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NASA's New Horizons Shows Pluto's Moon Charon Is a Strange, New World
MarkWhittington writes: NASA's New Horizons has returned a stunning series of images of Pluto, the dwarf planet that resides on the edge of the solar system, revealing a strange new world of ice mountains and glaciers of frozen nitrogen. NASA also released images of Pluto's largest moon Charon. Scientists expected a plain ball of rock pockmarked with craters, but what they saw was anything but plain and monotonous.
We can, when you're willing to call Vesta, Ceres, Haumea, Makemake, Eris, Sedna, Sila-Nunam, Varuna, Quaoar, Ocrus, Ixion, and likely hundreds of other objects of similar size to Pluto (yet to be identified, as the Kuiper Belt and scattered disc are large search spaces) planets as well.
In order to retain the use of the word "planet" in a context that is relatively closely related to its historical usage, a line has to be drawn somewhere. It is far more logical to draw that line above Pluto than below it. If you are advocating for every object which is large enough to pull itself into hydrostatic equilibrium by gravity, and is not in orbit around another non-stellar object a planet -- you're going to have upwards of 100 of them, and that's just what we know of right now.
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
The New Horizons team refers to it as a planet. New Horizons head Alan Stern is one of the leading advocates for the reversal of the IAU decision. Pluto and other large KBOs have been referred to many times as planets in peer-reviewed literature since the IAU decision. One of the NASA links in this article itself refers to Pluto as a planet ("At half the diameter of Pluto, Charon is the largest satellite relative to its planet in the solar system."). Large numbers of people in the field - I'd wager a solid majority of planetary scientists (who make up only a small minority of the IAU's membership but really should be the ones making these decisions) - think the IAU seriously screwed up here. There are literally dozens of reasons why it was a screwup - need I go into them?
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First, the IAU definition:
1. Nomenclature: An "adjective-noun" should always be a subset of "noun". A "dwarf planet" should be no less seen as a type of planet than a "dwarf star" is seen as a type of star.
2. Erroneous foundation: Current research suggests that most planets did not clear their own neighborhoods, and even that their neighborhoods may not always have been where they are. Jupiter, and Saturn to a lesser extent, have cleared most neighborhoods. Mars has 1/300th the Stern-Levison parameter as Neptune, and Neptune has multiple bodies a couple percent of Mars's mass (possibly even larger, we've only detected an estimated 1% of large KBOs) in its "neighborhood". Mars's neighborhood would in no way would be clear if Jupiter did not exist - even Earth's might not be. Should we demote the terrestrial planets as well?
3. Comparative inconsistency: Earth is far more like Ceres and Pluto than it is like Jupiter, yet these very dissimilar groups - gas giants and terrestrial planets - are lumped together as "planets" while dwarfs are excluded.
4. Poor choice of dividing line: While defining objects inherently requires drawing lines between groups, the chosen line has been poorly selected. Achieving a rough hydrostatic equilibrium is a very meaningful dividing line - it means differentiation, mineralization processes, alteration of primordial materials, and so forth. It's also often associated with internal heat and, increasingly as we're realizing, a common association with subsurface fluids. In short, a body in a category of "not having achieved hydrostatic equilibrium" describes a body which one would study to learn about the origins of our solar system, while a body in a category of "having achieved hydrostatic equilibrium" describes a body one would study, for example, to learn more about tectonics, geochemistry, (potentially) biology, etc. By contrast, a dividing line of "clearing its neighborhood" - which doesn't even meet standard #2 - says little about the body itself.
5. Mutability: What an object is declared at can be altered without any of the properties of the object changing simply by its "neighborhood" changing in any of countless ways.
6. Situational inconsistency: An exact copy of Earth (what the vast majority of people would consider the prototype for what a planet should be), identical down to all of the life on its surface, would not be considered a planet if orbiting in the habitable zone of a significantly larger star (harder to clear zone), or a young star (insufficient time to clear), a star without a Jupiter equivalent (no assistance in clearing), or so forth.
Crowd: What do we want? Fry: Fry's dog! Crowd: When do we want it? Fry: Fry's dog!
