Genetically engineered bacteria, for example, could outlive humankind. In relation to their migration hypothesis, the scientists Robert Bradbury and Milan Cirkovic considered how in the distant future, humankind could build post-biological computing entities that would migrate to the outskirts of the Solar System.

Accordingly, Romanovskaya proposed the Cosmic Descendants hypothesis in her research paper. The Cosmic Descendants hypothesis posits that if a non-human industrial civilization existed on Earth, Venus or Mars in the distant past and it created spacefaring intelligent machines and engineered bacteria working in concert with technologies, then the descendants of the intelligent machines and bacteria could survive the civilization and currently exist in the Solar System. Those spacefaring intelligent machines and their descendants could reside mostly beyond the orbit of Saturn to experience less negative impact of solar activity.

The machines could explore asteroids, Ceres and Jovian planets' moons for resources, and use engineered bacteria in asteroid biomining and other applications. They could send space probes to survey the Sun and Earth.

If the intelligent machines had no biological components and did not use biological matter, they could eventually leave the Solar System and migrate to the outskirts of the Galaxy. However, if the intelligent machines had non-biological components and biological components (for example, artificial silicon neurons interlinked with in vitro biological neural networks), then the machines could remain within the heliosphere of the Solar System that would protect them from galactic cosmic rays. In the distant future, a supernova going off in our galactic neighborhood or the Sun turning into a red giant could make them leave the Solar System.

The Cosmic Descendants hypothesis also posits that the hypothetical ancient non-human civilization and its intelligent machines could build biotechnospheres on Earth and elsewhere in the Solar System.

Romanovskaya describes biotechnospheres as systems of life forms and technologies working in concert toward common goals. For example, a localized biotechnosphere could be a combination of bacteria performing bioremediation of the radioactive waste from a nuclear power plant and technologies that would monitor the bacteria and guide its activities. Biotechnospheres could monitor and preserve the planetary environment, assist with space exploration, medical processes, industrial processes, mining, and food production.

The Cosmic Descendants hypothesis posits that if the hypothetical ancient non-human civilization built biotechnospheres with engineered bacteria in the past, the descendants of those bacteria could survive to our times and preserve the abilities that their ancestral bacteria had in the ancient biotechnospheres. A discovery of bacteria with such abilities on Earth could serve as evidence that an advanced non-human civilization existed on Earth in the distant past.

The descendants of the ancient bacteria of ancient biotechnospheres could also exist on Mars and elsewhere the Solar System. This is why Romanovskaya points out that "the discovery of bacteria that were part of such extinct biotechnospheres could blur the line between astrobiology, interstellar archeology and the search for the artefacts of extraterrestrial civilizations."

In her research paper, Romanovskaya coins the term 'biotechnosignatures' to describe observables and artefacts of alien biotechnospheres. She proposes several ways to search for the biotechnosignatures of alien civilizations in other planetary systems.

For example, if a planetary biotechnosphere regulated the planetary environment of an exoplanet, a biotechnosignature could be in the form of the planetary environment remaining steady from decades to millions of years.

Magnetic storms on exoplanets could also reveal alien biotechnospheres and their biotechnosignatures. Consider, for example, a solar proton event known as the Carrington event of 1859 that caused the powerful magnetic storm on Earth in September 1859. The magnetic storm did not damage life on Earth. Today, such a storm would disrupt radio communications in Earth's high-latitude regions and seriously damage electrical grid and satellite capabilities on Earth.

If a Carrington-like magnetic storm occurred on an exoplanet where a biotechnosphere was protecting the planetary environment, the storm could temporarily damage the biotechnosphere's technologies. This would cause unexpected variations in the planetary environment. So, a biotechnosignature could be unusual fluctuations of the exoplanet's environment happening after stellar flares, with the planetary conditions speedily returning to their pre-flare state.

Another biotechnosignature could be a rapid strengthening of the signs of bacterial activities on an exoplanet that experienced a mass extinction event. The biotechnosignature could arise if a planetary biotechnosphere with engineered bacteria existed on the exoplanet, survived the mass extinction event, and supported restoration of the planetary habitability.

A star turning into a red giant could reveal planetary biotechnospheres on the planets orbiting it. A biotechnosignature could be a combination of the signs of an advanced civilization migrating away from the star and colonizing the planetary system's outer regions and the signs of the engineered bacteria and biotechnospheres remaining on the civilization's home planet and experiencing a destruction by the dying star.

Biotechnospheres could also produce biotechnosignatures when used in terraforming of planets and moons in the Solar System and in other planetary systems.

Bio-inspired alien technologies could be another biotechnosignature. Almost all robotic systems created by humans are inspired by the properties of Earth-based life forms, and so Romanovskaya proposes that alien robotic systems could also have properties imitating the properties of the biological species that created them or the properties of other life forms known to such a biological species.

Romanovskaya suggests that If alien robotic systems were ever discovered, astrobiologists could work together with engineers to determine which properties of the alien robotic systems could "tell" us something about the properties of alien life.

About the Author : Irina Mullins writes under her maiden name, Irina K. Romanovskaya. She is a graduate of Rice University (Houston, Texas) and a professor of physics and astronomy at Houston Community College System.

Research Report:Planetary biotechnospheres, biotechnosignatures and the search for extraterrestrial intelligence

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