The planets in the solar system are a diverse lot. A new study indicates that extrasolar planetary systems are not.1

The eight planets in the solar system range in size from 3,400 miles in diameter (Mercury) to 86,882 miles in diameter (Jupiter). The mass range is much more dramatic, from 0.055 times Earth’s mass (Mercury) to 318 times Earth’s mass (Jupiter). Densities range from 0.687 times that of liquid water (Saturn) to 5.514 times that of liquid water (Earth).

The list of extrasolar planets with well-measured characteristics now numbers more than 3,700.2 The number of known multiple planet systems now stands at 621.3

A team of thirteen astronomers from Canada and the United States earlier this year studied 909 planets in 355 multi-planet systems discovered by the Kepler spacecraft.4 They found that “planets within a single multi-planet system tend to be closer in size than planets drawn randomly from the collection of multi-planet systems.”5 That is, where there are multiple planets in a planetary system, those planets tend to possess similar diameters. They also found that “adjacent planets within a given system tend to be spaced in a regular geometric progression.”6

Now, three astronomers at Yale University investigated whether this similarity in planetary size is accompanied by similarity in mass for planets in the same planetary system.7 For planets discovered by the Kepler spacecraft, their masses are much more challenging to measure than their diameters. The three astronomers applied a special technique developed by astronomers Eric Agol (Eric is a Christian who attended my Paradoxes Sunday class when he was at Caltech) and Daniel Fabrycky8 to use the transit time variation of planets to determine the planets’ masses. Using this technique, the three astronomers assembled a large database of measured masses for the “Kepler multis.” Kepler multis are planets discovered by the Kepler spacecraft with known planetary partners in the same system.

The team first noted that the majority of Kepler multis are either super Earths or sub-Neptunes. That is, they range in mass from 1.1–14 times Earth’s mass. This statistic is startling, given that none of the Sun’s planets fall in this mass range.

Second, the researchers noted that Kepler multis have much more tightly spaced orbits than do the solar system planets. Third, they affirmed their preconception that Kepler multis in the same planetary system tend to possess similar masses.

The three astronomers did observe that the Kepler multis manifest a wide range of masses. In fact, they manifest a much wider range than the solar system planets. For the solar system, the range is 0.055–318 Earth masses. For the Kepler multis, it is 0.4–8,586 Earth masses. The astronomers demonstrated, however, that within each multi-planetary system, the planets exhibit similar masses. Inter-system planet mass variability is large, while intra-system planet mass variability is remarkably small.

In the words of the research team, the similar diameters and masses of intra-system Kepler multis make them all “peas in a pod.”9 These peas in a pod are strikingly different from the eight planets in the solar system. The three astronomers have added to the ever-accumulating evidence that the solar system is unique and special in its exquisite design features that enable it to sustain advanced life on one of its planets.

Endnotes
  1. Sarah Millholland, Songhu Wang, and Gregory Laughlin, “Kepler Multi-Planet Systems Exhibit Unexpected Intra-System Uniformity in Mass and Radius,” Astrophysical Journal Letters 849 (November 9, 2017): id. L33, doi:10.3847/2041-8213/aa9714.
  2. “Catalog,” Exoplanet TEAM, The Extrasolar Planets Encyclopaedia, last updated 2015, http://exoplanet.eu/catalog/.
  3. “Catalog,” Exoplanet TEAM.
  4. Lauren M. Weiss et al., “The California-Kepler V. Peas in a Pod: Planets in a Kepler Multi-Planet System Are Similar in Size and Regularly Spaced,” (June 19, 2017), arXiv:1706.06204v.1, https://arxiv.org/pdf/1706.06204.pdf.
  5. Weiss et al., “California-Kepler V,” 1.
  6. Weiss et al., “California-Kepler V,” 1.
  7. Millholland, Wang, and Laughlin, “Kepler Multi-Planet Systems.”
  8. Eric Agol and Daniel C. Fabrycky, “Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets,” (July 24, 2017), arXiv:1706.09849v3, https://arxiv.org/pdf/1706.09849.pdf.
  9. Millholland, Wang, and Laughlin, “Kepler Multi-Planet Systems,” 1.

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.



Email Sign-up

Sign up for the TWR360 Newsletter

Access updates, news, Biblical teaching and inspirational messages from powerful Christian voices.

Thank you for signing up to receive updates from TWR360.

Required information missing

This site is protected by reCAPTCHA, and the Google Privacy Policy & Terms of Use apply.