On August 24, 2006 the International Astronomical Union (IAU) ruled to reclassify Pluto, formerly the ninth planet in our solar system, as one of three “dwarf planets.” This entirely new category will also include the asteroid Ceres and the newly discovered object, 2003UB313. The decision followed much debate on the definition of a planet after the 2005 announcement that the new body rivals Pluto in size. On September 13, 2006 the IAU gave 2003UB313 the official designation Eris and named its moon Dysnomia. Eris was the Greek goddess of discord or strife. Dysnomia was her daughter, Lawlessness. Pluto (now officially, minor planet 134340) and its cohort orbit the Sun along with many other asteroids and comets at the edge of the solar system.
We asked astronomer and AccessScience author Tobias C. Owen to share his musings on these changes in nomenclature and how he first became interested in planetary studies. He sent his responses from Berlin, where he was attending an international conference on planetary science before heading to Moscow to lecture on nitrogen and work with Russian scientists on their new mission to the Martian moon, Phobos.
Dr. Owen received his PhD from the University of Arizona in 1965 and was first invited to write for the Encyclopedia in 1975 when he was recommended as an "outstanding authority on the outer planets." He continues to update the AccessScience articles on Saturn, Uranus, Neptune, and Pluto as knowledge about them advances. A professor at the University of Hawaii-Manoa, Dr. Owen's research focuses on the origin and evolution of planet atmospheres; solar system exploration; the spectroscopy of planets, satellites, and comets; and the origin and cosmic distribution of life.
He has published his research in the journals Science, Nature, The Astrophysical Journal, and Icarus, among others, and has played an integral role in several planetary missions, including the conception and development of NASA's Cassini–Huygens mission to Saturn. In 2006 Dr. Owen received the University of Hawaii's Regents Medal for Excellence in Research and shared the Grand Prix Marcel Dassault of the French Academy of Sciences with two colleagues, awarded for developing the successful Huygens probe to the surface of Saturn's giant satellite Titan.
In his multidisciplinary text on astrobiology, The Search for Life in the Universe, Dr. Owen and his co-author dedicate the work in part to the memory of Giordano Bruno, "burned at the stake on February 17, 1600...(and) best known to posterity for his assertion that the cosmos contains multitudes of inhabited worlds." We are grateful that society looks more kindly on maverick thinkers these days and delighted that one of them would grace us with his thoughts.
-J.F.N.
Access Science: In many ways your research questions are like those of a bright, curious child that wonders, "What is it like on other worlds?" What did you wonder about as a child?
Tobias C. Owen: Kind of you to say! I have always admired the openness and imagination of children, they are qualities I try to keep when doing science.
That question about other worlds has been with me since I learned to know the planets and constellations as a child growing up in Denver and Santa Fe. The dark skies were conducive to stargazing, and noticing the planets move among the stars was my first sense of them as other worlds.
AS: What first inspired you to study the planets?
TO: That early naked-eye experience has stayed with me. The cast and brace required by a cracked vertebra when I was 11 severely restricted my activities and I used that time to grind and polish a mirror for a telescope. My first look at Jupiter was a great thrill! I went on to use that telescope to record brightness changes in variable stars, but came back to planets in college. That sense of other worlds was strongly appealing!
AS: You have studied winds on Saturn and the surfaces of its moons, Jupiter's origins, the Martian atmosphere, and methane on Pluto, among many other topics. Tell us about some of the larger themes in our understanding of the planets that have come to light since you began asking questions. . .
TO: Perhaps the most important cultural perspective provided by planetary exploration is the growing awareness of just how exquisitely precious our own planet truly is!! This perspective still hasn't hit home with the force it should. There is nowhere else for us to go. We have to regulate the human population and take better care of the Earth. Our behavior is simply scandalous!
One of the biggest scientific contributions of planetary exploration to the history of ideas was the realization that impacts of smaller bodies–asteroids, meteoroids, comets on the planets have had a major influence on their formation and subsequent history, for example, the Origin of Earth's Moon. In my own specialty, that new paradigm helps us understand the origin of our atmosphere and the formation of the giant planets.
Other major advances have been:
- The recognition of the importance of the "greenhouse effect," and hence the danger it poses to the Earth
- The absence of easily detectable biological activity or even organic matter on the surface of Mars
- The fundamentally hostile environments on Venus and Mars and the reasons for that hostility. Earth is it!
The assimilation of the other planets into our cultural awareness–these moving lights in the night sky have become real worlds, their pictures appearing in our books, movies and advertisements. From a position as bystanders on a distant shore, we have become sailors of the solar system, exploring these new worlds to know better how our own planet and we ourselves came to be.
AS: You write in your AccessScience article about Pluto that it has been an intriguing object since its discovery in 1930. . .why is that?
TO: Pluto never fit comfortably into the solar system, especially once we learned how tiny it is. Even before that, however, the high eccentricity and inclination of its orbit made it very different. The fact that its rotational period was close to the orbital period of Triton around Neptune suggested to some scientists that there might be a connection between these two distant worlds, but it was impossible to determine what that connection was.
AS: Many people are disturbed by what they call Pluto's demotion from planet to dwarf planet. What do you think. . .has it lost value?
TO: Not at all!! Borrowing a page from a famous fairy tale, when Pluto was classified as a planet, it was an "ugly duckling," but as a leading member of the Kuiper Belt, it sails serenely through the outer solar system like a beautiful swan!
AS: Pluto and other "icy planetesimals" orbit the sun beyond Neptune in that region called the Kuiper Belt. Briefly, what does this region tell us about the origins of the solar system?
TO: We're not completely sure about this yet. From my perspective, the Kuiper Belt looks like an assemblage of icy planetesimals left over from the formation of the giant planets. Briefly (indeed!), the leading idea for giant planet formation right now starts with the formation of a giant core made from icy planetesimals that formed at very low temperature, <25-30 K (<-245º C, -415º F). When this core reached a size of about 10 x the mass of the Earth, it could attract hydrogen and helium from the surrounding solar nebula gas, which collapses onto the core in a humongous "whoosh!", producing a giant planet. In this scenario, the Kuiper Belt represents icy planetesimals that never formed such a core, presumably because at this great distance from the Sun, there were simply not enough of them in a given volume of space. The solar nebula was too thin.
Now, as a result of occasional collisions or the gravitational perturbations of passing stars, one of these planetesimals is sent into an orbit that eventually brings it to the inner solar system, where we see it as a short period comet.
AS: The whole impetus for the reclassification came from the discovery of a body beyond Pluto that is even larger, 2003 UB313, just officially named Eris. What do you think about the name? How are Eris and her moon Dysnomia interesting?
TO: The names are terrific! These guys are interesting in the same way Pluto and the other KBOs are, perhaps more than Pluto, if it can be shown that these two never got as close to the Sun as Pluto is. The farther away they are, the colder, and hence the better the chances that they have preserved their original composition.
AS: What would you most like to know about Pluto and other bodies in the Kuiper Belt?
TO: Pluto is actually less interesting to me than a more distant example, for the reason just given. What I'd like to know about a distant object that's been preserved for the age of the solar system at a temperature below 25K (-4157ºF) is; What is it made of? Specifically, has it preserved the composition of the original solar nebula? The abundances of nitrogen and argon would be important clues.
