Dear PT5-The Hunt for Planet X Part 2-The Rise, and Fall, and Rise of Planet X

Dear PT5 /

This is Pluto. Isn’t it gorgeous?! This photo was taken by New Horizons by the way, the first space probe sent to Pluto and still merrily hurtling out of the solar system. Some of Clyde Tombaugh’s ashes are aboard.

Some Pluto facts. It’s two thirds the width of Earth’s Moon and 1/5th the width of Earth. The Sun is 1/900th the brightness it is on Earth, and there is a moment each day when the Sun is as bright here as it is on Pluto. So now you know where I’ll be at 4.10pm today.

Clyde Tombaugh, on the calculations of Elizabeth Langdon Williams and her colleague William H Pickering found Pluto on 8th February 1930. Percival Lowell, the adventurer astronomer who had funded the search didn’t live to see it and died in 1916. His widow Constance fought a bitter court battle with the Lowell Observatory over her husband’s legacy and the search for Planet X didn’t begin again until 1929 when Vesto Melvin Slipher, the director of the observatory, gave the newly hired 23 year old Clyde Tombaugh the job. What none of them knew then were that there were fourteen ‘precovery’ images, photos taken of Pluto which no one had spotted Pluto in. Lowell himself had captured two not long before his death.

Planet naming gets tricky, and William Herschel, whose sister Caroline we’ve talked about before was actually both the discoverer of Uranus and briefly christened it. Nevil Maskelyne, the Royal Astronomer at the time, asked him to name it and Herschel suggested Georgium Sidus, George’s Star, in honour of King George III. This did not go down well anywhere that wasn’t under the rule of the King, and a 70 year debate ensued before Johan Elert Bode suggested ‘Uranus’ and gifted centuries of school children of all ages with the easiest science joke in history. To get around all this, the Observatory tallied all the thousands of names that were suggested to them and broke it down to three. Pluto was the clear preference and on May 1st 1930, with the blessing of the American Astronomical Society and the Royal Astronomical Society, it was formally named. Venetia Burney, the eleven year Oxford school girl who was the first to suggest it was, I’m sure, delighted.

The name landed fast and stuck. The planetary status did not,

Planet X Falls
The issue with Pluto was it was too small. In fact estimates of its mass were constantly revised downwards through the 20th Century meaning it couldn’t be what was disrupting the orbits of other objects around it. Matters came to a head at two points. In 1978, Charon, Pluto’s moon was discovered and that allowed Pluto’s mass to be calculated for the first time. It turned out to be 0.2% that of Earth, meaning there was no pssible way it could have altered Uranus’ orbit as Planet X was expected to.

More damning still, in 1992, Myles Standish revised Neptune’s mass downwards by 0.5% (That’s one Mars, in new money). The discrepancies in its orbit weren’t there, just a rounding error. Pluto wasn’t Planet X. Nothing was Planet X. Lowell had been wrong twice, just decades apart.

Michael E Brown, a slightly built man in a blue shirt and glasses stands, arms folded by a bookshelf. He has glasses, salt and pepper hair and a goatee.

Michael E, Brown


This man delivered the killing blow. Michael E. Brown is known as the man who killed Pluto. So much so in fact that his book is called How I Killed Pluto, and Why It Had It Coming.’ Brown has discovered 29 minor planets, a type of astornomical object that orbits the Sun but is neither a planet or a comet. This, I know, feels a lot like splitting hairs, but there’s a pretty solid definition of them. If an object is large enough to have hydrostatic equilibrium, meaning that fluids (or plastic solids) can be at rest on its surface, then that’s the first indicator. The second is if it’s large enough to become an elipsoidal shape, meaning its a slightly compressed sphere because of its speed of gravitational rotation and its mass.

Brown specializes in Transneptunian Objects or TNOs. These are minor planets that orbit out past Neptune. As of this year, there are 901 numbered TNOs and 3000 unnumbered. Pluto is one of them. So Is Eris.

