Living with Tiny Aliens

The Image of God for the Anthropocene

Adam Pryor

• Publisher: Fordham University Press
• Year: 2020
• Print ISBN:
  9780823287710
  9780823288311
• eBook ISBN:
  9780823288328
• Edition: 1
• Topic: Theology & Religion
• Subtopic: Christian Theology

Astrobiology is changing how we understand meaningful human existence. Living with Tiny Aliens seeks to imagine how an individuals' meaningful existence persists when we are planetary creatures situated in deep time—not only on a blue planet burgeoning with life, but in a cosmos pregnant with living-possibilities. In doing so, it works to articulate an astrobiological humanities.

Working with a series of specific examples drawn from the study of extraterrestrial life, doctrinal reflection on the imago Dei, and reflections on the Anthropocene, Pryor reframes how human beings meaningfully dwell in the world and belong to it. To take seriously the geological significance of human agency is to understand the Earth as not only a living planet but an artful one. Consequently, Pryor reframes the imago Dei, rendering it a planetary system that opens up new possibilities for the flourishing of all creation by fostering technobiogeochemical cycles not subject to runaway, positive feedback. Such an account ensures the imago Dei is not something any one of us possesses, but that it is a symbol for what we live into together as a species in intra-action with the wider habitable environment.

CHAPTER 1

Exoplanets and Icy Moons and Mars, Oh My!

What exactly is astrobiology? Pointing to a date when the study of astrobiology begins, as a specific field or form of inquiry, can be a surprisingly difficult task. The term itself has a sort of lineage. While it is broader than earlier terms used, such as xenobiology (biology based on foreign chemistry) or exobiology (a search for life and extraterrestrial environments), it is certainly not unrelated to them. If the aim is simply to draw a line in the sand or note a seminal moment at which astrobiology research begins we might—at least loosely—point to NASA funding for exobiology research in 1959 or the establishment of the Exobiology Program in 1960 with its popularization by Joshua Lederberg. Yet the contemporary sense of astrobiology can hardly be understood without research in the 1980s and 1990s on extremophiles (organisms living in conditions originally thought to be uninhabitable). Perhaps, if we want a precise moment, we can point to the case made by Carl Woese, Otto Kandler, and Mark Wheelis in 1990 to rethink the taxonomic structure of biology in terms of three domains (Archaea, Bacteria, and Eucarya) as a beginning point: where a fundamental re-thinking in biology opens the door to the founding of astrobiology.¹ But, astrobiology needs to get us beyond the earth, does it not? What if the seminal moment for this new field belongs to the discovery of the first confirmed exoplanets in 1992, around Pulsar B1257+12, and the subsequent onslaught of newly discovered planetary bodies in other solar systems.²

Because astrobiology is so diverse, it is difficult (if not impossible) to tell its history in terms of typical principles—such as the development of an object and method of study—as we might with more traditionally unified scientific fields.³ Astrobiology brings together many distinct fields of scientific study but contextualizes them in terms of one another to address a particular problem and thereby begin shaping a style of inquiry not completely at home in any one of the participating fields. Thus, like so many other cross-disciplinary endeavors, it is challenging to try and categorize how exactly the various fields of study that are brought together under the heading of “astrobiology” actually intersect or whether all “astrobiologists” even agree about what this intersection might entail. A planetary scientist may consider astrobiology in very different ways from an evolutionary biologist, astrophysicist, or geologist who also participates in this cross-disciplinary inquiry.

If nothing else, I hope to dispel one popular misconception about astrobiology in this chapter: the commonsense or popular assumption that astrobiology deals specifically with aliens. For instance, when I started working on this project, a friend and chemistry professor quipped, “Great, you’re going to study the ‘science’ where they are still looking for the object they want to study.” Of course, as a theologian, I was unfazed because I cannot demonstrate the object of my own field of study exists! More to the point, the widely held supposition my friend invoked is that astrobiology is a study of alien life, but no such non-terran life is known to exist.

This widely held supposition needs to be challenged. Even simply acknowledging how NASA’s astrobiology research is guided by three overarching questions (How does life begin and evolve? Does life exist elsewhere in the Universe? What is the future of life on Earth and beyond?) suggests that more than demonstrating and analyzing the existence of alien life is at stake.⁴

Here we will look at four examples of astrobiological phenomena: Kepler-452b, Proxima Centauri b, Enceladus, and Mars. Other examples could be chosen, but these four are particularly helpful in that they represent three distinct types of phenomena that are of astrobiological interest. Kepler-452b and Proxima Centauri b are exoplanets. Enceladus is an icy moon within our own solar system. Finally, Mars is our planetary neighbor and was previously quite possibly habitable.

