Author: Tiffany Christian

Why Earth Bias Matters

In a new consideration of Earth-likeness, or Earth-equivalency in astrobiologist David Grinspoon’s words, the separation between the search for life and the search for Earth-like planets is crucial. Departing from the passionate interest that we have vested in extra-terrestrial life, I move to instead focus on the how the exoplanets that we consider Earth-like compare to Earth’s other qualities. In addition to lying in their stars’ habitable zone, how do they compare in terms of mass and what kind of stars they orbit? What sorts of planets share their solar systems? The more solar systems we encounter, the more we learn how much our other planets are less like Earth. There seems to be an infinite number of ways to form a solar system.[i] After each new discovery, we re-learn that the circumstances of the Earth’s existence are rare. Most stars are significantly dimmer than our sun, and many of them orbit in binary star systems. The more information we find about the conditions of other solar systems, the more I’m convinced that conditions that surround Earth, will be found uncommon.

Even in our own solar system, potentially habitable planets fall outside the limits of our own habitable zone. Jupiter’s moons, Europa and Io, are thought to have volcanic activity and water, respectively.[ii] If we limit our points of interest to just those that fall within the habitable zone we will miss potentially habitable places. The continuously habitable zone is another obstacle to finding life and habitable planets. [iii]Over time, a star becomes more luminous, and this change in luminosity causes a change in the location of the habitable zone.[iv] Another factor is that the atmosphere of a planet can greatly affect how hot its surface is. An atmosphere that contains a high level of greenhouse gases could retain more of its parent stars’ heat even outside of the supposed habitable zone. Astronomers and astrobiologist have grappled with this problem of what planets to consider habitable. We have the choice of looking at everything because we don’t have enough data to narrow things down, or to only look for life that we would be able to recognize and measure i.e. Earth-like life.

The problem here is the language. Earth-like is a loaded term, tethered to our understanding of our planet. For us, the Earth is alive, either through the life that is on the planet, or the planet itself. [v] When we deem a planet to be Earth-like, since Earth is synonymous with life, we surround these mysterious exoplanets with all the baggage that comes with Earth. The term encourages us to imagine Earth with its richness transplanted to a far corner of the universe. It comes with a specific meaning. While scientists crafted the term for its generality (the planets are of Earth size and terrestrial), it’s interpretation is all too narrow. Once we recognize that there is unintended connotation between the intended meaning of Earth-like and the understanding of the term, we can move toward the precise language that is needed in science.  Settling for Earth-sized, while a little more exact, still pushes us towards an association with Earth. When we find an Earth-sized planet, the conversation immediately goes to whether they will be habitable.

Is the Earth Earth-like? The answer should be an emphatic yes. It’s almost too obvious of a question. The question really is “Why is the Earth Earth-like?” Clearly its more than the size of our planet that determines the its qualities. But in our rush to separate the planets of interest from the terribly uninteresting exoplanets, we have brought along our Earth-bound thinking. In a field where we should be as objective as possible, we must struggle to release the weight of our subjectivity. Bayesian analysis takes our subjective knowledge and directs it towards objectivity, if we don’t pretend that we’re certain of anything. Hopefully even if our initial guess lies somewhere off center of the truth, with more information we will converge towards truth.[vi]

Water worlds, worlds that are entirely covered in a planetary-ocean don’t exist in our solar system, yet we know they can exist. However, they still capture associations with Earth, because we were also a water world, at one point in our development.[vii] When we claim associations with Earth, it gives us claims to legitimacy. It also makes the non-Earth-like planets available to be explored. In a game of six degrees of separation on a universal scale, we feel like we know these planets. While this intimate look at planets is good for making intangible objects feel more real, it also has a much graver effect. Much how we feel connected to someone who is a friend of a friend, we feel some kinship with these alien planets that have siblings here in our own solar system. This kinship makes it easier to claim ownership of these planets. Reflecting humanity’s drive to push and do, we feel like every no stone can remained unturned.

We view these alien planets as extensions of our own. A seemingly irrelevant quote that talks about the Mayan 2012 apocalyptic prediction “The 2012 commotion, Restall and Solari argue, is a testament to our continuing inability to stop viewing other societies as extensions of ourselves.” The end of the Mayan calendar in December 2012, did not mean the end of the world, instead it was a projection of the Western preoccupation with apocalyptic end times, driven by the apocalyptic books of the Christian Bible.[viii] Like always, our Earth activities don’t end when we look skywards. In our categorization of other exoplanets and solar systems, they become are a projection of our solar systems and of earth. Colonizers of the “New World” had to juggle experiencing an entirely new culture, while connecting it to familiar places. It seems that we are doing the same thing to the literal New Worlds. We can extend our touch to our cousin worlds and sister worlds out in the universe. Our attitudes directly impact how we feel entitled to other worlds.  We’ve already feel a sense of ownership to the rest of the solar system, we allow ourselves to send probes to other planets, and even feel free to litter space and other planets with our debris. Do we have the right to do this?

Moving forward as technology develops, and more of these strange worlds are accessible to us, finding how earth-like these planets really are would be the true test of our language and terms. Even more is finding whether it is “fair” to impose our limited understanding onto the hypothetical conditions of our planets. What happens when we arrive at these planets, like NASA’s fictional tourists, and we see that they are only Earth-like by the loosest definitions. Imparting our conception of a “good” terrestrial planet is limiting in both our categorical knowledge and our interpretation of the data. From our limited perspective is it fair that all planets must align with the planets that happen to be in our solar-system? I mean I’m not one to insist on each exoplanet being a unique snowflake, but that imposing our view onto the planets also forces them to view them in a certain way.  Seeing the exoplanets as associated with earth gives us a sense of ownership to the planet. They are free to explore without fear. Our solar system was formed under unique circumstances. When we looked towards exo-solar systems we expected them to find others like our own. Since we haven’t found a solar system like ours yet, maybe we can also hold off on trying to make the planets fit into our molds. We should ask not only is how Earth is Earth like, but is Jupiter Jupiter-like? Or Neptune, Neptune like? Moreover, can we expect all planets to fall in variations of our own nine groups. Are we lucky enough to exist in a solar system from which all the variations of planets stem? Clearly not.

