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Planet X or XX?
Discovery of new planet disrupts nine-planet theory
Wayne Wooten Special to Splash!
I knew this day was coming, and so did most text authors. On page 446 of the new edition of Horizons, Michael Seeds notes that Sedna and Quaoar are only slightly smaller than Pluto.
“As more and more of these objects are found, astronomers may eventually find one that is even bigger than Pluto,” it says.
Jeff Bennett in The Essential Cosmic Perspective (3rd. edition, page 246) notes “All things considered, Pluto stands out from other Kuiper belt comets only in its size. But, we already have found other Kuiper belt comets that are not much smaller than Pluto, and larger ones may yet be discovered.”
“Moreover, we are nearly certain that at least one object larger than Pluto once roamed the Kuiper Belt; Neptune’s moon Triton. Before Neptune captured Triton, Pluto held no better than second place among the objects of the Kuiper Belt.” Note that Bennett refers to Pluto not as a planet, but as a comet. (More on this later).
Perhaps the biggest loser from the new discovery is Astronomy magazine, whose lead article for September is “Pluto: King of the Kuiper Belt” (Well, kings are crowned to be dethroned, in astronomy as in sports and even politics).
Now, elementary school teachers, what to do with all the nine planets textbooks? We astronomers have been trying to wean the public from the nine planets concept since 1992, when the first KBO other than Pluto was found.
The total count of these large objects beyond Neptune is now over 1,000, and we now know they contain far more material than all the 30,000-plus asteroids lying between Mars and Jupiter do. In fact, we found Kuiper Belts around other stars, such as beta Pictoris and Fomalhaur,with IRAS in the early 1980’s, a decade before we found this outer rings of material around our own Sun.
Why was Pluto ever considered a planet to start with? Good PR helped. In 1930, it was found by Clyde Tombaugh, a Kansas farm boy whose skills as a dedicated amateur astronomer led to his hiring at Lowell Observatory to continue Percival Lowell’s quest for “Planet X.”
When discovered, Pluto lay near where Lowell had predicted his large jovian should, based on supposed perturbations of Uranus and Neptune’s orbit. The letters PL were merged as its symbol to immortalize Lowell’s role in its finding. But reality set in; Pluto was no jovian, nor even a terrestrial.
With the finding of its moon Charon in 1978 came the measurement of its exact size and mass. It was smaller, less massive, and less dense than our own Moon, and far behind Mercury, or the galilean moons of Jupiter, or Titan of Saturn, or Triton of Neptune.
Its orbit certainly was like no planet’s, for it climbs 17 degrees above the ecliptic, and cuts inside Neptune’s from 1979 until 1999. They do not collide because they have long ago worked out a “timesharing” arrangement where Pluto orbits the Sun twice for every three Neptune years, and at perihelion, Pluto rides millions of miles above Neptune’s orbit.
We now know of many other “Plutoinos” which also so show this 3:2 orbital resonance. Remember, this was the AMERICAN planet, found by a Kansas farm boy, and in the 1930’s we were desperate for any good news than would take our minds off the depression!
Clyde passed away a few years ago, but before he died, when asked if he would be saddened to find his discovery demoted from planetary status, he noted that either he had found the smallest, puniest of the planets, or the first of a whole new category of major solar system bodies. Kuiper had not in fact predicted the belt existed until 18 years after Tombaugh found Pluto. We can now all agree the latter was a greater accomplishment in the long run.
Rest in peace, Clyde Tombaugh..
What about Planet X? Is it a planet, just because it is bigger than Pluto? It was actually noted first detected in a computer scan of 48” Schmidt images taken on October 21, 2003, but its motion was not noted until a follow-up image was made this January 8.
It is bright enough at magnitude 18.9 to already be imaged by amateurs, but its highly included (44 degree) orbit meant it was far from the ecliptic, so most previous searches had not seen it. It is named 2003 UB 313, and now close to aphelion, about 97 AU from the Sun.
At perihelion, it will be as close as 38 AU, so about 280 years from now, it will be almost ten times brighter, or up to magnitude 16, still fainter than Pluto, which gets in to about 30 AU at perihelion.
In the New York Times editorial for August 2, “Too Many Planets Numb the Mind,” the staff writes. Try as they might, scientists could not come up with a definition that would retain Pluto as a planet without requiring that scads of other objects be deemed planets as well. Nor could they satisfy the legions of space enthusiasts who remain certain from their grade school lessons that there are nine planets no more, no less.
So now, Dr. Brown proposes that scientists give up the battle and accept a cultural definition of what a planet is. It’s either the nine planets we learned about in grade school, or those nine plus any new-found object orbiting the Sun that turns out to be bigger than Pluto.
He opts for the latter approach on the theory that most people, deep down, accept that definition. This definition would also, of course, qualify Dr. Brown for the historical footnotes as the discoverer of a new planet.
Our own preference is to take a cleaner way out by dropping Pluto from the planetary ranks. Scientists may well discover many more ice balls bigger than Pluto, and it’s a safe bet that few in our culture want to memorize the names of 20 or more planets.
Far better to downgrade Pluto to the status of an icy sphere that was once mistakenly deemed a planet because we had not yet discovered its compatriots on the dark fringes of the solar system.
There is precedent for such planetary pruning. When the first four large asteroids were found just after 1800, they gained planetary status, and high school astronomy students learned “Mercury, Venus, Earth, Mars, Vesta, Pallas, Juno, Ceres, Jupiter, Saturn, and Uranus.”
Somebody imagine a phrase to help them remember these in order, like the now obsolete “My very educated mother just served us nine pizzas.” But as a host of new asteroids were added to the belt, these new four were demoted to “minor planets.”
This is not a bad idea *I have already heard the term “dwarf planet” bandied about already, and it may be a good solution.
I suggested years ago that we define a planet as a spherical nonluminous body orbiting only a star. This seems to be where we are headed. I do not like Jeff’s Bennett’s term of Kuiper Belt comets “To me, a comet is a small, icy body, temporarily made luminous by its proximity to the Sun and violent sublimation of ices to form a much brighter coma and even gas and dust tails.”
Pluto, near perihelion now, does have a tenuous atmosphere, which I think will refreeze about the time NASA’s New Horizons mission gets out to it about 2015; comets by contrast, lose some of their ices and dust with every solar passage.
An interested case in point is Chiron, the next KBO (object to me is more generic and acceptable), found about 1980 in a Pluto-like orbit between Saturn and Uranus. It was first called an asteroid, then it got fuzzy near perihelion, so was renamed P/Chiron, for a periodic comet. But now we see it, like probably the Trojan “asteroids” orbiting 60 degrees ahead or behind Jupiter in its orbit, originally came from the Kuiper Belt.
In the new September Sky and Telescope, Robert Naeye on pages 18-19 describes “Chaos and Capture,” how jovian migration (Uranus and Neptune even swap places!) might have created the Oort Cloud and the Kuiper Belt, with some objects remaining close to the ecliptic, while others were pitchout out to high inclinations and eccentricities.
This certainly fits well with our new “Planet X’s” orbit, and even explains why the Trojan “asteroids” have the spectra of KBOs, not rocky asteroids!
I close with this suggestion. Four terrestrials: Mercury-Mars; four jovians: Jupiter-Neptune; the following presently known dwarf planets (minor planet is another term for asteroids, even though most are not spherical): Ceres, Chiron, Pluto, and about ten other KBOs known to be spherical.
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