My contention is that these examples are of real astrobiological significance; they are not simply placeholders for alien life scientists have yet to find. What emerges through a consideration of these astrobiological phenomena themselves is a vision of the cosmos committed to understanding the intra-action of living-systems and habitability. Working through these different sorts of examples, an astute reader will notice some common themes emerging: Astrobiology is very concerned with microbial life; it is concerned with living-systems more than individual organisms; and it is seeking clarity regarding how habitable conditions affect the occurrence and development of living-systems. I will analyze the social significance of these phenomena more explicitly in the next chapter, paying special attention to how the public presentation of findings in astrobiology might give us pause even if it also stresses that this research is about more than finding aliens. For now, my more modest hope is to expose, critically, the interdisciplinary factors that affect the scope and scale of this body of research, and make clear just how different this research is from astrobiology as it is popularly conceived.

Kepler-452b

If there is one exoplanet that the wider public has heard about, it is probably Kepler-452b. Astronomers discovered it as part of the Kepler mission in 2015. Kepler is a space observatory and has been, since 2009, a primary telescope involved in discovering exoplanets by the transit method. It uses this method because Kepler’s only instrument is a photometer: a device that measures light intensity. This photometer continually measures 145,000 main sequence stars in the constellation Cygnus.

The transit method, like all of our current means of finding exoplanets, is an indirect observation technique. We do not actually see the planet; we detect signs that indicate the given planet is almost certainly there. In the case of the transit method, Kepler is monitoring dips in starlight that result from an exoplanet passing between the observed star and the telescope. Once an exoplanet is discovered by the transit method, by continuously monitoring the dimming of starlight we can determine the orbital period of the exoplanet, estimate its distance from the star it orbits, and approximate its diameter in relation to the size of this star.⁵

It is worth bearing in mind that the dips in stellar output described here are very small. To detect an Earth-size exoplanet, Kepler has to register a 0.01 percent dip in the intensity of starlight for at least three transits (less than three dips could indicate a false positive); then the finding must be confirmed using an additional indirect technique for discovering exoplanets or subsequent ground observations. Moreover, observing such a dip at all relies on an exoplanetary system orbiting its star in, virtually, the same plane as our own solar system. (By contrast, imagine a system where the exoplanets orbit their star on a plane offset 90 degrees to our own; there would be no dip in starlight because the exoplanet would not pass between its star and us.)⁶

At the time of its discovery, Kepler-452b was something novel: It was only the sixth “super-Earth” (a planet with a radius less than two times that of the Earth) found within the conservative habitable zone of its star.⁷ Moreover, it had been in the habitable zone of its star for 6 billion years. In short, it had been in an orbit where the presence of surface water and an atmosphere could not be ruled out for a longer time than the Earth has had life on it.⁸

In addition, it boasted a striking number of similarities to the Earth. Kepler-452b orbits a G2-type star, one like our sun, every 385 days. This means it is only 5 percent farther from its star than Earth is from the Sun. Still, this “Earth cousin,” as popular reporting frequently dubbed it, is likely to be a little warmer than our planet because its star, Kepler-452, is 20 percent brighter and 10 percent larger in diameter than our Sun. This similarity of Kepler-452 to our own Sun proved important for the initial announcement of the discovery because it allowed for speculation about similarities between Earth and this exoplanet that made for headline grabbing sensationalism. As Dr. Daniel Brown at Nottingham Trent University was quoted, “This is so fascinating because Kepler-452b receives the same kind of spectrum and intensity of light as we do on Earth. This means plants from our planet could grow there if it were rocky and had an atmosphere. You could even get a healthy tan like here on holiday.”⁹

After the initial flurry of reporting on Kepler-452b, enthusiasm for the planet cooled considerably. Because it was discovered by the transit method, crucial information about Kepler-452b’s mass (information that would be required to confirm it was actually rocky and not just a small gas giant) could not be obtained. At the time, there was also no way to do follow-up observations via astrometry or radial velocity measurements to determine the mass of the planet. However, the initial article announcing the discovery suggested that there was still a 49–62 percent likelihood that the planet had a rocky composition given probabilistic forecasting relating planetary radii and masses. Subsequent forecasting decreased this probability significantly, to 13 percent, suggesting Kepler-452b might be much more like Neptune than Earth.¹⁰

Additionally, public excitement also began to wane because the star this exoplanet orbits is approximately 1,400 light years away. To put that in context, humans would need to have shot a probe moving at the speed of light into space as part of the first Olympiad in 776 bce for us to be expecting its return within the next decade. Alternatively, with the speed of current unmanned probes, it would take approximately 26 million years to reach this older Earth cousin.

