Picture from the Colorado DMV.
I'm super excited to report that the two KBOs we are deciding between are officially called 2014 MU69 (PT1) and 2014 PN70 (PT3). Those are a mouthful of random numbers and digits, huh? That's why we call provisional designations like these "license plates". My first thought was that I should get someone on our team to have this as their actual license plate. I'd do it myself, but I don't own a car. Sadly, CO license plates have a max of seven numbers.
They are also the first official names for our KBO targets, which means you can go to JPL's Horizons, type in those names, and learn where to look for the objects in the sky from any location in the Solar System. You know, if they weren't among the dimmest objects discovered in the Kuiper Belt and could be easily spotted in ground-based telescopes.
Once one submits positions of an object from more than one night to the Minor Planet Center (MPC), names are immediately assigned. So, why did this take so long for our KBOs to get designations from the MPC? Well, this one's our fault really. We wanted to send the MPC our very best orbit positions, not the first ones that came out of our computers. Or the second ones. So we waited until we had results that we thought were super reliable.
Since we didn't have submitted positions done by the announcement of the discovery of the two objects, we had to come up with alternate names. Internally, PT1 had been given the designation 1110113Y, a name that has zero meaning outside of the KBO search team. The name makes more sense if you think of it as 11-1-011-3Y . We called it that because it was discovered on HST visit pair 11-12, chip 1 (of 2) and it was the brightest on shift stack 011, though we could see it on many stacks (I explained our shift-stacking method here. At one point last summer, I got really excited because I thought I discovered a KBO, but nope, it was object 1110113Y again, popping up in a different stack. Nope, hopes dashed in 30 seconds flat.). The last two numbers are just alphanumerics because it was one of hundreds of potential sources that Marc Buie's program picked up per shift stack that he had to vet to determine if it was a real object. Using A-Z in addition to 0-9 gives us 1296 options for a 2 digit number, versus 100.
Among, us, perhaps Simon Porter was the only one who had the whole string memorized. We all called it object 11. It was really weird reading posts online and seeing people talk about 1110113Y, when none of us called it that in our own discussions. There was also object 7 (0720090F, found in the pilot), object 45 (4510067S), e3 (e31007AI - we switched to hexadecimal for the tens digit after visit pair 99-a0), and finally g1 (g12000JZ).
We really didn't want to be calling anything "object 11" in the news. We never had 11 objects and the "visit pair 11 and 12" concept just took too long to explain. So we needed alternate names, and Xena, Santa and Easter bunny were not our style. We knew we'd be getting the license plates eventually; so we needed something ... forgettable. