C (0°F) for Earth without a heat-trapping atmosphere. The 21°C (38°F) difference means that Kepler 1649c would need an atmosphere loaded up with much more carbon dioxide and/or methane than Earth. The extra greenhouse gases needed would not necessarily rule out microbial life, but they would rule out high-metabolism terrestrial animals like us.7

Planets Need More Than a Water Zone
Something not noticed in most popular web articles on this discovery is that Kepler 1649c orbits a star with only 20 and 0.5% the mass and brightness of the Sun, respectively. Such characteristics for the planet’s host star put Kepler 1649c squarely outside of the ultraviolet habitable zone. (I wrote about this zone in my book Improbable Planet8 and in an article I wrote in 2016.9) For a planet to be truly habitable for any kind of life, it must simultaneously reside in both the liquid water habitable zone and the ultraviolet habitable zone. Kepler 1649c does not.

Vanderburg and his team acknowledged that Kepler 1649c experiences “a very different environment (an extended era of ultraviolet (UV) irradiation, tidal locking, etc.) from planets in our own solar system.”10 Indeed, planets orbiting their host stars as closely as Kepler 1649c orbits Kepler 1649 (the star) will be tidally locked. Tidal locking means that one hemisphere of Kepler 1649c will permanently face its star, much like one hemisphere of our Moon permanently faces Earth. Tidal locking implies that one hemisphere of Kepler 1649c will be blisteringly hot while the other hemisphere will be extremely cold. Furthermore, it implies that any surface water on Kepler 1649c will be transported to its cold hemisphere where it will remain permanently frozen.

The dozen astronomers also acknowledged that Kepler 1649c may suffer orbital disruptions (catastrophic to advanced life) from mean-motion resonances resulting from other planets known to exist and likely to exist in the same planetary system. Figure 2 shows an artist’s rendition of the Kepler 1649 planetary system.

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Figure 2: Artist’s Rendition of the Kepler 1649 Planetary System. Image credit: NASA/Ames Research Center/Daniel Rutter

Another problem for habitability is that stars like Kepler 1649 are highly variable in their luminosity. Life would be exposed to intolerable temperature changes. Stars like Kepler 1649 also frequently emit deadly superflares. For this and several other reasons, planets orbiting stars as small as or smaller than Kepler 1649 are not habitable planets.

To date, astronomers have discovered thirteen distinct planetary habitable zones. I describe and list these zones in two previous blogs.11 So far, astronomers have discovered only one planet that simultaneously resides in more than two of these planetary habitable zones, the same planet that simultaneously resides in all thirteen. It seems no accident of nature but rather purpose from nature’s Creator that we live and thrive on this favored planet.

Featured image: Artist’s Conception of Kepler 1649c’s Surface, Assuming It Possesses Water. Image credit: NASA/Ames Research Center/Daniel Rutter

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Endnotes
  1. Michel Mayor and Didier Queloz, “A Jupiter-Mass Companion to a Solar-Type Star,” Nature 378, issue 6555 (November 23, 1995): 355–59, doi:10.1038/378355a0.
  2. Exoplanet TEAM, The Extrasolar Planets Encyclopaedia, The Catalog (April 24, 2020), http://exoplanet.eu/catalog/.
  3. Andrew Vanderburg et al., “A Habitable-Zone Earth-Sized Planet Rescued from False Positive Status,” Astrophysical Journal Letters 893, no. 1 (April 10, 2020): L27, doi:10.3847/2041-8213/ab84c5.
  4. Doyle Rice, “Has NASA Discovered Another Earth? Perhaps” USA Today (April 16, 2020), https://www.usatoday.com/story/news/nation/2020/04/15/has-nasa-discovered-another-earth/5139773002/.
  5. “New ‘Earth-Like’ Exoplanet Kepler 1649c Found! Scientists Analyze If It Can Sustain Life,” Financial Express (April 17, 2020), https://www.financialexpress.com/lifestyle/science/new-earth-like-exoplanet-kepler-1649c-found-scientists-analyze-if-it-can-sustain-life/1931902/.
  6. “New ‘Earth-Like’ Exoplanet.”
  7. Hugh Ross, “Complex Life’s Narrow Requirements for Atmospheric Gases,” Today’s New Reason to Believe (blog), July 1, 2019, https://reasons.org/explore/blogs/todays-new-reason-to-believe/read/todays-new-reason-to-believe/2019/07/01/complex-life-s-narrow-requirements-for-atmospheric-gases.
  8. Hugh Ross, Improbable Planet: How Earth Became Humanity’s Home (Grand Rapids, MI: Baker, 2016), 84–85, https://shop.reasons.org/product/283/improbable-planet.
  9. Hugh Ross, “Overlap of Habitable Zones Gets Much Smaller,” Today’s New Reason to Believe (blog), December 27, 2016, https://reasons.org/explore/blogs/todays-new-reason-to-believe/read/todays-new-reason-to-believe/2016/12/27/overlap-of-habitable-zones-gets-much-smaller.
  10. Vanderburg et al., 5.
  11. Hugh Ross, “Tiny Habitable Zones for Complex Life,” Today’s New Reason to Believe (blog), March 4, 2019, https://reasons.org/explore/blogs/todays-new-reason-to-believe/read/todays-new-reason-to-believe/2019/03/04/tiny-habitable-zones-for-complex-life; Hugh Ross, “Complex Life’s Narrow Requirements.”

 

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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