The Copernican Principle allows for estimations of planets not only in our galaxy, but in the known universe. The principle was used to approximate the number of stars in the galaxy. A 2012 study of planets found using the microlensing technique, was used to roughly estimate nearly 10 billion terrestrial planets across our galaxy. In a similar manner, NASA estimated the number of stars. While it is wonderful to get an idea of the almost incomprehensible size of the universe, there’s no way to verify our results. If we accept the Copernican Principle as fact, we don’t need to think about our findings probabilistically. We think about the existence of individual objects as subject to a source of error, but not about what these things mean.

Acknowledging the limitations of our scope, we use the Copernican Principle to extrapolate our results to the rest of the universe. Nicolaus Copernicus created a heliocentric model of the solar system in 1543, which challenged the then popular Earth-centered planetary system[ix]. Maybe popular isn’t the right word; the geocentric planetary system had the backing of the powerful and influential Catholic Church. Giordano Bruno, a monk with a fiery disposition, was literally burned at the stake for claiming that there were many planets that had intelligent life. A geocentric model explained many aspects of the motion of the stars, moon, and Sun, and fed into our anthropocentric ideals (a mere coincidence that egocentric and geocentric differ by a letter switch). Copernicus shifted the Earth and humanity from the center to the sidelines. Geocentrism was convenient theologically, because humans are in a unique position to acknowledge and worship God.  Why would God create us not in the starring role, when we are focus of the whole religion? And then why were the other planets not in our religious texts? (In the Catholic church, and additional snag occurs because now they would have to figure out if Jesus’ sacrifice counts for the aliens.)[x]  We cannot pretend that the changing significance of Earth only affects the objective scientific world, the understanding of ourselves must be adjusted as well.

We were just like all the other planets, circling the real center of our solar system, the Sun. The departure from the special to the mundane framed a change in our understanding of the universe. In Neil deGrasse Tyson’s words, “not only is Earth not in the center of the solar system, but the solar system is not in the center of the Milky Way galaxy, and the Milky Way galaxy is not in the center of the universe.”[xi] The Copernican principle implies that no part of the universe is special or in the center. There is nothing inherently exceptional about us.  Our extrapolations rest upon the assumption that Earth us not unique; scientist call this the principle of mediocrity. We infer that the areas of space we study, through being average, are representative of the greater universe. If exoplanets are common in our search of the small region of the Milky Way, then, through the Copernican Principle, they should be common in other galaxies. This is a clever way to go around the need for more complete sampling, since any sample is a perfect representation of a uniformly distributed universe.

When I first read Heavenly Errors, and Neil F. Comins described how scientists estimated of the number of stars in the universe I was amazed.[xii] Humanity, in our relentlessly creative way, had the gall to try to answer one our biggest questions. Although, the results are mind-blowing, they don’t leave much room for argument. While I am not wishing for a world of antiquity, it is undeniable that in the past, astronomical models were updated to accommodate unexpected results.  When the Greek models of seven celestial spheres that revolved around Earth couldn’t predict retrograde planetary motion, we moved to planets that existed in space, but in a geocentric model. And when that wasn’t accurate enough, we adopted Ptolemaic epicycles. These models turned out to be inaccurate representations of our universe. Maybe the constancy our model signals that we’ve struck astronomical modeling gold. After all, a model that is right, is as simple as possible and won’t require massaging to make the outliers fit.

We make a big show of being concerned about the ethical considerations of contaminating another planet with Earth organizations, but we don’t have the same concern for the planet as it exists. We own the Earth, although that may rub some people the wrong way, humanity’s actions can change the planet. We have the power to shape the Earth in profound and long lasting ways, and as the ability visit other planets we must ask ourselves if this control extend to the universe. Because we control the Earth, any connections to earth we put on another planet allow us to exert the same sort of ownership to these earth like planets. And since is earth is a living planet and a living state is better (in a sense that it is worth considerations) than a nonliving one, this gives us access to all the non-living planets. If a planet is non-living no ethical consideration needs to be made. We went to the Moon and even left a human souvenir: an American flag. Now that we’ve been there done that with our lunar companion, we set our sights on Mars. NASA, and Tesla CEO, Elon Musk have hopes of getting men on Mars within a few decades, since we are convinced of the planets dead-ness it is available for our exploitation.[xiii] Earth Bias has primed our brains that Earth-like planets or planets with life are the only ones that we need to ethically consider. Is there not something worth preserving in the planets existence as it is?

This subjectivity leeching into our process of discovery and interaction into the greater world at large is just another iteration of our species extrapolating our experiences to the life that we hope is out there. There is a reason that most alien encounters in science-fiction are violent wars, they reflect the often-violent clash of cultures here on our planet.[xiv]  It’s the same reason why sci-fi aliens tend to look like life here on earth.

Astrology and astronomy have often been confused, much to chagrin of professional astronomers, but I think they have and more in common than traditionally thought.  Astrology assigns the positions of the planets and celestial objects special significance in determining the characteristics of humans specifically. The positon of the constellations and the planets can reveal someone’s basic personality traits. The stars have long been thought to determine the conditions of human affairs (see star-crossed lovers, “it was written in the stars”), but now we are at a point in history where the influence can be exerted in the opposite direction.

On Earth, we have unprecedented connectedness across the planet (Not only can we exert influence over the stars but we have influence across the planet). We can talk to people across the globe at any given moment. Even where technology hasn’t bridged the physical gaps, human travel, has brought animals and plants far away from their native homes. Globalization in the non-economic sense, but in terms of life, has homogenized the plant. The constant interaction of life from different places, imitated by Christopher Columbus, has homogenized things here on Earth creating the Homogocene era, where invasive “generalist” species take over the local plant and animal life all over Earth.[xv]  In addition to the ecological impacts of globalization, we have cultural implications where people fight to maintain their local culture while participating in the new, usually Western culture.[xvi]  How can they preserve local traditions and ecosystems while sacrificing some of their individuality to get some of the goods/luxuries/conveniences that the “globalizing” culture offers? Globalizing has his difficulties (immigration, migration, urbanization, invasive species) and right now we are figuring out what that means to the development of both our future cultural and ecological landscape.

