A-1 - Encouraged by What You Read?

A few weeks ago, I discussed the possibility of finding habitable planets in binary star systems. Just a couple days ago, astronomers announced the discovery of an Earth-like exoplanet—called Proxima Centauri b—orbiting Proxima Centauri, one of the closest stars to Earth. Proxima Centauri also appears to belong to a multiple star system that includes the binary stars Alpha Centauri A and B. Let’s look at what this discovery means.

Details of the Host Star

Proxima Centauri sits 15,000 astronomical units (AU) away from the Alpha Centauri binary pair. If it orbits this pair of stars, it does so at least every 500,000 years. When viewed from Proxima Centauri b, the Alpha Centauri binary system would appear as two stars, both much brighter than Venus—the brightest object in the sky after the Sun and Moon. While Alpha Centauri A and B are similar in size to the Sun, Proxima Centauri has only 12 percent the mass of the Sun. Consequently, it gives off about one-tenth of a percent of the Sun’s radiation. The small mass and luminosity means that the habitable zone (as usually defined) has an inner boundary of 0.042 AU and an outer boundary of 0.082 AU. See the article in Nature for a full description of Proxima Centauri and Proxima Centauri b.

One other aspect of Proxima Centauri warrants mention. Astronomers have monitored the star for a number of years and have noticed frequent bursts of high-energy radiation from the star. Proxima Centauri is classified as moderately active, but gives off bursts of radiation that would measure 400 times larger on Proxima Centauri b than anything Earth experiences from the Sun.

Details of the Exoplanet

While most of the recent exoplanet discoveries arise from the transit method and the successful Kepler mission, Proxima Centauri b was found using the radial velocity (or Doppler) method. Given the limitations of this method, astronomers can only determine a minimum mass for the exoplanet of 1.3 times Earth’s mass. Proxima Centauri b orbits at 0.05 astronomical units (one AU is the distance from Earth to the Sun), ten times closer to its star than Mercury is from the Sun. Given this distance and the size of the star Proxima Centauri, it takes 11.2 days for the planet to complete an orbit. However, this orbit places Proxima Centauri b well within the habitable zone of Proxima Centauri!

Proxima Centauri b also has an Earth-like mass and orbits in its star’s liquid water habitable zone. However, the small distance between Proxima Centauri and Proxima Centauri b means that the planet is tidally locked, i.e., the same side of the planet always faces the star. While research shows that some tidally locked exoplanets could still have liquid water, the lack of a magnetic field (since there is no rotation) and the intense radiation bursts emitted by Proxima Centauri puts tremendous stress on the atmosphere and likely removes any water from the planet.

The Big Deal

Why am I excited about this discovery? Because the proximity of the exoplanet to Earth enhances the chance that astronomers could actually observe Proxima Centauri b (within a decade or two) in enough detail to determine if the planet has liquid water, if it has continents or clouds, and if it has any signs of life. Only data of this nature will truly answer what characteristics a planet must have to be truly habitable.

Subjects: Exoplanets

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About The Author

Jeff Zweerink

Since my earliest memories, science and the Christian faith have featured prominently in my life - but I struggled when my scientific studies seemed to collide with my early biblical training. My first contact with RTB came when I heard Hugh Ross speak at Iowa State University. It was the first time I realized it was possible to do professional work incorporating both my love of science and my desire to serve God. I knew RTB's ministry was something I was called to be a part of. While many Christians and non-Christians see the two as in perpetual conflict, I find they integrate well. They operate by the same principles and are committed to discovering foundational truths. My passion at RTB is helping Christians see how powerful a tool science is to declare God's glory and helping scientists understand how the established scientific discoveries demonstrate the legitimacy and rationality of the Christian faith. While many Christians and non-Christians see the two as in perpetual conflict, I find they integrate well. • Biography • Resources • Upcoming Events • Promotional Items Jeff Zweerink thought he would follow in his father's footsteps as a chemistry professor until a high school teacher piqued his interest in physics. Jeff pursued a BS in physics and a PhD in astrophysics at Iowa State University (ISU), where he focused his study on gamma rays - messengers from distant black holes and neutron stars. Upon completing his education, Jeff taught at Loras College in Dubuque, Iowa. Postdoctoral research took him to the West Coast, to the University of California, Riverside, and eventually to a research faculty position at UCLA. He has conducted research using STACEE and VERITAS gamma-ray telescopes, and currently works on GAPS, a balloon experiment seeking to detect dark matter. A Christian from childhood, Jeff desired to understand how the worlds of science and Scripture integrate. He struggled when his scientific studies seemed to collide with his early biblical training. While an undergrad at ISU, Jeff heard Hugh Ross speak and learned of Reasons to Believe (RTB) and its ministry of reconciliation - tearing down the presumed barriers between science and faith and introducing people to their personal Creator. Jeff knew this was something he was called to be a part of. Today, as a research scholar at RTB, Jeff speaks at churches, youth groups, universities, and professional groups around the country, encouraging people to consider the truth of Scripture and how it connects with the evidence of science. His involvement with RTB grows from an enthusiasm for helping others bridge the perceived science-faith gap. He seeks to assist others in avoiding the difficulties he experienced. Jeff is author of Who's Afraid of the Multiverse? and coauthor of more than 30 journal articles, as well as numerous conference proceedings. He still serves part-time on the physics and astronomy research faculty at UCLA. He directs RTB's online learning programs, Reasons Institute and Reasons Academy, and also contributes to the ministry's podcasts and daily blog, Today's New Reason to Believe. When he isn’t participating in science-faith apologetics Jeff enjoys fishing, camping, and working on home improvement projects. An enthusiastic sports fan, he coaches his children's teams and challenges his RTB colleagues in fantasy football. He roots for the Kansas City Chiefs and for NASCAR's Ryan Newman and Jeff Gordon. Jeff and his wife, Lisa, live in Southern California with their five children.

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