In the spring of 1806, two German astronomers were independently observing Venus
when they noticed something odd.
The hemisphere facing away from the Sun did not perfectly blend with the blackness of space.
Instead, it had a faint glow with a greyish red or ashen grey appearance.
This Ashen Light resembled a phenomenon known as Earthshine.
It's when sunlight, reflected by the Earth, faintly illuminates the nightside of the Moon.
It seemed reasonable, therefore, to ascribe the Ashen Light to a similar cause.
Namely, that sunlight reflected by a Venusian moon was faintly illuminating the nightside of Venus.
Only one slight problem, Venus doesn't have a moon.
This meant the Ashen Light resembled Earthshine in appearance only
because there was nothing in proximity of Venus to reflect any sunlight.
In the words of famed astronomer William Herschel:
"those regions that are turned from the sun cannot possibly shine by a borrowed light."
A few decades later, another German astronomer, Franz von Gruithuisen,
proposed a rather creative solution to this mystery.
The Ashen Light was the result of sweeping wildfires on the surface of Venus
deliberately ignited by its inhabitants.
As absurd as that sounds, there were tantalizing similarities between Venus and Earth.
The two planets were of similar size and, much like the Earth, Venus had an atmosphere.
A densely cloud-laden atmosphere which gave astronomers and science fiction authors alike
free rein to speculate about what could lie beneath.
A barren desert.
A planet-wide ocean.
A tropical rainforest.
Anything was possible.
It was in this context that Gruithuisen made his proposal in 1836.
He believed that Venus was inhabited by a humanoid species who would periodically light fires on the surface.
The purpose of which was either to clear land, to commemorate a religious occasion,
or to celebrate the coronation of a new Venusian emperor.
Gruithuisen did, perhaps, get a bit carried away,
but he was far from the first to suggest that Venus was inhabited.
Titans of astronomy like Christiaan Huygens and William Herschel
envisioned all the planets, including Venus, to be teeming with life.
And it took a long time for this romanticized image to fade.
In 1916, this illustration appeared in American newspapers with the caption:
"A Remarkable Drawing by Mr. Winsor McCay Illustrating the Conditions on Venus
as Astronomical Science Now Believes Them to Exist."
Even well into the space age, we still find echoes of this Earth-like perception.
In 1967, a Soviet spacecraft plunged into the clouds of Venus to attempt a landing on its surface.
While the probe did not survive the descent, it was actually designed to float
in case of a water landing.
History is ripe with stories much like this one.
Largely forgotten stories that, once upon a time, promised to end our cosmic solitude.
Bygone visions of life asunder, long since quelled by newfound wonder.
Venusian fire festivals were not the cause of the Ashen Light, but observations continued to be made.
By the end of the 19th century, some two dozen observations had been recorded.
But some astronomers would dedicate years to the study of Venus
without ever catching a glimpse of its elusive glow.
Instead, they would often be greeted by these vague streaks and patches.
They covered large portions of the planet and appeared to be features on the surface lurking beneath the clouds.
At least, that was the opinion of American astronomer Percival Lowell.
Far from the diffused shadings reported by his peers, Lowell could discern a distinctive network of branching spokes.
"It is as if a bright veil of some sort were drawn over the whole disk."
These spokes of Venus bore a striking resemblance to markings observed on both Mercury...
...and Mars.
The features on Mars were especially distinct and remarkably linear.
Lowell had been somewhat unimpressed by the spokes on Venus,
but he became nothing short of obsessed with the lineae on Mars.
"There are celestial sights more dazzling, spectacles that inspire more awe,
but to the thoughtful observer who is privileged to see them well
there is nothing in the sky so profoundly impressive as these canals of Mars."
Owing to their striking linearity, Lowell could reach but one conclusion.
The Martian Canals must be "the workings of an intelligence".
He carefully laid out his arguments in three lengthy books
filled with these intricate maps and illustrations.
