The Ephemeral Search for The Real Planet 9

By The Metric Maven

This last Summer I visited Lowell Observatory in Flagstaff Arizona. I saw the telescope where Percival Lowell (1855-1916) convinced himself he saw canals on Mars. In science one can easily fall in love with a hypothesis and begin to see what you expect to see. After the Martian canals had been vanquished, and Perceval Lowell had passed away, a young Astronomer by the name of Clyde Tombaugh (1906-1997) took up his search for a ninth planet. Tombaugh painstakingly photographed the night sky and miraculously discovered a new planet (expected to be at least Earth-sized) in the expected area of the sky predicted in February of 1930. The amazing part, is how lucky Tombaugh had been. Pluto has a 17 degree tilt upward from the ecliptic, which means its not in the plane of the other planets—where one would expect to find it. Pluto was in a location where it was very close to the ecliptic—a rare occurrence. With an orbital period of 280 years, if Pluto had been in its farthest part of its orbit, Tombaugh would have gazed into empty space. In many ways he won a cosmic lottery ticket. The new planet  became known as Pluto and as PL is also the initials of Percival Lowell, it was greeted with open arms at Lowell Observatory. All was fine until a team, lead by Mike Brown (1965- ) at Cal Tech, located Eris which is much farther out from the Sun than Pluto, and appeared to be larger than Pluto, was, for a while, considered Planet 10, with Pluto still designated as Planet 9.

Better measurements slowly reduced the mass, size and mathematical need for Pluto to provide an explanation of the now nonexistent gravitational perturbations. As we all know now, Pluto is at best considered a dwarf planet in the Kuiper Belt. After Pluto’s change in categorization, it stopped being the last planet discovered, and became the first Kuiper Belt object discovered. Planet 9 then vanished in an organizational puff of smoke. The description of our solar system from the Sun to the hypothetical Ort Cloud looked quite fixed at that point. In 2010, astronomer Mike Brown wrote a book titled How I killed Pluto and Why It Had It Coming. He had been at the forefront of Pluto’s nomenclatureral demise. Then in January of 2016, he and Konstantin Batygin (1986- ),  would ironically propose the existence of a new planet, based on orbital perturbations,  the same type of evidence that began the search for Pluto by Tombaugh.

The new non-Pluto Planet 9 begins its theoretical existence with a large mass of 60 000 Yottagrams, and an orbital distance that varies from 30 000 Gigameters to 180 000 Gigameters. It has a semi-major axis of about 105 000 Gigameters. Gigameter is the natural  metric unit for describing the distances of planets in a solar system. Planet 9 is estimated to take about 10 000 to 20 000 years for a single orbit around the sun. Uranus, at 87 000 Yottagrams, is slightly more massive than the hypothetical Planet 9.

In June of 2017, Kat Volk, and Renu Malhotra, both from the University of Arizona, announced that computations they undertook indicate that a 10th planet exists. They estimate it is about 9000 Gigameters from the Sun and possesses a mass about that of Mars. Again, unexpected gravitational perturbations led researchers to suspect the existence of another planet, other than Planet 9.

In order to compare the two newly hypothesized planets, with our existing list of Planets, Kuiper Belt objects, and human created spacecraft; I have updated a table given in my essay Long Distance Voyager (about metric distances and the universe) which is presented below:

The first change I noticed is that if Planet 9 exists, Voyager 1 and Voyager 2 would no longer be “outside our solar system.” So are the Voyager Spacecraft still in interstellar space, or do we redefine them as inside our solar system? Categorization can be a difficult objective for astronomy, but where the Voyager spacecraft are, will probably not stir up the controversy that Pluto did when Eris was discovered. Eris is appropriately named for the Greek goddess of Strife and discord. The other categorization problem is that Planet 10 is well inside the orbit of Planet 9, so one would think they should swap numbers so Planet 10 is the furthest out and Planet 9 the next planet toward the Sun. Planet 10 also finds itself outside of the Kuiper Belt, and is probably a Trans-Neptunian planet, although how meaningful this designation would be remains to be seen. Planet 10 is between Pluto and Eris, and Planet 9 is the farthest hypothetical planet out by about an order of magnitude compared to Planet 10.

In many cases, astronomical masses outstrip the metric system, and one must resort to scientific notation, but in the case of our solar system, it might be useful to express the values using a large metric prefix. We will use Yottagrams, as that is the last magnifying metric prefix. Below is a table of Planetary Mass for selected objects in our solar system.