We certainly haven’t figured that all out, which is not bad, but we are also on the verge of a new sort of globalization that will bring even more difficulties. The new globalization is a literal globalization, utilizing the synonym of globe: planets. As we move to leave Earth for other worlds, we risk repeating the same process here on Earth. But instead of having the colonized fighting against the colonizer, we have nothing.  No one to ensure the preservation of the planet before we were there. In the absence of life to act in its defense, we must play the role of both parties. Although there is a human curiosity about the worlds around us that can only be satisfied by doing, we have to balance our desires with the respect to the sovereignty/dignity of the planet, regardless of Earth-likeness or not, or whether life is there or not.  We do not own the other planets, like we do the Earth. The ramifications of globalizing the universe are something even more serious than the challenges that we face here on Earth.

We both extoll and mourn the successes of globalization. We enjoy having imported clothes and exotic foods, but mourn the agro-industrial complex, dead languages, and deforestation.[xvii] Understanding the challenges on creating a global civilization here at home, should make us attuned to the effects of broadening humanity’s span. But it hasn’t.

We have the unique chance here to mitigate the damage. Instead of exercising control in an outward direction but reaching towards these sister worlds, we can turn inwards and control our own behavior. Our Earth bias affects how we will treat these worlds, limited in a sense that we will never be able to understand. Everything about these alien worlds will be compared to something on Earth, and any attempts to understand them will cheapen their unique reality.  We can do right by these planets, in a way that we haven’t done our own. Human history is intertwined with Earth history and before we run out to our neighbors, we have a duty to take care of own home. While Earth-bias may need adjusting when we eye other planets, it is perfectly tuned for our own planet. At the risk of sounding like an Earth nationalist, we have a duty to use the view that the planet has cultivated in us to help it. Moving in an ever onward and upward trajectory, it makes it easier to find home in Earth-adjacent territory instead of the “real” thing.

Whoever chooses to be the first Mars colonizers, will make it clear to us what planetary homesickness feels like. In what may be a common phenomenon, people will complain of feeling the sun on their un-space suited skin, the sight/sounds/ of rain, the greenery of our forests, being at home in a place where you were meant to be.  Other planets may be Earth-like, but they will never be Earth.

[i] Rare Earth

[ii] Dartnell, Lewis. Astrobiology :Exploring Life in the Universe. 1st ed. New York, New York: Rosen Publishing Group, 2011.

 

[iii] Kasting, James F., and David Catling. “Evolution of a Habitable Planet.” Annual Review of Astronomy and Astrophysics 41, no. 1 (September 1, 2003): 429–63. doi:10.1146/annurev.astro.41.071601.170049.

 

[iv] “The Habitable Zone Lecture.” Accessed September 15, 2016. https://www.astro.umd.edu/~miller/teaching/astr380f09/lecture14.pdf.

 

[v] Grinspoon, David. Lonely Planets: The Natural Philosophy of Alien Life. First Edition. HarperCollins Publishers Inc., 2003.

[vi] Silver,Nate

[vii] Rare Earth

[viii] 1491

[ix] Scharf, Caleb

[x] Lonely Planets

[xi] https://www.nasa.gov/vision/universe/starsgalaxies/search_life_I.html

[xii] Comins, Neil F. Heavenly Errors: Misconceptions about the Real Nature of the Universe. Columbia University Press. 2003

[xiii] http://www.dailygalaxy.com/my_weblog/2017/01/destination-mars-elon-musk-and-trump-partnership-signal-nasa-shift-humans-a-multi-planet-species.html

[xiv] http://www.popsci.com/science/article/2010-04/hawking-aliens-are-out-there-and-want-our-resources%20

[xv] http://www.hcn.org/issues/341/16862

[xvi]  1493

[xvii] 1493

Methods for Detecting Exoplanets

As of January 12, 2017, there are almost 3,440 confirmed exoplanets, with 576 planets orbiting in multi-planet systems.[i] These numbers will continue to grow as more Kepler planet candidates are officially confirmed. The confirmed planets have been found using five main methods: radial velocity, transit, direct imaging, gravitational microlensing, and astrometry.  Radial velocity uses the Doppler effect to find exoplanets. When a planet orbits a star, it is not only the planet that is moving around the star, but the star is also circling around the center of mass of the planetary system. Viewed from Earth, as the star circles the center of mass it moves closer and farther away, changing the color of light of that star as observed from Earth. The color shifts between blue and red, blue indicating that it is moving closer (more compact wavelength of visible light), and red that it is moving away from us (more stretched out waves of light). This blue-ing and reddening of the wavelengths is called Doppler shift. (It is also responsible for the changing frequency of sound, when an ambulance siren is coming towards you and moving away from you). The transit method of finding exoplanets is by far the most successful of the methods, finding most of the total number of confirmed exoplanets. If a solar system happens to be lined up with Earth, we can see the planet “eclipse” their parent star. These eclipses or transits cause a dip in the star’s observed brightness.  This phenomenon is what the Kepler Space Observatory looks for. Direct imaging is a challenging method; it’s exactly what it sounds like, a direct image of the stars. Scientists do this by removing the glare from the planet’s host stars. Gravitational micro-lensing occurs when light from a distant star is focused by a moving star or planet. Particularly massive stars and planets gravity can focus the light of other stars, causing a temporary increase in brightness. The last method, astrometry, searches for hard to find minute changes. When planets orbit a star, the star is not stationary; it gets tugged around its center of mass. Without being able to see the planet itself the star will appear to move extremely tiny amounts relative to other stars as well as having periodic Doppler shift. [ii]

While all these methods are remarkable achievements in finding exoplanets, they have their limitations, the most obvious one being that these methods are not very sensitive to smaller planets. We’ve had the most success finding planets that are large and close to their stars. These “hot Jupiters” would never be considered Earth-like under our current definition. The technology is improving, but we still have more progress to make before Earth-sized [maybe even any Earth-like] planets around Sun-like stars are detectable. Transits, and lensing have the additional disadvantage of being localized occurrences. They aren’t predictable so we have to look are large areas of the sky over a long period to catch one as it is happening. The final limitation is that our region of search is only in a small region in our home galaxy, the Milky Way. We are far from getting a representative sampling of exoplanets.

