Elsevier

Space Policy

Volume 29, Issue 1, February 2013, Pages 40-48
Space Policy

The benefits and harm of transmitting into space

https://doi.org/10.1016/j.spacepol.2012.11.006Get rights and content

Abstract

Deliberate and unintentional radio transmissions from Earth propagate into space. These transmissions could be detected by extraterrestrial watchers over interstellar distances. This article analyzes the harm and benefits of deliberate and unintentional transmissions relevant to Earth and humanity. Comparing the magnitude of deliberate radio broadcasts intended for messaging to extraterrestrial intelligence (METI) with the background radio spectrum of Earth, we find that METI attempts to date have much lower detectability than emissions from current radio communication technologies on Earth. METI broadcasts are usually transient and several orders of magnitude less powerful than other terrestrial sources, such as astronomical and military radars, which provide the strongest detectable signals. The benefits of radio communication on Earth most probably outweigh the potential harm of detection by extraterrestrial watchers; however, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI.

Introduction

Does transmitting radio messages into space pose a risk to human civilization? Efforts to send messages to potential extraterrestrial watchers2 have raised concerns that such actions may provoke unwanted attention. Similar transmissions into space, though unintentional, occur as a result of radio communication on Earth, and pose similar risks. This paper analyzes deliberate and unintentional transmissions into space and the degree to which these activities could entail benefits or harm to Earth and humanity.
Electromagnetic waves have been used to communicate for over 100 years. Television broadcasts, mobile phone conversations, satellite transmissions, and military, civil and astronomical radars all use some part of the electromagnetic spectrum—particularly radio and microwave wavelengths—to transmit encoded information from a sender to a watcher. These technologies have transformed communication across the globe and have enabled human spaceflight and robotic exploration of the solar system. Nearly all terrestrial electromagnetic transmissions used for communication also radiate into space. Although such signals decrease in intensity as they move away from Earth, this leakage radiation can be detected over interstellar distances with a sufficiently sensitive telescope [1], [2].
Cocconi and Morrison [3] first suggested that a search for interstellar radio transmissions could uncover evidence of intelligent extraterrestrial life elsewhere in the galaxy. Over 50 years later, the search for extraterrestrial intelligence (SETI) has found no evidence of artificial signals in space, although efforts to broaden the search continue [4]. Another way to search for intelligence elsewhere in the universe involves transmitting messages toward target star systems. This is known as “messaging to extraterrestrial intelligence” (METI) [5]. The ultimate goal of METI is to transmit a signal that is eventually received by an extraterrestrial civilization, although the vast distances between stars render any conversation a multi-generational project [6]. Nevertheless, a handful of attempts at METI have been made over the past half century with messages increasing in size and complexity [7]. These efforts can be considered as symbolic or demonstrations of human technology rather than serious efforts to converse with extraterrestrial civilizations.
Both deliberate METI signals and unintentional leakage radiation contribute to the overall radio emission from Earth.3 There has been concern that this signature of our technological civilization could constitute a risk because it reveals our location in the galaxy to any potentially hostile extraterrestrial civilizations [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. There have even been calls for a moratorium on deliberate METI transmissions until international agreements on how to proceed have been reached [19]. Others have argued that METI broadcasts do not pose a significant risk [7], [20], [21], [22], [23] because any extraterrestrial watchers would be able to establish the presence of life on Earth by the spectrum of reflected ultraviolet, optical, and near-infrared sunlight into space from the surface and the atmosphere. An extraterrestrial watcher could also potentially learn of our existence by detecting artificial night-time lighting of large urban areas [24].
Optimists suggest that contact with extraterrestrials could bring about great benefits for humanity [25], while others note that contact with technological civilizations has often resulted in the collapse of stone-age societies on Earth [14]. Given the potential consequences [26], if the risk from transmission into space is not zero, should transmissions into space be permitted, regulated or banned? If human activities can be detected across astronomical distances, then should humanity cease or attempt to disguise such actions? Does METI significantly increase risks to Earth and human civilization? These questions have been raised repeatedly in the research literature as well as in media and political coverage of SETI and METI research. This paper addresses these questions by reviewing existing knowledge of the Earth's radio signature, which includes the relative strength of signals potentially detectable over interstellar distances. We then develop an analytical framework for evaluating the consequences of transmission and discuss this in the context of existing policies and protocols.

Section snippets

Detectability of radio transmissions from Earth

Before about 100 years ago, Earth was “radio quiet” with no significant emission of radio waves compared to other objects in the Solar System (particularly the Sun and the gas giant planets). The development of radio transmitters initiated a new era where the technological activity of humans altered the electromagnetic spectrum of Earth. Other changes in Earth's spectrum driven by its biosphere include the rise in atmospheric oxygen about 2.4 billion years ago [27] and the proliferation of

The possibility of extraterrestrial watchers

For extraterrestrial intelligence (ETI) to cause any harm or benefits associated with humanity transmitting into space, there must be ETI elsewhere in the universe and particularly elsewhere within the Milky Way. Star systems with planets are plentiful in the galaxy, with current transit surveys discovering rocky planets close in size to, and even smaller than, Earth [35], [36], [37]. Many of these planets reside within the habitable zone of their parent stars, so that liquid water (or perhaps

The value of transmitting

For detection of a signal by ETI to provide harm or benefits to humanity, the watchers must react in some way that would affect human society. The watching ETI civilization could do nothing, or could treat the detection exclusively as a scientific discovery or as something else that has no impact. These responses all result in zero value to Earth and humanity. ETI could also respond by transmitting back towards Earth, by sending exploratory probes or other objects here, or by visiting

Discussion

The framework established above describes the potential value of unintentional and deliberate transmissions into space that could be detected by ETI watchers. Although parameters such as the distribution of intelligent civilizations or the detection of a signal are highly uncertain, we can use this framework as a way to raise some critical questions regarding transmission into space.
Radio leakage has already given away the location of Earth in space to any nearby ETI watchers. If the

Regulating transmissions

If transmissions from Earth into space could potentially generate attention by extraterrestrial watchers, humanity should consider regulations to govern such transmissions. Existing laws and treaties do not adequately cover guidelines for transmission into space or the potential benefits or harm that could arise from such activities.
Since the beginning of modern SETI in 1959, there have been several proposals for an internationally regulated framework to guide how detection would be handled.

Conclusion

Both radio leakage and deliberate METI messages could be detected by any extraterrestrial watchers with sufficiently sensitive radio telescopes. Even if a signal cannot be interpreted, it provides evidence of a technological civilization on Earth.
Quantitatively assessing whether large-scale METI should continue in light of current radio communication strategies on Earth (and corresponding radio leakage) is hampered by two highly uncertain parameters: the probability of ETI detecting a

Role of the funding source

Lone Signal LLC provided funding for this research and requested that the Madley 49 transmitter be included in the analysis. The authors acknowledge scientific independence during the duration of this sponsored work. The design, methods, interpretation, writing, and submission of this study are the work of the authors alone and do not reflect, infer, or otherwise suggest any position held by Lone Signal LLC.

Acknowledgments

The authors thank Milan Ćirković, Edward Schwieterman Jr., Megan L. Smith, and an anonymous reviewer for helpful suggestions. Any errors or opinions are those of the authors alone.

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    Present address: Exobiology Branch, NASA Ames Research Center, Moffett Field, CA 94035, USA.
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