The Martian Canals represented a vast irrigation network
designed to carry melted ice water from the poles down to the equator.
While many were understandably skeptical,
the idea that Mars could be inhabited was an extremely compelling one.
Perhaps, even more so than Venus.
Legendary science fiction author H. G. Wells famously wrote The War of the Worlds.
A fictional story about a Martian invasion of Earth, first published in 1897.
But a decade later, Wells published a speculative nonfiction article titled The Things that Live on Mars.
Inspired by Lowell's fanciful interpretations, Wells goes on to envision the habitat...
...society...
...and appearance of real Martians.
To Wells and many others, the existence of Martians was not just possible, it was probable.
Indeed, to some, it had already attained a veneer of truth.
In 1891, the French Academy of Sciences was bequeathed a sum of 100 000 francs by a wealthy Parisian widow.
The money was to be awarded
to the first person who found the means of communicating with another planet.
With the notable exception of Mars.
Implying that communicating with Martians would have been far too simple of a challenge.
The reality of the Martian Canals was difficult to ascertain as they resided at the very limits of perception.
Telescopes were never quite good enough to conclusively prove nor disprove their existence.
A book commissioned by NASA as late as 1965 stated that:
"Although there is no unanimous opinion concerning the existence of the canals,
most astronomers would probably agree that there are apparently linear markings [on Mars]."
Indeed maps of the Red Planet published by the US military that very same year
featured sprawling networks of canals.
"A towering Atlas Agena rocket is the launch vehicle that hurtles the Mariner into the heavens."
"Scientific apparatus on the Mariner will try to measure the density of the planet's atmosphere."
"And a television camera will seek to make photographs of its surface."
"Giving man his first close-up look at Mars."
The American spacecraft Mariner IV
transmitted the first close-up photographs of the Martian surface in the summer of 1965.
Despite the complete absence of any linear markings, scientists at NASA were unwilling to give up hope.
"...nothing positive concerning the existence or lack of canals
can be concluded on the basis of the Mariner IV photographs."
Hesitation and dwindling hopes aside, the Martian Canals had come to an end.
"The canals, the cities, the Martians are all gone."
"Imaginative inventions."
"Optical illusions."
As early as 1903, had an experiment found that groups of students,
seated a few meters away from an illustration like this one,
could discern fine straight lines where none existed.
The experiment demonstrated that non-linear markings viewed from a distance
could evoke a linear appearance.
This sort of "visual inference" is even said to be apparent in certain photographs.
I mean, look at this. Not only is there a clear correlation between this sketch and this photograph of Mars,
but you can almost see these barely perceptible lines snaking across the plains.
The spokes on Venus, meanwhile, bear a curious resemblance to the inside of an eye.
It appears that Lowell constrained the aperture of his telescope to such an extreme
that the blood vessels inside his eye began to cast shadows.
Some of which might have fallen onto Lowell's retina,
creating the illusion of labyrinthine markings on distant worlds.
"It is as if a bright veil of some sort were drawn over the whole disk."
Whether it was optical illusions, indistinct shadings on the planets,
turbulence in the atmosphere, technological limitations,
or an untempered willingness to believe, these networks of lines were merely figments of the mind.
There is something incredibly tragic about these old misconceptions.
I mean, there was a time, not so long ago, when life beyond meant life right next door.
There is still hope of finding less complex forms of life on a select few planets and moons, which is very exciting,
but also a far cry from a tropical Venus or an ecumenopolis on Mars.
As our knowledge of the universe continues to expand, so, too, must our search for cosmic neighbors.
By the mid 20th century, the Ashen Light had been observed by not dozens but hundreds of observers.
Many of whom were as experienced as they were adamant of the phenomenon's existence.
Despite this preponderance of eyewitness accounts,
the lack of empirical evidence attracted a fair amount of skepticism.
In fact, doubts have plagued this phenomenon since the very beginning.
Italian astronomer Giovanni Riccioli is often recognized as the person who discovered the Ashen Light.
