10 Potential Hints of Extraterrestrial life

“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” – Arthur C. Clarke

While hard, irrefutable evidence able to answer the ultimate question, whether we are alone in the universe, has never been discovered, we have however seen various tantalising hints that the question may not be as easy to dismiss as it seems. In our past, answering the question actually seemed more simple than today. For example, astronomer Giovanni Schiaparelli (1835-1910) described what he described as ‘canali’ (channels) on Mars, which were widely mistranslated as ‘canals’. This theory was corroborated by Percival Lowell (1855-1916) who observed Mars from his observatory in Arizona before erroneously confirming these ‘canals’ were real. What Schiaparelli and Lowell actually observed and perceived as ‘canals’ were likely just a combination of natural Martian surface features and optical illusions as a result of their relatively primitive equipment. Nevertheless, the discovery of these ‘canals’ on Mars, especially given it was around the time canals on Earth, particularly in England, were popular, the hypothesis conceived was that an advanced but struggling extraterrestrial Martian race was active on Mars, possibly using canals to transport water from the Martian ice caps to the dryer areas around the centre of the planet. Lowell’s findings were said to influence H.G Wells’ famous novel The War of the Worlds (1898) further added to the psyche at the time that Mars was home to an advanced civilisation, perhaps one that could even threaten Earth and humanity and science at the time was largely shaped by this widely accepted idea.

In more modern times, possible signs of extraterrestrial life which have later been debunked include the pulsar known as PSR B1919+21. On 28th November 1967, Cambridge graduate student Jocelyn Burnell discovered what she described as ‘a bit of scruff’ on her chart recorder papers using the Interplanetary Scintillation Array in Cambridge. These signals had a precise 1.337 second repeating period, and this perfect accuracy was at first misconstrued as potentially a signal from a distant exocivilisation, perhaps a navigational beacon of some sort. The discoverers jokingly labelled the signal LGM-1 (Little Green Men) as the precise nature of the pulses seemed unlikely to be natural. However, Burnell also discovered a similar signal from a different source, meaning that the extraterrestrial hypothesis seemed unlikely. Eventually, Burnell announced the cause of the signals to be a newly discovered type of rapidly rotating neutron star known as a Pulsar. Although the signals were not an indicator of life, the possibility that life could be detected through radio signals spurred on the field of radio astronomy and later SETI (Search for Extraterrestrial Intelligence).

So how fruitful has humanity been in the search for extraterrestrial life? Surprisingly, although it is widely accepted that we have never discovered extraterrestrial life, unless one believes various UFO, Area 51 and ancient alien conspiracies, there is no shortage of potential leads in the search for the answer to the ultimate question. The first set are biosignatures, signs of life through chemical and physical means. The second set are technosignatures, signs of advanced intelligent life through technological means:

1. Allan Hills 84001 (ALH84001) Meteorite

On December 27th 1984, a team of American meteorite hunters from the ANSMET project discovered a small meteorite in the Allan Hills in Antarctica. Antarctica is very popular amongst meteorite hunters, as most of its landscape is old and undisturbed, and the chances of earthly contamination is far lower here, as the extremely low temperatures and harsh environment on the continent prove inhospitable to many organisms. Also, as most of Antarctica consists of ice sheets rather than rock, most rocks that are found tent to be meteorites, rather than terrestrial rocks, which fall and become lodged or buried under ice, meaning that the optimum place to find meteorites is at the termination point at which the ice melts into the sea- glaciers. The majority of meteorites found in Antarctica tend to be nickel-iron meteorites mostly originating from the asteroid belt between Mars and Jupiter, where asteroids constantly crash into each other sending smaller rocks towards the inner solar system. Weighing roughly 2kg, it was named ALH84001 and was proven to originate from Mars. It was likely ejected from the planet after a large impact, jettisoning into space due to the high amounts of energy caused by such an impact and Mars’ far weaker gravity and thinner atmopshere. From chemical analysis, ALH84001 is thought to have formed on the Martian surface at a time when liquid water was present on the surface of the planet. It is also believed to be much older than most Martian meteorites found on Earth, around 4 billion years old. It is primarily a basalt like most similar meteorites originating from the red planet, however it is thought to have originated from Mars’ earlier days, where the surface and atmopshere were far warmer than today, and crucially when liquid water was present in relative abundance on the surface. Most other Martian meteorites tend to show signs that they came from a Mars when the planet was more similar today, dry, barren and cold. Moreover, study of ALH84001 has suggested that it came from an area of Mars known as Valles Marineris, a canyon that is thought to be the largest canyon in the entire solar system. Isotopic analysis of ALH84001 suggested that the carbonates within the rock seem to have precipitated from water and also contained carbon dioxide, a tell-tale sign of the Martian atmopshere. They may also be associated with organic compounds. This analysis also shown that the rock may have been present in water beneath the surface of Mars, in an environment known as an aquifer. Dating analysis also points towards the meteorite being blasted off Mars between 15-20 million years ago, falling into Antarctica around 13,000 years ago. ALH84001 also became known for a different reason, when viewed using a scanning electron microscope, tiny shapes and structures were seen that strongly appear to resemble fossilised bacteria. However, if these structures were the fossils of ancient Martian bacteria, they were far smaller than any known terrestrial bacteria- perhaps being more akin to nanobacteria hypothesised to exist in microbiology. Whilst nanobacteria may or may not exist, the structures within the meteorite do strongly resemble shapes similar to fossilised microorganisms and most likely aren’t a result of contamination from Earth. Moreover, they do not bear any resemblance to earthly microbial contamination seen in other Martian meteorites. Whilst the structures seem too small to be any known form of life, they do contain carbon isotopes which are consistent with biological processes.

The discovery inside ALH84001 even led to US President Bill Clinton announcing the in 1996 as a positive finding of extraterrestrial life. However, whilst still unexplained, the structures are still not necessarily a result of life. They are far tinier than any known bacteria, and have been called strongly into question as the shapes could simply be natural and abiological, and the interpretation of them comes down to perception. More rock similar to ALH84001 would have to be returned to Earth as part of a sample return mission to prove more conclusively if it did indeed contain traces of ancient Martian life.

2. The Viking Labelled Release Experiments

In 1976, NASA’s Viking landers on the red planet carried an array of scientific equipment and tests designed to monitor and study the Martian atmosphere and surface. One of these tests, the ‘labelled release experiment’, still divides astrobiologists to this day. In this test, tiny samples of Martian soil were collected by the robotic rover and passed into a built-in laboratory. Here, it was put into a vial containing carbon-based compounds (nutrients)- formate, glycine, D-alanine, L-alanine, L-lactate, D-lactate, and glycolate. All nutrients which could hypothetically be consumed and metabolised by a native form of micro-organism. A detector would then wait to see if it could find any traces of waste gases consistent with metabolising micro-organisms, such as Carbon Dioxide (CO2), Carbon Monoxide (CO), Methane (CH4) or Oxygen (O). The test returned an initial positive, albeit with levels of reaction a small fraction of what similar tests would record on Earth, indicating possible metabolising of the nutrients provided. This was a surprise, as previous different experiments had failed to detect even organic compounds- relatively common on other bodies such as asteroids- on the Martian surface. Scientists decided to heat a new sample to a temperature of 160°C in order to sterilise any micro-organisms present. Even more encouragingly; this stopped any reaction taking place, leading to a negative result. This would make sense if the reactions discovered were being produced by micro-organisms. More tests took place, including the storing of a sample at 10°C for several months. This also lead to a negative result. Whilst 10°C for that period of time wouldn’t be deadly to most Earthly micro-organisms; normal surface temperatures on Mars are far lower, averaging around -62°C, therefore prolonged storage at 10°C would be an increase of over 70°C- likely deadly to any Martian micro-organisms. Further tests, heating the sample to 50°C returned a positive- but with a far lower, minuscule level of reaction. Whilst encouraging, these tests have also come under scrutiny, with many claiming Earthly contamination of the samples by bacteria transported on the lander from Earth were to blame for the positive results. It has been proven that spores and hardy microbes (extremophiles) can survive the cold vacuum of space for lengthy periods of time, even though spacecraft, especially those landing on other worlds, are required to be well sterilised due to Planetary Protection regulations. Another possibility is that a false positive was caused through an abiological means which could mimic metabolism, such as formate. However, it is unlikely formate is particularly prevalent on Mars. What Mars is rich in is perchlorate, which could also produce a false positive, although this shouldn’t have slowed down when the samples were heated, so the chances of the results being a result of perchlorate interaction with the substrates is unlikely. A 2013 study however did find that exposure to cosmic rays- of which Mars has little protection from- can cause perchlorate to break down, which yields hypochlorate which could break down itself when heated to produce a false positive. Strange rises in methane and oxygen levels on Mars have also been detected transiently, both of these being biosignatures which could possibly indicate active life.