Overfitting is when we take noise for signal, something that is easy to do in our unfortunate Earth-bound situation.  Without a clear idea of what is meaningful, things that are don’t reflect the reality of the situation can creep into our conclusions. Earth, right now, encompasses our signal and our noise. We are in the thick of it, not seeing the forest for the trees. Mainstream science could have under fitted the habitable zone, choosing only the size of the planet and the liquid water as the necessary components. Planets must be terrestrial and have water; we will not be looking for gaseous aliens on Jupiter or Neptune.[iii] The problem is that there is no verification. We sit, in front of a board with a scatterplot filled with numerous disorganized points, hopelessly tasked with discovering the connections, if any, there are between the Earth’s many qualities and the formation of life.

We have so much information about Earth, but the questions of habitability from a scientific perspective are recent. Many fields study the Earth, geology, biology, astronomy, and earth and atmospheric science, habitability is an intersection of these disciplines. It makes sense that there are respective beliefs about exactly which dots should connect. The general trend seems to be that scientists whose specialties are the intricacies of the Earth think that earth-like conditions are rare, while astronomers and physicists, who have more of an outward focus, believe that Earths are common.[iv] Each field will have their own well of information to draw from affecting how they approach the massive number of dots on the board.

Mathematicians bypass the messy business of picking the important bits of Earth’s history, and rely on the numbers. The logic behind it is that the sheer size of the universe would allow for an Earth-like planet to be out there. No matter the calculated prior beliefs or the assigned probability given to Earth-like planets, the vastness gives many trials for a success. Even if there is a one-in-a-billion chance of an Earth-like planet occurring, we would be guaranteed by the size of the universe for many Earth-like planets.[v] While this is a hopeful calculation for those who wish for some company on the cosmic scale, it sidesteps the problems of making connections and developing the relationships between the data points.

The nature of truth in astronomical observational data is a sticky concept itself. Is the truth reflected in our understanding or is it a goal out there, the universe as it exists, waiting for us to observe enough data to really “get” it? In astrophysicist, Ray P Norris’s paper, Discovering the Unexpected in Astronomical Survey Data, he admits that the traditional Popperian scientific method of hypothesis testing doesn’t apply to many astronomical surveys.[vi] Astronomy relies on an alternative discovery-based scientific method, because many hypotheses and theories are unfalsifiable. Their scientific process values exploration and data collection over specific hypothesis testing. Norris encourages future astronomy surveys and data collection to account for both known unknowns, and the unknown unknowns. In other words, discovering of a new type of object (quasars), and discovering entirely new kinds of phenomenon (dark energy, the expanding universe).[vii] While we would like to think each new discovery and even discrepancies between our theoretical and our sample data strides us towards a complete picture of the universe, I’m not sure if they are strides, or just dainty steps. If we are consistently discovering new objects, and if the field’s majority of the knowledge is unexpected it seems we take for granted that we really are close to the truth.

Our approximation of the truth is of course limited by our understanding of the universe as is and our data collection methods. The information we collect from the universe is our most important tool in framing the truth. Despite possible errors, and compounded by the fact that we are always finding something new, the data is the best reflection of the universe as it is (whether it behaves as we expect it to or not). When the data aligns with our simulations then we will have arrived at the truth. According to philosopher Alex Schmid, the truth of simulation comes from three distinct types of truth theory: coherence, correspondence, and consensus. He explains:

  1. A simulation model is true if and only if it corresponds to a matter of fact in reality.
  2. A simulation model is true if and only if it is rationally acceptable under ideal or optimal conditions.
  3. A simulation model is true if and only if it is a member of a coherent system of believes[sic].

 

Schmid goes on to unpack these terms in his own paper, but even just listing them we can see how they occur in our current scientific climate. These formulations go hand in hand with the popular conception of the Popperian scientific method.  In addition to being “true,” simulations must also meet two more criteria: validity and accuracy.  Validity is based on how well a model jibes with our expectations and fulfillment of its purpose, and accuracy refers to how it well it reflects the collected data.

In our discussion of math and approaches to the probability problem, we have become separated from what the probability and our estimation means. Sometimes when we focus on the numbers and the equations the truth of the data can be lost in the shuffle of us trying to numerically capture reality. Our understanding of the universe doesn’t affect how the universe itself operates.  Statistician William Briggs says on his blog,

“What is happening now is either being influenced by what has not yet occurred, or probability is physically real in the same way that mass or charge is. Yet there is, of course, zero evidence, and anyway its absurd, to think probability is material.” (cite)

 

Probability is not physical force, determining the data we receive. We create probability by measuring and counting. Predictive power is not something that we have mastered. While meteorological forecasts have gotten significantly better over the years, due to advances in computing power, there are still areas (both man-made and in nature) where we are hopeless at making accurate prediction: the stock market, earthquakes, pandemics, and the economy.[viii] These are phenomena that are affected by an unknown number of factors. And if these undeniably earthly activities are beyond our reach now, then how can we even begin to both identify and mathematically represent the factors involved in our whole planet?

In exoplanet research, our predictions usually are about the composition of the planets. Before we found our first exoplanets, we theorized the exo-solar systems would look like ours: terrestrial planets clustered towards the Sun and the gaseous larger planets farther out. Our solar system was the only “model” we had to base our theory on. However, once we found the first planet, we had to update our model. We had only theorized about massive Jupiter-like planets extremely close to their stars.[ix]  Now since these planets show up so often in our exoplanet surveys, we readily accept them as a normal part of solar system development. A recent exoplanet prediction comes from a statistical survey of 6 years’ worth of data from a ground based telescope. [x]Daisuke Suzuki, one of the researchers, claims that using previous results that “We conclude that Neptune-mass planets in these outer orbits are about 10 times more common than Jupiter-mass planets in Jupiter-like orbits.” This statement needs qualifying. Few planets have been found using the microlensing technique, and the paper only has a sample size of 30 planets. In addition, microlensing has the capability to survey a larger area of our galaxy. Does “10 times more common” mean in this larger search area or our entire galaxy?

