arXiv subjects

Manasvi Lingam

Publications and source records attributed to Manasvi Lingam.

At least 37 records · Page 2Linked to original sources

arXiv2023

Planetary Scale Information Transmission in the Biosphere and Technosphere: Limits and Evolution

Information transmission via communication between agents is ubiquitous on Earth, and is a vital facet of living systems. In this paper, we aim to quantify this rate of information transmission associated with Earth's biosphere and technosphere (i.e., a measure of global information flow) by means of a heuristic order-of-magnitude model. By adopting ostensibly conservative values for the salient parameters, we estimate that the global information transmission rate for the biosphere might be $\sim 10^{24}$ bits/s, and that it may perhaps exceed the corresponding rate for the current technosphere by $\sim 9$ orders of magnitude. However, under the equivocal assumption of sustained exponential growth, we find that information transmission in the technosphere can potentially surpass that of the biosphere $\sim 90$ years in the future, reflecting its increasing dominance.

physics.soc-ph↗

arXiv2023

On the importance and challenges of modelling extraterrestrial photopigments via density-functional theory

The emergence of oxygenic photosynthesis was a major event in Earth's evolutionary history and was facilitated by chlorophylls (a major category of photopigments). The accurate modelling of photopigments is important to understand the characteristics of putative extraterrestrial life and its spectral signatures (detectable by future telescopes). In this paper, we perform a detailed assessment of various time-dependent density-functional theory (TD-DFT) methods for predicting the absorption spectra of chlorophyll a, with particular emphasis on modern low-cost approximations. We also investigate a potential extraterrestrial photopigment called phot0 and demonstrate that the electronegativity of the metal ion may exert a direct influence on the locations of the absorption peaks, with higher electronegativity inducing blue-shifting and vice-versa. Based on these calculations, we established that global-hybrid approximations with a moderate percentage of exact exchange -- such as M06 and PW6B95 -- are the most appropriate compromise between cost and accuracy for the computational characterization of photopigments of astrobiological interest. We conclude with a brief assessment of the implications and avenues for future research.

physics.chem-ph↗

arXiv2023

A Birth-Death-Migration Model for Life in Astrophysical Environments

To assess the number of life-bearing worlds in astrophysical environments, it is necessary to take the intertwined processes of abiogenesis (birth), extinction (death), and transfer of life (migration) into account. We construct a mathematical model that incorporates this trio of mechanisms and accordingly derive the probability distribution function and other statistical properties (e.g., mean) for the number of worlds with biospheres. We show that a given astrophysical setting may become eventually saturated with life if the rate of successful transfers of organisms is higher than the extinction rate of biospheres. Based on the available data, we suggest that this criterion might be fulfilled for star-forming clusters (and perhaps the Galactic bulge under optimal circumstances), thereby indicating that such regions could constitute promising abodes for hosting and detecting life.

astro-ph.EP↗

arXiv2023

Excitation Properties of Photopigments and Their Possible Dependence on the Host Star

Photosynthesis is a plausible pathway for the sustenance of a substantial biosphere on an exoplanet. In fact, it is also anticipated to create distinctive biosignatures detectable by next-generation telescopes. In this work, we explore the excitation features of photopigments that harvest electromagnetic radiation by constructing a simple quantum-mechanical model. Our analysis suggests that the primary Earth-based photopigments for photosynthesis may not function efficiently at wavelengths $> 1.1$ $μ$m. In the context of (hypothetical) extrasolar photopigments, we calculate the potential number of conjugated $π$-electrons ($N_\star$) in the relevant molecules, which can participate in the absorption of photons. By hypothesizing that the absorption maxima of photopigments are close to the peak spectral photon flux of the host star, we utilize the model to estimate $N_\star$. As per our formalism, $N_\star$ is modulated by the stellar temperature, and is conceivably higher (lower) for planets orbiting stars cooler (hotter) than the sun; exoplanets around late-type M-dwarfs might require an $N_\star$ twice that of the Earth. We conclude the analysis with a brief exposition of how our model could be empirically tested by future observations.