3. Europa’s streaks

Europa, one of the four main Jovian or Galilean moons of Jupiter, has long been cited as perhaps the most likely body other than Earth to host life in the solar system. This is primarily due to it having a vast subsurface ocean of liquid water, heated by radioactive decay at the core of the moon and tidal flexing by the gravitational pull of Jupiter. This ocean may also contain hydrothermal vents which transfer heat, energy and chemicals from the core of the moon to the ocean through the ocean floor. Up to now, no evidence of such life has been discovered in the ocean, however interesting observations of the moon can be made from looking at its icy surface.

The peculiar red staining around the cracks, or linea, on Europa’s surface has lead to speculation that microbes deep below or perhaps frozen in the ice are the cause. Whilst some maintain it is simply the result of the discolouration of salts and minerals by Jupiter’s magnetosphere, it is still unclear what chemical processes could cause this. In 2002, planetary geologist Brad Dalton of NASA’s Jet Propulsion Laboratory (JPL) looked at this red staining in the infrared and compared it to the infrared signature of photosynthetic algae that lives around hot water springs in the Yellowstone National Park here on Earth. The infrared signatures of both the red staining on Europa and the algae were surprisingly similar. In addition, Dalton took a variety of other microorganisms and subjected them to Europa-like conditions, and found that their infrared signatures were loosely similar to Europa’s red staining. The infrared spectra obtained of Europa by the Galileo spacecraft did show that these areas consisted of water ice bound to another material. This could well be salts such as or similar to Epsom salts, although these typically appear white- and do so on Enceladus- so the red colouration is unusual, if indeed the hypothesis of the discolouration being caused by Jupiter’s magnetic field turns out to be false. Moreover, no mix of salts exists that are a precise match to the infrared signatures seen from the stained areas on Europa. Another potential explanation is that the staining has been caused by different sulfur compounds, perhaps again being the chemical product of radiation from Jupiter hitting the surface of Europa. A possible explanation for such sulfur compounds being present on the surface of Europa is its sister moon, Io. Io is wildly volcanic, and spews sulfur out into space incessantly, and there is evidence that some of this sulfur has collected on the surface of Europa. The way in which both planets orbit, and the fact Jupiter rotates rapidly, far faster than Europa orbits, means the majority of Io’s jettisoned sulfur settles on the trailing side of Europa- Europa being tidally locked to Jupiter, eternally presenting the safe face to the planet akin to Earth’s moon due to gravity. The proposal that deposited sulfur compounds from the volcanoes of Io are responsible for the staining on Europa does make sense, however, it does not explain why the staining is almost exclusively situated on and around the cracks in the surface. This clearly shows that the staining is directly related to the cracks, and it seems beyond unlikely that sulfur deposits from Io would collect around the cracks and almost nowhere else. Although the infrared spectra of the cracks resembled that of biology on Earth, it wasn’t a perfect match. However, Dalton also noted that the difference in the spectra of two bands in the Earthly bacteria correspond with amide bonds in the protein coatings of their cells. Amide bonds are essentially the link that bind or hold proteins together, and without them you just have amino acids which are commonly found abiologically in space, particularly on asteroids. Although this could explain why the infrared spectra of the Europa colouration isn’t an exact match to bacteria in similar conditions on Earth, even if it is indeed frozen microorganisms responsible for the staining on Europa’s cracks, Dalton also proposed amide bonds could be broken on Europa’s surface due to high levels of radiation, and if those bonds are put back together in a stronger form then their infrared spectra could more closely resemble the Europa data. Dalton does also note that amide bonds are strong, and even in the highly radioactive environment of Europa’s surface may remain unbroken, although amide bonds absorb ultraviolet light (UV) at 205 nanometre wavelengths, and this from the sun in conjunction with radiation from Jupiter could possibly cause the bonds to break. Whilst far from definitive proof of microbial life, Dalton’s findings do remain on the table as far as evidence for life on Europa is concerned. Some scientists have even proposed that they would be surprised if Europa doesn’t harbour life, and that if it does, it could even be more than microbial.

