Monday, March 16, 2015

#DEARPLUTO Announcement



Share your thoughts about Pluto!

2 comments:

Frankie said...

Laurel, we discussed planethood on Ars Technica a few years ago. You advocated for a definition that was independent of the planet's neighbors.

I had a question for you: should Titan and Callisto be planets? Should "Moon" be a planet? They're all a lot bigger than Pluto. Position independence!

IMO, the KBOs should be called the Plutoids, to reinforce the understanding that they are like the asteroids: a collection of thousands of related bodies, none of which are full planets.

Laurel Kornfeld said...

I support the idea of classifying Titan, Calliston, Earth's Moon, and all spherical planetary moons as secondary or satellite planets. Those in hydrostatic equilibrium have the structure and processes that the primary planets have; the only difference is they orbit other planets instead of orbiting the Sun directly. Some in our solar system may even have subsurface oceans that could host microbial life. In exoplanet systems, the spherical moons of gas giants could potentially be habitable for life as well.

Your proposal about calling all KBOs "Plutoids" has exactly the same problem as the IAU definition, namely, it classifies a whole group of objects first and foremost by their location rather than by their intrinsic properties. Not all KBOs are the same. To advocates of the geophysical planet definition, those KBOs that are in hydrostatic equilibrium like Pluto, Eris, Haumea, and Makemake ARE full planets. They are significantly different from the thousands of tiny, shapeless KBOs around them and therefore are NOT like asteroids.

There really is no need for the term "Plutoids" at all. We can simply acknowledge that those objects that are large enough and massive enough to be in hydrostatic equilibrium should be dually classed as both small planets (of the dwarf planet subcategory) and KBOs. The first tells us what they are; the second tells us where they are.