NASA may redefine planet again to re-include Pluto - Also the Moon, and over 100 other things in our solar system

http://www.sciencealert.com/nasa-sc...on-for-planets-and-it-could-change-everything

NASA scientists have published a manifesto that proposes a new definition of a planet, and if it holds, it will instantly add more than 100 new planets to our Solar System, including Pluto and our very own Moon.

The key change the team is hoping to get approved is that cosmic bodies in our Solar System no longer need to be orbiting the Sun to be considered planets - they say we should be looking at their intrinsic physical properties, not their interactions with stars.

"In keeping with both sound scientific classification and peoples' intuition, we propose a geophysically-based definition of 'planet' that importantly emphasises a body's intrinsic physical properties over its extrinsic orbital properties," the researchers explain.

The team is led by Alan Stern, principle investigator of NASA's New Horizons mission to Pluto, which in 2015 achieved the first-ever fly-by of the controversial dwarf planet.

Pluto was famously 'demoted' to dwarf planet status back in August 2006, when astronomer Mike Brown from the California Institute of Technology (Caltech) proposed a rewrite of the definition of planets.

The International Astronomical Union (IAU), which controls such things, declared that the definition of a planet in our Solar System reads as follows:

"A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit."

Having not yet cleared the neighbourhood of its orbit in space, Pluto could no longer hold the designation of a planet under these new guidelines.

Stern, who obviously has a great fondness for Pluto, having led the mission that showed us all its adorable heart pattern for the first time, recently called the decision "bullshit".

"Why would you listen to an astronomer about a planet?" Stern, a planetary scientist, pointed out to Kelly Dickerson at Business Insider in 2015.

He said asking an astronomer, who studies a wide variety of celestial objects and cosmic phenomena, rather than a planetary scientist, who focusses solely on planets, moons, and planetary systems, for the definition of a planet is like going to a podiatrist for brain surgery.

"Even though they're both doctors, they have different expertise," Stern said. "You really should listen to planetary scientists that know something about this subject. When we look at an object like Pluto, we don't know what else to call it."

Now, Stern and his colleagues have rewritten the definition of a planet, and are submitting it to the IAU for consideration.

"We propose the following geophysical definition of a planet for use by educators, scientists, students, and the public," they write.

"A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters."

If that's a little too jargony for you, their 'layman's version' is simply: "Round objects in space that are smaller than stars."

The definition sounds incredibly simple, but it's deceptively narrow - there aren't a whole lot of objects objects in the known Universe that would qualify, as it excludes things like stars and stellar objects such as white dwarfs, plus neutron stars and black holes.

"In keeping with emphasising intrinsic properties, our geophysical definition is directly based on the physics of the world itself, rather than the physics of its interactions with external objects," the researchers explain.

This would mean that our Moon, and other moons in the Solar System such as Titan, Enceladus, Europa, and Ganymede, would all qualify as planets, as would Pluto itself, which has already been looking more and more 'planet-like' of late.

The researchers don't just argue that their definition holds more merit than the current one in terms of what properties we should be using to classify a planet - they say the current definition is inherently flawed for several reasons.

  • "First, it recognises as planets only those objects orbiting our Sun, not those orbiting other stars or orbiting freely in the galaxy as 'rogue planets'," they explain.
  • Second, the fact that it requires zone-clearing means "no planet in our Solar System" can satisfy the criteria, since a number of small cosmic bodies are constantly flying through planetary orbits - including Earth's.
  • Finally, and "most severely", they say, this zone-clearing stipulation means the mathematics used to confirm if a cosmic body is actually a planet must be distance-dependent, because a "zone" must be clarified.

    This would require progressively larger objects in each successive zone, and "even an Earth-sized object in the Kuiper Belt would not clear its zone".
Of course, nothing changes until the IAU makes a decision, and if it decides to rejig the definition of a planet, either by these recommendations or others in the future, it's going to take a whole lot of deliberating before it becomes official.

But the team claims to have the public on their side, and if this public debate is anything to go on, maybe it's time for a rethink - even if Stern just really wants to stop having to answer the question: "Why did you send New Horizons to Pluto if it's not a planet anymore?"

You can read the proposal in full here.
 
No, sorry. Pluto should not be a planet. Unless we want to force everyone to remember like 100 different "planets". Or we have one definition based on feels and one based on something that actually makes sense.
Why does it matter anyway, Pluto is interesting regardless of if we call it a planet or not.
Science advances, knowledge adapts.

Stern, who obviously has a great fondness for Pluto, having led the mission that showed us all its adorable heart pattern for the first time, recently called the decision "bullshit".
Much science wow
 
oh yes, I'm sure there won't be a problem with 100 new planets

not gonna be hard to remember Mercury, Venus, Earth, The Moon, A'Hearn, AAS, AMOS, ANS...
 
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The "how will children remember 100 planets?" thing is a really dumb reason to be against this, since it's not like we expect people to list over 200 countries on demand. Also, having seen young children easily memorize dinosaur names I wouldn't put it past them to learn new planets easily.

