planet Vulcan, if it really had existed, would probably
have been similar to Mercury (above) but quite a bit smaller.
Throughout the centuries astronomers have
searched for new planets, often without success. Is there a 10th
planet in our solar system still waiting to be found, or is looking
for it simply a wild goose chase?
On December 22, 1859, Urbain LeVerrier, of the Paris
Observatory, opened a letter from a man named Lescarbault. As
he read it, he felt a rush of excitement come over him. Lescarbault
was a country doctor and amateur astronomer. According to the
letter, on March 26th of that year, Lescarbault had observed a
round black spot moving across the face of the sun in an upward-slanting
path for one hour and a quarter.
LeVerrier put the letter down. If what the doctor
said was true, it might prove one of LeVerrier's predictions:
that there was an unknown planet in the solar system. A planet
that circled within the orbit of Mercury, which was then the closet
known planet to the sun.
This was not the first time LeVerrier had predicted
the existence of an unknown planet. In 1781 the German-British
astronomer William Heschel spotted a star that seemed to move
from night to night. He soon realized it was a new planet, the
first discovered since ancient times. The planet, which was located
beyond Saturn, was given the classical name Uranus. In
1846 LeVerrier had noticed irregularities in the movement of Uranus
and predicted that there must be another unknown planet beyond
Uranus causing the disruption. LeVerrier was able to predict the
location of the planet and it was then spotted in the sky by the
German astronomers Johann Galle and Heinrich d'Arrest.
planet Neptune might have been named LeVerrier
if one of the finders had had his way. (NASA)
LeVerrier, not one to avoid publicity, suggested
that Uranus be renamed for Heschel, the finder, and the new planet
be named for himself. Unfortunately for LeVerrier, a British mathematician
named John Couch Adams had actually predicted the location of
the planet almost a year earlier than LeVerrier. The two men wound
up sharing the credit (Adams would have gotten full credit for
the prediction except he couldn't convince any British astronomers
to take the time to turn their telescopes to look for it - see
sidebar) The planet, rather than being named LeVerrier,
was given the name of the Roman God Neptune.
LeVerrier badly wanted sole credit for discovering
a planet so he turned his eyes toward the other end of the solar
system. He noticed that the planet Mercury also had irregularities
in its orbit. This led LeVerrier to predict there would be found
a small planet closer to the sun than Mercury. The observation
by Lescarbault might be the proof of his prediction.
After finding a colleague to go with him as a witness,
LeVerrier set out immediately to the village of Orgeres where
Lescarbault resided. Without identifying himself, LeVerrier rudely
confronted the doctor, demanding to know how Lescarbault came
to the absurd conclusion that he had observed "an intra-Mercurial
planet." Lescarbault recounted the story in detail. LeVerrier,
now convinced of the doctor's tale, revealed who he was and congratulated
the somewhat bewildered physician. Returning to Paris, LeVerrier
saw to it that the doctor was awarded the Legion of Honor.
Costs the British a Planet
Couch Adams completed his calculations about the location
of Neptune in September of 1845 about nine months before
LeVerrier published his findings. He could have clearly
claimed to have been its sole discoverer if only he could
have convinced someone who owned a telescope to look for
was first brushed off by James Challis, director of the
Cambridge Observatory. Challis sent Adams to George Airy,
the Astronomer Royal at the Greenwich Observatory outside
of London. Despite a letter of introduction from Challis,
Airy refused to see Adams. Adams, son of a farmer and
unknown in astronomical circles, was not worth the time
to talk to, concluded Airy.
later sent a note to Adams saying the Greenwich Observatory's
was too busy to check his work. Airy did send Adams'
calculations onto the amateur astronomer Reverend William
Dawes, but Dawes was busy building an observatory. Dawses
passed them onto William Lassell, a London Brewer and
amateur astronomer, but Brewer was laid up with a badly
injured ankle and couldn't take advantage of them.
Airy saw LeVerrier's paper on Neptune he realized he had
made a serious mistake by ignoring Adams and did the only
sensible thing. He planned a long trip out of the country
so that he wouldn't be around when the English realized
that he had cost them the honor of being the first to
find the planet Neptune in the heavens.
The astronomical world was soon filled with excited
discussion about LeVerrier's new planet. He calculated the size
of the planet to be one-seventh that of Mercury. The new planet
he figured would transit the sun every April and October. LeVerrier,
deciding to avoid the controversy he had with Neptune, suggested
that the new planet should be named Vulcan.