In early 1643, Riccioli witnessed a band of colors enveloping the disc of Venus.
The nightside was tinted greenish-blue, enclosed by a semi-circle of light.
Riccioli ascribed the vivid colors to light being refracted inside his telescope.
An effect known as chromatic aberration.
In other words, Riccioli thought the faint glow on Venus was an optical illusion.
Okay, so, a quick aside. I managed to find an observation that, to my knowledge,
has gone completely unnoticed and actually predates the one made by Riccioli.
A German priest and scholar named Athanasius Kircher wrote in 1660 that he, too, had observed a band of colors on Venus.
No date was given, but Kircher did provide a location. Palermo, Sicily.
Based on historical records, Kircher paid his last and only visit to Palermo in the spring of 1638.
So Kircher observed the Ashen Light five years before Riccioli and should thus be credited with its discovery.
Okay, back to the video.
Riccioli's doubts about the Ashen Light echoed through the centuries, and by the 1900s,
it was not uncommon for sightings to be dismissed as a mere trick of the eye.
Not only were observations infrequent and unpredictable, but they were often inconsistent.
Brightness, color, and the extent to which the nightside was illuminated
could vary drastically between accounts.
With no hard proof of its existence and a lack of concordance between those who had seen it,
the Ashen Light appeared destined to join the ranks of myth and misconception.
But, in 1975, the Soviet spacecraft Venera 9 became the first to successfully orbit Venus.
Diving into the shadow of this faded twin, it detected faint flashes of light
emanating from the clouds below.
Venus and Mars have historically been the two prime candidates for cosmic neighbors.
But the other planets have not gone completely ignored.
Scottish astronomer James Ferguson had few reservations about life in the Solar System.
When it came to Mercury, for instance, Ferguson thought that Mercurians
simply possessed greater resilience to heat.
"It is very likely that the people [on Mercury] have the same opinion of us
[as] we have of the inhabitants of Jupiter and Saturn; namely, that we must be intolerably cold,
and have very little light at so great a distance from the Sun."
Inspired by Ferguson's optimism, William Herschel took it a step further.
In 1795, Herschel confidently announced that the inside of the Sun was home to an alien civilization.
This might seem incredibly bizarre, but, at the time, it was not uncommon to view the Sun
as an enormous planet encased by a luminous atmosphere.
Herschel expanded upon that idea by regarding sunspots as openings in this flaming shell
that momentarily exposed the true surface underneath.
This concealed surface was "richly stored with inhabitants"
who were shielded against the immense heat by intermediate layers of clouds.
"...we have great reason to look upon the sun as a most magnificent habitable globe..."
Apart from the planets and the Sun, another bygone candidate for intelligent life is the Moon.
Using stunning contraptions of tubes, wires, and lenses, pioneering selenographer Johannes Hevelius
produced some of the earliest detailed maps of the lunar surface.
Whereas you and I see a barren landscape devoid of life,
Hevelius espied upon the Moon a near-perfect copy of Earth.
Mountains and valleys, rivers and lakes, swamplands and woodlands, islands and capes.
This vivid interpretation can be traced to an ancient belief that
bright and dark patches delineate continents from oceans.
In fact, this fallacy is still reflected in the nomenclature we use today.
Dark plains on the Moon all have aquatic names such as the Ocean of Storms...
...the Lake of Dreams...
...and the Sea of Tranquility.
"Tranquility Base here, the Eagle has landed."
Though water never filled these gloomy basins, it's not entirely inaccurate to call them ancient seabeds,
for they are the volcanic scars left behind by vast oceans of molten rock.
Making the Lake of Death an especially apt name.
While Hevelius never observed any creatures on the Moon,
its subjective resemblance to the Earth convinced him that Lunarians must exist.
A conviction still being upheld more than a century later by, who else, if not William Herschel.
"I hope, and am convinced, that some time or other
very evident signs of life will be discovered on the moon."
