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This book is a collection of essays written by those who have led, and continue to lead, the search for extraterrestrial intelligence. It reviews the history of the subject, details present-day science and technology, and looks ahead to the future.

The purpose of this extended paper is to provide a review of the chirp function and the chirplet transform and to investigate the application of chirplet modulation for digital communications, in particular, the transmission of binary strings. The significance of the chirp function in the solution to a range of fundamental problems in physics is revisited to provide a background to the case and to present the context in which the chirp function plays a central role, the material presented being designed to show a variety of problems with solutions and applications that are characterized by a chirp function in a fundamental way. A study is then provided whose aim is to investigate the uniqueness of the chirp function in regard to its use for convolutional coding and decoding, the latter case (i.e. decoding) being related to the autocorrelation of the chirp function which provides a unique solution to the deconvolution problem. Complementary material in regard to the uniqueness of a chirp is addressed through an investigation into the selfcharacterization of the chirp function upon Fourier transformation. This includes a short study on the eigenfunctions of the Fourier transform, leading to a uniqueness conjecture which is based on an application of the Bluestein decomposition of a Fourier transform. The conjecture states that the chirp function is the only phase-only function to have a self-characteristic Fourier transform, and, for a specific scaling constant, a conjugate eigenfunction. In the context of this conjecture, we consider the transmission of information through a channel characterized by additive noise and the detection of signals with very low Signal-to-Noise Ratios. It is shown that application of chirplet modulation can provide a simple and optimal solution to the problem of transmitting binary strings through noisy communication channels, a result which suggests that all digital communication systems should ideally by predicated on the application of chirplet modulation. In the latter part of the paper, a method is proposed for securing the communication of information (in the form of a binary string) through chirplet modulation that is based on prime number factorization of the chirplet (angular) bandwidth. Coupled with a quantum computer for factorizing very large prime numbers using Shor's algorithm, the method has the potential for designing a communications protocol specifically for users with access to quantum computing when the factorization of very large prime numbers is required. In this respect, and, in the final part of the paper, we investigate the application of chirplet modulation for communicating through the 'Water-Hole'. This includes the introduction of a method for distinguishing between genuine 'intelligible' binary strings through the Kullback-Leibler divergence which is shown to be statistically significant for a number of natural languages. Finally, a conjecture is developed in regard to focusing on the emission of intelligent signals from multiple star systems in the search for extraterrestrial intelligence. Prototype MATLAB code is given in the Appendix so that interested readers can reproduce some of the results given and modify and/or develop further the algorithms provided. The paper concludes with a number of open questions and some ideas for further investigation.

Penetrating planetary regolith is extremely important to explore the secrets inside extraterrestrial celestial bodies. Applying the concept and method of bionics to endow planetary regolith-burrowing robots (PRBRs) with elegant and flexible mobility as natural creatures is gradually becoming a research hotspot in the field of planetary robotics. Compared with traditional penetrating methods, such as drilling and excavation, bioinspired burrowing methods are still seldom studied. This work presents a detailed review of the progress and perspective of bioinspired PRBRs. According to the burrowing mechanisms and strategies of creatures, the current bioinspired PRBRs are divided into seven categories, namely wriggling, undulating, dual-anchoring, grabbing-pushing, reciprocating, granular fluidizing methods inspired by animals, and root growth method inspired by plants. The general characteristics of these robots are summarized in-depth, and the advantages and disadvantages are compared. Then, the key technologies of determining the functionalities and performance of bioinspired PRBRs are comprehensively analyzed, including bioinspired mechanism design, motion control, robot-regolith interaction, and terrestrial validation. Finally, the development trend of bioinspired PRBRs is presented, including new mechanisms and materials, autonomous burrowing control, and intelligent perception and communication.

My focus is on the contemporary astrobiological activity of Messaging ExtraTerrestrial Intelligence (METI). This intentional astrobiological signaling typically involves embedding digital communications in powerful radio signals and transmitting those signals out into the cosmos in an explicit effort to make contact with extraterrestrial others. Some who criticize METI express concern that contact with technologically advanced extraterrestrial life could be seriously harmful to Earth or humanity. One popular response to this critique of messaging is an appeal to causal impotence sometimes referred to as the ‘Barn Door’ Argument—we are already engaged in many other detectable activities not intended for cosmic communication. If the Barn Door Argument is correct, then those who engage in messaging arguably have a moral excuse. They are permitted to continue messaging because there is no point in abstaining. I develop three ways in which the claim of causal impotence in the Barn Door Argument could be understood. I evaluate each of these in turn and demonstrate that only one is appropriate to contemporary messaging. However, this interpretation does not generate the moral excuse on which the proponents of the Barn Door Argument rely; thus, the argument fails. Finally, I entertain and respond to candidate objections.

\"Explores the search for life on other planets. From exoplanets to rocks on Mars and radio waves to infrared telescopes, readers will learn about signs of life in the universe\"--Amazon.

Data complexity is an important concept in the natural sciences and related areas, but lacks a rigorous and computable definition. This paper focusses on a particular sense of complexity that is high if the data is structured in a way that could serve to communicate a message. In this sense, human speech, written language, drawings, diagrams and photographs are high complexity, whereas data that is close to uniform throughout or populated by random values is low complexity. I describe a general framework for measuring data complexity based on dividing the shortest description of the data into a structured and an unstructured portion, and taking the size of the former as the complexity score. I outline an application of this framework in statistical mechanics that may allow a more objective characterisation of the macrostate and entropy of a physical system. Then, I derive a more precise and computable definition geared towards human communication, by proposing local compositionality as an appropriate specific structure. Experimental evaluation shows that this method can distinguish meaningful signals from noise or repetitive signals in auditory, visual and text domains, and could potentially help determine whether an extra-terrestrial signal contained a message.

Any effort to contact extraterrestrial life invokes existential risks to humanity. Scientists and politicians would, ideally, need to figure out how to communicate the news to the world in a constructive and culturally sensitive way. Any attempt at active communication with extraterrestrials poses even greater moral challenges, which past messaging attempts have tended to ignore. This problem continues today, as some private groups have started talking seriously about transmitting powerful directed signals toward other stars.

This paper presents a comprehensive study of ultra-wideband (UWB) and multi-band orthogonal frequency-division multiplexing (MB-OFDM) technologies for lunar rover navigation and communication in challenging terrains. Lunar missions pose unique challenges, such as signal propagation in the lunar environment, terrain elevation, and rover movement constraints. To address these challenges, we propose a hybrid communication and navigation system that leverages UWB technology for high-precision positioning and MB-OFDM for robust and high-throughput communication. We develop a realistic simulation framework that incorporates terrain elevation, obstacles, and rover movement constraints, along with a simple fading model for communication. Simulation results demonstrate the effectiveness of the proposed system in navigating lunar rovers to their target locations while maintaining reliable communication links with a lunar lander. A novel approach based on game theory for rover navigation is also presented. The study provides valuable insights into the design and optimization of communication and navigation systems for future lunar missions, paving the way for seamless integration of advanced terrestrial technologies in extraterrestrial environments.