Ward and Brownlee, authors of Rare Earth: Why Intelligent Life is Uncommon in the Universe, created their own formula that reflects their belief of the rarity of earth life. Instead of assigning lower probabilities to get a low number of intelligent life, they increase the number of factors that they deem necessary. The formula comes at the end of the book, the result of them building a case against intelligent life’s commonness. Looking at their Rare-Earth Equation gives a hint of how the authors developed their prior probabilities.

N= N* x fp x fpm x ne x ng  x fi x fc x fl x fm x fj x fme

Where:

N* = stars in the Milky Way galaxy

Fp= fraction of stars with planets

Fpm=fraction of metal rich planets

Ne=planets in a star’s habitable zone

Ng = starts in a galactic habitable zone

Fi-fraction of habitable planets where life does arise

Fc= fraction of planets where complex metazoans arise

Fl= percentage of lifetime of a planet that is marked by presence of complex metazoans

Fm = fraction of planets with a large moon

fj= fraction of solar systems with Jupiter size planets

Fme = fraction of planets with critically low number of mass extinction events

 

Compared to the Drake Equation, the Rare-Earth equation has already set itself to reflect their beliefs. Looking at the factors that they deem most important, we are invited to see how they develop the argument of their book. Without reading the entire case, we can understand what conditions (to them) make a planet Earth-like for the authors factors that Frank Drake didn’t put into his own equation. When we lay out equations out like this, we peek into a Bayesian world.

Frank Drake, Sara Seager, Peter Ward and Donald Brownlee have all developed equations to find the number of alien worlds out there. Drake was concerned with those who could contact us, while Seager, Ward, and Brownlee focused more on life in any form (intelligent or not). Although the Copernican Principle forms the foundation of their accepted factors, it allows for personal probabilities. The Drake equation makes use of our Copernican principle to establish estimates for the 2 of the 7 factors: the average rate of star formation per year in the Milky Way, and the fraction of starts that have planets. The rest of the factors, instead of turning outwards for physical evidence, we turn inward and assess our own probabilities. These personal probabilities can skew the result, in this case the number gets closer to 0 or more than 1. The number reflects our probabilities.

If I’m a skeptic of all this alien business, and I chose .001 for fl, fi, and fc, with 100 years as the lifetime of a situation and .125 as fraction of earthlike planets per solar system, I get .00000625 as the number of communicative civilizations within the Milky Way. Conversely, taking the same for value of L, and Ne, and increasing the fl, fi, and fc to 1, we get 6.25, a comparatively large number.  Bayesian analysis is the reason why we can have a book that assures us intelligent life is an uncommon occurrence in the universe, and another that swears that the probability is 100 percent!

In a frequentist world, on the other hand, the truth can be found through perfect sampling. Our errors in estimating probabilities result from errors in our sampling methods. I do not believe that the frequentist approach works when it comes to probabilities of the existence of celestial objects (in our case habitable “earth-like worlds”). Measurements of exoplanets taken from our small blue orb can hardly represent planets in every corner of the universe. In fact, there’s a limit to how much of the universe we can observe. In the real world, more measurements and sampling would not lead to the objective truth.[xi] The useful data, the information needed to arrive at an accurate understanding could be different from the data being collected.

Astronomy is not a field of probabilities. Studies of our region result in updates to our understanding of the universe.  If there is a possibility that we are wrong, we don’t concern ourselves with the hypothetically correct model. We operate in a permanent world that is subject to change. The frequentist school of thought is suitable to this oxymoronic world.

The beautiful thing about probabilities is that we entertain wrongness. We flirt with the idea of instability— a disconcerting thought if the instability is affecting the foundation of our knowledge. Unexpected results and wrong hypotheses drive the process of discovery. With our current understanding, we don’t allow for the possibility that we can be wrong at the most basic level. In admitting our unsureness of the phenomenon that we are trying to predict, we make ourselves less wrong. If we fully committed to always or never (100% or 0%) lines of thinking, we leave out the things that we consider impossible that are fully possible.[xii] I do not like being wrong, but I understand it as a necessary component of learning. Instead of thinking about elsewhere Earths as Probability 1 or near zero, we can assign a range of probabilities, based upon constant updates to our knowledge.  Space is an area where we can’t be certain. There are few direct measurements and everything comes with a degree of uncertainty. In the absence of direct measurements, we check statistically for false positives and aberrant data. The continuous learning and updating of our beliefs of is the hallmark of Bayesian statistics. Complacency is the enemy of prediction. Professional forecaster Nate Silver hails the benefits of the Bayesian process.[xiii]This attitude would freshen up the unchanging models of rare Earth discussions. It’s not of matter if the factors undoubtedly contribute (or not) to what makes the Earth Earth-like, but reflected in how much we think these factors are important to the development of our planet.

These formulas provide a streamlined map of Ward and Brownlee’s train of thought, while also forcing us to reflect upon our own beliefs. If Drake looked at the Rare Earth equation, he would either think of his own comparatively sparse equations or question why Ward and Brownlee believe that so many factors are crucial to the development of life on Earth. Either way, the result is the same: both examples encourage research into the information that is different than the author’s own which the author can either pass up or incorporate into a new and hopefully improved formula.

Sara Seager looked at Drake’s whiteboard with his 8-term formula, and created her own, which of course, picks out factors that are most important to her. She determined that the number of planets with detectable life forms was more important than the intelligence of the life forms. Seager’s “revised” Drake Equation showed the strength of her beliefs by creating her own equation. [xiv]She lamented that it would be a shame to miss out on extraterrestrial life because we weren’t looking for the right signs. She recognizes the Bayesian aspects to her own equation:

I carefully crafted the last term of this equation so one could actually add more information in. Does life produce detectable signature? Are there systematic effects that rule out some bio signature gases being detected in some planets? Can we not find the signature for technical reasons?[xv]

 

In this mishmash of personal beliefs, it becomes hard to pick out the factors that contribute to my own beliefs. Being in a field where we have a lot information confuses the process of determining relevant information. It also brings the issue of testability. Bayesian hypothesis testing can be fine-tuned with experiments, but without hard proof, the pertinent factors are difficult to verify. Do Ward and Brownlee justify including Jupiter, extinction events, and large moons, in their equation? Do the any of the above scientists’ factors reflect reality? We cannot be sure. This field is particularly sticky because of the dearth of information. All formulas are valid until proven otherwise. Of course, ridiculous claims that the number of planets is somehow related to the current number of rhinoceroses still alive, we can be skeptical of. There’s no clear signal and a lot of noise, in Silver’s words.

