DOCSLIB.ORG

The Drake Equation As a Function of Spectral Type and Time Jacob Haqq-Misra1,2,* and Ravi Kumar Kopparapu1,2,3,4

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Drake Equation As a Function of Spectral Type and Time Jacob Haqq-Misra1,2,* and Ravi Kumar Kopparapu1,2,3,4 The Drake Equation as a Function of Spectral Type and Time Jacob Haqq-Misra1,2,* and Ravi Kumar Kopparapu1,2,3,4 1 Blue Marble Space Institute of Science, 1001 4th Ave, Suite 3201, Seattle, WA 2 NASA Astrobiology Institute’s Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 3 NASA Goddard Space Flight Center, 8800 Greenbelt Road, Mail Stop 699.0 Building 34, Greenbelt, MD 4 Department of Astronomy, University of Maryland, College Park, MD *Email: [email protected] Published in Habitability of the Universe Before Earth, R. Gordon and A. Sharov (Eds.), Elsevier Abstract This chapter draws upon astronomical observations and modeling to constrain the prevalence of communicative civilizations in the galaxy. We discuss the dependence of the Drake equation pa- rameters on the spectral type of the host star and the time since the galaxy formed, which allow us to examine trajectories for the emergence of communicative civilizations over the history of the galaxy. We suggest that the maximum lifetime of communicative civilizations depends on the spectral type of the host star, which implies that F- and G-dwarf stars are the best places to search for signs of technological intelligence today. 1. Introduction The Drake equation is a probabilistic expression for the number of communicative civilizations in the galaxy (Drake, 1965). This equation typically takes the form = , (1) ∗ where R∙* is ∙the rate∙ ∙ of ∙star ∙ formation, fp is the fraction of stars with planets, ne is the number of habitable planets per system, fl is the fraction of habitable planets that develop life, fi is the fraction of inhabited planets that develop intelligence, fc is the fraction of planets with intelligent life that develop technology capable of interstellar communication, and L is the average communicative lifetime of technological civilizations (c.f. Ćirković and Vukotić, 2008). The original formulation of this equation was developed by Frank Drake during a 1961 conference at Green Bank, West Virginia, with the goal of identifying the key factors needed for a planet to develop life and tech- nology that could communicate with Earth. Since this discussion at Green Bank, the Drake equa- tion has seen wide use among scientists and educators, with some studies proposing methods for constraining the Drake equation with observable quantities (Frank and Sullivan, 2016) or statistical methods (Maccone, 2010; Glade et al., 2012) in order to guide future search for extraterrestrial intelligence (SETI) surveys. Others have extended the traditional representation of the Drake equa- tion to include time-dependent quantities, in an effort to understand the distribution of civilizations across the history of the galaxy (Ćirković, 2004; Glade et al., 2012; Prantzos, 2013). In this chapter we discuss the functional dependence of the Drake equation parameters on the spectral type of the host star and the time since the galaxy formed. We discuss observations, plan- etary formation models, and climate models that provide constraints on the values of R*, fp, and ne, as well as looser bounds on fl and fi. We also examine common assumptions for estimating the parameter L and develop two approaches for calculating the maximum value, Lmax, as a function of spectral type. We use these constraints to develop an expression for N(s,t), the number of com- municative civilizations in the galaxy as a function of spectral type s and time since galaxy for- mation t. We also discuss and critique the possibility that N has distinct phases in time, such that certain events are impossible or unlikely until a particular galactic era. Ćirković and Vukotić (2008), fol- lowing Annis (1999), describe this behavior as a ‘phase transition,’ suggesting that phenomenon such as supernovae, gamma ray bursts, or other physical phenomena could have been more prev- alent during the early phase of the galaxy compared to today. The idea of a phase transition indi- cates that astrophysical factors may have inhibited the emergence of communicative civilizations until relatively recently in galactic history. We argue that phase transitions for N are most likely to emerge from the dependence of Lmax on stellar spectral type. 2. Constraints from Observations In this section we discuss observational constraints on the parameters R*, fp, and ne along with their dependence on spectral type and time. We consider F-, G-, K-, and M-dwarf stars in the majority of our analysis, so that { , , , }, as these present the most likely candidates for supporting intelligent life. However, casting the Drake equation as a function of spectral type also allows for consideration of O-, B-, and∈ A-dwarf stars (which will explicitly show why such stars are deemed unlikely for advanced life) and even planets around evolved stars. 