It didn't take long for these very evident signs to make themselves apparent.
"...I am almost convinced that those numberless small Circuses we see on the Moon
are the works of the Lunarians and may be called their Towns."
Herschel nearly convinced himself that the cratered landscape of the Moon
had been engineered by its inhabitants.
Craters, or "circuses", were not the remnants of violent impact events
but skilfully constructed towns and cities.
While Herschel obsessed over circular dwellings, astronomers like Franz von Gruithuisen
espied habitats of all shapes and sizes.
"[This] star-like structure [...] appears to be a kind of temple,
and, because of its star-shape, perhaps it is dedicated in service to the stars."
"The circle in the south, the two highest mountains in the north [...],
and the two hills in the south-west are natural objects."
"[But] it is highly probable that [these embankments]
serve as the dwellings of sentient beings on the Moon."
In reality, Gruithuisen mistook some oddly shaped terrain for intelligent design.
The increasingly speculative nature of these extraordinary claims
culminated in a truly in-credible sighting by John Herschel, the son of William Herschel.
"...whilst gazing upon [a rock formation on the Moon]
we were thrilled with astonishment to perceive four successive flocks of large winged creatures..."
"They were like human beings..."
"...their wings possessed great expansion, and were similar in structure to those of the bat..."
The Moon was evidently home to a species of walking and flying "man-bats".
This was a truly profound, if not bemusing, discovery. Not just for the world but also for John Herschel.
Because, upon being inquired about his remarkable find, John responded with confusion.
He had had no knowledge of any "man-bats" on the Moon.
It turns out the story had been fabricated by an American journalist named Richard Locke.
Locke had sought to lampoon the often frivolous debate about life on other worlds
perpetuated by the likes of William Herschel and Franz von Gruithuisen.
Instead, the Great Moon Hoax of 1835 convinced thousands around the world
that the Moon was inhabited by bat-like humanoids, unicorned bison, bipedal beavers,
as well as, well, storks and goats.
There's also this image of a man-bat besat aflat upon the back of a fellow man-bat,
helivaced by a pack of man-bats.
As to why this guy is copping a whiff, history has declined to answer.
As time went on and telescopes improved,
it became increasingly difficult to argue in favor of the Moon's habitability.
With no apparent atmosphere, this dry and barren wasteland seemed an improbable abode for life as we know it.
But, by the mid 19th century, the life debate had been resurrected
by a new hypothesis about the shape of the Moon.
The argument was that gravitational forces had stretched the Moon into the shape of an egg.
This uneven distribution of mass meant that any atmosphere or fluids
would have coalesced on whichever side was closer to the center of gravity.
If that happened to be the farside of the Moon, an argument could be made for its habitability.
As one author put it:
"...though the near hemisphere is a lifeless desert, having neither water nor air to sustain life,
the hidden hemisphere may have a teeming population..."
Among the proponents of this radical hypothesis was none other than John Herschel.
"[An egg-shape] would fully account for the total absence both of air and of water
on the side of the moon turned towards us,
and would be quite compatible with the abundant existence of both,
and of a habitable hemisphere, on the opposite side..."
Had history played out differently,
perhaps we'd be dealing with egg-mooners instead of flat-earthers at this point.
No, but that's lunacy. Okay.
While skeptics made quick work of the egg-shaped Moon hypothesis,
farside inhabitants could not be so easily dismissed.
After all, the farside of the Moon is unseeable from Earth and thus ripe for speculation.
"So, then I subjected them to a spectrographic analysis. It's dust. A great amount of radioactive dust."
"Larry, what you're saying is that, somehow, for some reason,
the Moon has been encircled by a ring of highly radioactive dust?"
"Something's going on on the other side of the Moon. The invisible side."
"Something that we oughta know about."
By placing aliens on the farside of the Moon,
early science fiction authors were able to skirt the line of plausibility.
