We contacted Eric Christensen, Principal Investigator at the Catalina Sky Survey, which discovered object WT1190F, and he provided some excellent detail on how CSS assigns alphanumeric designations to newly discovered objects.

Since CSS reports millions of asteroid positions per year to the Minor Planet Center (MPC), we need a way to automatically assign unique identifiers to each object we detect.  If we were to accidentally assign the same identifier to two separate objects, the observations could cause problems for the linking routines used by the MPC.  CSS has been using the following convention for several years:


  • Character 1: W is for the year 2015 (2014 was V, 2013 was U.  Next year we’ll roll over to X)
  • Character 2: T is for the half-month, like MPC uses (A+B for January, C+D for February…T+U for October.  Capital “i” is skipped)
  • Character 3: 1 is in the range assigned to the telescope that detected the object (0-3 is the Catalina Schmidt, 4-7 belonged to the Siding Spring Survey that we previously operated in Australia, 8-B is for the Mt. Lemmon Survey, and C-F is reserved for laboratory reprocessing or a future survey)
  • Characters 4-7: A simple hexadecimal counter from 0000 to FFFF.

So, actually, one out of every 16 objects we reported in the first half of October received a temporary designation that started with “WT” and ended with “F”.  This is a combination that only could have appeared between 1-15 October 2015. We’re now assigning designations that begin with “WU,” and next month that will increment to “WV,” etc.

It doesn’t seem to be well-understood in the news stories that WT1190F is only the latest designation that we assigned to this object.

It was observed twice in 2013, receiving the designations UDA34A3 and UW8551D.  Now that you know the naming algorithm, you can work out when and where this was assigned, at least to the half-month (late February 2013 and late November 2013, from the Mt. Lemmon Survey telescope).

Note that for asteroids, after they are designated by the Minor Planet Center, nobody refers to the survey-assigned temporary designation any more.

But since WT1190F is not an asteroid, it got stuck with our automatically generated designation.


— Eric J. Christensen
Principal Investigator
Catalina Sky Survey
Lunar and Planetary Laboratory
The University of Arizona