Saturday, June 21, 2008

How Many Planets Part IV

To continue with a discussion that we started a couple of years ago, I will again visit the question of how many planets are there in the Solar System. The answer today is more complex than it was three or four years ago when we could say, simply, "Nine."

The International Astronomical Union (hereafter referred to as the IAU) created another category for objects that are large enough to be relatively spherical shape, that orbited the sun but that aren’t large enough to have cleared their obits of additional debris... which was the new, third criterion for a planet and which always struck me as a nonsensical way of demoting Pluto from its status as a planet.

Pluto and another Kuiper Belt object (Pluto on left, Eris on right), Eris, are now known as Plutoids rather than dwarf planets. That distinction belongs to Ceres which once was considered a planet and then the largest of the asteroids. It was demoted to asteroid when more and more of them were discovered. In fact, Ceres might be the only object of its kind and at the moment is the lone dwarf planet that is not also a Plutoid.

Plutoids, then, are objects that a spherical, orbit the sun beyond Neptune, and are objects in the Kuiper Belt known as Kuiper Belt Objects (KBO which seems to be broken down into Classical KBOs or Cubewanos and Resonant KBOs) and are also Trans-Neptunian Objects (TNO) and I’m sure that if I looked farther I could find more qualifications. Oh, yes, the moons of Plutoids (or more properly, the satellites) are not Plutoids and therefore not KBOs or TNOs. The question that springs to my mind is which is the satellite and which is the Plutoid in the Pluto - Charon system.

There are about another dozen objects that are being considered as Plutoids. These include 2003 EL 61, Sedna, 2005 FY 5, Quaoar, Orcus and Ixion, all larger than Ceres and then 2002 AW 197, Varuna and 2002 TC302 which are smaller. Now some of these are cubewanos, or SDOs (which are scattered disc objects) or plutinos (which, apparently are TNOs that orbit the sun twice for every three orbits of Neptune)... Are you confused now? Yeah, me too.

Well, let’s see if we can’t complicate this even more. There are two additional objects that are in the process of being named Plutoids. There are called Easterbunny and Santa and both have other, long designations. And, I seem to remember something about an object way out, maybe beyond the Kuiper Belt and into the area of the Oort Cloud. It’s about the size of Mars. What are they going to do about that if the size is verified?

In fact, in the last couple of days, astronomers have suggested a large object out there that would be, currently, the largest of the Plutoids, but this is not based on observation. It’s based on the gravitational permutations of the various objects out there. This is how Pluto was discovered in the first place. They were looking for a planet that caused disturbances in the orbits of the outer planets which makes me wonder if all that debris out there might not account for the trouble. What this means is that there might be something else out there that is the size of a "real" planet... or if this new speculation is true, there might be two.

What we can now say about the Solar System is that there are eight planets. These range in size from those small, rocky planets of the inner Solar System (Mercury, Venus, Earth and Mars) and the large gas giants of the outer Solar System (Jupiter, Saturn, Uranus and Neptune). It strikes me that we could further define planet if we wanted to, breaking them into two additional categories because the inner planets are certainly different than the outer planets in size, structure and number of satellites (there are only three known for the inner planets and about 150 for those in the outer system... in fact two of these satellites are larger than Mercury, but I digress).

Beyond Neptune are the Plutoids, that is, Pluto and Eris (which between them have more satellites than the four inner planets combined). They might be joined by a dozen others, including two that are in the process of being accepted as Plutoids, as I mentioned. There are some estimates that suggest there might be fifty of these objects, some about a light year or so from the Sun. These objects, like Pluto and Eris (which is thought to be slightly larger than Pluto) have diameters between 2000 kilometers and about 700, making the smallest, smaller than Ceres.

Ceres, because of what it is, the size it is, and the location of it, is currently the lone dwarf planet that is not also a Plutoid. There is speculation that there will be other Ceres-class dwarf planets, though I don’t know where they would be hidden.

So, the answer to the question of how many planets, is still eight. But now we have several other large objects that are being grouped under a variety of categories, which falls under planet... more or less. If you have questions about this, don’t ask me. I’m as confused as the rest of you.


cda said...

Fascinating stuff.
I think by "gravitational permutations" you meant "perturbations".
Pluto was a bit of a 'fluke' discovery, in that although Clyde Tombaugh located it in approximately the right position, it was far too small to have caused the observed perturbations in Neptune's orbit. The problem is that we have means of detecting objects in orbit that nobody ever thought of in the 1930s. Who would ever have thought the number of Jupiter's satellites would one day reach 60? Or that the Kuiper belt would yield so many new orbiting objects? And what about all the extra-solar planets, which now total over 100? The mind boggles at it all. However, you are correct that there are only 8 true planets. Do you recall the days when the satellites of Mars were thought (by some) to be artificial? Even further back, the canals of Mars were believed artificial! And Lowell was no nut case either, but a competent professional astronomer of his day.

starman said...

The # of known extrasolar planets is now over 300. Of course there were no real "canals" on Mars. Although a pro, Lowell incurred ridicule. Remarkably, though, Keyhoe took the "canals" seriously in one of his books, published as late as the 1970s!

cda said...

Keyhoe had some dotty ideas. He wrote in 'Aliens From Space' that the AF tried to silence the International Mars Committee of 1954, in case they wanted to tell the world that the canals were artificial! I wonder what Keyhoe would have said had he lived when the news of the famous Mars meteorite was announced to the world in 1996, with the biggest fanfare imaginable. No USAF suppression then, was there Mr Keyhoe?

Bob Koford said...

My interest in UFO history never really brought out any deep interest in Astronomy. Maybe its because I never really cared where "they" are coming from, and my interest is/was in the UFOs. At any rate, I wouldn't really have anything useful to add to this topic if it weren't for the opportunity that has presented itself to stick up for Donald Keyhoe. So, if you will forgive me for continuing this branch away from the interesting planetoid (I mean...Plutoid) post, I feel it is warrented.

Unlike any of us, Donald Keyhoe was present when Governence was altered from being one that valued an informed public, into one which valued secrecy instead. Before the change, Keyhoe had been viewed as an ally, yet by the late 1950s, early 1960s, he had become the Air Force's punching bag, because he called for Congressional investigations. Keyhoe coined the term "the silence group" because from his perspective that is what the UFO group had become. They became more concerned with keeping a lid on information on the subject than telling the public what they knew...and that is an established fact. No one could really blame him for becoming skeptical, and angry about the Air Force's flip-flop, in regards to telling the truth. He had seen them go from truth-tellers, to lie-tellers, right before his very eyes.

He was also aware that several experts who were "in-the-know" about the flying objects ["real, and not visionary"] were contemplating where these apparent visitors were arriving from. The two most popular beliefs were bases on Mars, and/or bases on the Moon, and they also knew that we would need to expand our own space exploration efforts in order to find out.

To paint keyhoe, as you have done here, as being some nut-case who would believe anything, like canals on Mars, is just absolutely unjust. He had been told many stories about little people and such, yet only briefly mentions them because he didn't want to veer off course too much. He mostly discussed what he had the most data on, and that was sightings of the strange objects themselves, made by competent military pilots and radar operators.

I have absolutely no problem putting him more in the category of a hero, rather than a nut, as you have obviously done.

starman said...

I wouldn't call Keyhoe a nut but he did strike me as being either highly naive, or possibly deceptive. It's one thing to think the ETs may have bases on Mars, another to believe in an indigenous Martian civilization. The whole "canal" notion had fallen out of favor by about 1920. It was inexcusable to take it seriously in a book published as late as '73. Not only that, but Keyhoe's scheme to induce ETs to land and learn about us prior to a meeting was silly. They undoubtedly already know all about us.

starman said...

Btw did you hear about the death of UFOlogist Robert Blechtman? He used to live very close by in this Manchester CT neighborhood. Friedman knew him. He said he spoke to Blechtman a few weeks ago and knew the end was near. Smoking and cancer did him in. For many years Blechtman strove tirelessly to get full disclosure. I considered those efforts futile. Friedman thinks most of us will also go before the full truth is known.