4. UV Absorption on Venus

In many ways, Venus is seen as the definition of a hell planet, and this assumption is probably quite accurate. A combination of crushing atmospheric pressure (around 92 times the atmospheric pressure on Earth at sea level) and extremely hot surface temperatures (often well above 450 degrees Celsius) means that the surface is almost definitely inhospitable and hostile to any form of life. Venus was likely much more Earth like in its ancient past, yet a runaway greenhouse effect caused by an increase in luminosity of the sun led to liquid water on the planet evaporating and forming water vapour molecules which broke apart due to UV radiation, and this and a build up of carbon dioxide coupled with the loss of hydrogen to space led to the planet becoming increasingly hot, and the atmospheric pressure becoming crushing. The extreme atmospheric pressure and thick, continuous clouds of sulfuric acid are so efficient and redistributing heat that the planet is more or less the same temperature at the surface. It has been estimated Venus, often nicknamed Earth’s sister planet due to its relative closeness and almost identical size, had shallow liquid water oceans for around 2 billion years. The presence of water, the universal solvent for life on Earth, means that there is a possibility that life evolved on Venus during its early history. Assuming this hypothetical life was surface based, perhaps living in or around Venus’ oceans, it is next to impossible that this life survived and persisted after the runaway greenhouse effect on the planet stripped it of its water and increased the pressure and temperature to hostile levels. Moreover, any signs of this life, if it indeed it existed, is likely long gone as Venus seems to periodically resurface itself through large-scale volcanism which would bury and destroy any fossil or chemical evidence. However, recent studies have shown that the upper atmosphere of Venus is far less hot than the surface, and at a height of around 165,000ft the atmospheric pressure is roughly the same as sea level on Earth. This area high in the clouds of Venus possibly hosts the most Earth-like conditions in the solar system. It is far less hostile here than on or near the surface, to the point that a human may not need a full pressurised spacesuit to survive here due to near equalised atmospheric pressure, simply an oxygen supply and a thick Hazmat suit to protect you from sulfuric acid may be enough. Therefore, it has been proposed that this area of Venus hypothetically could host microbial life that long ago arose on the surface, and adapted to live at high altitudes to escape the hell that the runaway greenhouse effect caused on the surface. Life at high altitudes does exist on Earth, and it is even possible that this area of Venus may be more hospitable to life than at the high altitudes on Earth at which life is still detected.