Astronomers all over the world began to watch for
Vulcan during the period it should have been visible according
to LeVerrier's calculations. They were usually disappointed. With
the exception of some erroneous observations (which usually turned
out to be sunspots) Vulcan was never seen. By the end of the 19th
century most rational astronomers no longer believed in the planet
and in the early 20th century Einstein's General Theory of Relativity
explained how the curvature of space-time would cause the irregularity
of Mercury's orbit. With that, LeVerrier's planet Vulcan disappeared.
Shortly after the discovery of Neptune, astronomers
began to conjecture that there must be another planet farther
out. Neptune did not fully explain the disturbances in the orbit
of Uranus, and Neptune itself seemed to have an irregular orbit.
A number of mathematicians and astronomers tried to predict the
location of this planet and find it, but without success. Perhaps
the most persistent of these searchers was a man named Percival
Percival Lowell was born into a wealthy Boston family
in 1855. He built his own fortune, then took an interest in astronomy
after reading Camille Flammarion's book, La Plančte Mars,
in 1893. Mars would be coming into opposition (its closet approach)
with the Earth in 1894 and Lowell decided to fund an expedition
to Arizona for the purpose of observing it in the clear, dark
western skies. Lowell paid to build a private observatory which
was constructed near Flagstaff, Arizona.
Lowell was a brilliant man, but he often let his
imagination run wild. In 1877 the Italian astronomer Giovanni
Schiaparelli discovered what looked like a series of "channels"
across the face of Mars. This was improperly translated as "canals"
in English, a word which carried with it the suggestion of intelligent
design and construction. Lowell built upon this "canal"
theory and said he had observed changes along the surface of Mars
that seemed to relate to the growing seasons and perhaps farms.
In his own words:
Lowell thought he saw signs of intelligent life on Mars.
Speculation has been singularly fruitful as to
what these markings on our next to nearest neighbor in space may
mean. Each astronomer holds a different pet theory on the subject,
and pooh-poohs those of all the others. Nevertheless, the most
self-evident explanation from the markings themselves is probably
the true one; namely, that in them we are looking upon the result
of the work of some sort of intelligent beings. . .
Later observations by others showed no canals on
Mars and we now know there is no intelligent life on the planet.
It has never been clear what exactly Lowell, Schiaparelli and
others observed, but it may have been optical illusions introduced
by their telescopes.
In addition to his interest in Mars, Lowell was
also determined to discover the hypothetical planet past Neptune
and coined the term "Planet-X" to describe his quarry.
He conducted two searches for the planet, one ending in 1909 and
the other in 1915, without success. Lowell died in 1916 and his
failure to find Planet-X was the biggest disappointment of his
life. In 1929 an amateur astronomer, Clyde Tombaugh from Kansas,
was hired by the Lowell observatory to continue the search.
planet Pluto with its moon, Charon. (NASA)
Almost a year after he had started his work, Tombaugh
examined some photos he'd taken a few days apart in January of
1931. When Tombaugh compared the two, which were of the same section
of the sky, he noticed one of the "stars" had moved.
Since stars do not move relative to the rest of the stars in the
sky, the object must really have been an asteroid, comet, or new
planet. Further observations confirmed that the object appeared
to be a planet beyond Neptune. It was given the name Pluto.
Lowell's Planet-X had been found.
Or had it been? Predictions said that in order to
explain the kind of disturbances in the orbits of Neptune and
Uranus, Planet-X would have to be more than six times the mass
of Earth. Observations now show that Pluto, along with its tiny
moon Charon, have only about one four hundredths the mass of Earth.
Some scientists now argue that Pluto doesn't even deserve the
status of a planet, but instead should just be considered the
largest object in a swath of billions of comets called the Kuiper
Belt that surround the orbit of Neptune.
Tombaurgh continued his search for another Planet-X
for 13 years without success and decided that no tenth planet
was out there. "I observed seventy percent of the entire
sky and would have found it if it existed," he said.
Makes a Planet Anyway?
discovery of Eris, a body larger than Pluto, called into
question what should be considered a planet. If any body
that orbited the sun and was big enough to take a round
shape was considered a planet, there might be dozens more
like Eris soon to be discovered and added to the list.
On the other hand, if Eris and the others like it were
considered too small to be planets, then Pluto, which
had been on the list of planets for most of the 20th century,
should also be eliminated. In 2006 the International Astronomical
Union (which is incharge of naming such bodies) decided
to adopt a defination that put Eris, Pluto and any other
small round objects into a catogory called "Dwarf Planets."
Major planets now must be large enough not only to be
round under their own gravity, but be able to clear their
orbital path of other small objects. The decision, which
demoted Pluto and leaves our solar system with eight planets,
did not please everyone.