2.1 Rate of Star Formation Common analyses of the Drake equation cite a value of 7 to 10 star/yr as an estimate of R*. Because R* is difficult to measure directly, one way of calculating this rate is to write = , where n* is the current number of stars in the galaxy and t0 ≈ 13 Gyr is the current age of the galaxy. ∗ ∗ 0 However, this uniform approach assumes that the rate of star formation has remained constant⁄ over the history of the galaxy (Ćirković, 2004), proportional to the stellar population today. As an im- provement to previous estimates that offer a single value of R*, we calculate values of R* that depend on spectral type. Analysis of Spitzer data (Robitaille and Whitney, 2010) finds that the stellar mass formation rate is 0.68 to 1.45 Msun/yr (where Msun is the mass of the sun). To convert this number into a value for R*(s), we separate the spectral types into mass ranges based on the initial mass function categories of Kroupa (2001). We assume an initial mass of 1 Msun for F- and G-dwarfs, 0.5 Msun for K-dwarfs, and 0.1 Msun for M-dwarfs. We then divide the observed stellar mass formation rate by this initial mass function to give R*(s), with units of number of stars formed per year. F- and G-dwarfs have the lowest rate of R*(F) ~ R*(G) ~ 1 star/yr. K-dwarfs have a rate of R*(K) ~ 1.3 to 3 star/yr (we use R*(K) = 2.2 star/yr in our analysis), while M-dwarfs have the highest rate of R*(M) ~ 7 to 14 star/yr (we use R*(M) = 10.5 star/yr in our analysis). We summarize these values for R* in Table 1. Star R* fp ne fl·fi·fc L* F-dwarf 1 star/yr 1 0.2 1 4 Gyr 0 Gyr 2 Gyr G-dwarf 1 star/yr 1 0.2 1 10 Gyr 6 Gyr 5 Gyr K-dwarf 2.2 star/yr 1 0.2 1 30 Gyr 26 Gyr 15 Gyr M-dwarf 10.5 star/yr 1 0.2 1 100 Gyr 96 Gyr 50 Gyr Table 1: Summary of Drake equation parameters discussed in this chapter. 2.2 Fraction of Stars with Planets Ground- and space-based observations all suggest that terrestrial planets are commonplace around all stars. Microlensing observations indicate that typical stellar systems contain one or more bounded planets (Cassan et al., 2012). Furthermore, analysis of Kepler data indicates that there are ~2 planets per cool star (Teff < 4000 K) with periods <150 days (Morton and Swift, 2014). This orbital period encompasses the habitable zone (HZ) of cool stars. Therefore, we can safely assume that fp = 1 for all spectral types F, G, K, and M (c.f. Frank and Sullivan, 2016). Lineweaver et al. (2004) developed a model for the evolution of the galaxy and found that rocky planets could not have formed until about t = 4 Gyr, due to the lower metallicity of stars at the time. If planet formation were lower during the early history of the galaxy, then this would suggest a phase transition for the emergence of planets in the galaxy. However, these results of Lineweaver et al. (2004) are inconsistent with observations of planets orbiting stars nearly as old as the galaxy itself. The Kepler-444 system is one of the oldest known to host exoplanets, with five planets smaller than Earth orbiting this 11.2 Gyr old K-dwarf. At least for the long-lived K- and M-dwarf stars, fp = 1 for t > 1 Gyr, which is close to the age of the galaxy. Even if F- and G-dwarf stars develop planets slightly later than this due to metallicity limitations, we remain skeptical that dif- ferences in metallicity over the history of the galaxy are responsible for a phase transition in the Drake equation. We therefore maintain the expression fp(s, t) = 1. 2.3 Number of Habitable Planets Per System A common approach to estimating ne is to focus on the related quantity “eta-Earth”, ηearth, which is defined as the fraction of stars with at least one terrestrial mass/size planet within the HZ. The value of ηearth can be estimated from Kepler data (Dressing and Charbonneau, 2013, 2015; Kop- parapu, 2013; Gaidos, 2013; Petigura et al., 2013; Morton and Swift, 2014; Foreman-Mackey et al., 2014), with current estimates varying between 22% (Petigura et al., 2013) to 2% (Foreman- Mackey et al., 2014) for G- and K-dwarfs, and 20% for M-dwarf stars (Dressing and Charbonneau, 2015). In reality, and ηearth are describing the same quantity: the average number of habitable planets (which we will assume means terrestrial planets located within the HZ) per system, is the same as the fraction of stars with at least one terrestrial planet in the HZ. This means that is in the range of 0.02 to 0.22 for G- and K-dwarfs, and 0.20 for M-dwarfs.