I actually like this proposed definition, since even though it isn't perfect it has some good points. While it would be weird calling the Moon a "planet", the major moons of the gas giants are all geologically fascinating and active. The IAU definition is also incredibly flawed and isn't even well liked within the astronomical community. The definition was basically rushed through after we started finding more Kuiper Belt Objects and less than 5% of the IAU members were able to vote on the issue. Also one of the major points used to "demote" Pluto was that Eris (the dwarf planet whose discovery necessitated the vote) was larger than Pluto. However, new measurements from New Horizons has since disproved this, along with showing that Pluto is very geologically active.
 
Theres clearly an inappropriate emotional aspect to Stern's interest in altering the definition of what constitutes a planet. The current definition has issues but this seems like the worst possible way to resolve them.
 
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The real question is, what does any of this really change besides re-redefining Pluto? NASA will begin to call Ceres and several moons a planet on paper, but I won't, and nobody besides scientists at NASA will, something I doubt many of them will take to heart. If there was much justification for making so many classifications of rocks in space, we'd have already figured out some objective way to class them instead of spending decades arguing over the semantics of dwarf planets vs planets.

The only thing that comes close to an objective qualifier is the barycenter of its system, but there wouldn't be any argument about Pluto being a planet if that were a good enough definition, since it's rather ambiguous for Pluto. With that method discounted, we have no way to make a scientifically significant distinction between whether Pluto is a big rock or a small rock. Considering the ambiguity, it begs the question of what difference it makes at all whether Pluto itself is a dwarf planet or not.

What is terrible about this definition though is that it removes the distinction of moons, which have no issues in their current definition, Charon notwithstanding. Unlike the nebulous distinction between Mars and Pluto that is made by current nomenclature, that of, say, Jupiter and Io, has significant ramifications. It is quite significant that Io orbits Jupiter, and making Pluto a planet at the cost of throwing out such a significant classification shows that these scientists are motivated by a boner for Pluto more than anything else.
 
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Well I tried reading the paper or the summary of it, it's only two pages long

many members of the public, in our experience, assume that alleged “non-planets” cease to be interesting enough to warrant scientific exploration, though the IAU did not intend this consequence [1]. To wit: a common question we receive is, “Why did you send New Horizons to Pluto if it’s not a planet anymore?” To mitigate this unfortunate perception, we propose a new definition of planet, which has historical precedence
I'm not sure why they care. A large percentage of the population believes the month they were born in somehow corresponds to a constellation that can predict their personal future.

Planetary Pedagogy: With the above definition of a planet, we count at least 110 known planets in our Solar System (Figure 1). This number continues to grow as astronomers discover more planets in the Kuiper Belt [e.g., 7]. Certainly 110 planets is more than students should be expected to memorize, and indeed they ought not. Instead, students should learn only a few (9? 12? 25?) planets of interest. For an analogy, there are 88 official constellations and ~94 naturally occurring elements, yet most people are content to learn only a few. So it should be with planets

Understanding the natural organization of the Solar System is much more informative than rote memorization. Teaching the zones of the Solar System from the Sun outward and the types of planets and small bodies in each is perhaps the best approach: The zone closest to the Sun consists of rocky planets; the middle zone consists of gaseous, rocky, and icy planets; and the third zone consists of icy planets. All zones al
Can't argue with that I guess but it seems a little optimistic

The eight planets recognized by the IAU [1] are often modified by the adjectives “terrestrial,” “giant,” and “ice giant,” yet no one would state that a giant planet is not a planet. Yet, the IAU does not consider dwarf planets to be planets [1]. We eschew this inconsistency. Thus, dwarf planets and moon planets such as Ceres, Pluto, Charon, and Earth’s Moon are “fullfledged” planets. This seems especially true in light of these planets’ complex geology and geophysics [e.g., Lunar and Planetary Science XLVIII (2017) 1448.pdf 6]. While the degree of internal differentiation of a given world is geologically interesting, we do not use it as a criterion for planethood in the spirit of having an expansive rather than a narrow definition.
I support Planned Planethood :mad:
 
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The "how will children remember 100 planets?" thing is a really dumb reason to be against this, since it's not like we expect people to list over 200 countries on demand. Also, having seen young children easily memorize dinosaur names I wouldn't put it past them to learn new planets easily.

I actually like this proposed definition, since even though it isn't perfect it has some good points. While it would be weird calling the Moon a "planet", the major moons of the gas giants are all geologically fascinating and active. The IAU definition is also incredibly flawed and isn't even well liked within the astronomical community. The definition was basically rushed through after we started finding more Kuiper Belt Objects and less than 5% of the IAU members were able to vote on the issue. Also one of the major points used to "demote" Pluto was that Eris (the dwarf planet whose discovery necessitated the vote) was larger than Pluto. However, new measurements from New Horizons has since disproved this, along with showing that Pluto is very geologically active.
>"How will children remember 100 planets?"
>"How will children remember 63 gender identities?"
 
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