New rule: there's only 8 rivers on Earth, and all others are "dwarf rivers" and don't really count as rivers. In order to retain the use of the word "river" in a context that is relatively closely related to its historical usage when people were primitive tribesmen and only knew of a few rivers in their area, a line has to be drawn somewhere. It is far more logical to draw that line above the Brahmaputra than below it. If you are advocating for every river which is large enough to be too deep and fast flowing to ford a river -- you're going to have upwards of 100000 of them, and that's just what we know of right now.
New rule: there are only organs in the human body, and all others are "dwarf organs" and don't really count as organs. In order to retain the use of the word "organ" in a context that is relatively closely related to its historical usage, a line has to be drawn somewhere. It is far more logical to draw that line above the spleen than below it. If you are advocating for every object which is large enough to have a distinct biological function, and is not a part of another organ an organ -- you're going to have many hundreds if not thousands of them, and that's just what we know of right now.
New rule: there are only 8 elements, and all others are "secondary elements" and don't really count as elements. In order to retain the use of the word "element" in a context that is relatively closely related to its historical usage, a line has to be drawn somewhere. It is far more logical to draw that line above bismuth than below it. If you are advocating for every particle which contains a unique number of protons to be called an element -- you're going to have 118 of them, and that's just what we know of right now.
Shall I keep going?
It is in no way, shape or form scientific to define what something is based on whether schoolchildren can memorize a list of all of them. Time and time again, ancient peoples have created names for things thinking that there's only a small number of them, and later scientists discovered that there's actually a vast diversity of them. Well, guess what, you deal with that and accept that the universe is a fascinating place rather than trying to hide it with definitions that aren't even internally consistent or in alignment with our models of what actually cleared most "neighborhoods" in our solar system (hint: it wasn't planets like Mars).
And you certainly don't do so in opposition to the very perception of the word itself. People look at pictures of Pluto and they see a planet. Because it's a giant chunk of rock orbiting a star - yes, there are bigger ones, but it's still huge, so large that gravity crammed it into a sphere, setting of processes of mineralization, tectonics, and so forth - which more to the point appear to be still active to this day. People turn on Star Trek and when they see the Enterprise arrive at a body like Pluto, they expect to hear Captain Kirk say "Beam me down to the planet", not "Beam me down to this... hmm, Spock, I'm not sure what to call it, could you run a long-range scan to see if it has "cleared its neighborhood"... oh wait, I forgot, "planets" can only be objects in orbit around the sun, there is no name for whatever this thing is!"
Crowd: What do we want? Fry: Fry's dog! Crowd: When do we want it? Fry: Fry's dog!
Hmm.
I hate to respond to my own comment, but something just occurred to me.
That was in reference to the fact that the "water streaks" are not "water", but rather deliquescent perchlorate salts that managed to draw enough water out of the atmosphere to create damp streaks on the surface. Perchlorates are most famously used as the oxidizer in a number of rocket fuel mixtures, and seem to be very abundant in the Martian regolith, all over the planet - it makes up about half a percentage of its mass. This is of course bad for the search for life - they make a better hand sanitizer than they do a growth medium.
But could one actually use them for what we use them for on Earth - rocket fuel?
They're readily soluble - many are even deliquescent - and so should be very easy to extract with nothing more than water in a closed loop, consuming little energy (compared to the amount of energy needed to produce oxygen as an oxidizer on Mars). And the oxidizer is the heavier portion of a rocket propellant. Rather than the concept of making Mars return propellant from turning atmospheric CO2 and water-electrolysis hydrogen (or Earth-imported hydrogen**) into methane, and liquefying oxygen as an oxidizer, you could use the easy-to-extract perchlorates as your oxidizer. A clever rover wheel or tread design could scoop up regolith as it crawls, wash it, dry it, and return it in a continuous process.
