Planetary Geoscience
Pluto and the Kuiper Belt
Fifteen years ago, textbooks described the Solar System as consisting of nine planets, the last being a small, icy oddball in a somewhat eccentric and very lonely orbit that reached ~40 AU from the Sun. That oddball, Pluto, is no longer so odd or lonely, but it is also no longer a planet! In the past decade-and-a-half, astronomers have discovered more than 1200 objects that orbit the Sun beyond Neptune, and more are being discovered every day. Pluto, it turns out, is just one member of the Kuiper Belt, a belt of icy bodies analogous to the asteroid belt of rocky bodies between Mars and Jupiter. Several of these Kuiper Belt objects (KBOs) are similar in size to Pluto, and one is even bigger than Pluto! Some KBOs travel to much greater distances than Pluto – one, Sedna, swinging to nearly 1000 AU from the Sun.
KBOs show some interesting groupings in their orbits that provide strong evidence that Neptune did not form where we see it now. Rather, astronomers now think that Neptune formed closer to the Sun, and migrated to its present orbit early in Solar System history. Researchers in the UT EPS department are investigating the surface compositions of KBOs using ground-based and space-based telescopes. These bodies are so cold that, along with silicates (rocky material) and organic material, their surfaces consist of ices (solid phases) of CH4 (methane), CO2 (carbon dioxide), CO (carbon monoxide), N2 (molecular nitrogen), NH3 (ammonia), H2O (water). Correlating compositions of KBOs with orbital groups will provide additional information on when and how Neptune migrated and how that migration may have affected the rest of the Solar System.
Prof. Emery is involved in multiple aspects of this work.