We can reasonably suspect that we will know more about Kepler-452b soon. The Characterizing Exoplanets Satellite (CHEOPS) mission will gather information about the size of exoplanets for which we already know the mass, increasing the number of data points used in forecasting models. This will allow better predictions about whether planets observed by direct transit are likely to be rocky. Moreover, Kepler-452b remains a good candidate for observation by the James Webb Space Telescope in order to identify its likely atmospheric gases. Even if it turns out that Kepler-452b is not so much an Earth cousin but something more like a third cousin twice removed (perhaps a sub-Neptune with a primarily hydrogen or helium atmosphere instead of a super-Earth), it will likely remain an interesting object of study—especially for planetary scientists interested in issues of formation. It is interesting because despite the many similarities to Earth that made it so tantalizing in the first place, it seems as though Kepler-452b might be far more different from our planet than was first assumed.

It is so different that recent analysis suggests it might not even exist! Arguing against confirmation of exoplanets by statistical means and the possibility of signal-to-noise disruptions, a new paper in The Astrophysical Journal contends Kepler-452b may have only a 16 percent chance of existing if the signal-to-noise threshold used to analyze Kepler mission data is changed. Kepler-452b is particularly vulnerable to such a shift because its period of orbit is so long (much like our own) compared to other exoplanets that we have discovered with an orbital period of less than two hundred days.¹¹ Whether “Earth cousin” or nonexistent statistical blip, Kepler-452b has been and remains a significant object of concern for astrobiology.

Proxima Centauri b

Next, consider Proxima Centauri b. It is the closest Earth-sized exoplanet to our solar system found so far. Discovered in 2016, it was found using a different detection method than that used for Kepler-452b: radial velocity. This method, sometimes called Doppler spectroscopy, was the first used to detect exoplanets and remains a critical tool for confirming the existence of these other worlds. It relies on the fact that stars do not remain perfectly still when they are orbited by a planet. The star moves very slightly in a circle or an ellipse around its center of mass because of the gravitational pull of the orbiting planet. It is as though the star wobbles in the sky. In our own solar system, the Sun evidences just such a wobbling that coincides with Jupiter’s twelve-year orbit and Saturn’s twenty-nine-year orbit.

These small shifts have an effect on a star’s spectral lines. These lines, recorded by a spectrograph, are like a barcode for a star. The spectrograph refracts white light from a given star into a frequency spectrum (imagine a band of rainbow colors) and records it. If there were nothing between you and the star, you would see a continuous spectrum (an uninterrupted band). However, this is not what we see.

Instead, a frequency spectrum with dark bands in it appears. These dark bands represent the presence of specific elements in the stellar atmosphere of the star. In the case of Proxima Centauri (the star around which we can find Proxima Centauri b) there is a strong spectral line at a wavelength of 280nm indicative of ionized magnesium.¹² Each star will have dark bands in its spectrum that correspond to the elements present in its stellar atmosphere, giving us a distinctive barcode or fingerprint for the star.

If a star has an orbiting planet and we compare the spectral lines over time, the position of the dark bands in the spectrum will shift slightly. This is not because the stellar atmosphere has suddenly changed. It is a result of the Doppler Effect: an emitted frequency becoming higher as it moves toward an observer or lower as it moves away from an observer. (This same effect accounts for the change in pitch we perceive as emergency vehicle sirens pass by us.) Because the star with an orbiting planet is moving very slightly around its center of mass, the spectral lines of the star will move higher (or bluer) in the spectrum as the star is moving toward the Earth and lower (or redder) in the spectrum as the star is moving away from the Earth.

If we observe a repeating pattern of red-shifting and blue-shifting in the spectral lines of a star, this indicates the presence of a planet. How often the pattern repeats allows us to estimate the orbital period of the planet. Additionally, the size of the shift allows us to surmise a minimum mass for the orbiting planet (i.e. while the mass could be greater, the planet’s mass cannot be less than the indicated amount given the degree of red-shifting and blue-shifting observed).¹³

Because Proxima Centauri b was detected by the radial velocity method, ou...

Table of contents

• Cover
• Series Page
• Title Page
• Copyright
• Dedication
• Contents
• Introduction: Being in Outer Space
• 1. Exoplanets and Icy Moons and Mars, Oh My!
• 2. Astrobiology’s Intra-Active Aliens
• 3. Being a Living-System
• 4. The imago Dei as a Refractive Symbol
• 5. Conceptualizing Nature
• 6. The Anthropocene as Planetarity in Deep Time
• 7. An Artful Planet
• 8. Living-Into Presence, Wonder, and Play
• Epilogue: Ad Astra Per Aspera
• Acknowledgments
• Notes
• Bibliography
• Index
• Series List