arXiv subjects

Jacob Haqq-Misra

Publications and source records attributed to Jacob Haqq-Misra.

At least 73 records · Page 4Linked to original sources

arXiv2019

Constraining the magnitude of climate extremes from time-varying instellation on a circumbinary terrestrial planet

Planets that revolve around a binary pair of stars are known as circumbinary planets. The orbital motion of the stars around their center of mass causes a periodic variation in the total instellation incident upon a circumbinary planet. This study uses both an analytic and numerical energy balance model to calculate the extent to which this effect can drive changes in surface temperature on circumbinary terrestrial planets. We show that the amplitude of the temperature variation is largely constrained by the effective heat capacity, which corresponds to the ocean-to-land ratio on the planet. Planets with large ocean fractions should experience only modest warming and cooling of only a few degrees, which suggests that habitability cannot be precluded for such circumbinary planets. Planets with large land fractions that experience extreme periodic forcing could be prone to changes in temperature of tens of degrees or more, which could drive more extreme climate changes that inhibit continuously habitable conditions.

astro-ph.EP↗

arXiv2019

Habitable Zone Boundaries for Circumbinary Planets

We use a one-dimensional (1-D) cloud-free climate model to estimate habitable zone (HZ) boundaries for terrestrial planets of masses 0.1 M$_{E}$ and 5 M$_{E}$ around circumbinary stars of various spectral type combinations. Specifically, we consider binary systems with host spectral types F-F, F-G, F-K, F-M, G-G, G-K, G-M, K-K, K-M and M-M. Scaling the background N2 atmospheric pressure with the radius of the planet, we find that the inner edge of the HZ moves inwards towards the star for 5ME compared to 0.1ME planets for all spectral types. This is because the water-vapor column depth is smaller for larger planets and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. The outer edge of the HZ changes little due to competing effects of the albedo and greenhouse effect. While these results are broadly consistent with the trend of single star HZ results for different mass planets, there are significant differences between single star and binary star systems for the inner edge of the HZ. Interesting combinations of stellar pairs from our 1-D model results can be used to explore for in-depth climate studies with 3-D climate models. We identify a common HZ stellar flux domain for all circumbinary spectral types

astro-ph.EP↗

arXiv2019

Absolute Prioritization of Planetary Protection, Safety, and Avoiding Imperialism in All Future Science Missions: A Policy Perspective

The prioritization and improvement of ethics, planetary protection, and safety standards in the astro-sciences is the most critical priority as our scientific and exploratory capabilities progress, both within government agencies and the private sector. These priorities lie in the belief that every single science mission - crewed or non-crewed, ground-based or not - should heed strict ethical and safety standards starting at the very beginning of a mission. Given the inevitability of the private sector in influencing future crewed missions both in and beyond low-Earth orbit, it is essential to the science community to agree on universal standards of safety, mission assurance, planetary protection, and especially anti-colonization. These issues will impact all areas of space science. Examples that are particularly relevant to the Astro2020 Decadal Survey include but are not limited to: light pollution from satellites, the voices and rights of Native people when constructing telescopes on their lands, and the need to be cognizant of contamination when searching for and exploring habitable environments beyond Earth. Ultimately, moving international space law and domestic space policy from a reactive nature to a proactive one will ensure the future of space exploration is one that is safe, transparent, and anti-imperialist.

astro-ph.IM↗

arXiv2019

Does the evolution of complex life depend on the stellar spectral energy distribution?

This paper presents the proportional evolutionary time hypothesis, which posits that the mean time required for the evolution of complex life is a function of stellar mass. The "biological available window" is defined as the region of a stellar spectrum between 200 to 1200 nm that generates free energy for life. Over the $\sim$4 Gyr history of Earth, the total energy incident at the top of the atmosphere and within the biological available window is $\sim$10$^{34}$ J. The hypothesis assumes that the rate of evolution from the origin of life to complex life is proportional to this total energy, which would suggest that planets orbiting other stars should not show signs of complex life if the total energy incident on the planet is below this energy threshold. The proportional evolutionary time hypothesis predicts that late K- and M-dwarf stars (M < 0.7 M$_{\odot}$) are too young to host any complex life at the present age of the universe. F-, G-, and early K-dwarf stars (M > 0.7 M$_{\odot}$) represent the best targets for the next generation of space telescopes to search for spectroscopic biosignatures indicative of complex life.