So, is there any hints that this life exists? Probes sent to Venus in the latter half of the 20th century detected a chemical called carbonyl sulfide high in the atmopshere of Venus. A possible biosignature, carbonyl sulfide is rare and hard to produce without the presence of biology, although it has also been known to be produced through volcanism, and Venus seems to possess volcanism. However, we have yet to detect any active volcanism, or recent volcanism on the planet which could explain the presence of carbonyl sulfide, although still relatively little is known of the surface of Venus and any active volcanoes could simply be hidden by Venus’ thick clouds.

An even more intriguing sign that the upper atmopshere of Venus could harbour microbial life exists in the form of unexplained dark patches high in the clouds, which seem to absorb solar radiation. It is possible that this is simply the result of chemical processes, such as ferric chloride, but a biological explanation is also possible. Recent studies have indicated that whatever these absorbers are, they seem to be affecting Venus’ atmosphere as a whole. As we know, Earth’s atmopshere is massively affected by life and this would also be detectable from afar. In 2019, scientist Yeon Joo Lee published a paper providing evidence of a relationship between the solar driven winds of Venus and the clouds. The absorbers affect the albedo of the planet (how much solar radiation and energy is reflected back into space) and this causes notable temperature changes which drive and alter winds. The possibility stands that these unknown absorbers are biological in nature and are affecting Venus’ atmopshere. Even more encouragingly, the same team found that the particles making up these mystery absorbers were consistent with some known atmospheric microorganisms on Earth physically, chemically and spectrally. However, the team also acknowledged that far more and longer study of Venus would be needed in order to better understand the phenomena and to astatine conclusively whether it is biological in nature. Also, the absorption is even more interesting when seen in ultraviolet (UV). Dark lines can be seen high in Venus’ atmopshere when viewed in UV. It is possible therefore that if the absorbers are indeed life, they may be using UV light as an energy source. Most life on Earth doesn’t tend to deal well with ultraviolet, although certain corals have evolved to be able to re-radiate UV, showing that life can adapt to UV in some ways, if not to directly use it as an energy source. Also detected in the atmopshere of Venus are what are known as S8 molecules. These are ‘immune’ to the effects of sulfuric acid, of which much of Venus’ clouds are made of. It has been proposed that these could be incorporated by microorganisms as protection from the sulfuric acid present. Moreover, the Venera missions also detected mystery elongated particulate matter slightly lower in the atmopshere that were about the same size as bacterium.

5. Nikola Tesla’s signals

During the latter years of the 19th Century, speculation regarding a potential alien civilisation inhabiting the planet Mars was rife. As was the science around radio waves. The famous Serbian-American inventor Nikola Tesla (1846-1943), a somewhat eccentric pioneer in the field of electrical engineering and radio waves, claimed in 1899 to have picked up signals from Mars, or possibly Venus, using his 280ft tower he built at his laboratory in Colorado Springs. His instruments were powerful enough to detect any electromagnetic disturbances within a radius of well over 1,000 miles. During his tests, he recorded mysterious radio signals that were periodic and repetitive, unlikely to be any man-made signal at the time. Tesla was convinced these were communications from extraterrestrials, likely from the planet Mars which was thought to be home to an advanced alien race at the time due to observations made by Giovanni Virginio Schiaparelli (1835-1910) who claimed to see ‘canali’ on the surface of the planet- mistranslated as ‘canals’. Tesla wrote:

“I was familiar… with such electrical disturbances as are produced by the sun, Aurora Borealis and earth currents, and I was as sure as I could be of any fact that these variations were due to none of these causes…”

“The nature of my experiments precluded the possibility of the changes being produced by atmospheric disturbances. . . . Although I could not decipher their meaning, it was impossible for me to think of them as having been entirely accidental . . . a purpose was behind these signals. . . . They are the results of an attempt by some human beings, not of this world; to speak to us by signals…”

“I am absolutely certain that they are not caused by anything terrestrial…”

“The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.”