Load more

Recommended publications
  • David Grinspoon Planetary Science Institute 2017 Report Report On
    David Grinspoon Planetary Science Institute 2017 Report Report on research and education activities: My research activities in 2017 included contributing to the Japanese Akatsuki Venus mission as a Contributing Scientist. Several papers are in preparation. Also this year I continued work on the ROCKE3D node of the NASA NexSS (NASA Nexus for Exoplanet System Science). Out of this work I am co-author of a paper that was published in Geophysics Research Letters. I also contributed as Co-I to the proposal for the Venus New Frontiers missions VICI and VISAGE, neither of which was selected for Phase A funding. On the heels of this loss I am now a Co-I on a team that is preparing a proposal for the next Discovery competition. This year I completed a book entitled “Chasing New Horizons”, co-authored with Dr. Alan Stern, which chronicles the history of the New Horizons mission to Pluto. It will be published May 1, 2018, by Picador Books. Also, this year This year I joined the Committee on the Status of Women of the American Astronomical Society. I gave invited talks at Princeton University, Hunter College, University of Iowa, University of Victoria, University of Utrecht, University of Stellenbosch (South Africa),Stevens Institute of Technology, MIT, Johns Hopkins University and at the American Geophysical Union meeting in New Orleans I have participated in numerous public outreach activities including magazine writing, hosting and appearing as a guest on radio shows, moderating public discussions, and giving lectures. I also joined the scientific advisory board of the SETI Institute. Publications: Way, M.
    [Show full text]
  • Bayesian Analysis of the Astrobiological Implications of Life's
    Bayesian analysis of the astrobiological implications of life's early emergence on Earth David S. Spiegel ∗ y, Edwin L. Turner y z ∗Institute for Advanced Study, Princeton, NJ 08540,yDept. of Astrophysical Sciences, Princeton Univ., Princeton, NJ 08544, USA, and zInstitute for the Physics and Mathematics of the Universe, The Univ. of Tokyo, Kashiwa 227-8568, Japan Submitted to Proceedings of the National Academy of Sciences of the United States of America Life arose on Earth sometime in the first few hundred million years Any inferences about the probability of life arising (given after the young planet had cooled to the point that it could support the conditions present on the early Earth) must be informed water-based organisms on its surface. The early emergence of life by how long it took for the first living creatures to evolve. By on Earth has been taken as evidence that the probability of abiogen- definition, improbable events generally happen infrequently. esis is high, if starting from young-Earth-like conditions. We revisit It follows that the duration between events provides a metric this argument quantitatively in a Bayesian statistical framework. By (however imperfect) of the probability or rate of the events. constructing a simple model of the probability of abiogenesis, we calculate a Bayesian estimate of its posterior probability, given the The time-span between when Earth achieved pre-biotic condi- data that life emerged fairly early in Earth's history and that, billions tions suitable for abiogenesis plus generally habitable climatic of years later, curious creatures noted this fact and considered its conditions [5, 6, 7] and when life first arose, therefore, seems implications.
