This week’s post comes from Brandon Reddell (BS in physics and petroleum engineering from the University of Texas at Austin, MS in applied physics from Johns Hopkins University, and PhD in physics from the University of Houston). Brandon is part of RTB’s apologetics community and serves as president of the RTB Houston, TX Chapter. He currently works in the space industry with a focus on space radiation environments and effects.

A Bad Weather Day for M Dwarfs

On August 24, 2016, the European Southern Observatory announced the discovery of a planet around our nearest star, Proxima Centauri. Six months later, NASA announced that they found a system of seven Earth-like planets around another very close star, TRAPPIST-1. Both of these planetary systems are connected with M-dwarf stars, which are small-mass and low-temperature stars that make up three-quarters of all main sequence stars. Together, this news gives us strong hope of finding life close to Earth—or does it?

Habitability on Exoplanets around M Dwarfs

The recent news of these exoplanet discoveries near our solar system created a wealth of excitement and seemed to back up the claims that there are 40 billion habitable planets in our galaxy.1 The optimism of a planet containing liquid water being so close to home is profound. It has already been pointed out that the liquid water habitable zone of a planet orbiting an M-dwarf star is close to the host star. This usually leads to tidal locking of the planet’s rotation, where one side of the planet always faces the star. Additionally, this level of proximity can lead to exposure to more intense ultraviolet (UV) radiation from the host star, a key process in space weather.

What Is Space Weather?

“Space weather” refers to the collection of phenomena experienced near a star. A host star emits a lot of energy, in various forms, that affects objects orbiting the star. It can cause ground effects (e.g., power outages), atmospheric effects (e.g., aurora, communications loss), and even equipment effects in spacecraft (e.g., charging and single-event effects). Two major components of space weather, solar flares and coronal mass ejections, can be very problematic for planets. Solar flares are primarily bursts of high-energy UV radiation. Coronal mass ejections (CMEs) are larger bursts containing material emitted from the star (primarily protons and electrons). For a planet without a magnetic field to deflect the CMEs, the intense bursts of radiation would erode the atmosphere and provide lethal doses of radiation. Solar flares, because they are mostly intense UV light, do not interact with the magnetic field but do interact with a planetary atmosphere. Solar flares are categorized by their intensity, with the most intense being X-class, often referred to as “XUV flares.”

Solar Flares on Exoplanets

A recent publication looked at space weather effects for M-dwarf exoplanets having any atmosphere that contains oxygen and nitrogen.2 According to the study, exoplanets around M dwarfs are expected to receive XUV fluxes up to 200 times more intense than fluxes seen on exoplanets around Sun-like stars. This increased flux of XUV radiation significantly ionizes the exoplanet atmosphere. Electrons escape to space because of their light mass. The resulting excess of positive charge creates a radial electric field that is very efficient at accelerating the oxygen and nitrogen ions off the planet. Given enough time, planets with mostly oxygen and nitrogen atmospheres can lose their whole atmosphere to this process. The study shows that Earth-like atmospheres on exoplanets of various sizes can be drained in tens to hundreds of millions of years, thus creating a very strong case against the habitability of these exoplanets. The same study estimates that Proxima Centauri b, with a similar atmosphere, will lose its atmosphere in only 10 million years. The authors conclude that the best candidates for truly habitable Earth-like planets reside around Sun-like stars with mild space weather conditions. This feature alone limits the possible candidate stars to less than 10 percent of all main sequence stars.

Implications for Life in the Universe

While this is exciting work that will help researchers understand the Earth-Sun connection, it reveals formidable constraints for any exoplanet truly capable of supporting life. The space weather conditions of M-dwarf stars greatly reduce the likelihood of finding exoplanets, while limitations of current and foreseen technologies place additional difficulties in detecting exoplanets around Sun-like stars. As more research and discovery continues, it is expected that additional constraints will be found. It is becoming increasingly difficult to find exoplanets with conditions similar to those of Earth, thus revealing the uniqueness of our home and pointing to the careful design and planning necessary to host life.

Endnotes

  1. Erik Petigura, Andrew Howard, and Geoffrey Marcy, “Prevalence of Earth-Size Planets Orbiting Sun-Like Stars,” Proceedings of the National Academy of Sciences, USA 110 (November 2013): 19273–78, doi:10.1073/pnas.1319909110; Dennis Overbye, “Far-Off Planets like the Earth Dot the Galaxy,” New York Times, November 4, 2013, http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html.
  2. Vladimir S. Airapetian et al., “How Hospitable Are Space Weather Affected Habitable Zones? The Role of Ion Escape,” Astrophysical Journal Letters 836 (February 2017): L3, doi:10.3847/2041-8213/836/1/L3.

Subjects: Earth, Exoplanets, Space Weather, Life on Other Planets

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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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