The New and Improved SETI Toolbox Is Here
SETI hunting (Search for Extraterrestrial Intelligence) started just 60 years ago. At that time, good old radio signals were the primary search method. Since then the SETI-toolbox has been drastically improved, as well as our understanding of the Universe as a whole.
Exoplanets, planets outside our solar system, are believed to outnumber the 300 billion stars in the Milky Way. Rocky planets are harder to study than gas giants, but there are an increasing number of tools and methods available. In the old days the scientists would have to rely on primarily radio signals for ET-hunting.
Radio signals can travel long distances through space with relatively little attenuation, meaning they can still be detected even after traveling many light-years. Additionally, radio signals are a common communication method used by humans and may also be used by other intelligent civilizations.
SETI radio signal searches typically look for narrowband signals, which are signals that are concentrated at a single frequency or a narrow range of frequencies. This is because such signals are unlikely to occur naturally and are more likely to be produced by intelligent beings.
One of the challenges with SETI radio signal searches is distinguishing between signals that may be of extraterrestrial origin and those that are of human origin or have some other natural explanation. This is why SETI researchers have developed a variety of new techniques and instruments to carefully analyze any candidate signals they detect.
New Advanced Space Telescopes
Researchers just confirmed an exoplanet, using NASA’s James Webb Space Telescope for the first time. Formally classified as LHS 475 b, the planet is almost exactly the same size as our own, clocking in at 99% of Earth’s diameter.
The team notes that while it’s possible the planet has no atmosphere with oxygen, there are some atmospheric compositions that have not been ruled out, such as a pure carbon dioxide atmosphere.
Webb also revealed that the planet is a few hundred degrees warmer than Earth, so if clouds are detected, it may lead the researchers to conclude that the planet is more like Venus, which has a carbon dioxide atmosphere and is perpetually shrouded in thick clouds.
The researchers also confirmed that the planet completes an orbit in just two days, information that was almost instantaneously revealed by Webb’s precise light curve. Although LHS 475 b is closer to its star than any planet in our solar system, its red dwarf star is less than half the temperature of the Sun, so the researchers project it still could have an atmosphere.
Upgraded Earth Telescopes
CRIRES+ is an abbreviation for CRyogenic InfraRed Echele Spectrography. It is a spectrographic instrument mounted on top of the ESO Paranal Observatory in the Atacama Desert in the Andes. The + sign means that it is an upgrade from a previous instrument installed already in 2014.
CRIRES+ can break up the starlight that is passing through the atmosphere of a planet transiting in front of the hosting star. By measuring the fraction of stellar light able to penetrate the atmosphere at different wavelengths, the chemical composition of the atmosphere can be inferred. This method is called the Transit Spectroscopy Method.
JWST and CRIRES+ covers the same wavelengths and came into operation about the same time. By combining the strengths of both instruments it may now be possible to make qualified analyses of the atmospheres of Earth like planets.
Optical signals
Optical signals are light-based signals, such as laser beams, that could potentially be used for communication over vast distances in space. One approach is to look for brief pulses of light, which may indicate a signal being transmitted from a distant source. Another approach is to look for continuous, steady sources of light that may indicate the presence of a civilization.
Like radio signals, optical signals have the advantage of being able to travel long distances without being significantly attenuated, making them a potentially effective means of communication for advanced civilizations. Additionally, the use of lasers for communication has been explored by human researchers, making it a plausible technology for extraterrestrial civilizations as well.
However, there are some challenges associated with searching for optical signals. For example, optical signals are more susceptible to interference from atmospheric conditions, making it more difficult to distinguish between natural and artificial sources of light. Additionally, the directionality of laser beams means that any signals may be more difficult to detect if they are not pointed directly towards Earth.
Artificial Structures
SETI also considers the possibility of detecting artificial structures created by extraterrestrial civilizations. This includes looking for large-scale engineering projects, such as megastructures or Dyson spheres, that could potentially be detected using telescopes and other instruments.
A Dyson sphere is a hypothetical megastructure that an advanced civilization might construct around a star to harness its energy output. Such a structure would likely be massive and could potentially cause a detectable change in the star’s brightness. SETI researchers have therefore considered looking for such changes in the light output of stars to search for signs of extraterrestrial megastructures.
Other potential signs of artificial structures that SETI researchers might look for include unusual patterns or shapes in planetary or asteroid orbits, which could potentially indicate the presence of artificial gravitational sources or propulsion systems.