As an aspiring statistician, I think data overload seems like the best problem to have. A small sample will not hold up to rigorous statistical testing. From either approach, frequentist or Bayesian, more data is better. However, the amount of data we must work through hampers us from making meaningful connections. Earth’s history stretches back to the formation of our solar system, and maybe even our universe. I am looking a timeline that starts at the Big Bang and goes through everything, even the minutiae of Earth’s history. This includes the Big Bang, the formation of early stars, the planetary disk that formed the Sun and our solar system, and then every single event on Earth. While the details of early Earth history seem hazy and far off, there is a possibility that they affected the conditions on Earth. Earth is more than just what happens on its surface. At this stage, decoding the Earth-like qualities from the extensive history of the planet is nearly impossible. Once we find another planet that is truly Earth-like we can cross- reference that planet’s history to find out what qualities we share.

Taking this attitude towards our understanding of the universe we still make guesses about the distributions of the subjects we are trying to study to accommodate for unknown unknowns. In probability and statistics, phenomena are thought to follow either a known or unknown probability distribution. This means that the probabilities of certain assigned values look like functions that change with certain parameters. Visualizing the data, can help clarify if the data aligns with one of the known distributions.[xvi] If it doesn’t we have to question “the sum of our understanding of the universe.” Usually astronomers develop characteristic distributions based on the data collected and compare it to distribution based on simulated models. While models, by definition, attempt to capture something accurately, they cannot be perfect, and are vulnerable to inaccuracies in reflecting truth. In this case, our simulation tests our theoretical understanding. It’s fascinating because here we have a direct comparison between the “truth” in the data and our truth approximate (the “truth” as we expect it to be).

WM Briggs, a statistician and professor at Columbia University believes that traditional frequentists and Bayesians are trapped in parameter estimation and over-certainty. Probability is based on data and nothing else. The universe is not beholden to us to behave according to the models. When our model coincides generally with the universe (meaning the data that we have measured), it doesn’t mean that we’ve captured reality, but only that we’ve captured the data. If our models fit the data, it is not a predictive tool of what else it out there. It only is based on the data that we have acquired, not that data-in-waiting. Like a financial firm on Wall-Street, a model’s past performance is not indicative of future success.

Briggs encourages a predictive approach to probability, but leaves us on our own to figure out how to apply it to a field such as astronomy.  His finds issue with over certainty and unnecessary quantification. But in astronomy, aren’t we trying to “quantify the unquantifiable?” Understanding for us comes in the form of mathematically consistent equations, and anything less feels a little too intangible. Once we have created a formula, we feel like we truly “know” something. Probability, for Briggs, is a “soft” form of prediction. Good predictions require many things but a solid understanding of the phenomena in question is essential

“Knowledge of cause and essence is at the base of every probability.” “Probability is always a measure of our understanding — not of what exists what we can know of what exists.” These quotes represent astronomy’s fight to convert the field to Briggs’ preferred brand of predicative statistics.  Probability does not spring from the head of the data fully formed like Athena from Zeus. Even simple probabilities, according to Briggs, are conditional and based on a multitude of factors. But predictive statistics rely on conditionals, even when we are not sure what the conditionals are. What would the conditionals be earth-like planets? What are our qualifications for our astronomical predictions? It is not enough to state the probability, without fully grounding it in the reality of the data. We collected the data from the real world, so our interpretation must be returned to that context.

If we are consistently discovering new factors, and not testing hypotheses, then how much knowledge of “cause and essence” do we really have? We find probabilities in the hopes that they predict the next data sets that we collect. When we say that 1.08% (percentage derived by dividing 1 for Earth/ 8 the number of planets in the solar system) of exoplanets are habitable, it is not a statement about the population of planets outside our solar system, but rather stating a fact about the data. I think that this separation is crucial. It’s the same sort of qualification that we see in poll results. If a poll reports that 17% of people believed that Movie A was better than Movie B, that it doesn’t tell me that 17% of everybody shared the same opinion. Of course, our hope is that our conclusions about the data are representative of whatever our greater population is. But there is a lot to unpack in a simple statement. Who are the people polled? Where were they polled? How were the questions asked? These are all factors that affect how representative of the results of the poll are. In this same line, any statements we make about exoplanets, only reflects the small area of the of the Milky Way we can observe. We don’t need random sampling, we need representative sampling. Unlike polling, we don’t have the luxury of being able to model our population accurately. Since we don’t know all the conditionals that affect the development of planets, we cannot develop a representative sample. In addition, we can only collect data as far as the technology will allow.   Not only that are we limited by that, we are limited by uncertainty in our measurements themselves. Not all the “planets” we find are actual planets, there is rigorous testing to determine false positives.[xvii]

Subjective beliefs have found their place into science. Although Bayesian statistical techniques acknowledge the subjective determination of a prior, we have the goal of objective knowledge in science. When we say something is scientifically proven, we want undeniably accepted fact. When we look out into space, it’s almost like we are trolling the darkest parts of the ocean. We kind of know what sorts of creatures live down there, but many of them are weirder than we’ve ever expected and often we find new ones before we even know what we are looking for. The establishment of a prior probability requires knowledge, in our case it is ignorance.[xviii] This is not to say that we know nothing, rather that there is a lot out there that we don’t know or can’t predict. This lack of knowledge is enough of a problem where we need to look at the data being produced in studies for unexpected results.

The process of confirmation/consensus/observation as a pathway to objective truth becomes obsolete in astronomy. We are literally talking about everything that there is, and we only know a small fraction of it. There is no consensus/confirmation truth of the whole universe simply through the fact that we can’t observe the whole universe. It seems to me that for this Frequentist statistics and data reduction methods have been applied to astronomy without considering the philosophical implications. We’ve already made several assumptions about how to interpret our observations. And while there are error bounds that exist in our modeling, there are no error bounds for our base assumptions. How comfortably can make claims about the world around us, when our understanding isn’t falsifiable?

