New Horizons' New Target: Kuiper Belt Ice Chunk 2014 MU69

Vox reports on the next target destination for NASA's New Horizons probe, an ice chunk in the Kuiper Belt designated 2014 MU69. The plan is not yet final; like any space mission, complications are bound to come up. But if this selection sticks, New Horizons should reach 2014 MU69 in 2019. (Re/Code has the story, too.)

Comments

Re:Still no word on if its discoverer gets to name

[Rei]

Such a program already exists. And guess what - shock of all shocks, the IAU is throwing a hissy fit about it. They're basically at war with NH's director Alan Stern and are planning to refuse a large portion of the NH team's feature names for Pluto.

While we're on the topic...

[Rei]

... here's 19 reasons why the IAU's Pluto decision was ridiculous. But first, the definition

The IAU...resolves that planets and other bodies in the Solar System be defined into three distinct categories in the following way:
(1) A planet [1] is 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.

(2) A "dwarf planet" is 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 [2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects [3] orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

[2] An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

1. Nomenclature: An "adjective-noun" should always be considered 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 individual planets do not necessarily cleared their own neighborhoods, and their neighborhoods may not always have where they are. Jupiter, and Saturn to a lesser extent, have cleared most neighborhoods.

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.

7. Ambiguous definition: There is still no consensus on what defines having "cleared the neighborhood" - in particular, what the "neighborhood" is.

8. Lack of terminology: Exoplanets - indeed, including any potential Earthlike planets - are arbitrarily declared to not be planets. This deprives those studying exoplanets of an IAU-acceptable term to refer to them by.

9. Inability to describe exoplanets even if not ruled out: There is no way that even if

Re:While we're on the topic...

[athmanb]

1. Is just a nomenclature problem. The key issue was whether Pluto belongs in the same category as Mercury through Neptune.

2. If a planet changes its orbit, one of two things will happen:

• It clears its new neighborhood
• It gets cleared out by a new neighbor or falls into a resonance with it

In both of these cases the new category that object will fall in is quite clear

3. and 4. In geological terms yes, but I think the IAU was correct in preferring to define planets through orbital characteristics over geological ones.

5. The neighborhood of a planet cannot be simply changed without significant consequences. If through some freak incident a formerly solitary planet ends up suddenly having a neighbor of significantly higher mass, that planet will not remain a planet for very long. Its "mutability" is then not even restricted to definition games, it will quite be literally destroyed or thrown away into deep space.

6. An Earth-copy that hasn't cleared its neighborhood yet won't be an Earth-copy due to frequent crust destroying meteorite impacts. Such a child solar system will probably not be described well by our current terminology but these systems are also very rare because that phase of life only lasts for a very short time.

7. There will clearly eventually be edge cases, but Pluto isn't. There is an object with 10000 times its mass within its perihel and apohel. Its orbital period is not independantly "chosen" but defined by Neptune

8. - 10. Those are all things that we are just now starting to discover. They might eventually change up the definition of the word planet again, such as when we do find the first binary pair of planets with similar mass in the same orbit. But for now it should be perfectly acceptable to delay that decision until we have solid data.

11+ are mostly political points where you can have an opinion either way. But scientifically the question is: Are Pluto, Ceres, Eris and the 100+ other yet to be discovered KBOs really similar enough to the big eight to be in the same category.

Re:Ice, again?

[Rei]

New Horizons has cost about $45 million a year on average during the 15 years it was under development and operation, not $18 billion. And it was not developed by private corporations.