astro-ph.EP↗

arXiv2023

A Bayesian Analysis of Technological Intelligence in Land and Oceans

Current research indicates that (sub)surface ocean worlds essentially devoid of subaerial landmasses (e.g., continents) are common in the Milky Way, and that these worlds could host habitable conditions, thence raising the possibility that life and technological intelligence (TI) may arise in such aquatic settings. It is known, however, that TI on Earth (i.e., humans) arose on land. Motivated by these considerations, we present a Bayesian framework to assess the prospects for the emergence of TIs in land- and ocean-based habitats (LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs and OBHs, we demonstrate that the evolution of TIs in LBHs (which includes humans) might have very low odds of roughly $1$-in-$10^3$ to $1$-in-$10^4$, thus outwardly contradicting the Copernican Principle. Hence, we elucidate three avenues whereby the Copernican Principle can be preserved: (i) the emergence rate of TIs is much lower in OBHs, (ii) the habitability interval for TIs is much shorter in OBHs, and (iii) only a small fraction of worlds with OBHs comprise appropriate conditions for effectuating TIs. We also briefly discuss methods for empirically falsifying our predictions, and comment on the feasibility of supporting TIs in aerial environments.

astro-ph.EP↗

arXiv2023

Beyond Mediocrity: How Common is Life?

The probability that life spontaneously emerges in a suitable environment (abiogenesis) is one of the major unknowns in astrobiology. Assessing its value is impeded by the lack of an accepted theory for the origin of life, and is further complicated by the existence of selection biases. Appealing uncritically to some version of the ``Principle of Mediocrity'' -- namely, the supposed typicality of what transpired on Earth -- is problematic on empirical or logical grounds. In this paper, we adopt a Bayesian statistical approach to put on rigorous footing the inference of lower bounds for the probability of abiogenesis, based on current and future evidence. We demonstrate that the single datum that life has appeared at least once on Earth merely sets weak constraints on the minimal probability of abiogenesis. In fact, the {\it a priori} probability assigned to this event (viz., optimistic, pessimistic or agnostic prior) exerts the strongest influence on the final result. We also show that the existence of a large number of habitable worlds does not necessarily imply, by itself, a high probability that life should be common in the universe. Instead, as delineated before, the choice of prior, which is subject to uncertainty (i.e., admits multiple scenarios), strongly influences the likelihood of life being common. If habitable worlds are uncommon, for an agnostic prior, a deterministic scenario for the origin of life might be favoured over one where abiogenesis is a fluke event.

astro-ph.EP↗

arXiv2022

Can We Fly to Planet 9?

Planet 9 is an hypothetical object in the outer Solar system, which is as yet undiscovered. It has been speculated that it may be a terrestrial planet or gas/ice giant, or perhaps even a primordial black hole (or dark matter condensate). State-of-the-art models indicate that the semimajor axis of Planet 9 is $\sim 400$ AU. If the location of Planet 9 were to be confirmed and pinpointed in the future, this object constitutes an interesting target for a future space mission to characterize it further. In this paper, we describe various mission architectures for reaching Planet 9 based on a combination of chemical propulsion and flyby maneuvers, as well as more advanced options (with a $\sim 100$ kg spacecraft payload) such as nuclear thermal propulsion (NTP) and laser sails. The ensuing mission duration for solid chemical propellant ranges from 45 years to 75 years, depending on the distance from the Sun for the Solar Oberth maneuver. NTP can achieve flight times of about 40 years with only a Jupiter Oberth maneuver whereas, in contrast, laser sails might engender timescales as little as 7 years. We conclude that Planet 9 is close to the transition point where chemical propulsion approaches its performance limits, and alternative advanced propulsion systems (e.g., NTP and laser sails) apparently become more attractive.

astro-ph.EP↗

arXiv2022

The Case for Technosignatures: Why They May Be Abundant, Long-lived, Highly Detectable, and Unambiguous