If aliens wanted to conceal their presence and, perhaps, observe humanity from a distance,
this cosmic blindspot was the perfect hiding place.
At least, that was the opinion of famed American astronomer Carl Sagan.
"It is not out of the question that artifacts [...] or even some kind of base is maintained within the solar system..."
"Because of weathering and the possibility of detection...
it might have appeared preferable not to erect such a base on [Earth]."
"The Moon seems one reasonable alternative site for a base."
Humanity got its first glimpse of the farside of the Moon in late 1959
when the Soviet spacecraft Luna 3 relayed these images back to mission control.
Subsequent missions improved upon the quality but, alas, revealed nothing but more Moon.
But this idea of concealment lingers to this day.
Many are still holding out hope that, somewhere in the Solar System,
the ruins or technology of some unknown intelligence lie waiting to be found.
In 1988, the Soviet Union launched a probe known as Phobos II.
As the name implies, part of its mission was to investigate the Martian moon Phobos.
The probe arrived at Phobos without any major complications and, in late March of 1989,
began preparations to plant two instruments on its surface.
But then, contact with Phobos II was lost.
In the weeks and months that followed, rumors began to circulate.
Puzzling features and shadows were said to be visible on some of the final images transmitted by Phobos II.
The nature and origin of which supposedly defied explanation.
Through various articles, conferences, and television programs,
these images were gradually unveiled to the public.
They appeared to depict an unidentified craft in orbit round Mars.
It was said to be an alien spaceship that had attacked and disabled Phobos II.
Not only that, but it cast an enormous elliptical shadow upon the surface of Mars.
But this shadow appeared quite suddenly and we didn't immediately understand what it was,
and probably didn't pay enough attention to it.
Because then it continues again as a strip.
So it's not an object hanging above the surface but a shadow on the surface of the planet?
Probably, probably.
Because, well, it doesn't completely cover, so to speak, the signal from the surface of Mars.
It looks like...
...a rocket taking off from the surface of Mars with a contrail following it.
How do you feel about this?
Well, if you let your imagination run wild, then, of course, you can believe these kinds of explanations.
But we tend to believe completely real...
...although still unexplained circumstances that created such a trace.
Most likely, it's still a shadow from some object on the surface,
because surface elements are visible through the shadow.
The mystery persisted for about a decade or two
until the raw data from the Phobos II mission became readily accessible.
The unidentified craft looked an awful lot like an overexposed transmission artifact.
In fact, all the infrared images featured the same white streak.
Meanwhile, the elliptical shadow belonged to Phobos.
Its elongated shape was due to multiple scans or photographs being taken in sequence
before assembling the final image.
Stories like the Phobos Incident have become rather par for the course.
Some initial event or discovery leaves an information vacuum which is immediately filled by fantastical speculation.
A printing artifact becomes a tower on the Moon.
The happenstance of light and shadow begets a human face on Mars.
And these prominent boulders on both Mars and Phobos conjure images of a certain Stanley Kubrick film.
More recently, a Chinese rover on the Moon captured this image of what some described as a hut.
Upon closer inspection, everyone was absolutely gobsmacked when the hut was exposed as a rock.
Whether you're an amateur or professional, have no experience or decades worth,
you're never quite immune to this kind of self-deception.
When you want something to be true, it can be deceptively easy to convince yourself that it is.
Remember that prize money? The 100 000 francs offered to anyone
who discovered a means of communicating with another planet, excluding Mars.
Well, in 1937, there was a claim on that prize.
The claimant was none other than world-renowned inventor Nikola Tesla.
In 1899, Tesla had been experimenting with wireless radio communication.
During some of those experiments, he picked up some rather odd transmissions.
"Although I could not decipher their meaning [...] the feeling is constantly growing on me
that I [have] been the first to hear the greeting of one planet to another."
"A purpose was behind these electrical signals..."
Tesla described the signals as a repeating sequence of either three or four pulses.
Decades later, Tesla was still convinced that he'd received an interplanetary message
and had even deduced its origin.