 

 

[i] Exoplanets Data Explorer | Exoplanets – Form Search | DataIR.” Accessed September 18, 2016. http://datair.soe.ucsc.edu/experiment/exoplanet/search/exact.

 

[ii]  “5 Ways to Find a Planet.” Accessed September 9, 2016 https://exoplanets.nasa.gov/interactable/11/.

“________641639209_orig.jpg (2239×1476).” Accessed February 17, 2017.

 

[iii] Dartnell, Lewis. Astrobiology: Exploring Life in the Universe. 1st ed. New York, New York: Rosen Publishing Group, 2011.

 

[iv] Scharf, Caleb. The Copernicus Complex. First. New York, New York: Scientific American, 2014.

 

 

[v] Aczel, Amir. Probability One: Why There Must Be Intelligent Life in the Universe. Harcourt, Brace, & Company, 1998.

 

[vi] Norris, Ray P. “Discovering the Unexpected in Astronomical Survey Data.” Publications of the Astronomical Society of Australia 34 (2017). doi:10.1017/pasa.2016.63.

 

[vii]  Norris, Ray P. “Discovering the Unexpected in Astronomical Survey Data.” Publications of the Astronomical Society of Australia 34 (2017). doi:10.1017/pasa.2016.63.

 

[viii] Silver, Nate. The Signal and the Noise

[ix] Mirror Earth

[x] Suzuki, D., D. P. Bennett, T. Sumi, I. A. Bond, L. A. Rogers, F. Abe, Y. Asakura, et al. “The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass.” The Astrophysical Journal 833, no. 2 (2016): 145. doi:10.3847/1538-4357/833/2/145.

 

[xi] Silver Nate

[xii] Silver, Nate

[xiii] Silver,Nate

[xiv]

[xv] Powell, Devin, Astrobiology Magazine | September 4, and 2013 06:18pm ET. “The Drake Equation Revisited: Interview with Planet Hunter Sara Seager.” Space.com. Accessed February 24, 2017. http://www.space.com/22648-drake-equation-alien-life-seager.html.

 

[xvi] “Probability Distribution Functions.” Accessed March 18, 2017. http://astrostatistics.psu.edu/STScI/prob_distributions2011STScI_4.pdf.

 

[xvii] “Statistical Analysis of Viable Exoplanet Candidates.” Accessed September 9, 2016. http://arxiv.org/pdf/1608.00620v2.pdf.

 

[xviii] Romeijn, Jan-Willem. “Philosophy of Statistics.” In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Spring 2017. Metaphysics Research Lab, Stanford University, 2017. https://plato.stanford.edu/archives/spr2017/entries/statistics/.

 

Questions of Habitability

Now what does it mean for planet to harbor life or to be habitable? We simply don’t know. We can make educated guesses, but without an example of extra-terrestrial life to go on we don’t know which conditions are essential to the development of life.  The consensus is that liquid water is a requirement, so the concept of a “habitable zone” or “goldilocks zone” was developed.[i] The zone is the distance from star where a planet can maintain liquid water. This distance changes depending on the size and brightness of the star. If the planet is too small or large it will not retain its water. We give priority to the exoplanets that we find that are both a similar size to our own planet and lie in the “just right” goldilocks zone.  This reduction of life-giving features (based on Earth’s conditions) has divided the scientific community on whether life will develop inevitably given ideal conditions (whatever those may be), or if Earth is special because life is rare. Obviously, knowing the exoplanet may contain liquid water is not enough for us to know if it contains the unknown, but necessary components of life. The upshot being that if Earth has liquid water and intelligent life, then planets that also have liquid water could also have intelligent life. The argument is not about how rare the Earth is, but how rare intelligent life is. Since we do not know if life is an inevitable occurrence given the correct conditions, the rare-Earth argument has become an argument for the rarity of intelligent life. I believe that the distinction between the ideas of rarity of Earth-like planets and the rarity of intelligent life is necessary.

It seems that the goldilocks zone’s only use is to narrow the search for extra-terrestrial life. The number of planets we have found is in the thousands; using the habitable zone criteria, the number of potentially habitable planets falls to 34.[ii] The habitable zone provides a way to decrease the amount of work we must do to analyze these planets once the technology improves.  An improvement in technology would allow scientist to analyze exoplanet atmospheres for bio-signature gases by looking at spectroscopy. These are gases that could be markers of life. On Earth, the abundance of highly reactive oxygen would be a sign that something is producing it. Without a continuously replenishing source the oxygen would react with the other elements. For any aliens looking at our atmosphere’s makeup it would tip them off that something is going on Earth.[iii]

Earlier this year, NASA teased its Instagram followers with a secret announcement. Before making the reveal, they let us know, perhaps the assuaging the disappointment of its nearly 20 million followers, that it was definitely not aliens. But it was something much more grounded in reality:  a planetary system with seven Earth-like planets only 40 light-years away. Even cooler is that three of them lie in their star’s habitable zone.[iv] While NASA tried to mitigate our imaginations, we immediately concluded that there were aliens, some memes even calling to the faraway aliens to save us from our Earth-bound existence. Although the public is already dreaming of little green men, the excitement comes from the astronomers too. This is a momentous discovery, marking the most number of habitable planets found in a single planetary system. Scientists do not have separate minds for research and for their everyday life; rather, their opinions about what they are studying can affect how they view the results of their research.

We presume that it is less outlandish for us to make claims of a planet’s habitability, than to announce the discovery of aliens. The information we have about the Trappist 1 system is limited. We only know of the masses of the planets, the type of star, as well as the orbiting distance. We know nothing of their atmosphere of these planets, or their surface conditions. The star of this seven-Earth solar system, is one- twelfth the size of our Sun. The star is a red, “ultra-cool dwarf” and found more commonly than our Sun.[v]

The Sun shapes many of the conditions on Earth. Sunlight refracted by atmospheric particles and water, give us our trademark blue sky and our planet’s distinctive blue coloring. How Earth-like can these planets be orbiting a red star? Is a planet with a red sky really Earth-like? Having reduced Earth’s tangled web of interactions between life on the planet and the planet itself, to just two conditions–mass and density—it seems a stretch to say that these planets are Earth-like, rather than Earth-sized. Confidently declaring the seven Trappist 1 planets as Earth-like, is just another form of our Earth Bias finding its way into our scientific language.

