The Subject Was Dwarfs!

Dr. Mark Sykes and Dr. Tom Fleming

Dwarf planets, that is... I frequently attend the Steward Observatory Public Evening Lecture Series, which usually meet a couple Monday nights per month (while school is in session) at the big lecture hall at Steward Observatory - the same location that the Tucson Amateur Astronomy Association meets. The lecture series has been going on since the Observatory was started over 90 years ago! Of course, the University of Arizona is well known for its astronomy department, but it is across the street from the headquarters of Kitt Peak National Observatory, as well as the Lunar and Planetary Lab. So you can imagine the speakers and variety of topics is second to none! And as if you needed another excuse to go, they open the 21" telescope in the old dome for observing if the weather permits!

Such was the case last month when I attended the last talk of the semester - Dr. Mark Sykes CEO and Director of the Planetary Sciences Institute (also in Tucson!) gave a talk on recent discoveries on Ceres, Charon and Pluto. Since New Horizons spacecraft flew past Pluto last July, data has been trickling out as the data is downloaded from across the solar system. So It was going to be great to see the latest images and hear early interpretations of what is being seen.


The lectures are great - well attended by a wide variety of folks - both older people, of which group I include myself, and a good percentage of young college students, some of which obtain extra credit for attending the lecture. Dr. Tom Fleming, Sr. Lecturer at Steward acts as emcee, making announcements, introducing the speaker, and marking off students attendance for their class credit. At left is a 2-frame mosaic of some of the crowd as Tom makes his introductions.

Of course, the first thing Dr. Sykes had to do was talk about the demotion of Pluto from planet to dwarf planet, one of his first slides shown at right. It turns out that the issue isn't a matter of size, but rather if it has "cleared" its orbit of other bodies. As the plot shows, even if Pluto was the size of the Earth (red arrow), it wouldn't be considered a planet! The former asteroid Ceres, now considered a dwarf planet, is the question mark symbol near the bottom - also way too small to be considered a planet.


It has been a golden age recently in spacecraft missions to the planets. Not only the big missions everyone has heard of like Cassini at Saturn, and the parade of Mars landers, but smaller missions like Dawn, spending a year at asteroid Vesta, now orbiting Ceres. And of course, the New Horizons spacecraft flew past Pluto last year. Of course, when the mission was developed and finally launched in 2006, Pluto hadn't been demoted, and was considered off to the final planet of the solar system yet to be explored.

Mark started out with the ongoing Dawn mission at Ceres. One of the greatest mysteries as it approached were the bright spots associated with several craters seen from millions of miles away. At left is his closeup of crater Occator. Dr. Sykes said that scientists were ready to announce that the bright spots were salts or brine likely containing magnesium sulfate hexahydrite. Moving on to the New Horizons results, he showed some incredible images, including the two at right. Scientists had thought it would be a quiet icy world, but has been found to be incredibly diverse, both geologically and chemically.


Another thing that Mark talked about was naming issues. Almost as fast as the images came down, scientists starting naming plains, craters, features, which is generally a no-no unless approved by the IAU, conforming to naming conventions. He showed a map of Pluto's moon Charon showing jokingly (I think!) features named after characters from Star Trek, Star Wars, and other works of fiction (map shown at left).

I almost forgot! There are podcasts of the lectures, so if you want to peruse past lectures, check out the podcast link to the Public Evenings page above. When you do that you can actually watch the slides of the lecture on your computer while you listen - it is great! That means also you can hear/see Dr Sykes' talk there too!