Year: 2020
Type: article
Abstract: The search for spectroscopic biosignatures with the next generation of space telescopes could provide observational constraints on the abundance of exoplanets with signs of life. An extension of this spectroscopic characterization of exoplanets is the search for observational evidence of technology, known as technosignatures. Current mission concepts that would observe biosignatures from ultraviolet to near-infrared wavelengths could place upper limits on the fraction of planets in the Galaxy that host life, although such missions tend to have relatively limited capabilities of constraining the prevalence of technosignatures at mid-infrared wavelengths. Yet searching for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolution-the Great Filter-is probably in our past. But if we find that life is commonplace while technosignatures are absent, then this would increase the likelihood that the Great Filter awaits to challenge us in the future.
Source: Astrobiology
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1655399185, NEARLY 50% OF SUN-LIKE STARS IN OUR GALAXY ARE IN BINARY STELLAR SYSTEMS. RECENT DISCOVERIES BY THE KEPLER MISSION AND GROUND-BASED SURVEYS HAVE SHOWN THAT DYNAMICALLY STABLE PLANETARY SYSTEMS EXIST AND ARE ABUNDANT AROUND MANY BINARY STARS. FUTURE MISSIONS SUCH AS TESS AND PLATO WILL DISCOVER NEARBY PLANETS IN BINARY SYSTEMS WHICH COULD BE FURTHER CHARACTERIZED SPECTROSCOPICALLY WITH JWST. THE RECENTLY LAUNCHED GAIA ASTROMETRY TELESCOPE WHICH OBSERVES 1 BILLION STARS IN OUR GALAXY (1% OF THE GALACTIC STELLAR POPULATION) IS PROVIDING UNPRECEDENTED POSITIONAL AND RADIAL VELOCITY MEASUREMENTS THAT CAN REVEAL FURTHER PLANETS IN BINARY SYSTEMS. AS WITH PLANETS AROUND SINGLE STARS THESE PLANETS IN BINARY SYSTEMS CONTINUE TO RAISE QUESTIONS ABOUT THEIR POTENTIAL HABITABILITY. PREVIOUS STUDIES OF THE HABITABLE ZONE (HZ) OF BINARY SYSTEMS CONSIDERED ONLY THE EFFECT OF CHANGES IN THE PEAK OF THE COMBINED SPECTRAL ENERGY DISTRIBUTION (SED) OF THE TWO STARS; HOWEVER THE SPECTRAL ENERGY DISTRIBUTION (SED) FOR PLANETS IN BINARY SYSTEMS SHOULD BE A SUPERPOSITION OF BOTH HOST STARS. HABITABILITY IS DEFINED AS THE ABILITY OF A TERRESTRIAL PLANET TO SUSTAIN LIQUID WATER ON ITS SURFACE WHICH IS DETERMINED BY THE ENERGY BALANCE OF A PLANET S ATMOSPHERE. GREENHOUSE GASES LIKE WATER VAPOR AND CARBON DIOXIDE ABSORB RADIATION AT BOTH LONG (INFRARED) AND SHORT (ULTRAVIOLET) WAVELENGTHS WHICH MAKES THE CLIMATE SENSITIVE TO THE FULL COMBINED SED OF BOTH STARS. WE EXPECT THAT THE HZ FOR PLANETS IN BINARY SYSTEMS SHOULD BE A FUNCTION OF THE SED OF THE BINARY SYSTEM WHICH WILL DEPEND UPON THE EVOLUTIONARY HISTORY OF EACH STELLAR SYSTEM. WE WILL ALSO STUDY THE DIFFERENCES IN DIURNAL PATTERNS OF SOLAR INSOLATION CAUSED BY BOTH P-TYPE AND S-TYPE PLANETARY ORBITS WITHIN BINARY SYSTEMS. WE EXPECT THE ORBITAL CONFIGURATIONS OF BINARY SYSTEMS TO PLAY A SIGNIFICANT ROLE IN THE DEFINITION OF HABITABLE ZONES. METHODS