astro-ph.EP↗

arXiv2019

Searching for Technosignatures: Implications of Detection and Non-Detection

The search for technosignatures from the Galaxy or the nearby universe raises two main questions: What are the possible characteristics of technosignatures? and How can future searches be optimized to enhance the probability of detection? Addressing these questions requires an interdisciplinary approach, combining i) the study of Anthropocene as a planetary transition and thus a possible proxy also for other planets, ii) the active search for technosignatures in the radio/optical and infrared range, and iii) the statistical modelling of technosignatures and Bayesian inference methods to learn from both detection and non-detection. This strategy (combining modelling and observations) offers the best scientific opportunity in the next decade to discover the possible existence of technological civilizations beyond Earth.

astro-ph.EP↗

arXiv2019

Introduction: Detectability of Future Earth

Earth's future detectability depends upon the trajectory of our civilization over the coming centuries. Human civilization is also the only known example of an energy-intensive civilization, so our history and future trajectories provide the basis for thinking about how to find life elsewhere. This special issue of Futures features contributions that consider the future evolution of the Earth system from an astrobiological perspective, with the goal of exploring the extent to which anthropogenic influence could be detectable across interstellar distances. This collection emphasizes the connection between the unfolding future of the Anthropocene with the search for extraterrestrial civilizations. Our rate of energy consumption will characterize the extent to which our energy-intensive society exerts direct influence on climate, which in turn may limit the ultimate lifetime of our civilization. If the answer to Fermi's question is that we are alone, so that our civilization represents the only form of intelligent life in the galaxy (or even the universe), then our responsibility to survive is even greater. If we do find evidence of another civilization on a distant exoplanet, then at least we will know that our trajectory can be managed. But as long as our searches turn up empty, we must stay vigilant to keep our future secure.

physics.gen-ph↗

arXiv2018

Can Deep Altruism Sustain Space Settlement?

Space settlement represents a long-term human effort that requires unprecedented coordination across successive generations. In this chapter, I develop a comparative hierarchy for the value of long-term projects based upon their benefits to culture, their development of infrastructure, and their contributions to lasting information. I next draw upon the concept of the time capsule as an analogy, which enables a comparison of historical examples of projects across generational, intergenerational, and deep time. The concept of deep altruism can then be defined as the selfless pursuit of informational value for the well-being of others in the distant future. The first steps toward supporting an effort like space settlement through deep altruism would establish governance and funding models that begin to support ambitions with intergenerational succession.

physics.pop-ph↗

arXiv2018

Population Growth, Energy Use, and the Implications for the Search for Extraterrestrial Intelligence

Von Hoerner (1975) examined the effects of human population growth and predicted agricultural, environmental, and other problems from observed growth rate trends. Using straightforward calculations, VH75 predicted the "doomsday" years for these scenarios (2020-2050), when we as a species should run out of space or food, or induce catastrophic anthropogenic climate change through thermodynamically unavoidable direct heating of the planet. Now that over four decades have passed, in this paper we update VH75. We perform similar calculations as that work, with improved data and trends in population growth, food production, energy use, and climate change. For many of the impacts noted in VH75 our work amounts to pushing the "doomsday" horizon back to the 2300s-2400s (or much further for population-driven interstellar colonization). This is largely attributable to using worldwide data that exhibit smaller growth rates of population and energy use in the last few decades. While population-related catastrophes appear less likely than in VH75, our continued growth in energy use provides insight into possible future issues. We find that, if historic trends continue, direct heating of the Earth will be a substantial contributor to climate change by about 2260, regardless of the energy source used, coincident with our transition to a Kardashev type-I civilization. We also determine that either an increase of Earth's global mean temperature of 12K will occur or an unreasonably high fraction of the planet will need to be covered by solar collectors by about 2400 to keep pace with our growth in energy use. We further discuss the implications in terms of interstellar expansion, the transition to type II and III civilizations, SETI, and the Fermi Paradox. We conclude that the "sustainability solution" to the Fermi Paradox is a compelling possibility.

