On the likelihood of non-terrestrial artifacts in the Solar System

Haqq-Misra, Jacob; Kopparapu, R.

doi:10.1016/j.actaastro.2011.10.010

Cited by 50 publications

(50 citation statements)

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“…The lack of settlement success could come for many reasons ranging from failure of interstellar vessels capable of establishing persistent settlements to the inability to develop viable progeny civilizations on new worlds. Because Hart's conclusions stem from his assumption that we would have noticed if extraterrestrial technology had ever settled the Solar System, they are challenged by the work of Freitas (1985), Schmidt & Frank (2018), Davies (2012), andKopparapu (2012) who show that this is not necessarily the case.…”

Section: Discussionmentioning

confidence: 99%

“…Here we take indirect detection to mean the search for technosignatures (Tarter 2007) from distant sources outside the solar systems (e.g. Siemion et al 2013;Wright et al 2014) while direct detection means material evidence for an exo-civilization's visit to Earth or our solar system (Davies 2012;Haqq-Misra and Kopparapu 2012;Wright 2018) Such a distinction between direct and indirect detection is important. In Hart's formulation of the Fermi Paradox his "Fact A" was the lack of aliens on Earth now.…”

Section: Introductionmentioning

confidence: 99%

“…In Schmidt & Frank (2018) it was shown that evidence of previous industrial civilizations in Earth's deep past would likely be found only in isotopic and chemical stratographic anomalies and that the experiments needed to pinpoint non-natural origins for such signals had yet to be performed. The question of solar system artifacts of previous civilizations (alien or otherwise) has also been addressed in Davies (2012), Kopparapu (2012), andWright (2018).…”

Section: Introductionmentioning

confidence: 99%

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The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

Carroll-Nellenback

Frank

Wright

et al. 2019

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We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We are motivated to explore the problem in a way that avoids assumptions about the 'agency' (i.e. questions of intent and motivation) of any exo-civilization seeking to settle other planetary systems. We begin by considering the speed of an advancing settlement front to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. Our models for the front speed include the directed settlement of nearby settleable systems through the launching of probes with a finite velocity and range. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. As part of our model we also consider that only a fraction f of planets will have conditions amenable to settlement by the space-faring civilization. The results of these models demonstrate that the Milky Way can be readily 'filled-in' with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates. We then move on to consider the question of the galactic steady-state achieved in terms of the fraction X of settled planets. We do this by considering the effect of finite settlement civilization lifetimes on the steady states. We find a range of parameters for which 0 < X < 1 i.e. the galaxy supports a population of interstellar space-faring civilizations even though some settleable systems are uninhabited. In addition we find that statistical fluctuations can produce local over-abundances of settleable worlds. These generate long-lived clusters of settled systems immersed in large regions which remain unsettled. Both results point to ways in which Earth might remain unvisited in the midst of an inhabited galaxy. Finally we consider how our results can be combined with the finite horizon for evidence of previous settlements in Earth's geologic record. Using our steady-state model we constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy. Explicitly, our solutions admit situations where our current circumstances are consistent with an otherwise settled, steady-state galaxy.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

Carroll-Nellenback

Frank

Wright

et al. 2019

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“…If we analogously relax Fact A and assert merely that there are no alien machines in the Solar System today, then its truth becomes quite uncertain because we have not done much searching for such machines (e.g. Haqq-Misra & Kopparapu 2012;Davies 2012).…”

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confidence: 99%

How Much SETI Has Been Done? Finding Needles in the n-dimensional Cosmic Haystack

Wright

Kanodia

Lubar

2018

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Many articulations of the Fermi Paradox have as a premise, implicitly or explicitly, that humanity has searched for signs of extraterrestrial radio transmissions and concluded that there are few or no obvious ones to be found. Tarter et al. (2010) and others have argued strongly to the contrary: bright and obvious radio beacons might be quite common in the sky, but we would not know it yet because our search completeness to date is so low, akin to having searched a drinking glass's worth of seawater for evidence of fish in all of Earth's oceans. Here, we develop the metaphor of the multidimensional "Cosmic Haystack" through which SETI hunts for alien "needles" into a quantitative, eight-dimensional model, and perform an analytic integral to compute the fraction of this haystack that several large radio SETI programs have collectively examined. Although this model haystack has many qualitative differences from the Tarter et al. (2010) haystack, we conclude that the fraction of it searched to date is also very small: similar to the ratio of the volume of a large hot tub or small swimming pool to that of the Earth's oceans. With this article, we provide a Python script to calculate haystack volumes for future searches and for similar haystacks with different boundaries. We hope this formalism will aid in the development of a common parameter space for the computation of upper limits and completeness fractions of search programs for radio and other technosignatures.

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“…However, this would bring it into some conflict with the so-called Fermi's paradox, since we would have to explain why none of these probes (or their signals) have been detected thus far (Brin, 1983;Webb, 2015). Nevertheless, since we have not comprehensively surveyed the Solar neighbourhood, the presence of such probes cannot be ruled out definitively (Freitas, 1983;Loeb and Turner, 2012;Haqq-Misra and Kopparapu, 2012). 14 In the future, interstellar objects passing through the Solar system, like 'Oumuamua, can be searched for signs of electromagnetic signals (Enriquez et al, 2018;Tingay et al, 2018) or be subjected to detailed in situ exploration (Seligman and Laughlin, 2018).…”

Section: The Relative Likelihood and Its Implicationsmentioning

confidence: 96%

Relative Likelihood of Success in the Search for Primitive versus Intelligent Extraterrestrial Life

Lingam

Loeb

2019

Astrobiology

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We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Based on the current federal funding allocated to the search for biosignatures, our analysis suggests that the search for extraterrestrial intelligence (SETI) may merit a federal funding level of at least $10 million per year, assuming that the average lifetime of technological species exceeds a millennium.

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On the likelihood of non-terrestrial artifacts in the Solar System

Cited by 50 publications

References 30 publications

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

How Much SETI Has Been Done? Finding Needles in the n-dimensional Cosmic Haystack

Relative Likelihood of Success in the Search for Primitive versus Intelligent Extraterrestrial Life

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