The intuition suggested by the Drake equation implies that technology should be less prevalent than biology in the galaxy. However, it has been appreciated for decades in the SETI community that technosignatures could be more abundant, longer-lived, more detectable, and less ambiguous than biosignatures. We collect the arguments for and against technosignatures' ubiquity and discuss the implications of some properties of technological life that fundamentally differ from nontechnological life in the context of modern astrobiology: It can spread among the stars to many sites, it can be more easily detected at large distances, and it can produce signs that are unambiguously technological. As an illustration in terms of the Drake equation, we consider two Drake-like equations, for technosignatures (calculating N(tech)) and biosignatures (calculating N(bio)). We argue that Earth and humanity may be poor guides to the longevity term L and that its maximum value could be very large, in that technology can outlive its creators and even its host star. We conclude that while the Drake equation implies that N(bio)>>N(tech), it is also plausible that N(tech)>>N(bio). As a consequence, as we seek possible indicators of extraterrestrial life, for instance, via characterization of the atmospheres of habitable exoplanets, we should search for both biosignatures and technosignatures. This exercise also illustrates ways in which biosignature and technosignature searches can complement and supplement each other and how methods of technosignature search, including old ideas from SETI, can inform the search for biosignatures and life generally.

astro-ph.EP↗

arXiv2022

Opportunities for Technosignature Science in the Astro2020 Report

The Astro2020 report outlines numerous recommendations that could significantly advance technosignature science. Technosignatures refer to any observable manifestations of extraterrestrial technology, and the search for technosignatures is part of the continuum of the astrobiological search for biosignatures. The search for technosignatures is directly relevant to the "World and Suns in Context" theme and "Pathways to Habitable Worlds" program in the Astro2020 report. The relevance of technosignatures was explicitly mentioned in "E1 Report of the Panel on Exoplanets, Astrobiology, and the Solar System," which stated that "life's global impacts on a planet's atmosphere, surface, and temporal behavior may therefore manifest as potentially detectable exoplanet biosignatures, or technosignatures" and that potential technosignatures, much like biosignatures, must be carefully analyzed to mitigate false positives. The connection of technosignatures to this high-level theme and program can be emphasized, as the report makes clear the purpose is to address the question "Are we alone?" This question is also presented in the Explore Science 2020-2024 plan as a driver of NASA's mission. This white paper summarizes the potential technosignature opportunities within the recommendations of the Astro2020 report, should they be implemented by funding agencies. The objective of this paper is to demonstrate the relevance of technosignature science to a wide range of missions and urge the scientific community to include the search for technosignatures as part of the stated science justifications for the large and medium programs that include the Infrared/Optical/Ultraviolet space telescope, Extremely Large Telescopes, probe-class far-infrared and X-ray missions, and various facilities in radio astronomy.

astro-ph.IM↗

arXiv2021

Interstellar Now! Missions to and Sample Returns from Nearby Interstellar Objects

The recently discovered first high velocity hyperbolic objects passing through the Solar System, 1I/'Oumuamua and 2I/Borisov, have raised the question about near term missions to Interstellar Objects. In situ spacecraft exploration of these objects will allow the direct determination of both their structure and their chemical and isotopic composition, enabling an entirely new way of studying small bodies from outside our solar system. In this paper, we map various Interstellar Object classes to mission types, demonstrating that missions to a range of Interstellar Object classes are feasible, using existing or near-term technology. We describe flyby, rendezvous and sample return missions to interstellar objects, showing various ways to explore these bodies characterizing their surface, dynamics, structure and composition. Interstellar objects likely formed very far from the solar system in both time and space; their direct exploration will constrain their formation and history, situating them within the dynamical and chemical evolution of the Galaxy. These mission types also provide the opportunity to explore solar system bodies and perform measurements in the far outer solar system.

astro-ph.IM↗

arXiv2021

Physical Constraints on Motility with Applications to Possible Life on Mars and Enceladus

