2003 UB313, the ’10th planet’ discovered by Michael Brown (California Institute of Technology), continues to fuel the debate over what constitutes a planet and where the division between planet and Kuiper Belt object should be. A new Hubble photograph shows the object to be slightly larger than Pluto, but nowhere near the 25 to 50 percent larger that Brown originally estimated.

But Brown was the first to state, early in the game, that we needed better data to get an accurate size estimate. And you can see why his original view made sense: if 2003 UB313 really is not much larger than Pluto, then it reflects over 90 percent of the light that hits it. What causes the additional brightness (Pluto, for example, reflects just 60 percent of incoming light) remains conjectural. But this must be an icy surface, and the distinctions between the new world and Pluto will continue to spur controversy.

Meanwhile, we have a new paper on another Kuiper Belt find, the object called 2003 EL61. The authors, who include David Rabinowitz (Yale Center for Astronomy and Astrophysics) and the aforementioned Brown, report on the detection of crystalline water ice on the surface. From the abstract: “The signature of crystalline water ice is clear and obvious in all data collected. Like the surface of many outer solar system bodies, the surface of 2003EL61 is rich in crystalline water ice, which is energetically less favored than amorphous water ice at cold temperatures, suggesting resurfacing processes may be taking place.”

The paper (submitted to the Astrophysical Journal) is “The Surface of 2003EL61 in the Near Infrared,” now available at the arXiv site.

And finally, a nice Plutonian note from the Lawrence Journal-World reminds us that Clyde Tombaugh will be honored this Saturday at the University of Kansas. January 4 would have been the KU alumnus’ 100th birthday. How fitting that the featured speaker will be Alan Stern, principal investigator for New Horizons, aboard which a portion of Tombaugh’s ashes now make their way to the world he discovered.

For more on Tombaugh, I lean toward David Levy’s ClydeTombaugh: Discoverer of Planet Pluto (Tucson: University of Arizona Press, 1991), but also check Margaret Wetterer’s Clyde Tombaugh and the Search for Planet X (Minneapolis: Carolrhoda Books, 1996).