Whilst we now know that Mars is not home to an advanced alien civilisation, let alone one sending signals to Earth, what is clear is that Tesla did pick up radio signals he was unable to explain. Tesla’s discoveries however were long before modern radio astronomy, and it wasn’t known at the time the extent that natural cosmological bodies and phenomena can give off radio waves. For example, nowadays it is possible to listen to radio waves emitted by Jupiter’s magnetic field, or magnetosphere, using even basic radio equipment. Back at the time of Tesla’s experiments, this was not known and radio waves were a very new technology, therefore any signals detected were believed to be from artificial sources. One alternative theory is that Tesla was actually picking up signals from the experiments of Italian inventor and electrical engineer Guglielmo Marconi (1874-1937) who, at around the same time, was experimenting with radio signals himself. It has been speculated that Marconi may have been broadcasting the letter S (dot-dot-dot) which were received by Tesla who rightly interpreted them as being under intelligent control, just not of alien origin. Although highly unlikely to be signals from extraterrestrial beings, Tesla’s signals are still technically unexplained as to study and verify his findings today would be very difficult as the frequencies at which Tesla picked up the signals are now extremely saturated by terrestrial interference that in order to pick up such hypothetical signals, the receiver would have to be placed on the far side of the moon, at the closest.

6. Long Delayed Echo (Radio)

In radio, a Long Delayed Echo (LDE) is an occurrence in which a broadcaster sends out a signal then receives it back after a long period of time, which in radio means anything from a few seconds to a minute or two. These have often been recorded by radio astronomers and although technically unexplained, they are more than likely a completely natural occurrence caused by the radiowaves bouncing off objects in space such as comets, asteroids or even planets and coming back just at the right time. Signals could also get trapped in a loop in the upper atmosphere of Earth and repeat back under certain conditions. However, whilst the cause of these LDE’s is almost definitely natural, as it is yet to be fully explained, the possibility of extraterrestrial involvement can’t be completely ruled out. The Milky Way is extremely old, almost 14 billion years old, which means there has been more than enough time for sufficiently advanced civilisations to form. A proposed way for these civilisations to explore the galaxy is through self-replicating probes known as Von Neumann probes. These are small probes that could be sent out to all corners of the galaxy and make copies of themselves using resources readily available in solar systems and on comets. Rapidly replicating themselves, these probes could theoretically cover almost every star system in the galaxy in under a million years, which is extremely quick if you’re a civilisation that has been around for hundreds of millions or even billions of years, and the cost and resources needed would likely be relatively low as only a few initial Von Neumann probes would be needed. In fact, producing Von Neumann probes is not beyond possible for humanity in the next hundred years or so, with advancements in spacecraft, artificial intelligence and 3D printing becoming reality. As it is so feasible for Von Neumann probes to be developed, one of the arguments against them existing is that they should technically be everywhere and easy to detect. Whilst unlikely, the presence of an alien Von Neumann probe could explain LDE’s as one stationed in our solar system could be repeating our signals back at us as an attempt at communication, in a way not dissimilar to how some animals repeat the same sounds back to each other to alert each other of their presence.

7. Gamma Ray Bursts and Alcubierre Warp Drives

An Alcubierre Warp Drive (named after its proponent Mexican physisist Miguel Alcubierre) is a highly contentious form of extremely advanced theoretical technology which could be used to travel vast distances quickly. Basically, although matter sitting in space cannot travel faster than the speed of light, space itself is not bound to that rule and can. Therefore, if a ‘piece’ of space is split off, you could in theory accelerate it to unlimited speeds. If a spacecraft is placed in this isolated chunk of space, it could then be sent travelling within it, meaning faster than light travel is possible whilst still remaining consistent with Einstein’s theory of relativity, as the spacecraft (matter itself) isn’t actually moving, only the space surrounding it is. Whilst producing an Alcubierre Warp Drive would likely be next to impossible, and if it was it would require a colossal amount of energy, advocates maintain a sufficiently advanced species could achieve it. Such a spacecraft would also need extreme shielding to protect it and its occupants from gamma radiation and dangerously blueshifted particles. A by-product of an Alcubierre Warp Drive is thought to be the release of huge amounts of gamma rays. Gamma rays, such as the ones emitted during gamma ray bursts, are quite easily detected at extremely long distances. In fact, we do detect from time to time unusual gamma ray bursts which are not easily explained. A possibility for these unexplained gamma ray bursts, albeit an extremely remote one, is that these are being produced by alien Alcubierre Warp Drives.