Motility is a ubiquitous feature of microbial life on Earth, and is widely regarded as a promising biosignature candidate. In the search for motile organisms, it is therefore valuable to have rough estimates for the number of such microbes that one may expect to find in a given area or volume. In this work, we explore this question by employing a simple theoretical model that takes into account the amount of free energy available in a given environment and the energetic cost of motility. We present heuristic upper bounds for the average biomass density and the number density of motile lifeforms for the Martian subsurface and the ocean of Enceladus by presuming that the motile microbes in question derive their energy from methanogenesis. We consequently demonstrate that the resultant densities of motile organisms might be potentially comparable to, or much lower than, the total microbial densities documented in various extreme environments on Earth.

astro-ph.EP↗

arXiv2021

Theoretical constraints imposed by gradient detection and dispersal on microbial size in astrobiological environments

The capacity to sense gradients efficiently and acquire information about the ambient environment confers many advantages like facilitating movement toward nutrient sources or away from toxic chemicals. The amplified dispersal evinced by organisms endowed with motility is possibly beneficial in related contexts. Hence, the connections between information acquisition, motility, and microbial size are explored from an explicitly astrobiological standpoint. By using prior theoretical models, the constraints on organism size imposed by gradient detection and motility are elucidated in the form of simple heuristic scaling relations. It is argued that environments such as alkaline hydrothermal vents, which are distinguished by the presence of steep gradients, might be conducive to the existence of "small" microbes (with radii of $\gtrsim 0.1$ $μ$m) in principle, when only the above two factors are considered; other biological functions (e.g., metabolism and genetic exchange) could, however, regulate the lower bound on microbial size and elevate it. The derived expressions are potentially applicable to a diverse array of settings, including those entailing solvents other than water; for example, the lakes and seas of Titan. The paper concludes with a brief exposition of how this formalism may be of practical and theoretical value to astrobiology.

astro-ph.EP↗

arXiv2021

Feasibility of Detecting Interstellar Panspermia in Astrophysical Environments

The proposition that life can spread from one planetary system to another (interstellar panspermia) has a long history, but this hypothesis is difficult to test through observations. We develop a mathematical model that takes parameters such as the microbial survival lifetime, the stellar velocity dispersion, and the dispersion of ejecta into account in order to assess the prospects for detecting interstellar panspermia. We show that the correlations between pairs of life-bearing planetary systems (embodied in the pair-distribution function from statistics) may serve as an effective diagnostic of interstellar panspermia, provided that the velocity dispersion of ejecta is greater than the stellar dispersion. We provide heuristic estimates of the model parameters for various astrophysical environments, and conclude that open clusters and globular clusters appear to represent the best targets for assessing the viability of interstellar panspermia.

astro-ph.EP↗

arXiv2021

Interstellar Objects in the Solar System: 1. Isotropic Kinematics from the Gaia Early Data Release 3

1I/'Oumuamua (or 1I) and 2I/Borisov (or 2I), the first InterStellar Objects (ISOs) discovered passing through the solar system, have opened up entirely new areas of exobody research. Finding additional ISOs and planning missions to intercept or rendezvous with these bodies will greatly benefit from knowledge of their likely orbits and arrival rates. Here, we use the local velocity distribution of stars from the Gaia Early Data Release 3 Catalogue of Nearby Stars and a standard gravitational focusing model to predict the velocity dependent flux of ISOs entering the solar system. With an 1I-type ISO number density of $\sim$0.1 AU$^{-3}$, we predict that a total of $\sim$6.9 such objects per year should pass within 1 AU of the Sun. There will be a fairly large high-velocity tail to this flux, with half of the incoming ISOs predicted to have a velocity at infinity, v$_{\infty}$, $>$ 40 km s$^{-1}$. Our model predicts that $\sim$92\% of incoming ISOs will be residents of the galactic thin disk, $\sim$6\% ($\sim$4 per decade) will be from the thick disk, $\sim$1 per decade will be from the halo and at most $\sim$3 per century will be unbound objects, ejected from our galaxy or entering the Milky Way from another galaxy. The rate of ISOs with very low v$_{\infty}$ $\lesssim$ 1.5 km s$^{-1}$ is so low in our model that any incoming very low velocity ISOs are likely to be previously lost solar system objects. Finally, we estimate a cometary ISO number density of $\sim$7 $\times$ 10$^{-5}$ AU$^{-3}$ for 2I type ISOs, leading to discovery rates for these objects possibly approaching once per decade with future telescopic surveys.

