Exploring and Defining Planetary Systems

Now that we’re about a decade and a half into the “new” century, it’s not a bad time to look at where we are as we explore the cosmos. Planetary science has always been one of my great interests, so I’ll take a look at that in this musing (and then explore other aspects of astronomy in the 21st Century in other musings).

Planetary science is, essentially, the study of the origin and evolution of solar system objects and is now embracing the study of exoplanets as well.  There are BIG stories in planetary science, ranging from the continued characterization of objects we know about and the continued discovery of others far out in the distant reaches of our solar system. This week the AAS Division of Planetary Sciences is meeting, and I know there are some very cool stories to be shared! Due to these stories, I think that planetary science has more than come into its own as a discipline. It’s more than dividing planets into rocky ones and gas giants, or (in the extreme) getting upset about the planetary status of Pluto.

I’ve written several times in the past few years about Pluto and the whole “is it or isn’t it a planet” discussion that has been raging since the 2006 vote at the International Astronomical Union that supposedly stripped Pluto of its planet status. There are many questions about why the vote was held, what the IAU’s authority was to hold a vote, and why so few planetary scientists (who are also IAU members) were involved in a decision that is squarely in their domain (and not in the stellar astrophysics domain, for example). It’s an ongoing controversy and one that does call in to question the IAU’s actions at that time and since then.

The IAU is an international coordinating body that is charged (among other things) with doing the cosmic bookkeeping necessary so that we don’t (for example) have three planets named Saturn, or two asteroids with the same name, or misnumber a comet. In that sense, they provide a valuable service. The group has also waded into the whole “definitions” arena, and this is where it has been less than successful in terms of serving science. Lately, the group has also stepped into arenas (such as the Pluto vote) that call into question its self-assumed authority over something so simple as naming a crater on Mars or naming exoplanets.

It has always been my understanding that the IAU’s responsibility over names was simply to make sure there were no duplicates, or that a suggested name was appropriate within a theme. For example, craters on Venus are named after famous names or bear other female names. In recent years, the IAU has taken on a role wherein it assumes it has sole and undisputed authority, not to mention the moral high ground, to name things, rather than simply being the bookkeeper. It has gone as far as to sponsor an event to name exoplanets, but bristles if any other group wants to do the same thing. Seems rather curious for an organization that is supposed to serve science and scientists. I won’t go into details here. If you’d like to read the rather extensive analysis I did a couple of years ago, you can find articles here.

I digress a bit. Let’s get back to Pluto and the magnificent importance of planetary science.

For the record, I’ve always held that Pluto IS a planet. It is in the category of dwarf planet, which tell us something about its size in relation to the rest of the solar system objects that also carry the status of planet. It’s perfectly fine category, and in fact, dividing planets into finer subdivisions isn’t a bad thing to do. We already have rocky planets, gas giants, ice giants, and dwarf planets. As planetary scientists explore and learn more about worlds in the outer solar system, they’ll find more and different ways to distinguish worlds from each other. Each definition and distinction will presumably tell us more about an object’s history, its structure, orbit, and relationship to other objects in its immediate vicinity.

The most exciting mission for planetary science is the one that discovers new places and explore ones we haven’t had a chance to visit before. Mars is a good example, and we are treated daily to amazingly cool sights from the Red Planet. Saturn is another, and the Cassini Mission continues to dazzle us with a years-long visit to the ringed world, its moons and rings.

For my money (and everybody else’s), the New Horizons mission to Pluto and beyond is going to redefine the solar system for us. Note that I said the mission is going to do the redefining. It’s an important distinction. The mission scientists are already finding themselves at the forefront of some amazing discoveries. Pluto and Charon will at last be revealed up close and personal. But, what fascinates ME is what we’ll find beyond these two. We already have found several more dwarf planets, and New Horizons has two worlds to study after Pluto and Charon. The Kuiper Belt phase of the mission will be the very essence of the term “discovery” and I think we’re going to find out just how little we knew about the solar system before that. We’re going to have more worlds than we know what to do with, and at that point, the discoveries will blow imposed definitions of distant worlds out of the water.

Planetary science is uniquely suited to do this kind of study, and the people who have devoted their lives to the discipline are trained in a number of scientific areas that apply specifically to worlds: geology, atmospheric science, chemistry, biology, and physics, to name a few. Many also have astronomy backgrounds, and in fact for a long time, planetary science was considered an offshoot of astronomy. These days that is changing. The American Astronomical Society’s largest offshoot organization is devoted solely to planetary science, and is no longer an afterthought on the last day of the meeting. Planetary science has, in essence, become its own science. It’s not astronomy (as in the study of the stars), it’s … planetary.

In the 21st century, planetary science has the role of teaching us the fine points of solar system science. And, because we are now seeing evidence of planetary formation around other stars, and have in fact discovered a growing number of those worlds, planetary science is moving into a very important role in helping understand those worlds, and our own solar system’s early epochs.

And, getting back to the IAU, given the phenomenal growth in planetary science and its scientific disciplines, perhaps it’s time to review what role the organization has in serving planetary science. Getting up a contest to name exoplanets (while fussing about the Uwingu exoplanet contest, for example) isn’t really serving planetary science. In fact, not many people outside of Europe have heard of this contest, so I can’t even say that it’s serving science outreach.

Nor is getting involved in coming up with arbitrary definitions of “planet” and other terms a necessary part of IAU’s role. After watching the whole “definition debacle” play out, I’m coming to the firm opinion that when it comes to defining the terms of the field, it’s best left to planetary scientists themselves. After all, they are on the front lines of research, not the bookkeepers.

The IAU has a fine service record, and it can still fill a role. But, maybe, just maybe, it should pay much  more respect to the planetary scientists (many of whom are members) and the job they’re doing. It is the expertise of the planetary science community that will help us and future generations understand planetary systems. IAU’s role should be (as it was for so many years) as support crew for what is turning out to be one of the most exciting science disciplines in the 21st century. And, that’s as it should be.

As for planetary science itself, I can’t wait to see what the community will discover here in the solar system — and beyond. Every time we think we’ve got it all figured out, our instruments and spacecraft uncover something new and never-before-seen. Like the astronomers who are expanding our view of the cosmos out to the epochs of the first stars, planetary scientists are literally showing us our past— and our future — as citizens of a still-largely-unexplored sector of the galaxy.