"...the signals consisted in a regular repetition of numbers,
and subsequent study convinced me that they must have emanated from Mars..."
"I believe the Martians used numbers for communication because numbers are universal."
Then, in 1937, Tesla announced his plans to unveil a new technology
capable of not just interplanetary but interstellar communication.
With such impressive technology at hand, Tesla felt confident that he'd soon be awarded the 100 000 francs.
"[I intend to] claim the Pierre Guzman prize..."
"I am just as sure the prize will be awarded to me as if I already had it in my pocket."
"They have got to do it."
They didn't do it.
The prize was, instead, awarded to the crew of Apollo 11 in 1969.
As for the alleged message from Mars, well, we don't really know.
While Earth was much quieter back in 1899, it was still far from radio silent.
Who knows? Perhaps it was nothing but the rumbling noise of a distant thunderstorm.
Upon sailing into the shadow of Venus in 1975, Venera 9 detected faint flashes of light.
The emissions were broadly consistent with lightning, but it's a matter of interpretation.
Data gathered by subsequent missions are likewise consistent with Venusian thunderstorms
yet fall short of any conclusive evidence.
Presuming that lighting does occur on Venus, could it explain the Ashen light?
Well, it's been estimated that the nightside of Venus
would need to maintain a rate of some 1 000 lightning strikes per second
to yield a glow that's visible from Earth.
That's more than 20 times the mean rate on Earth and would likely have been observed a long time ago.
In the blunt words of another paper:
"...lightning is not acceptable as an explanation for [the] ashen light."
But in certain parts of the world there is another striking phenomenon illuminating the night sky.
These vibrant curtains of light are the result of charged particles ejected by the Sun
colliding with the Earth's magnetic field.
Could something akin to the Northern Lights be responsible for the Ashen Light?
Aurorae have indeed been observed on planets like Jupiter and Saturn so
it might seem like an obvious solution.
What makes it not so obvious is that the magnetic field around Venus is virtually nonexistent.
It is extremely weak and transient and is generated by a completely different process than here on Earth.
In spite of this, when caught in the path of a solar storm, Venus has, in recent years,
been observed to glow.
The underlying mechanism of this glow is still poorly understood, but there is an apparent link
between solar activity and diffused emissions of light on the nightside of Venus.
Not only that but there is a weak correlation between solar activity and Ashen Light observations.
According to author John Barentine, who's written the definitive book on the subject:
"The data are inconclusive [but] there are hints in this figure that something is indeed up."
"The apparent spike in the number of Ashen Light sightings in the 1950s
correlates with one of the strongest solar maxima of the past 250 years."
While all of this sounds quite promising, it's a bit too early to celebrate.
Nothing conclusive has been found and, despite many attempts to do so,
the Ashen Light has never been recorded on camera.
Until that happens, this nearly 400 year old mystery remains in limbo.
Should it be ascribed to the atmosphere of Venus or the mind of the observer?
Perhaps we should have listened to Giovanni Riccioli from the very beginning?
Perhaps it is nothing more than a convincing illusion?
The search for cosmic neighbors continues.
Many scientists now believe that both Venus and Mars used to resemble Earth in the distant past.
Perhaps a relict biosphere or the remnants of a once teeming population
can still be found in Venusian clouds or Martian soil.
There's mounting evidence that the Jovian moons Europa, Ganymede, and Callisto,
along with Enceladus and Titan of Saturn, all host a vast subglacial ocean.
Could resilient microbes or even larger organisms have found a way to thrive beneath the frozen crusts?
Who knows, an apparent hut on the Moon or a monolith on Mars
might, one day, match our most outlandish expectations.
Even if Earth should prove the sole harbor of life within the Solar System,
every dot in the night sky has the potential to host another.
And with the launch of the James Webb Telescope, there's no telling what secrets are about to be unveiled.
Always remember that, if, at first, you don't understand, it's definitely aliens.