    [Show full text]
  • The Copernican Principle Rules out BLC1 As a Technological Radio Signal from the Alpha Centauri System
    Draft version January 13, 2021 Typeset using LATEX twocolumn style in AASTeX62 The Copernican Principle Rules Out BLC1 as a Technological Radio Signal from the Alpha Centauri System Amir Siraj1 and Abraham Loeb1 1Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138, USA ABSTRACT Without evidence for occupying a special time or location, we should not assume that we inhabit privileged circumstances in the Universe. As a result, within the context of all Earth-like planets orbiting Sun-like stars, the origin of a technological civilization on Earth should be considered a single outcome of a random process. We show that in such a Copernican framework, which is inherently optimistic about the prevalence of life in the Universe, the likelihood of the nearest star system, Alpha Centauri, hosting a radio-transmitting civilization is ∼ 10−8. This rules out, a priori, Breakthrough Listen Candidate 1 (BLC1) as a technological radio signal from the Alpha Centauri system, as such a scenario would violate the Copernican principle by about eight orders of magnitude. We also show that the Copernican principle is consistent with the vast majority of Fast Radio Bursts being natural in origin. Keywords: technosignatures; astrobiology; search for extraterrestrial intelligence; biosignatures 1. INTRODUCTION lihood of searches for primitive and intelligent life, us- The Copernican principle asserts that we are not priv- ing a Drake-type approach. Westby & Conselice(2020) ileged observers of the Universe. Successes of its appli- applied the Copernican principle to the search for intel- cation include the rejection of Ptolemaic geocentrism ligent life, but in forms that featured strict boundaries and the adoption of the modern cosmological princi- in time, thereby not reflecting a truly random process.
    [Show full text]
  • The 29Th Annual Meeting the 29Th Annual Meeting of the Society Took Place on April 17Th, 2016 Program and Abstracts Program
    The 29th annual meeting The 29th annual meeting of the society took place on April 17th, 2016 Program and Abstracts Program: Program of the 29th annual meeting Time Lecturer Lecture Title 8:45- Refreshments & Gathering 9:05 Session 1 -Astrobiology (Doron Lancet, Chair; Amri Wandel, Organizer) 9:05- Gonen Ashkenasy Opening Remarks 9:15 (BGU) 9:15- Ravit Helled Methane-Rich Planets and the Characterization of Exoplanets 9:45 (TAU) 9:45- Sohan Jheeta (NoR Formation of Glycolaldehyde (HOCH2CHO) from Pure 10:10 HGT, LUCA) Methanol in Astrophysical Ice Analogues 10:10- Joseph Is Liquid Water Essential for Life? A Reassessment 10:35 Gale (HUJI) 10:35- Coffee break 11:00 Session 2 - Evolution (Addy Pross, Chair) 11:00- Robert Pascal Identifying the Kinetic, Thermodynamic and Chemical 11:40 (CNRS Conditions for Stability and Complexity in Living Systems Montpellier) 11:40- Omer Markovitch Predicting Proto-Species Emergence in Complex Networks 12:05 (Newcastle) 12:05- Amir Aharoni Engineering a Species Barrier in Yeast 12:30 (BGU) 12:30- Jayanta Nanda Spontaneous Evolution of β-Sheet Forming Self Replicating 12:55 (BGU) Peptides 12:55- Lunch 14:05 Session 3 - Origins of Order and Complexity (Gonen Ashkenasy, Chair; Tal Mor, Organizer) 14:05- Prof. Zvi HaCohen, Greetings 14:15 Rector (BGU) 14:15- Doron Composomics: a Common Biotic Thread 14:45 Lancet (WIS) 14:45- Avshalom Elitzur Living State Physics: Does Life's Uniqueness Elude Scientific 15:10 (IYAR) Definition? 15:10- Tal Mor Origins of Translation: Speculations about the First and the 15:35
    [Show full text]
  • Astrobiology and the Search for Life Beyond Earth in the Next Decade
    Astrobiology and the Search for Life Beyond Earth in the Next Decade Statement of Dr. Andrew Siemion Berkeley SETI Research Center, University of California, Berkeley ASTRON − Netherlands Institute for Radio Astronomy, Dwingeloo, Netherlands Radboud University, Nijmegen, Netherlands to the Committee on Science, Space and Technology United States House of Representatives 114th United States Congress September 29, 2015 Chairman Smith, Ranking Member Johnson and Members of the Committee, thank you for the opportunity to testify today. Overview Nearly 14 billion years ago, our universe was born from a swirling quantum soup, in a spectacular and dynamic event known as the \big bang." After several hundred million years, the first stars lit up the cosmos, and many hundreds of millions of years later, the remnants of countless stellar explosions coalesced into the first planetary systems. Somehow, through a process still not understood, the laws of physics guiding the unfolding of our universe gave rise to self-replicating organisms − life. Yet more perplexing, this life eventually evolved a capacity to know its universe, to study it, and to question its own existence. Did this happen many times? If it did, how? If it didn't, why? SETI (Search for ExtraTerrestrial Intelligence) experiments seek to determine the dis- tribution of advanced life in the universe through detecting the presence of technology, usually by searching for electromagnetic emission from communication technology, but also by searching for evidence of large scale energy usage or interstellar propulsion. Technology is thus used as a proxy for intelligence − if an advanced technology exists, so to does the ad- vanced life that created it.
