In July of 2005, Mike Brown and his team members announced the discovery of 2003 UB 313, what very well appears to be the 10th member of our solar system, orbiting our Sun at the mindboggling distance of 97 astronomical units. In October of last year it was further announced that “Xena” (it’s decidedly unofficial nickname) has a moon.

Image credit: Robert Hurt (IPAC)

Initial observations of 2003 UB313 indicated that the object was larger than Pluto. As reported recently by Emily Lakdawalla at The Planetary Society, it appeared that those size estimates were being diminished, according to this article by Robert Irion at ScienceNOW:

A new Hubble Space Telescope image reveals that a bright object in the outer solar system is Pluto’s near-twin in size, not a big brother. The so-called “tenth planet,” announced last July to much fanfare, is a “smidge” bigger than Pluto rather than earlier estimates of 25% to 50% larger, a planetary scientist reported here on 25 January. The downsizing puts a new focus on an ongoing struggle among astronomers to define the lowest size limit for planets.

It turns out that this report was premature. Mike Brown has stated “Contrary to rumors otherwise, we’re just in the preliminary stages of analyzing the HST data. When we are done we should have a very precise measurement. I hope that we will have the HST analysis done within perhaps a month, and I’ll be able to say more then.” The latest news posted on Brown’s website describes the recent observations completed using the IRAM radio telescope (press release here):

When an object is too far away to directly see how big it is, astronomers use an indirect method instead where they measure the heat coming from the object. If we wanted to measure the size of a fire, for example, we could do it by measuring the total amount of heat coming from the fire. The temperature of the flames in a match and a bonfire are essentially the same, but a bonfire emits much more heat because it is much bigger. The same is true of distant planets. Because we know how far away the planet is we have a pretty good idea of the surface temperature (a frosty 405 degrees below zero!), thus when we measure the total heat we can tell how big the object is. Unfortunately, the new planet is so far away and so cold that our first attempt at measuring the heat, using the Spitzer Space Telescope, could not detect the heat output. This fact tells us that the object must be smaller than about 3300 km.

In the meantime, observations have been made by a group from the University of Bonn from the 30-meter IRAM telescope. This telescope, like Spitzer, measures the heat output. IRAM measures the heat output in a region of the spectrum where much less heat is given off, but IRAM is a much larger telescope than Spitzer. The observations were successful in finally detecting the heat of 2003 UB313. From the amount of heat measured they determined that 2003 UB313 has a diameter of 3000 +/- 400 km. This size measurement puts 2003 UB313 right in the range of the expected albedos listed above. A very nice discussion of the measurement and what the uncertainties mean can be found at the press release web page.

So, a bit of unnecessary confusion unfortunately (and temporarily) seemed to enter the equation. I very much look forward to seeing the complete results become available from the latest round of Hubble observations. For further reading on the subject, take a look at this new article by Amir Alexander, as well as the latest coverage of the stories on Space.com and SpaceRef.

The most commonly discussed issue on the ‘net has centered upon whether or not 2003 UB313 will officially be deemed a planet by the IAU (and Mike Brown has commented on those ongoings, here). Personally, I’ve never really grasped the wrangling over nomenclature, examples of which can be found on many popular astronomy message boards (and some are most passionate, pro and con). A planetary declaration would certainly serve as quite a distinction for the discoverers from CalTech and Yale who’ve invested so much time and effort in the observations. It should be noted, though, that size does not a planet make. I’m exponentially more interested in the object’s properties and characteristics, and what its study can reveal about our cosmic neighborhood.