Searching for artificial structures comes with several challenges. For one, such structures would need to be very large and advanced to be detectable from Earth, which makes them relatively rare and difficult to find. Additionally, natural astronomical phenomena can also produce similar signals, making it difficult to distinguish between artificial and natural sources.
Biosignatures
Detecting the atmospheric composition of exoplanets in order to search for signs of life or intelligence is based on the assumption that life on a planet can potentially cause changes in the chemical composition of the planet’s atmosphere.
For example, Earth’s atmosphere contains significant amounts of oxygen, which is produced by photosynthetic organisms like plants. The presence of oxygen in an exoplanet’s atmosphere could therefore potentially indicate the presence of life.
Similarly, the presence of certain gasses or chemicals that are produced by industrial or technological processes could indicate the presence of an intelligent civilization.
A study from UC Santa Cruz suggests that methane can be a compelling biosignature. Finding a large amount of methane in an exoplanet’s atmosphere might even be our most reliable indication that life’s at work there. There are abiotic sources of methane, but for the most part, methane comes from life.
Scientists use telescopes and other instruments to study the light that passes through or is reflected by exoplanets. By analyzing the spectrum of this light, they can potentially identify the chemical composition of the planet’s atmosphere and look for any unusual or potentially artificial signatures.
Other biosignatures may be water, complex organic molecules and irregular atmospheric composition. Researchers tend to look for combinations of biosignatures, which could indicate that life is present.
Biosignatures can be difficult to distinguish from natural sources, such as volcanic activity or geological processes. Additionally, the distance between Earth and exoplanets is often very large, making it difficult to obtain high-quality atmospheric data.
Technosignatures
Technosignatures are analogous to biosignatures, which signal the presence of life, whether intelligent or not. A study suggests that if aliens exist, they may have established communications networks and may already have probes in the solar system whose communication may be detectable.
Extrasolar asteroid mining may also reveal extraterrestrial intelligence and it has been suggested that information could be hidden within the transit signatures of other planets, i.e. advanced civilizations could “cloak their presence, or deliberately broadcast it, through controlled laser emission”.
Various astronomers have proposed that artificial light from extraterrestrial planets, such as that originating from cities, industries, and transport networks, could be detected and signal the presence of an advanced civilization.
Other characteristics proposed as potential technosignatures include peculiar orbital periods such as arranging planets in prime number patterns, altered coronal and chromospheric activity on stars and free-floating planets (rogue planets) for interstellar transportation with a number of proposed possible technosignatures.
Vanishing stars
Stars shouldn’t be able to disappear without a trace. But for the first time in the history of astronomy, researchers have discovered a group of objects appearing and disappearing at the same time. Are advanced civilizations intentionally hiding from our telescopes?
The discovery was made within the framework of the research project VASCO (Vanishing & Appearing Sources during a Century of Observations), which since 2017 has been looking for vanished stars by comparing the old images from the 1950s and 1960s with modern mapping of the sky.
No natural phenomena can explain the presence of the objects in an old photographic plate from 1950. The group carefully indicated that either nuclear fallout from unlisted atomic bombs contaminated the plates or that a new celestial phenomenon might be behind.
According to astrophysicist Beatriz Villarroel at the Nordic Institute for Theoretical Physics in Stockholm:
Either physics unknown to us caused it to disappear, or superintelligent aliens hid it from our telescopes.
Alien Spacecrafts
Interstellar spacecraft may be detectable from hundreds to thousands of light-years away through various forms of radiation, such as the photons emitted by an antimatter rocket or cyclotron radiation from the interaction of a magnetic sail with the interstellar medium.
Such a signal would be easily distinguishable from a natural signal and could hence firmly establish the existence of extraterrestrial life, were it to be detected. In addition, smaller Bracewell probes within the Solar System itself may also be detectable by means of optical or radio searches.
Self-replicating spacecraft or their communications networks could potentially be detectable within our Solar system or in nearby star-based systems, if they are located there. Such technologies or their footprints could be in Earth’s orbit, on the Moon or on the Earth.
In Conclusion
After 60 years of discoveries and technological development, the odds for finding extraterrestrial life have gone up drastically. But at the moment we can only be certain about one thing: There is at least life on one planet…that is us. That is Earth.
However, most scientists seem to agree that intelligent life is common but sparse throughout the universe. This means that life should exist everywhere but most likely not in our own backyard due to the immense distances.
And the observable universe contains at least a trillion Milky Ways. This means that there may be thousands of trillions of broadcasting civilizations in the observable universe right now and we cannot get in contact with any of them. And remember we can only observe a tiny part of the universe.