Some scientists agree, arguing that the perceived
irregularities in the orbits of Uranus and Neptune are the result
of observational errors made by early astronomers who didn't have
access to cameras and had to sketch the position of the planets
by hand. Other aren't so sure. Many astronomers seem to agree
that there is still a possibility that there are several Pluto-sized
planets moving in orbits around or beyond Neptune. Fewer think
that a planet about the size of Earth, or larger, may still be
hiding in the skies. Those that do think a large planet may be
out there think it may follow a highly-elliptical orbit that takes
it far past Pluto, or that it is currently located in the southern
sky in a very dense portion of the Milky Way where it would be
difficult to spot.
It there the possibility that there is a Jupiter-like
planet or something even larger in orbit around our Sun at a distance
many times that of Pluto?
Scientists had long noticed that every 26 million
years or so there seemed to be a mass extinction of life on earth.
In 1984, Daniel P. Whitmire and John J. Matese of the University
of Southern Louisiana developed a theory that this was caused
by a low mass companion star of the sun, which they called Nemesis
(after the Greek God of vengeance). According to their theory,
Nemesis (following an elliptical orbit) plows through a belt of
billions of comets called the Oort cloud every 26 million years
sending swarms of them sunward. Some of them hit the Earth, causing
It is not at all strange that the sun might be part
of a binary star system. Most stars seem to form in pairs. However,
in order for the existence of this second star not to be obvious
to us because of its light, it would have to be a very dim type
of star (called a red dwarf) or a dark type of star, known
as a brown dwarf. According to the theory it would also
be very far away, perhaps as far as 3 light years.
small scope at the Lowell Observatory used to discover Pluto.
(Copyright Lee Krystek, 2007)
Another possibility suggested by Whitmire is that
Nemesis is not a star at all, but a planet. Another Planet-X,
so to speak. If this were the case it might be about the size
of two to five earths and orbit the sun at perhaps three times
the distance of Pluto. In this version of the theory the planet
would pass through the Kuiper Belt of comets every 26 million
years, sending some of them earthward.
While some astronomers continue to search for Nemesis,
or the new Planet-X, most are skeptical of its existence, pointing
out that the 26 million extinction cycle may not be as regular
as was once thought.
There are certainly more worlds to find in space.
On November 28, 2000, astronomers discovered a new member of the
solar system in the Kuipter Belt. It was subsequently named Varuna.
Although Varuna was smaller than Pluto (it is only 550 miles wide
compared to Pluto's 1,440) and not considered a planet, it did
demonstrate that there may be other undiscovered objects at the
edge of our solar system. Then in January of 2005 astronomers
using the Palomar Observatory in California, found a body in space
orbit in the sun at a distance of 10 billion miles - 3 times farther
away than Pluto. The object, which was slightly larger than Pluto
and has a small moon, was been designated UB313 (Later given the
name Eris). It's finders originally called it the 10th
planet, but officially it has been designated a "Dwarf Planet"
along with Varuna and Pluto. Ironically finding a "10th planet"
didn't increase the number of planets at all, but caused the demotion
of poor Pluto so that now our solar system only officially has
Astronomers continue to search the skies for additional
members of the solar system, and there are hints that Eris is
not the only body out there. Even if we find no more major planets
in our solar system, however, there are still planets in the skies.
of a map of the Martian "canals" as drawn by Lowell.
In the fall of 1991 astronomer Alex Wolszczan of
Cornell University was studying a type of star called a pulsar
when he noticed something unusual. Some pulsars normally spin
at over a hundred rotations per second and each time they turn
send a strong radio "pulse" out into space. The spin
of such a pulsar never varies, making the bursts of radio incredibly
regular. Wolszczan was amazed to find that this particular pulsar,
designated PSR 1257+12, changed the timing of its pulses over
time. Sometimes the pulses came late, sometimes early. Wolszczan
realized that the only explanation was that the star was wobbling
due to the pull of the gravity of several planets in orbit around
Since then many more planets have been discovered
outside our solar system and there are probably billions more
to find. Although because of the huge distances involved astronomers
have to infer their existence by observing their effects on their
star rather than seeing them in a telescope, scientists are confident
they are there and have even been able to make some predictions
about their size and climate based their gravitational effects.
In the future NASA is hopeful the a super space based super-telescope
may be put into actions to that we can directly observe these
distant bodies and gain more information on what the are like.
One thing is sure, now that we are looking beyond
our own solar system, there will never be a shortage of "Planet-X's"
for astronomers to search for.
Copyright 2000-2007 Lee
Krystek. All Rights Reserved.