Thanks to MOVA globes for sponsoring today’s video.
It is something hardwired into humans to want to be remembered. For thousands of years of
mankind’s history, people have erected monuments to themselves and performed great deeds, all to
endure after they’d passed on. It’s no wonder some people might want to be the one who made a great
scientific discovery – like discovering a special star, or a planet – so they’ll be remembered for
all time. However, being over-zealous could lead to being remembered for all the wrong reasons.
I’m Alex McColgan, and you’re watching Astrum. And in today’s video, we’re going to be looking at the
fascinating discovery of a planet in our Solar system closer to the Sun than Mercury. It was
observed dozens of times by various astronomers. The only problem? It doesn’t actually exist.
Let’s rewind to the year 1846, when something astounding had just happened in the scientific
community. Urbain-Jean-Joseph Le Verrier, a French astronomer and mathematician, had just
helped discover the planet Neptune using nothing but pure mathematics. He had been examining the
rotation of the (then) 7 planets, when he noticed that something was off about Uranus.
It didn’t seem to be moving in line with the theories of gravity proposed by Newtonian physics.
Le Verrier reasoned that the only explanation for this was that there must be a planet out beyond
the orbit of Uranus that was perturbing its motion to account for this discrepancy. He did
some maths, and then declared that his 8th planet must exist at an exact point in the night sky.
The incredible thing was, after hearing his prediction, Le Verrier’s friend Johann Gottfried
Galle got out a telescope, searched in that location, and sure enough discovered the planet
Neptune in a single hour. It was almost exactly where Le Verrier had predicted that it would be.
The scientific community went wild with this discovery, and Le Verrier was rightly celebrated
for his incredible deductions. So it’s not surprising that a decade later, when he predicted
the location of a 9th planet using the same methodology, the scientific community listened.
In fairness, he had not been the first to predict that such a planet existed. It
was as far back as 1601 that German astronomer Christoph Scheiner had claimed to have noticed
a strange black spot moving in front of the Sun, and had claimed that this was a planet
(in reality, it was most probably a Sunspot).
Other alleged sightings had happened throughout the years. Capel Lofft in 1818, Franz von
Gruithuisen in 1819, J.W. Pastorff between 1822 and 1837 all claimed to have seen an object or
objects orbiting around the Sun. Pastorff claimed to have seen it at least 12 different times!
People had even begun to spitball a name for this hypothetical planet. In 1846 French
astronomer Jacques Babinet suggested calling it Vulcan, after the Roman god of volcanoes,
fire and metalwork. This would have been an appropriate name, as any planet closer to the Sun
than Mercury would have been exceptionally hot. Mercury already experienced temperatures of 427°C.
Vulcan would have been even hotter. And yet, for all these sightings, confirmation of the planet
remained elusive. But what made Le Verrier’s claim stand out was the way he had come to make it.
In 1845, before his discovery of Neptune, Le Verrier had been asked by the director of the
Paris Observatory to apply Newton’s laws of physics to the orbit of the planet Mercury,
to see if the two lined up. Le Verrier did so, laying out a theoretical orbit
that Mercury would take around the Sun based on Newtonian physics. Once his prediction was made,
astronomers observed Mercury to see how well it matched up… only it did not.
Le Verrier tried again. Reasoning that it was possible his maths had been out, he did a much
more thorough study in 1859, using multiple observed sightings of Mercury as his baseline,
he once again mapped out Mercury’s orbit. But once again, his predictions were out. Not by much –
only 45 arcseconds per century – but enough that there was conclusively something weird going on.
Confident of his maths this time, Le Verrier reached the conclusion that there must be
some mass pulling Mercury out from the idealised orbit – either a planet, or a series of asteroids.
Given his success by now at locating Neptune, many astronomers believed him. Scientists rushed to
telescopes to try and spot the alleged planet. And it wasn’t long before results began to come in.
Spotting a planet so close to the Sun was inherently difficult. The glare of the Sun would
completely obliterate the reflected shine of a tiny planet. As such, the most effective method of
spotting such an object was to see the darkening it caused as it travelled across the Sun.
And in 1859, Edmond Modeste Lescarbault claimed to have seen just that.
Lescarbault was a French amateur astronomer and physician who, using basic tools in a homemade
observatory, claimed to have spotted a small black object passing by the Sun on the 22nd of December.
He wrote to Le Verrier, who was so taken by his claim that he travelled by train
to visit the man’s home, unannounced, to verify it. He questioned Lescarbault,
heard his observations, and came to the conclusion that the man was telling the truth.
So, the two of them announced to the scientific community Lescarbault’s discovery. They named the
planet Vulcan. The scientific community was once again very impressed. Lescarbault was
given the Légion D’honneur, the highest order of merit in France. He got to speak at meetings of
learned scholars. There was only one problem… The planet he had discovered didn’t actually exist.