It is clear that Jupiter dominates the mass total of our solar system. One can estimate immediately that Jupiter is somewhere on the order of three times the mass of
the next most massive planet Saturn. Mercury, the smallest planet, is well over an order of magnitude more massive than Pluto or Eris. Pluto and Eris are an order of magnitude larger than Ceres the largest asteroid in the Asteroid Belt. It is clear that Jupiter, Saturn, Uranus, and Neptune form a Gas Giant mass class that is separate, and dominates all the other planets. The new Planet 9, should it exist, would be the runt member of this fraternity–unless it is not a Gas Giant, we then might need to implement a new designation from boxing and call them the Heavymass planets. The new Planet 10 would currently be grouped with the current Rocky planets, but from a distance perspective it would be the only member of this designation outside of the classical distance grouping of the inner and outer planets that are bounded on either side by the Asteroid Belt. Perhaps the less massive rocky planets could be called the Lightmass rocky planets, unless Planet 10 is gaseous? Whatever the Astronomical Union decides, the metric system is there for them, whether they use it, or not.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page.

Related Essays:

Long Distance Voyager

The Expanding Universe


The Metric Maven has published a book titled The Dimensions of The Cosmos. It examines the basic quantities of the world from yocto to Yotta with a mixture of scientific anecdotes and may be purchased here.


Old Days

Wikimedia Commons

By The Metric Maven

I read a “fun fact” recently, that stated because metal expands when heated, the Eiffel Tower is actually 150-170 mm taller in the Summer than in the Winter. This fact reminded me of an old physics textbook, New Practical Physics by Black and Davis (1929 edition) that I’ve had for sometime but never really inspected. The section at the front on the metric system has an interesting graphic:

The authors of the book show a comparison of English and metric, with inches divided into tenths. This is interesting, because the general usage in the US (even in
High School or College physics classes) employs a common yardstick where inches are divided into fractions. It is very interesting that the textbook authors note both centimeters and millimeters are on the metric rule in their illustration. They seem to be falsely equate inches and tenths with centimeters and millimeters to provide a non-existent continuity between metric and Ye Olde English. Centimeters are the only labeled graduations, and it seems they do not contemplate using millimeters alone as an option. As I’ve said in the past, centimeters are so identified with inches in the US they are the default small metric unit, and a poor choice.

Black and Davis note that US currency is decimalized, but:

Our system of weights and measures, on the other hand, is not a decimal system, and is very inconvenient. Nevertheless, since the pound, foot, quart, gallon,
and bushel are still in general use in the United States and Great Britain, we must be familiar with them.

The basics of the metric system are touched upon and the definition of the:

Meter and yard. The meter is the distance between two lines on a metal bar (Fig. 2)

which is preserved in the vaults of the International Bureau of Weights and Measures near Paris.

Since the length of this metal bar changes a little with temperature, the distance is measured at the temperature of melting ice. A very accurate copy of the bar is deposited in the United States Bureau of Standards in Washington, D.C., and this copy is the legal meter of the United States.

In the United States the yard is legally defined as 3600/3937 of a meter.

My Father’s friend Mark was looking through a surveying kit, owned by his father, that appears to be from the 1930s, and found this interesting ruler:

Click to enlarge

One side has temperature correction for Lufkin steel measuring tapes. The difference for the 50 foot length is given on the left side and expanded for a 100 foot length on the right hand side. The wooden ruler itself is graduated in tenths of inches. I have no idea how prevalent rulers with 1/10th inch graduations were, but I suspect they were about as rare as they are now.

The back side:

Click to enlarge

Has hundredths of a foot, and is marked in tenths of a foot with integers. Below it is a scale with 1/16ths of an inch (of course millimeters would be 1/25). The value of a chain is a foot, divided into tenths and hundredths.

A footnote at the beginning of the textbook reminds us:

It was originally intended that the meter should be equal to one ten-millionth part of the distance from the equator to either pole of the earth, but it is impossible to reproduce an accurate copy of the meter on the basis of this definition. Later measurements have shown that the “mean polar quadrant” of the earth is about 10,002.100 meters.

First the Earth was used, and it had considerable difficulties as a standard, then metal bars, that needed to be measured at a precise temperature. Now the current definition is in terms of the speed of light in a vacuum, and is very, very accurate and reproducible. We still have some issues with better usage and simplification, but before that, we have to adopt the metric system exclusively in the US.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page

Related essay:

The Chain Gang

The Americans Who Defined The Meter

The Metric Maven has published a book titled The Dimensions of The Cosmos. It examines the basic quantities of the world from yocto to Yotta with a mixture of scientific anecdotes and may be purchased here.