8. Borra/Trottier’s signals

In 2012, Ermanno Borra of Laval University, Canada, published a paper in which he proposed that pulsed laser emissions consistent with the ventures of extraterrestrial civilisations could be detected within the spectra of stars. He suggested that these pulsed laser emissions could even be an exocivilisations means of communication, saying “The kind of energy needed to generate this signal is not crazy,” and outlining that the Helios laser at the Lawrence Livermore National Laboratory could, for example, produce such a signal if humanity decided to announce our presence to the cosmos by means of laser emissions.

Borra, along with his graduate student Eric Trottier, then searched the sky through the Sloan Sky Survey, looking for such pulsed laser emissions in the spectra of stars. Combing through around 2.5 million stars, Borra and Trottier eventually published their findings in late 2016. They reported that they had actually found these type of signals in precisely 234 different stars, all within our Milky Way galaxy. Borra and Trottier also found that the vast majority of these 234 stars were so-called sun-like stars, many yellow dwarfs, and were of a sufficient age and relative stability that they could theoretically have developed advanced exocivilisations. Borra claims it is indeed possible that the data shows 234 exocivilisations are beaming pulsed laser emissions towards us, all at around the same periodicity (1.65 picoseconds). Both scientists have ruled out other explanations for the unusual laser signals, such as rapid pulsations in the stellar atmospheres and rotational transition in molecules. “We have to follow a scientific approach, not an emotional one,” Ermanno Borra explained “But intuitively – my emotion speaks now – I strongly suspect that it’s an ETI signal.”
Whilst intriguing, especially because the signals came from primarily sun-like stars (which astrobiologists believe hold the best chance of developing life), the conclusion of extraterrestrial involvement is still unlikely. Stars of all kinds emit a vast array of unusual and strange signals, so a natural explanation is likely still the most favourable.

9. KIC 8462852/Boyajian’s Star

KIC 8462852, also known as Boyajian’s Star or Tabby’s Star, or even informally as the WTF Star, is an F-Type main sequence star located the the Cygnus constellation, just under 1,500 light years away from Earth. In 2011, the Keplar space telescope observed the star and discovered that it within its light curve were many strange dips consistent with something large passing in front of it, blocking its light. Usually, dips in light curves from stars aren’t abnormal, after all the primary way exoplanets are discovered is through the transit method where dips in light from stars are attributed to exoplanets moving in front of them. Even young stars have large discs of debris, known as protoplanetary discs, moving around them where planets and other bodies are forming around them. However, the motion of the star suggests it is no longer in its infancy, and should not be in possession of such a protoplanetary disc. Some have suggested an extraterrestrial race exisiting around KIC 8462852 are blocking the light through massive megastructures, such as a Dyson sphere. A Dyson sphere, named after its proponent theoretical physicist Freeman Dyson (1923-2020) is a large structure build around a star in order to capture its entire energy output. Such a civilisation would be a Type-II civilisation on the Kardashev scale, as it would be capable of harnessing all the energy radiated by its star. Such a construction would explain the unusual dimming and light fluctuations of Boyajian’s star, which have been recorded to be as much as 22 percent. Many natural hypotheses have been put forward to explain the dimming of KIC 8452852, however many of them have drawbacks. One such hypothesis is that two large planets in the system collided, creating a massive debris field which formed a new disc, resembling a protoplanetary disc. However, the odds that we would just be happened to be looking at the star at the time these planets collided (or at least when the light from the star at the time of the collision happened) are monumentally small. Planetary collisions do occur, but in astronomical time-scales are extremely short-lived, brief events. Another problem with this theory is that discs of this kind tend to absorb light from their star, and radiate it back out in the infrared, yet no infrared radiation was detected coming from the star that could be definitely attributed to such a disc, meaning that whatever material is causing the fluctuations it is more than likely cold. Another theory is that comets are to blame, and comets are very cold objects which would account for the lack of infrared radiation. It has been suggested that a passing red dwarf star, which does exist, disturbed the Oort cloud of Boyajian’s star and sent comets in towards it. Although this theory seems credible, we know from our own solar system that Oort cloud objects such as comets can be sent into the inner solar system during certain events, studies show that the dimming of KIC 8462852 has been occurring for well over a century. This means that the amount of comets needed would have to be extremely large, estimated at around 700,000 all passing in front of the star in a certain pattern. The comet theory, therefore, is possible but also unlikely. Whilst again an alien origin for this phenomena is unlikely, it remains on the table for Boyajian’s star as all natural theories are too uncertain to be the cause.