THIS RESEARCH WILL CONSTRAIN THE HZ FOR PLANETS IN BINARY SYSTEMS BY USING A HIERARCHY OF EXISTING CLIMATE MODELS. WE WILL USE OBSERVED STELLAR SPECTRA AND STELLAR EVOLUTIONARY MODELS TO DEVELOP SEVERAL SCENARIOS FOR THE COMBINED SED OF BOTH P-TYPE AND S-TYPE BINARY SYSTEMS. WE WILL FIRST STUDY THE EFFECT OF SUPERPOSITION OF MULTIPLE STELLAR SPECTRA USING A LINE-BY-LINE RADIATIVE TRANSFER MODEL. THESE CALCULATIONS WILL SET BENCHMARKS FOR EVALUATION OF THE CORRELATED-K RADIATIVE TRANSFER CODES USED SUBSEQUENTLY. WE WILL THEN EVALUATE THE HZ FOR BINARY SYSTEM IN COMBINATIONS OF F G K AND M TYPES USING A ONE-DIMENSIONAL RADIATIVE CONVECTIVE CLIMATE MODEL WHICH WILL PROVIDE A BASIS OF COMPARISON AGAINST CLASSIC SINGLE-STAR HZ CALCULATIONS IN THE LITERATURE. WE WILL NEXT USE THIS 1-D MODEL TO PARAMETERIZE THE RADIATIVE TRANSFER IN A 2-D LATITUDINAL ENERGY BALANCE MODEL WHICH WILL ALLOW US TO CONSIDER THE CONTRIBUTIONS TO HABITABILITY OF NON-CIRCULAR ORBITS AND ICE-ALBEDO FEEDBACK. WE WILL THEN EXAMINE THE EFFECT OF BINARY SED ON ATMOSPHERIC DYNAMICS BY USING FULL THREE-DIMENSIONAL GENERAL CIRCULATION MODELS TO QUANTIFY CHANGES IN LARGE-SCALE CIRCULATION THAT AFFECT HABITABILITY. BY USING THESE 3-D MODELS WE CAN SELF-CONSISTENTLY SIMULATE ALL ASPECTS OF CLIMATE WHICH INCLUDES GEOPHYSICAL AND ORBITAL PROPERTIES RADIATIVE TRANSFER DYNAMICS AND CLOUDS. RELEVANCE THIS PROPOSED RESEARCH IS RELEVANT TO NASA S HABITABLE WORLDS PROGRAM AS A THEORETICAL STUDY OF THE CLIMATES OF EXTRASOLAR TERRESTRIAL PLANETS AND THEIR ABILITY TO SUSTAIN THE PRESENCE OF WATER. THE RESULTS OF THIS RESEARCH WILL HELP TO IDENTIFY THE CHARACTERISTICS AND THE DISTRIBUTION OF POTENTIALLY HABITABLE ENVIRONMENTS IN THE SOLAR SYSTEM AND BEYOND (C.4-1) BY USING A HIERARCHY OF EXISTING CLIMATE MODELS TO CONSTRAIN THE HZ OF PLANETS IN BINARY STAR SYSTEMS. THE SCOPE OF THIS RESEARCH FOCUSES ON THE HABITABILITY OF EXTRASOLAR PLANETS SO THIS PROPOSAL IS NOT RELEVANT TO THE EMERGING WORLDS PROGRAM THE EXOBIOLOGY PROGRAM OR ANY EXISTING DATA ANALYSIS PROGRAMS., TO ENABLE AND ADVANCE NASA S SEARCH FOR LIFE BEYOND THE SOLAR SYSTEM THE VIRTUAL PLANETARY LABORATORY TEAM WILL FOCUS ON A COMPELLING SCIENTIFIC QUESTION: HOW DO WE RECOGNIZE WHETHER AN EXOPLANET CAN OR DOES SUPPORT LIFE? IN ADVANCE OF CHALLENGING OBSERVATIONS THE VPL WILL COMBINE SCIENTIFIC MODELS OBSERVATIONS AND FIELD AND LABORATORY DATA FROM MANY DISCIPLINES TO EXPLORE HOW A PLANET BECOMES AND REMAINS HABITABLE AND IDENTIFY NEW BIOSIGNATURES IN THE CONTEXT OF THEIR ENVIRONMENTS. THIS RESEARCH WILL INFORM TARGET SELECTION FOR JWST FROM K2 TESS AND GROUND-BASED EXOPLANET DISCOVERIES; HELP OBSERVERS RECOGNIZE THE SIGNS OF PLANETARY HABITABILITY AND LIFE; AND INFORM UPCOMING NASA MISSIONS THAT WILL OBSERVE TERRESTRIAL EXOPLANETS SUCH AS JWST AND THE HABEX OST AND LUVOIR MISSION CONCEPTS. FIVE RESEARCH TASKS WILL ADDRESS OUR SCIENTIFIC QUESTION. TASKS A-D PROVIDE A SUITE OF SELF-CONSISTENT PLANETARY ENVIRONMENTS BASED ON