physics.pop-ph↗

arXiv2018

Exploring exomoon atmospheres with an idealized general circulation model

Recent studies have shown that large exomoons can form in the accretion disks around super-Jovian extrasolar planets. These planets are abundant at about 1 AU from Sun-like stars, which makes their putative moons interesting for studies of habitability. Technological advances could soon make an exomoon discovery with Kepler or the upcoming CHEOPS and PLATO space missions possible. Exomoon climates might be substantially different from exoplanet climates because the day-night cycles on moons are determined by the moon's synchronous rotation with its host planet. Moreover, planetary illumination at the top of the moon's atmosphere and tidal heating at the moon's surface can be substantial, which can affect the redistribution of energy on exomoons. Using an idealized general circulation model with simplified hydrologic, radiative, and convective processes, we calculate surface temperature, wind speed, mean meridional circulation, and energy transport on a 2.5 Mars-mass moon orbiting a 10-Jupiter-mass at 1 AU from a Sun-like star. The strong thermal irradiation from a young giant planet causes the satellite's polar regions to warm, which remains consistent with the dynamically-driven polar amplification seen in Earth models that lack ice-albedo feedback. Thermal irradiation from young, luminous giant planets onto water-rich exomoons can be strong enough to induce water loss on a planet, which could lead to a runaway greenhouse. Moons that are in synchronous rotation with their host planet and do not experience a runaway greenhouse could experience substantial polar melting induced by the polar amplification of planetary illumination and geothermal heating from tidal effects.

astro-ph.EP↗

arXiv2018

Policy options for the radio detectability of Earth

The METI risk problem refers to the uncertain outcome of sending transmissions into space with the intention of messaging to extraterrestrial intelligence (METI). Here, I demonstrate that this uncertainty is undecidable by proving that that the METI risk problem reduces to the halting problem. This implies that any proposed moratorium on METI activities cannot be based solely on the requirement for new information. I discuss three policy resolutions to deal with this risk ambiguity. Precautionary malevolence assumes that contact with ETI is likely to cause net harm to humanity, which remains consistent with the call for a METI moratorium, while assumed benevolence states that METI is likely to yield net benefits to humanity. I also propose a policy of preliminary neutrality, which suggests that humanity should engage in both SETI (searching for extraterrestrial intelligence) and METI until either one achieves its first success.

physics.pop-ph↗

arXiv2018

The Origins Space Telescope: Towards An Understanding of Temperate Planetary Atmospheres

The Origins Space Telescope (OST) is one of four mission concepts currently being studied by NASA in preparation for the Astrophysics 2020 Decadal Survey. With active cooling (~4 K), OST will be sensitive in mid- to far-IR wavelengths, using imaging and spectroscopy to probe the furthest reaches of our galaxies, trace the path of water through star and planet formation, and place thermochemical constraints on the atmospheres of exoplanets ranging in size from Jupiter to Earth. This contribution to the Exoplanet Science Strategy committee discusses the significant advancements that the OST Mid-Infrared Imager, Spectrometer, and Coronagraph (MISC) instrument can make in studying cool planetary atmospheres. We particularly focus on the atmospheres of transiting rocky planets in the habitable zones of mid-to-late M stars. We discuss how OST thermal infrared observations can significantly enhance our understanding of the temperature structure and molecular abundances of biologically interesting gases on these worlds, including O3, CH4, H2O, and CO2.

astro-ph.EP↗

arXiv2018

Exoplanet Diversity in the Era of Space-based Direct Imaging Missions

This whitepaper discusses the diversity of exoplanets that could be detected by future observations, so that comparative exoplanetology can be performed in the upcoming era of large space-based flagship missions. The primary focus will be on characterizing Earth-like worlds around Sun-like stars. However, we will also be able to characterize companion planets in the system simultaneously. This will not only provide a contextual picture with regards to our Solar system, but also presents a unique opportunity to observe size dependent planetary atmospheres at different orbital distances. We propose a preliminary scheme based on chemical behavior of gases and condensates in a planet's atmosphere that classifies them with respect to planetary radius and incident stellar flux.