Calcium perchlorate, for example, is a common Martian perchlorate - Ca(ClO4)2. It burns with hydrogen (14 H2) to produce CaO + Cl2 + 7 H2O. It burns with methane (3,5 CH4) to produce CaO + Cl2 + 3,5 CO2 + 3.5 H2O. In the former case, that's 28 AMU of hydrogen per 239 AMU of calcium perchlorate, or a ratio of 1:8.5. In the latter case, it's 14 AMU of hydrogen per 239 of calcium perchlorate, or a ratio of 1:17 - meaning you need very little hydrogen per unit mass of oxidizer (which is a very good thing!**). LOX/H2 and LOX/CH4 are, by contrast, ratios of 1:4 and 1:8, respectively. Now, using perchlorate as an oxidizer yields a propellant that's not as high ISP as using LOX, of course, but for the first stage (the heavy stage), you don't need a super-high ISP. Calcium perchlorate is 2 1/2 times denser than LOX (a huge advantage in terms of reducing tankage mass), suffers no thermal management issues at practical Martian temperatures, and being a solid rather than a liquid does not slosh. The ISP of the propellent mix can be improved by converting the calcium perchlorate to ammonium perchlorate, at a cost of complexity and additional raw materials (imported hydrogen + local Haber process or imported NH3). If a pure solid rocket is desired rather than a hybrid, methane can be polymerized with heat and catalysts to heavier hydrocarbons that will solidify when allowed to cool to Martian ambient temperatures. This process would further reduce the amount of hydrogen that needs to be imported, as hydrogen gas gets released during polymerization.
Not saying that this is the best of approaches. It's just an approach I haven't heard discussed before as far as locally produced propellants are concerned.
** While most people assume local Martian hydrogen and oxygen from electrolysis of Martian ice, this is far harder than most people assume, and not simply because mining hard materials on another world is so potentially difficult. Our history of experience with electrolysis in space has been fraught with problems (see the ISS for examples), and that's with about as tightly controlled feedstocks as you can get. On Mars you're dealing with not pure water ice, but rather frozen muck. Hence the lower-risk proposals call for using a solid oxide fuel cell to convert CO2 to CO+O2 to get the oxygen and importing the hydrogen.
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Yes, it's stupid, confusing, and the IAU needs to revisit their bad decision even if only for this reason, rather than letting it fester.
You apparently see no problem grouping together the rocky inner planets with the enormous gas and ice giant outer planets. Yet you have a fundamental problem with grouping the rocky inner planets with bodies like Ceres and Pluto that they share far more in common with.
And yes, Pluto and Charon are KBOs. KBOs are an orbital designation, one type among many. Mercury, Venus, Earth and Mars also have an orbital designation, for example - "inner planets". An orbital designation can quite happily sit side by side with a classification of an object based on what its actual physical characteristics are.
You're avoiding the question: why? What's so damned logical about grouping Mars with Jupiter, but not with Ceres or Pluto? And what was "currently deemed planets" included Pluto until the IAU decided to butt in, so that argument buys you nothing. They changed the status quo, they weren't preserving it.
Hydrostatic equilibrium is a highly logical dividing line. It has meaning, unlike whether a neighborhood has been cleared (usually by a larger second party, I should add, not by the planet itself - the IAU definition is built on a foundation that is a lie, that the "8 planets" cleared their own neighborhoods). When a body relaxes into hydrostatic equilibrium, it not only changes shape, but it differentiates and remineralizes. It becomes a fundamentally new type of body, with internal structure, non-primordial minerals, and internal heat flows (even if they - like everything else - eventually die). One studies bodies that are in non-hydrostatic equilibrium to learn about the primordial solar system, while one studies bodies that are in hydrostatic equilibrium to learn about planetary evolution, to search for life, etc. It's a distinct dividing line. Let's not pretend that it's not there. Or that it doesn't need a term to refer to it. Such as the term we've been using this whole damned time - "planet".
Which is why the ancients knew of Uranus and Neptune, right? Oh wait... Sorry, I guess they're not planets!
And again: why don't we just lock all sciences down by what the ancients knew? Sorry, guys, there's only 8 elements - copper, sulfur, tin, gold, antimony, mercury, and lead - everything else is just "earths"! Or maybe we should just stick with the 4 elements? Because that's the whole point of science, after all - rote memorization of things that people in long-extinct societies declared in their ignorance.
"all" is of course a falsehood. For many KBOs, Neptune has little effect. And here's a category for you to ponder while you're at it: the Sednoids. One of the leading theories is that there's a body out there, potentially in the ballpark of the size of the Earth, that's scattering them;
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Is it just me or did Earth get stuck with possibly the most boring satellite in the entire solar system?