DATA AND MODELS THAT ARE VALIDATED AGAINST SOLAR SYSTEM PLANETS. THESE PLANETARY ENVIRONMENTS ARE THEN INPUT TO TASK E TO SIMULATE PLANETARY OBSERVATIONS AND DETERMINE THE DETECTABILITY OF SIGNS OF HABITABILITY AND LIFE. TASK A: SOLAR SYSTEM ANALOGS FOR EXOPLANETS. WE WILL USE OBSERVATIONS AND ATMOSPHERIC MODELS OF EARTH AND VENUS AS WELL AS REALISTIC SIMULATIONS OF THE DISTANT SOLAR SYSTEM AND OTHER PLANETARY SYSTEMS TO EXPLORE PROCESSES AND REMOTE-SENSING DISCRIMINANTS RELEVANT TO HABITABLE ENVIRONMENTS BIOSIGNATURES AND FALSE POSITIVES. TASK B: THE EARTH THROUGH TIME. WE WILL UNDERTAKE AN INTERDISCIPLINARY SYNTHESIS OF FIELD LABORATORY AND MODELING EFFORTS TO CONSTRAIN ENVIRONMENTAL ECOLOGICAL AND REMOTELY OBSERVABLE PARAMETERS OF EARLY EARTH AND SIMILAR EXOPLANETS AROUND OTHER STARS AS A FUNCTION OF DOMINANT METABOLISM. TASK C: THE HABITABLE PLANET. WE WILL DEVELOP AND USE COUPLED STELLAR ORBITAL INTERIOR AND 1-D TO 3-D ATMOSPHERIC MODELS TO EXPLORE TERRESTRIAL EXOPLANET FORMATION DYNAMICS COMPOSITION ATMOSPHERIC EVOLUTION AND HABITABILITY. THESE ANALYSES WILL INFORM HABITABILITY ASSESSMENTS TO PRIORITIZE PROMISING EXOPLANETS FOR BIOSIGNATURE SEARCHES. TASK D: THE LIVING PLANET. WE WILL INTEGRATE FIELD AND LABORATORY RESEARCH WITH COUPLED CHEMICAL CLIMATE AND ECOSYSTEM MODELS TO EXPLORE THE NATURE AND DETECTABILITY OF BIOSIGNATURES FOR DIFFERENT GEOCHEMICAL AND STELLAR ENVIRONMENTS. WE WILL IDENTIFY NEW REMOTESENSING ATMOSPHERIC SURFACE AND TEMPORAL BIOSIGNATURES AND THEIR FALSE POSITIVES AND NEGATIVES AND QUANTIFY THE ENVIRONMENTAL LIMITS TO PHOTOSYNTHETIC PRODUCTIVITY. TASK E: THE OBSERVER. WE WILL COMBINE OBSERVATIONS ANALYSIS TECHNIQUES AND SIMULATIONS TO IMPROVE THE DETECTION AND CHARACTERIZATION OF POTENTIALLY HABITABLE EXOPLANETS. WE WILL IMPROVE RETRIEVAL OF PLANETARY PROPERTIES FROM EXOPLANET MAPPING AND FROM DIRECT IMAGING TRANSIT TRANSMISSION AND HIGH-RESOLUTION SPECTROSCOPY. OUR ANALYSES WILL DETERMINE OPTIMAL MEASUREMENTS AND OBSERVATION STRATEGIES FOR TERRESTRIAL EXOPLANET CHARACTERIZATION. THE PROPOSED EFFORT BENEFITS ASTROBIOLOGY AND THE NAI WITH A PROVEN PRODUCTIVE INTERDISCIPLINARY SCIENCE TEAM WHOSE RESEARCH ADDRESSES KEY ASTROBIOLOGY PROGRAM GOALS INCLUDING CONSTRUCTING HABITABLE WORLDS IDENTIFYING EXPLORING AND CHARACTERIZING ENVIRONMENTS FOR HABITABILITY AND BIOSIGNATURES AND THE COEVOLUTION OF LIFE AND THE PHYSICAL ENVIRONMENT. THE UW S ASTROBIOLOGY DUAL-TITLE PHD PROGRAM AND OUR ASTROBIOLOGY RESEARCH OPPORTUNITIES FOR MINORITY UNDERGRADUATES STRONGLY SUPPORT THE TRAINING OF THE NEXT GENERATION OF ASTROBIOLOGISTS. OUR TEAM MEMBERS WILL CONTINUE TO PROVIDE KEY SCIENTIFIC LEADERSHIP FOR RELEVANT NASA MISSIONS. THE VPL WILL LEVERAGE THE MASSIVELY INTERDISCIPLINARY COLLABORATION ENABLED BY THE NAI TO PROVIDE A UNIQUE SYNTHESIS OF NASA PLANETARY AND EARTH SCIENCE MISSION DATA MODELING AND RETRIEVAL TECHNIQUES THAT INFORM AND SUPPORT NASA ASTROBIOLOGY AND ASTROPHYSICS MISSION OBJECTIVES.
OpenAlex ID: W3023429893