    [Show full text]
  • 51. Astrobiology: the Final Frontier of Science Education
    www.astrosociety.org/uitc No. 51 - Summer 2000 © 2000, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112. Astrobiology: The Final Frontier of Science Education by Jodi Asbell-Clarke and Jeff Lockwood What (or Whom) Are We Looking For? Where Do We Look? Lessons from Our Past The Search Is On What Does the Public Have to Learn from All This? A High School Curriculum in Astrobiology Astrobiology seems to be all the buzz these days. It was the focus of the ASP science symposium this summer; the University of Washington is offering it as a new Ph.D. program, and TERC (Technical Education Research Center) is developing a high school integrated science course based on it. So what is astrobiology? The NASA Astrobiology Institute defines this new discipline as the study of the origin, evolution, distribution, and destiny of life in the Universe. What this means for scientists is finding the means to blend research fields such as microbiology, geoscience, and astrophysics to collectively answer the largest looming questions of humankind. What it means for educators is an engaging and exciting discipline that is ripe for an integrated approach to science education. Virtually every topic that one deals with in high school science is embedded in astrobiology. What (or Whom) Are We Looking For? Movies and television shows such as Contact and Star Trek have teased viewers with the idea of life on other planets and even in other galaxies. Illustration courtesy of and © 2000 by These fictional accounts almost always deal with intelligent beings that have Kathleen L.
    [Show full text]
  • Monday, November 13, 2017 WHAT DOES IT MEAN to BE HABITABLE? 8:15 A.M. MHRGC Salons ABCD 8:15 A.M. Jang-Condell H. * Welcome C
    Monday, November 13, 2017 WHAT DOES IT MEAN TO BE HABITABLE? 8:15 a.m. MHRGC Salons ABCD 8:15 a.m. Jang-Condell H. * Welcome Chair: Stephen Kane 8:30 a.m. Forget F. * Turbet M. Selsis F. Leconte J. Definition and Characterization of the Habitable Zone [#4057] We review the concept of habitable zone (HZ), why it is useful, and how to characterize it. The HZ could be nicknamed the “Hunting Zone” because its primary objective is now to help astronomers plan observations. This has interesting consequences. 9:00 a.m. Rushby A. J. Johnson M. Mills B. J. W. Watson A. J. Claire M. W. Long Term Planetary Habitability and the Carbonate-Silicate Cycle [#4026] We develop a coupled carbonate-silicate and stellar evolution model to investigate the effect of planet size on the operation of the long-term carbon cycle, and determine that larger planets are generally warmer for a given incident flux. 9:20 a.m. Dong C. F. * Huang Z. G. Jin M. Lingam M. Ma Y. J. Toth G. van der Holst B. Airapetian V. Cohen O. Gombosi T. Are “Habitable” Exoplanets Really Habitable? A Perspective from Atmospheric Loss [#4021] We will discuss the impact of exoplanetary space weather on the climate and habitability, which offers fresh insights concerning the habitability of exoplanets, especially those orbiting M-dwarfs, such as Proxima b and the TRAPPIST-1 system. 9:40 a.m. Fisher T. M. * Walker S. I. Desch S. J. Hartnett H. E. Glaser S. Limitations of Primary Productivity on “Aqua Planets:” Implications for Detectability [#4109] While ocean-covered planets have been considered a strong candidate for the search for life, the lack of surface weathering may lead to phosphorus scarcity and low primary productivity, making aqua planet biospheres difficult to detect.
