Measuring sticks

I like perspective. Not just the kind used in photography, but the kind that changes the way we think about something. It’s very interesting sometimes, in that there are bare facts, and then there’s the way we feel about them, how we classify the information and relate to it. It comes up quite a bit in the spirited (read: vehement) discussions of free will which, whether it exists or not (it doesn’t,) still doesn’t change how our lives operate. A curious place for it to spring up, however, is in regards to Pluto.

This is perhaps the most contentious astronomical subject, at least to the general public, and a lot of it has to do with how we phrase things. As most people know, Pluto was one of the nine planets almost from the moment it was discovered, up until 2006, when its nomenclature was changed to dwarf planet. Invariably, this is referred to as being ‘demoted,’ and the qualifying term dwarf probably also contributes. A lot of people resent this change, even refusing to accept it, and get surprisingly emotional about it.

First off, there is no such thing as demoting a planet, since there is no status or prestige a planet can hold anyway, except in our own eyes. Pluto remains unchanged, and quite likely (barring a lot of our physics knowledge being dramatically overturned) completely unaware of its title, or indeed anything at all – it’s a frozen rock, and was long before we apes started jumping around and worrying about HBO series. The reason the classification was changed was to help distinguish various bodies found in our solar system. We make up all of these terms, including ‘planet,’ just to communicate, and any changes are intended to facilitate this (though perhaps not successful in this endeavor.) Yet they remain just abstract ideas in our heads.

Let’s go ahead and get dwarf planet out of the way. It’s defined by a solar system object a) orbiting the star, and not another body like a planet, b) large enough to shape itself through its own gravity, and c) incapable of clearing its orbit of any debris. That last bit is the clincher, since Pluto sits in the Kuiper Belt with a lot of other, smaller bits of rock and ice, while the eight major planets have gathered up the majority of loose matter and absorbed it. Another dwarf planet, Ceres, sits within the asteroid belt between Mars and Jupiter, while most of the others are out there in Kuiper territory with Pluto, some even beyond that.

We have millions of bits of stuff in our system. The asteroid belt contains lots of rocky bodies with highly irregular shapes, lacking enough mass to pull themselves into a sphere, the most gravitationally stable of shapes. Many satellites (‘moons’) of the planets are large enough to have done this, but of course orbit their planets and not the sun, thus that distinction – this is notable, since a lot of them, including Earth’s moon, are larger than Pluto.

One of the potential new classifications, back in 2006, was that a planet must be substantially larger than its moons, which would also have ruled out Pluto. Every moon exerts its own gravitational influence on the host it orbits, tugging it around in proportion to its mass, causing a wobble in the host’s orbital path around the sun. Pluto’s largest moon Charon is large enough that they pretty much orbit each other; the common center of gravity between them lies outside of Pluto’s diameter, so it doesn’t just wobble, it circles, like two skaters spinning with joined hands.

Now for fun, let’s look at some other qualifications that we could use:

A planet should be able to support an atmosphere. Pluto would make it, Mercury would not.

A planet must have a moon. Pluto wins out again over Mercury, and Venus as well. It has, in fact, five moons, so it ranks well above Earth (one moon) and Mars (two minuscule moons) in that respect as well.

A planet should have an axial tilt relative to the orbital plane. In other words, it should spin ‘upright’ in relation to its path around the sun. This depends on how sloppy you want to get, since none fit this bill, but Mercury is closest with 2°, Venus and Jupiter close behind with 3°; the rest, including Pluto, are tilted significantly, Uranus being totally screwed. And Venus rotates the opposite direction from all the rest.

A planet should be a rocky body. As opposed to being gaseous like Jupiter, Saturn, Uranus, and Neptune.

We could go on, but basically, one can create any sort of criteria one wants and pin this label on anything at all. Pluto is unique in a lot of ways, and can be appreciated for those. It is probably far older than the Earth, if you count being in a solid shape or stable orbit; Earth’s moon was likely formed by a collision with another Mars-sized object early on, and both had to restabilize. Earth may only exist, at least where it is now, because of the gravitational influence of Jupiter, which both prevented it from being drawn closer to the sun and helped clear away other bodies that would have caused catastrophic impacts. Pluto may also harbor the oldest molecules in the solar system, or very close; it is too far out for heat from the sun to cause many effects in its atmosphere, and too small to produce gravitational pressure that would catalyze any elements it possesses, which cannot be said for any of the major planets, and a few of the dwarves.

And what this is demonstrating is that all of the bodies in our system are unique. We can apply any labels to them as desired, when we think broad classifications are useful, but this in no way makes anything either unremarkable, or part of a prestigious group. In a way, this starts to sound like the misguided validation trend of the ’90s, where every child was special, but this doesn’t exactly apply; humans have a desire for recognition and improvement, and moreover very good reasons for pursuing these, so thwarting them by lowering the bar denies their usefulness. In contrast, all of the bodies in our system have something they can teach us, and no benefit to be accrued from either improvement (whatever arbitrary definition one uses) or change of any kind. Worry about the label only when the label has some application.

But this brings us to New Horizons. New Horizons is a probe currently on its way to visit Pluto, having begun its journey in January of 2006. On December 6th of this year, it will awaken from hibernation for the last time to begin its primary mission, while in January it will start actively collecting data about Pluto and its various moons. On July 14th of 2015, it will make its closest pass of Pluto before it trundles on towards even further reaches.