10. The Wow! Signal

Perhaps one of the most well known potential technosignatures is that of the Wow signal. Detected on August 15th 1977 by the Big Ear Radio Telescope in Ohio, USA. It was a narrowband radio signal, and bore all the hallmarks of what a radio transmission from an exocivilisation might look like. Coming from the constellation Sagittarius, the signal looked extremely artificial, so much so that it gains its name- the Wow! Signal- from the fact its discoverer Jerry Ehmen wrote ‘Wow!’ in the margin of the printout of the signal. The signal came at a frequency pretty much exactly what radio astronomers would expect an alien signal to come from. The electromagnetic spectrum is very noisy and busy, and countless objects in space emit radiowaves which could potentially interfere with artificial radiowaves. Too low in the spectrum there is far too much noise from astronomical objects to make broadcasting at this range useful, too high and a broadcaster would run into an issue called quantum noise which would make these higher frequencies useless. The electromagnetic spectrum has a window of around 1 to 10 gigahertz where it is more clear and useful. Moreover, planetary atmospheres block different areas of the spectrum, through absorption and reflection. Earth only has two areas of the spectrum where it is completely tranparent, namely visible light and curiously, between 1 and 10 gigahertz- meaning that any broadcast at these frequencies would appear to have been sent with Earth’s atmosphere in mind. However, such as signal would also have to be sent at a frequency the desired receiver is likely to be looking. There are several such frequencies which would make sense in this regard, predominently the 21cm hydrogen line- located at the frequency of 1.42GHz, which is the frequency at which neutral hydrogen emits radiowaves. Hydrogen is the most abundant element in the universe, meaning that wherever one points a radio telescope they are likely to pick up this frequency. The Wow! Signal was exactly on the hydrogen line and didn’t appear to be from terrestrial interference as the radio telescope which picked it up is stationary, so any deep space originating signal would last a period of 72 seconds, rising in intensity for 36 seconds then falling for 36 seconds. Interference from Earth would not do this, and the Wow! Signal did, meaning it most likely did originate in deep space. Moreover, the bandwidth of the signal was extremely narrow, further adding to the evidence that it was artificial in origin as natural emitters of radiowaves tend to emit at wider bandwidths. Whilst the signal was extremely promising in the search for extraterrestrial life, it has never repeated. It can be assumed that were it a deliberate attempt at communication, it would be repeated at least until a reply or acknowledgement was received. However, contrary to some reports, the signal did not contain any data or message and was merely a raw radio burst. This opens up the possibility that if indeed it is artificial, it may be some kind of navigational beacon or radar signal being used by an exocivilisaiton to map or assess the galaxy, or even more specifically our solar system. Although the Wow! Signal remains possibly the most promising sign of extraterrestrial intelligence we have detected, no real assumptions can be made, and any natural explanations ruled out until it repeats, if it ever does.

– @Lukewhostalking