astro-ph.EP↗

arXiv2018

The Astrobiology of the Anthropocene

Human influence on the biosphere has been evident at least since the development of widespread agriculture, and some stratigraphers have suggested that the activities of modern civilization indicate a geological epoch transition. The study of the anthropocene as a geological epoch, and its implication for the future of energy-intensive civilizations, is an emerging transdisciplinary field in which astrobiology can play a leading role. Habitability research of Earth, Mars, and exoplanets examines extreme cases relevant for understanding climate change as a planetary process. Energy-intensive civilizations will also face thermodynamic limits to growth, which provides an important constraint for estimating the longevity of human civilization and guiding the search for extraterrestrial intelligence. We recommend that missions concepts such as LUVOIR, HabEx, and OST be pursued in order to make significant progress toward understanding the future evolution of life on our planet and the possible evolution of technological, energy-intensive life elsewhere in the universe.

astro-ph.EP↗

arXiv2017

Habitable Moist Atmospheres On Terrestrial Planets Near the Inner Edge Of the Habitable Zone Around M-dwarfs

Terrestrial planets in the habitable zones (HZs) of low-mass stars and cool dwarfs have received significant scrutiny recently because their shorter orbital periods increase their chances of detection and characterization compared to planets around G-dwarfs. As these planets are likely tidal-locked, improved 3D numerical simulations of such planetary atmospheres are needed to guide target selection. Here we use a 3-D climate system model, updated with new water-vapor absorption coefficients derived from the HITRAN 2012 database, to study ocean covered planets at the inner edge of the HZ around late-M to mid-K stars ($2600$ K <= Teff <= 4500K). Our results indicate that these updated water-vapor coefficients result in significant warming compared to previous studies, so the inner HZ around M-dwarfs is not as close as suggested by earlier work. Assuming synchronously rotating planets with background 1 bar N2 atmospheres, we find that planets at the inner HZ of stars with Teff > 3000K undergo the classical "moist-greenhouse" (H2O mixing ratio > 10-3 in the stratosphere) at significantly lower surface temperature (~ 280K) in our 3-D model compared with 1-D climate models (~ 340K). This implies that some planets around low mass stars can simultaneously undergo water-loss and remain habitable. However, for star with Teff <= 3000K, planets at the inner HZ may directly transition to a runaway state, while bypassing the moist greenhouse water-loss entirely. We analyze transmission spectra of planets in a moist green-house regime, and find that there are several prominent H2O features within JWST instruments range. Thus, relying only upon standard Earth-analog spectra with 24-hour rotation period around M-dwarfs for habitability studies will miss the strong H2O features that one would expect to see on synchronously rotating planets around M-dwarf stars, with JWST.

astro-ph.EP↗

arXiv2017

The Drake Equation as a Function of Spectral Type and Time

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 parameters 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.

physics.pop-ph↗

arXiv2017

Why do we find ourselves around a yellow star instead of a red star?

M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyze this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

physics.pop-ph↗

arXiv2017

Funding the Search for Extraterrestrial Intelligence with a Lottery Bond

I propose the establishment of a SETI Lottery Bond to provide a continued source of funding for the search for extraterrestrial intelligence (SETI). The SETI Lottery Bond is a fixed rate perpetual bond with a lottery at maturity, where maturity occurs only upon discovery and confirmation of extraterrestrial intelligent life. Investors in the SETI Lottery Bond purchase shares that yield a fixed rate of interest that continues indefinitely until SETI succeeds---at which point a random subset of shares will be awarded a prize from a lottery pool. SETI Lottery Bond shares also are transferable, so that investors can benefact their shares to kin or trade them in secondary markets. The total capital raised this way will provide a fund to be managed by a financial institution, with annual payments from this fund to support SETI research, pay investor interest, and contribute to the lottery fund. Such a plan could generate several to tens of millions of dollars for SETI research each year, which would help to revitalize and expand facilities such as the Allen Telescope Array. The SETI Lottery Bond is a savings product that only can be offered by a financial institution with authorization to engage in banking and gaming activities. I therefore suggest that one or more banks offer a lottery-linked savings product in support of SETI research, with the added benefit of promoting personal savings and intergenerational wealth building among individuals.

physics.pop-ph↗

arXiv2017

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO2, under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures (Ts); snowball (Ts < 235 K), waterbelt (235 K < Ts < 250 K), temperate (275 K < Ts < 315 K), and moist greenhouse (Ts > 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea-ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having Ts ~ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ~1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO2, habitability can be maintained for an upper limit of ~2.2, ~2.4 and ~4.7 Gyr around F-, G- and K-dwarf stars respectively due to main sequence brightening.

astro-ph.EP↗