    [Show full text]
  • Is It the First Use of the Word Astrobiology ? Author
    Title : Is it the first use of the word Astrobiology ? Author : Danielle Briot Adress : Observatoire de Paris 61 avenue de l’Observatoire 75014 Paris France tel : 33(0)1 40 51 22 39 and 33(0)1 45 07 78 57 [email protected] running title : First use of the word Astrobiology ? 1 Abstract The research of life in Universe is a ancient quest that has taken different forms over the centuries. It has given rise to a new science, which is normally referred as Astrobiology. It is interesting to research when this word was used for the first time and when this science developed to represent the search for life in Universe as is done today. There are records of the usage of the word "Astrobiology" as early as 1935, in an article published in a French popular science magazine. Moreover this article is quite remarkable because its portrayal of the concept of the subject is very similar to that considered today. The author of this paper was Ary J. Sternfeld (1905 - 1980), who was ortherwise known as a poorly respected great pioneer of astronautics. We provide a brief description of his life, which was heavily influenced by the tragic events of the 20th century history, from Poland and France to Russia. He was a prolific scientific writer who wrote a number of very successful scientific books and papers. Keywords : History – Pioneers 2 1. Introduction The question of the life in the Universe, in relation with the question of the multiplicity of worlds, is very ancient and probably dates back to Greek philosophers.
    [Show full text]
  • Evolutionary Processes Transpiring in the Stages of Lithopanspermia Ian Von Hegner
    Evolutionary processes transpiring in the stages of lithopanspermia Ian von Hegner To cite this version: Ian von Hegner. Evolutionary processes transpiring in the stages of lithopanspermia. 2020. hal- 02548882v2 HAL Id: hal-02548882 https://hal.archives-ouvertes.fr/hal-02548882v2 Preprint submitted on 5 Aug 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. HAL archives-ouvertes.fr | CCSD, April 2020. Evolutionary processes transpiring in the stages of lithopanspermia Ian von Hegner Aarhus University Abstract Lithopanspermia is a theory proposing a natural exchange of organisms between solar system bodies as a result of asteroidal or cometary impactors. Research has examined not only the physics of the stages themselves but also the survival probabilities for life in each stage. However, although life is the primary factor of interest in lithopanspermia, this life is mainly treated as a passive cargo. Life, however, does not merely passively receive an onslaught of stress from surroundings; instead, it reacts. Thus, planetary ejection, interplanetary transport, and planetary entry are only the first three factors in the equation. The other factors are the quality, quantity, and evolutionary strategy of the transported organisms.
    [Show full text]
  • 2015 October
    TTSIQ #13 page 1 OCTOBER 2015 www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-water-flows-on-today-s-mars Flash! Sept. 28, 2015: www.space.com/30674-flowing-water-on-mars-discovery-pictures.html www.space.com/30673-water-flows-on-mars-discovery.html - “boosting odds for life!” These dark, narrow, 100 meter~yards long streaks called “recurring slope lineae” flowing downhill on Mars are inferred to have been formed by contemporary flowing water www.space.com/30683-mars-liquid-water-astronaut-exploration.html INDEX 2 Co-sponsoring Organizations NEWS SECTION pp. 3-56 3-13 Earth Orbit and Mission to Planet Earth 13-14 Space Tourism 15-20 Cislunar Space and the Moon 20-28 Mars 29-33 Asteroids & Comets 34-47 Other Planets & their moons 48-56 Starbound ARTICLES & ESSAY SECTION pp 56-84 56 Replace "Pluto the Dwarf Planet" with "Pluto-Charon Binary Planet" 61 Kepler Shipyards: an Innovative force that could reshape the future 64 Moon Fans + Mars Fans => Collaboration on Joint Project Areas 65 Editor’s List of Needed Science Missions 66 Skyfields 68 Alan Bean: from “Moonwalker” to Artist 69 Economic Assessment and Systems Analysis of an Evolvable Lunar Architecture that Leverages Commercial Space Capabilities and Public-Private-Partnerships 71 An Evolved Commercialized International Space Station 74 Remembrance of Dr. APJ Abdul Kalam 75 The Problem of Rational Investment of Capital in Sustainable Futures on Earth and in Space 75 Recommendations to Overcome Non-Technical Challenges to Cleaning Up Orbital Debris STUDENTS & TEACHERS pp 85-96 Past TTSIQ issues are online at: www.moonsociety.org/international/ttsiq/ and at: www.nss.org/tothestarsOO TTSIQ #13 page 2 OCTOBER 2015 TTSIQ Sponsor Organizations 1.
