Thursday, March 12, 2015

Alan Stern: New Horizons and Pluto |

Alan Stern: New Horizons and Pluto |

This is a great talk by Alan Stern about New Horizons and Pluto, including why the IAU got it wrong. You can listen to the hour-long talk by playing it online--scroll down to the end of the article for the player--or you can download it.


Foo Bar said...

Laurel, why does Pluto deserve to be a planet?

Is it tradition? Then Pallas, Parthenope, etc, should be planets first.

Is it size? Then Titan, "Moon", etc, should be planets first.

Just like Ceres is first among the asteroids, Pluto is first among the Plutoids. Why not be happy for it?

Laurel Kornfeld said...

No, it is not tradition. Pluto is a planet according to the geophysical planet definition, which many planetary scientists prefer over the dynamical one. The geophysical planet definition classifies objects first and foremost by their intrinsic properties rather than by their location. Pluto is large enough and massive enough to be rounded by its own gravity, a state known as hydrostatic equilibrium, which is what makes it a planet.

Parthenope is far too small to be in hydrostatic equilibrium while Pallas, like Vesta, is a borderline case. Both Pallas and Vesta, being close to hydrostatic equilibrium, should have their own, intermediate category between asteroid and dwarf planet, such as proto-planet or sub-dwarf planet. I would like to see a mission like Dawn visit Pallas to compare it with Vesta.

Ceres is not an asteroid, as it clearly IS in hydrostatic equilibrium. Calling it the "first of the asteroids" was a 19th century position. At the time, telescopes of the day could not resolve Ceres into a disk, so no one knew that unlike the other objects between Mars and Jupiter, it is spherical and therefore has the same complexity as the larger terrestrial planets. Today, we know that not only is Ceres round; it also may very well have a subsurface ocean that could potentially host microbial life.

The same is true for Pluto. It is a small planet. New Horizons has shown it to have a degree of geological and atmospheric complexity greater than that of Mars. It too may have a subsurface ocean. Like Alan Stern, I see no use for the term "Plutoids." Pluto is in no way like the majority of the tiny KBOs beyond Neptune, and it makes no scientific sense to blur the distinction between two very different types of objects. Asteroids and most tiny KBOs are loosely held together rubble piles. Ceres and Pluto are nothing like them.

I cannot "be happy" for a poor definition that fails to acknowledge the important difference between two very different types of objects simply because of the objects' locations.