Pluto's Status Has Kids Confused

via Livescience, the confusion of astronomers about the definition of planet and the subsequent impact on the status of the solar object called Pluto has left American school chidren (and probably children and adults globally) pretty confused. Traditionally accepted as a planet since its discovery in 1930, the International Astrnomical Union redefined the world as a "dwarf planet" two years ago, only to recently coin yet another term for it and object like it, "plutoid".

"Science teachers and publishers already worked to update their resources to read "dwarf planet." And now, boom, that category is out of favor among astronomers.

"Students who have just learned about the concept of dwarf planets must now be taught the new concept of plutoid," said Janis Milman, who teaches earth science at Thomas Stone High School in Maryland. "This will lead to confusion in the classroom and resistance to learning the new terms, because the students will question, why learn something that might change again in a year or so?"

This has left educators and textbook manufacurers scrambling to keep up and everyone scratching their heads, and has left even some astronomers vowing to keep up the good fight to maintain Pluto's status as a planet. The difference between a dwarf planet and a plutoid appears to be simply location: plutoids are small rocky/icy objects located outside the orbit of Neptune, so recently discovered Kyper Belt Object Eris is also a plutoid, leaving the object Ceres (formerly an asteroid) as the only true "dwarf planet" - even my head is spinning and I follow this stuff pretty closely.

Stay tuned for further developments.

Pluto's Small Moons Adopted?

The Universe Today takes a look at the satellites of the "dwarf planet" Pluto, Charon, Hydra and Nix. The last two smaller moons were only recently discovered by the Hubble Space Telescope in 2005 and named the next year. The currently accepted theory of Pluto moon formation is much like that of the Earth's; a major impact event of two objects chipped Charon from Pluto, with the other satellites remaining as leftovers from the collision.

However, the orbits of the two smaller moons lead this theory into question. If they were the result of debris from the impact event, their orbits would almost certainly be irregular and elliptical. However, they are not only both in a near regular circular orbit, they are in resonance with Charon, with Nyx orbiting Pluto 4 times for every Charon orbit and Hydra 6, mcuh like the Jupiter system moons of Io, Europa and Ganymede. The question then remains if they could have simply formed from a cold disk of dust that may have remained from the impact. Again, however, the modelling researchers have conducted of the impact event leads us to believe such a dust disk would be very compact around Pluto - far inside the orbits of the two small moons.

Another possibility is that the two moons formed quite close to Pluto but later migrated due to gravitational interaction between Pluto and Charon, but the simulations conducted so far don't seem to support that idea either. Thus, we are left with the only other solution; that they formed outside of the Pluto-Charon system and were likely captured at some later point as Pluto orbited the Sun.

While the research will continue, it is likely that no definitive answer will be forthcoming until the New Horizons probe visits Pluto in 2015. And perhaps not even at that time.

More on Pluto

via National Geographic.

Astronomer Mike Brown of CalTech discoverer of several Kuiper Belt Objects (KBOs) in the distant reaches of our solar system, has led a new analysis of the dwarf planet Eris (formerly called Xena and 2003 UB313) that places its mass firmly ahead (up to a third larger) of our old friend Pluto, demoting it not only from planet status but also as the King of the KBOs. The key was getting the mass of Eris' moon, Dysnomia.

"The key to finding Eris' mass was its tiny moon, Dysnomia. Brown and Schaller used Keck and Hubble to capture images of the moon's position over time. The data suggest that Dysnomia is Eris' only moon and orbits every 15 days. The researchers also calculated the total mass of the pair—about 1.27 times that of Pluto—and revealed that the objects are made of around 70 percent rock, making them as dense as Pluto and Triton, a moon of Neptune."

Of course, it has been Brown's work on the region that has ignited the controversy over the definition of the word planet and the status of our formerly ninth planet in the first place. However, there are still those who favor the initial IAU (International Astronomical Union) definition that would allow Pluto to maintain its planetary status, and add both Eris and Ceres (formerly an asteroid) all now both "dwarf planets". However, after much discussion, that definition was shelved in favor of another more restrictive one that resulted in the creation of the new "dwarf planet" category that the three solar objects now dubiously enjoy.