    [Show full text]
  • Does the Rapid Appearance of Life on Earth Suggest That Life Is Common in the Universe?
    ASTROBIOLOGY Volume 2, Number 3, 2002 © Mary Ann Liebert, Inc. Does the Rapid Appearance of Life on Earth Suggest that Life Is Common in the Universe? CHARLES H. LINEWEAVER 1,2 and TAMARA M. DAVIS 1 ABSTRACT It is sometimes assumed that the rapidity of biogenesis on Earth suggests that life is common in the Universe. Here we critically examine the assumptions inherent in this if-life-evolved- rapidly-life-must-be-common argument. We use the observational constraints on the rapid- ity of biogenesis on Earth to infer the probability of biogenesis on terrestrial planets with the same unknown probability of biogenesis as the Earth. We find that on such planets, older than ,1 Gyr, the probability of biogenesis is .13% at the 95% confidence level. This quan- tifies an important term in the Drake Equation but does not necessarily mean that life is com- mon in the Universe. Key Words: Biogenesis—Drake Equation. Astrobiology 2, 293–304. THE BIOGENESIS LOTTERY duction–oxidation pairs are common (Nealson and Conrad, 1999). UCHOFCURRENTASTROBIOLOGICALRESEARCH Mis focused on learning more about the early It is difficult to translate this circumstantial ev- evolution of the Earth and about the origin of life. idence into an estimate of how common life is in We may be able to extrapolate and generalize our the Universe. Without definitive detections of ex- knowledge of how life formed here to how it traterrestrial life we can say very little about how might have formed elsewhere. Indirect evidence common it is or even whether it exists. Our exis- suggesting that life may be common in the Uni- tence on Earth can tell us little about how com- verse includes: mon life is in the Universe or about the proba- bility of biogenesis on a terrestrial planet because, Sun-like stars are common.
    [Show full text]
  • The Drake Equation the Drake Equation, Which We Encountered in the Very First Lecture of This Class, Is a Way to Take the Questi
    The Drake Equation The Drake equation, which we encountered in the very first lecture of this class, is a way to take the question “How many communicative civilizations are there currently in our galaxy?” and break it into several factors that we estimate as best we can. In this class we will go into detail about this equation. We will find that we now have a decent idea of the values of a couple of the factors, but that many are still guesswork. We’ll do our best to make our guesses informed. We will also discover that some people have reformulated the equation by adding a number of other factors they consider crucial to having technologically adept life. The remarkable and subtle effect of this is that, depending on how many factors you think appropriate, you can get the conclusions you want while appearing reasonable and conservative throughout. That is, if you think many civilizations exist, you can use the Drake equation to demonstrate this. If you think we are the only ones, you can get the equation to say that as well. With this in mind, we should approach the Drake equation as a way of framing our discussion as opposed to as a method of determining the answer rigorously. The equation itself and its factors The original form of the equation was written by Frank Drake in 1960 in preparation for a meeting in Green Bank, West Virginia. It says: ∗ N = R × fp × ne × fl × fi × fc × L . (1) Here: • N is the number of currently active, communicative civilizations in our galaxy.
    [Show full text]