There were numerous proofs of this. For one, naturally, other scientists wanted to take a look
at this new planet Vulcan. Le Verrier calculated from Lescarbault’s observations that Vulcan must
orbit 21 million km out from the Sun, and did so once every 19 days and 17 hours. So, it would be
easy to spot, as it would be calculable when it would pass the Sun again next. Astronomers
pointed their telescopes towards the Sun at the appointed time… But Vulcan was a no-show.
Le Verrier was troubled by this, but by then more reports were coming in of the planet’s sighting.
Other astronomers were going back through their records and were matching up phenomena they had
seen with the new planet Vulcan. Some of these were years out of date and not even listed as
to when in the year they had happened, but Le Verrier still used these to tinker with his model,
reasoning that perhaps his maths were just out. So he would predict,
and would not see Vulcan, and would rework his theory, and would not see it again.
Another piece of damning proof came from Emmanuel Liais, another French astronomer. Liais claimed
that he had been coincidentally looking at the Sun at the exact same moment Lescaurbault had, with
a twice as powerful telescope, and had not seen the planet Lescaurbault claimed to have observed.
Vulcan’s existence floated through murky waters as there were renowned scientists who did claim
to see it from time to time. Le Verrier died in 1877, but just a year later in 1878,
two well-renowned astronomers both claimed to see Vulcan at the same point in the sky at the
same time during a solar eclipse. They even both claimed that the planet was a reddish colour. The
corroboration was compelling… Yet Vulcan still did not exist. In science, if a fact is true,
then it is repeatable. And in spite of all of these observations throughout the years,
Vulcan was never repeatably observed. It was never seen during a solar eclipse again – in time, that
corroborated sighting was put down to calculation errors, and misidentifying a known star.
But ultimately, the one who finally put the idea of Vulcan to rest was Albert Einstein,
and he did so by thinking of something completely different. Numerous scientists over the years had
attempted to see Le Verrier’s planet Vulcan, because mathematically, they were certain it
had to exist. Newtonian physics demanded that it did. They strained to see it,
and in that confirmation bias they did see it, again and again… just never in the same place.
But Einstein realised that it was Newtonian physics that was at fault. In 1915,
he proposed a model of physics that accurately described the motion of the universe but relied
on things like the curvature of spacetime, rather than gravity. At slow speeds it looked
a lot like Newtonian physics. But when you placed objects like Mercury next to very massive objects
like the Sun, Special relativity predicted a different path for their orbits. And sure enough,
Einstein’s model predicted the exact orbit that Mercury made around the Sun, deviations and all.
And with that, the case for Vulcan’s existence evaporated. Under Special Relativity,
it couldn’t exist. There could be no object next to the Sun of a planetary size, or it
would mess with Mercury’s orbit so that it would no longer line up with the maths. And this time,
Einstein was able to prove his maths correct, through tests like the Eddington experiment. There
is a lesson in this, somewhere. Sometimes, if we want to see something too much, we find it
regardless of whether it is really there or not. Sometimes it takes thinking outside the
box and challenging our previously held beliefs before the truth can be found. As scientists,
and equally as laypeople, it’s important that we do not hold on too tightly to our ideas. The truth
does not need our fervour. It will prove itself, given time and opportunities for repetition.
So there you have it. The planet Vulcan; a planet of fire that was nothing but smoke and mirrors,
a yearning for something, but never a reality. Newtonian physics were replaced
by Einstein’s theories of relativity. And now, Special relativity is here
to stay. At least until it is supplanted by something even more comprehensive too.
As a youtube creator, I’m never likely going to discover a planet. I probably won’t travel
to outer space any time soon, or visit far-away places like Mars, or Jupiter. But that doesn’t
stop the planets from coming to me. On my desk spins a captivating globe of Jupiter. It
has no wires or messy cables. Its rotation is cleverly powered by the room’s ambient light,
and incredibly by taking advantage of the Earth’s own magnetic fields. It’s there
because of the sponsor of today’s video, MOVA globes. I find these replicas of the planets of
our solar system stunning. The elegant way they rotate is fascinating. Some of their 40 designs
are made using hundreds of real-life photographs taken by NASA, while others are classical artwork
or planetary designs. They’re a fantastic gift for someone who loves space. By using my promo
code “ASTRUM” when you go to buy, you can get 10% off your purchase of any 6” or 8.5” MOVA
globes available. Use my link in the description below to check it out. I heartily recommend it!
Thanks for watching. Want to know about another hypothetical planet in our solar
system that hasn’t been disproven? Check out this video for Planet 9. A big thanks to my
patrons and members for your support too, your help goes a long way. If you want to have your
name added to this list, check the links below. All the best and see you next time.