We know that Earth is more than conditions on Earth’s surface and we know nothing of the surface conditions on these 7 planets that reside 235 trillion miles away. It’s like using our nearsighted vision to look out at two blurry people of the same height and shape out in the distance, and declaring with confidence that they are twins. How is this any more outlandish then declaring that these planets are inhabited? Robert Miller, author of The Christians as the Romans Saw Them, questions, “Yet is it not equally true that how something appears how it is perceived by others is an aspect of what it is?”[vi]While this question deals with attitudes towards early Christians in the Roman Empire, I think it is apt to our current situation. When scientists declare that a planet is Earth-like, the people think the planet is inhabited. If scientists hesitate to make the claim of aliens, they should also be wary of declaring something Earth-like, because people arrive at the same conclusion: alien life.

[i] Close, Laird. “Lecture 26.” Astronomy 204: Great Debates in Astronomy, 2001. http://exoplanet.as.arizona.edu/~lclose/teaching/a202/lect26.html.

 

[ii]  “Exoplanets Data Explorer | Exoplanets – Form Search | DataIR.” Accessed September 18, 2016. http://datair.soe.ucsc.edu/experiment/exoplanet/search/exact.

 

[iii] Dvorsky, George. “A New Equation Reveals Our Exact Odds of Finding Alien Life.” io9. Accessed September 14, 2016. http://io9.com/what-a-brand-new-equation-reveals-about-our-odds-of-fin-531575395.

 

[iv] Gillon, Michaël, Amaury H. M. J. Triaud, Brice-Olivier Demory, Emmanuël Jehin, Eric Agol, Katherine M. Deck, Susan M. Lederer, et al. “Seven Temperate Terrestrial Planets around the Nearby Ultracool Dwarf Star TRAPPIST-1.” Nature 542, no. 7642 (February 23, 2017): 456–60. doi:10.1038/nature21360.

 

 

[v] Gillon, Michaël. “Dwarf Planetary Systems Will Transform the Hunt for Alien Life,” n.d. https://aeon.co/ideas/dwarf-planetary-systems-will-transform-the-hunt-for-alien-life?utm_source=Aeon+Newsletter&utm_campaign=842570fcee-EMAIL_CAMPAIGN_2017_05_05&utm

 

[vi] Miller, Robert. The Christians as the Roman Saw Them. Yale University Press. 1986

 

We only know the Earth.  Humans have spent their entire existence on the Earth, and although our consciousness is rooted in this special planet, we do not know what features of our planet make it unique. Is it the abundance of liquid water? Is it the 93 million miles between us and the Sun? Or maybe Earth is unique because we may have Jupiter acting as a guardian, flinging possible planet-destroying asteroids away from Earth? [i] Our sense of our position in the universe reflects what is knocking around in our collective brains.

After Galileo’s discovery of Jupiter’s moons in the 16th century, we had proof that literally everything does not revolve around us.[ii]  While astronomers had theorized that other planets must exist, it wasn’t until 1995 that we found our first exoplanet.[iii] Even before we knew of other solar systems, ancient astronomers fantasized about the other planets in our solar system. People have imagined what these alien planets could look like. Since we are so familiar with life on Earth, we thought that these worlds would be just as inhabited as our own. Ancient cultures from across the globe believed that life was in the stars.  From anthropomorphic angels, gods and animals that make the constellations, to amateur astronomer Percival Lowell’s absolute conviction of intelligent life on Mars, extraterrestrial life has been a preoccupation of humans for millennia.[iv] The modern rendition of our hope of not being alone is present in our technological search for information about our solar system and our galaxy.  We have searched for life on Mars (a search informed by Earth life), which yielded disappointing results.[v] Now that we’ve almost accepted that Earth is the only planet with life in our solar system, we’ve moved our search to other solar systems in the Milky Way. While discovering other planets helps us understand more of the universe, the search has another goal. In NASA’s own words, the goal is “to discover planets around other stars, to characterize their properties and to identify planets that could harbor life.”[vi] While NASA’s website simply states the goals of exoplanet research, they never explain the process of discovery. It turns out that this process of learning about planets that cannot be directly observed has many interesting considerations. Many of the planets we wish to study cannot be directly observed, so astronomers rely on statistical models to tease out the reality from the data. In this construction of the world around us, our biases and wishes must be regarded. Our biases show up in our research which makes for interesting things to analyze. Also, the use of statistical models as measures of truth provides an arena where personal subjective beliefs meet with the scientific process. Scientists decide not only what factors they will include in their model, but have to use the results of their modeling to create meaningful interpretations. Bias has its role at both ends of the process of discovery.

In this paper, I will examine the role of subjectivity in statistical approaches, and this examination will be followed into the cultural development of those subjective biases. On the statistical end, I will discuss the role of subjective belief in the two major statistical schools: Frequentism and Bayesian statistics. Statistics and modeling are crucial parts to the discovery processes in astronomy, so the scientific methods of looking for exoplanets will be explained. From there, the epistemological value of statistical models in astronomy will be explored. Truth about the universe (things we can never see) is usually related into concepts we can think about here on Earth. Examining how we interpret information about the universe, and how we make it more tangible for our earth-bound life, reveals a lot about how we think about the universe and humanity’s role on Earth and in space.

[i] Ward, Peter D, and Donald Brownlee. Rare Earth: Why Complex Life in Uncommon in the Universe. New York, New York: Copernicus, 2000.

 

[ii] Grinspoon, David. Lonely Planets: The Natural Philosophy of Alien Life. First Edition. HarperCollins Publishers Inc., 2003.

 

[iii] Lemonick, Michael. Mirror Earth: The Search for Our Planets Twin. Bloomsbury Publishing,  2012.

[iv] Hathaway, Nancy. The Friendly Guide to the Universe. Viking, 1994

[v] Ward and Brownlee

[vi] “Habitable Worlds.” Exoplanet Exploration: Planets Beyond Our Solar System. Accessed September 13, 2016. https://exoplanets.nasa.gov/the-search-for-life/habitable-zones.