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Time Markers for SETI in Binary Systems: History and Prospects

Year: 2025
Type: article
Abstract: Contemporary surveys in the search for extraterrestrial intelligence (SETI) typically make one-off “spot scans” across the sky to search planetary systems for narrow-band radio signals that would indicate the presence of intelligent life. Spot scans may span a duration of seconds to minutes in order to observe a large number of targets with limited resources, but such a strategy does not necessarily consider the timing of exactly when to listen for extraterrestrial signals. Several ideas for possible time markers were suggested in the first few decades of SETI, such as the use of recurrent supernovae, gamma ray bursts, or pulsars as a way of establishing directionality and attracting attention toward an extraterrestrial beacon. Civilizations in binary systems might even choose the points of periastron and apastron in its host system to send transmissions to other single-star civilizations. However, all of these timing considerations were developed prior to the age of exoplanets, which enables a more detailed assessment of targets suitable for SETI. This paper suggests SETI strategies for circumbinary and circumprimary planets based upon the timing of orbital events in such systems. Events such as orbital extremes could represent a logical time marker for extraterrestrial civilizations to transmit, if they desire to be detected. Likewise, a transiting binary pair with inhabited planets around each star could yield maximum detectability of leakage radiation when both stars eclipse within our field of view. As planets in binary systems continue to be discovered, limited-duration SETI surveys should selectively target such systems based upon the occurrence of reasonable time markers.
Source: Astronomy
DOI: 10.3390/astronomy4040019
Language: English
Open Access status: gold
Estimated APC paid: $1,207
Award: 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.
OpenAlex ID: W4415450196
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