astro-ph.EP↗

arXiv2021

Characteristics of aquatic biospheres on temperate planets around Sun-like stars and M-dwarfs

Aquatic biospheres reliant on oxygenic photosynthesis are expected to play an important role on Earth-like planets endowed with large-scale oceans insofar as carbon fixation (i.e., biosynthesis of organic compounds) is concerned. We investigate the properties of aquatic biospheres comprising Earth-like biota for habitable rocky planets orbiting Sun-like stars and late-type M-dwarfs such as TRAPPIST-1. In particular, we estimate how these characteristics evolve with the available flux of photosynthetically active radiation (PAR) and the ambient ocean temperature ($T_W$), the latter of which constitutes a key environmental variable. We show that many salient properties, such as the depth of the photosynthesis zone and the net primary productivity (i.e., the effective rate of carbon fixation), are sensitive to PAR flux and $T_W$ and decline substantially when the former is decreased or the latter is increased. We conclude by exploring the implications of our analysis for exoplanets around Sun-like stars and M-dwarfs.

astro-ph.EP↗

arXiv2021

The Extended Habitable Epoch of the Universe for Liquids Other than Water

At high redshifts, the temperature of the cosmic microwave background (CMB) was higher than its value today. We explore the possibility that life may have arisen early because the higher CMB temperature would have supplied the requisite energy for the existence of different solvents on the surfaces of objects. At redshifts of $z \lesssim 70$, after the first stars are predicted to have formed, a number of molecules (but not water) might have existed in liquid form over intervals of $\sim 10$ Myr to $\sim 100$ Myr. We delineate the challenges and prospects for life in the high-redshift Universe, and assess the various candidates for alternative biochemistries in this context -- of the options considered herein, we conclude that ethane is probably the most promising contender.

astro-ph.EP↗

arXiv2020

A Precursor Balloon Mission for Venusian Astrobiology

The potential detection of phosphine in the atmosphere of Venus has reignited interest in the possibility of life aloft in this environment. If the cloud decks of Venus are indeed an abode of life, it should reside in the "habitable zone" between ~ 50-60 km altitude, roughly coincident with the middle cloud deck, where the temperature and pressure (but not the atmospheric composition) are similar to conditions at the Earth's surface. We map out a precursor astrobiological mission to search for such putative lifeforms in situ with instrument balloons, which could be delivered to Venus via launch opportunities in 2022-2023. This mission would collect aerosol and dust samples by means of small balloons floating in the Venusian cloud deck and directly scrutinize whether they include any apparent biological materials and, if so, their shapes, sizes, and motility. Our balloon mission would also be equipped with a miniature mass spectrometer that should permit the detection of complex organic molecules. The mission is augmented by contextual cameras to search for macroscopic signatures of life in the Venusian atmospheric habitable zone. Finally, mass and power constraints permitting, radio interferometric determinations of the motion of the balloons in Venusian winds, together with in situ temperature and pressure measurements, will provide valuable insights into the poorly understood meteorology of the middle cloud region.

astro-ph.IM↗

arXiv2020

Constraints on the abundance of $0.01\,c$ stellar engines in the Milky Way

Stellar engines are hypothesized megastructures that extract energy from the host star, typically with the purpose of generating thrust and accelerating the stellar system. We explore the maximum potential speeds that could be realizable by stellar engines, and determine that speeds up to $\sim 0.1\,c$ might perhaps be attainable under optimal conditions. In contrast, natural astrophysical phenomena in the Milky Way are very unlikely to produce such speeds. Hence, astrometric surveys of hypervelocity stars may be utilized to conduct commensal searches for high-speed stellar engines in the Milky Way. It may be possible to derive bounds on their abundance, but this requires certain assumptions regarding the spatiotemporal distribution of such engines, which are not guaranteed to be valid.

physics.pop-ph↗