Two computer images show a small yellow dot against a red sky. In one, there's a dot visible next to it. In the next, the dot is labelled as Dysnomia, Eris' moon and the central larger dot as Eris with Dysnomia's orbit marked in a circle around it.
[Left] – This is an image of the dwarf planet Eris (centre) and its satellite Dysnomia (at 9 o’clock position) taken with NASA/ESA’s Hubble Space Telescope on Aug. 30, 2006. Hubble observations were obtained on Dec. 3, 2005 and Aug. 30, 2006 using the Advanced Camera for Surveys. The Hubble images were combined with images from the Keck telescopes taken on Aug. 20, 21, 30, and 31 to measure the satellite’s orbit and calculate a mass for Eris, which is the largest dwarf planet in the Solar System. [Right] – Labeled version of the above mentioned image of dwarf planet Eris and its satellite Dysnomia taken with NASA/ESA’s Hubble Space Telescope on Aug. 30, 2006. Dysnomia’s projected orbit around Eris is superimposed on the image.

Eris was discovered by Michael E. Brown, Chad Trujillo and David Rabinowitz on January 5th 2005. The same day other teams announced the discovery of minor planets Makemake and Haumea and the controversy surrounding that is a whole other article. What matters here is that Eris was proved to be larger than Pluto. NASA originally described it as the tenth planet of the solar system but there was a problem. TNOs were part of the Kuiper Belt, the doughnut of icy bodies (An artisanal solar system sized planetary ring if you will) outside Neptune’s orbit. There were countless objects in the Belt, including Pluto. And planets bigger than Pluto. If Eris was the 10th Planet, then Makemake or one of the others could be argued to be the 11th, Haumea the 12th and so on.

Something had to be done, and depressingly, that something was bureaucracy.

In August 2006, the International Astronomical Union defined a planet as follows:

  • is in orbit around the Sun,
  • has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
  • has “cleared the neighbourhood” around its orbit.

That last one was the death knell for Pluto. It’s neighbourhood was crowded and always would be due to its presence in the Kuiper belt. Despite controversy about the timing of the vote, and Brown getting death threats, the resolution passed. Tombaugh, Langdon Williams, Pickering and Lowell had found the first minor planet, not Planet X.

Planet X Rises

But Planet X persists and scientists are still hunting for it. One of them is Michael Brown. Along with Konstantin Batygin brown has been searching for Planet X since 2014. It’s the exact same approach as Williams, Pickering and Tombaugh all those years ago. Calculate the area of space you want to look at and search for gravitational discrepancies, ‘wobbles’ in other objects’ orbits. Batygin has talked at length about the simulations they’ve run on one group of TNOs and how a ninth planet is the most likely explanation. Even if the offhand reference he makes to long dead planets having influenced these orbits conjures delicious images of ghostly worlds gone by.

I love how after all this time, the procedural ghosts of Lowell’s planet hunters are whispering in their ears. I love too that Brown has taken up the search., It feels like an evolution, and salute, to what’s been done before and the scientists who did it. It also feels very fitting that Pluto is part of the search. That crowded space around it, the Kuiper belt, is the perfect place to spot those anomalies and that’s exactly where Brown and Batygin, and colleagues are looking. They’re also expecting something big. Brown’s argument is that Planet X is a ‘Super Earth’ (Every Helldivers 2 player you know just had some libertea) up to ten times the size of Earth. That would explain the anomalies they’re seeing, even if they haven’t found it yet. Those anomalies include the haunting realization, explained by Princeton Astronomer Amir Siraj, that comets and asteroids are clustered on one side of the solar system. Either we don’t understand something about the mechanics of the solar system, or something we haven’t found yet altered their robits so they all ened up there. Planet X or, as Susanne Pfalzner and her team theorize, Star X.

If there is a Planet X, it may very well be found by the Vera C. Rubin Observatory. Located in Chile, it’s going to be completed next year and is home to the LSST, the largest digital camera ever built. That camera, is the size of a small car, weighs 6200 pounds and is designed to produce hugely detailed, images of vast tranches of the night sky, supposedly in the time it takes to shoot a selfie. Planet X hunters are planning on using it to scan their target areas and discover the truth once and for all.

Conclusion

The way you find planets is by looking where they aren’t. The orbits of other, smaller objects nearby will be altered by a larger body passing by. Like wakes on a boat, or an asteroid popping by for a partial orbit of the Earth. Scientists, adventurers, computers and hunters, all dragged along in the wake of something amazing, passing by out in the night.I love that it re-frames Pluto as a gateway world to a larger puzzle box of a solar system. Not to mention giving me the perfect excuse to end on a song. So here’s to Pluto, to Planet X and to everyone chasing them.

See you next week, PT5

References

Pluto

Scientists

Minor Planets and Trans-Neptunian Objects

Planet X

Organizations

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