This might seem odd, but it’s a flyby mission, unlike many others that we know of, such as Cassini and the Mars Global Surveyor. As mentioned in an earlier post, it took quite a bit of maneuvering to get New Horizons on a path to intercept Pluto in the first place, because it’s so damn far out there; it used Jupiter’s gravity as a slingshot boost to be able to reach Pluto without relying on rocket thrust. Basic premise: thrust requires fuel, which is mass/weight. Mass/weight requires fuel to move. The more fuel you boost into space, the more fuel is needed just for the fuel’s own mass. The goal is to need as little fuel as possible so the mass being boosted is something more productive, like instrumentation.

Now, to reach Pluto in the nine years it’s currently taking, New Horizons has to be booking right along; presently it’s clocking 52,704 kph (32,749 mph) in relation to the sun, mostly ‘straight out.’ So in order for it to orbit, it would not only have to turn, it would also have to slow down to orbital velocity, somewhere below Pluto’s escape velocity of 4,320 kph. That’s a lot of fuel, that it would have had to carry the entire way. Long story short: it doesn’t, and is only going to whiz past Pluto and further into the Kuiper Belt, but not before gathering as much info as possible.

Which should be significant, since nearly all of the information we have has been gathered from Earth’s immediate vicinity. There have certainly been probes that have been much farther from Earth than, say, the Hubble Space Telescope, but that doesn’t mean that they were any closer to Pluto. We tend to think in terms of the concentric circles of the orbital plots that we always see illustrated, lining up the planets (and dwarf planets and non-planets) nicely, but they all orbit; while Cassini is hanging out at Saturn, this still might be on the other side of the sun from Pluto, even farther away than Earth. The New Horizons mission had some pretty crucial timing, in that using Jupiter for velocity assistance required Earth, Jupiter, and Pluto to reach appropriate positions in their orbits, something that wasn’t going to happen again for 300 years.

So most of what we know has been obtained from a great distance – always at least 4.28 billion kilometers (2.66 billion miles,) which is the point where Earth’s and Pluto’s positions come closest together. Hubble has been responsible for the best looks of Pluto to date, which haven’t been all that detailed.

Hubble Maps Pluto

That’s it; that’s all the detail we have. Are those blobs clouds? Craters? The missing Martian canals? A Monolith stockpile? We don’t know yet. You’ve seen some of the detail that Hubble is capable of, so this illustrates just how small and distant Pluto is, but if that’s not enough, how about an animation of Pluto and Charon, taken by New Horizons in August of this year?

Wait – they’re not round? No, they are, they’re just too dim for all of the surface features to show in the exposures used, not to mention they’re shaped by the pixel dimensions of the camera sensor, so they get irregular outlines; again, check the distances listed in the image itself. New Horizons traveled from 429 million kilometers away to only 422 million during this animation – in comparison, Earth’s closest approach to Mars is 54.6 million kilometers, and you know what that looks like in the sky.

Also note, as explained on the page that the image links to, that both Pluto and Charon are wobbling. This is not from bad camera aiming, but because the image is pinned on the common gravitational center of the two, the barycenter. Discussing this illustrates the difficulty and relativity of orbital mechanics. If you’re on Pluto, it would seem rock-steady and Charon would be orbiting, but the same in reverse would be seen from Charon, just as we sit here on Earth orbiting the sun and think the sun ‘rises’ and ‘sets.’ But if you took Pluto’s time and distance to orbit the sun to obtain an average orbital speed, that’s the barycenter, and Pluto advances and retreats routinely around this due to Charon’s gravitational influence.

Another interesting note is that New Horizons’ mission is still being planned, with the Hubble Space Telescope still scouting targets of potential interest after the probe passes Pluto. Part of this is because the timing of the probe’s launch was crucial; part of this is because there’s a huge demand on Hubble’s time, from astronomers all over the world – anyone can apply to use the scope, but they have to petition for it and make their case for how important their research is (so you’re welcome to try, but don’t hold your breath.) As yet, while there are some potential targets in range of New Horizons‘ path and limited fuel, to the best of my knowledge nothing has been confirmed yet. Suffice to say that the folks at Jet Propulsion Laboratory, the ones that control New Horizons, don’t consider the mission over once the probe passes out of effective range of Pluto, even though the flyby is the only confirmed mission; everything else will be gravy.

So keep watching the astronomy news. In a few months, New Horizons will be pumping out images and information about this little dwarf and its moons, providing a hell of a lot more information than we’ve been able to determine since its discovery in 1930. Meanwhile, you can go to the mission site for details and what we’ve accumulated so far.

Now for a little bonus. The change of Pluto’s status wrecked the mnemonic that untold people recited to recall the order of the planets in their distance from the sun, such as “Mother very eagerly makes jelly sandwiches using no peanutbutter,” or, “Mary’s violet eyes make Johnny stand up now period” (a ridiculous number of them use “very” in a stunning lack of originality.) It’s easy enough to change them to leave off the final P, but what about all of the other dwarf planets? Shouldn’t we be reciting them too?

And so, I took it upon myself to create one that includes them all:Missing velvet earmuffs mean cold January storms unleash numbing pain on helpless quaking men’s red ears since breakfast.

Got that?

It’s simple: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Orcus, Hauma, Quaoar, Makemake, 2007 OR10, Eris, Sedna, 2012 VP113.

Now, I know you’re questioning a couple of them, but bear with me. 2007 OR10 was originally nicknamed “Snow White” due to its supposed albedo, the reflectance it possessed; later on, it was determined to be red in color instead, and the original Snow White stories (before Disney) sometimes featured her sister, Rose Red – I am not making this up – so this was the obvious choice. And 2012 VP113 is occasionally nicknamed “Veep” or “Biden,” so I went with the latter, mostly because ending a sentence with “very” is awkward.

You’re welcome.

Comments are closed.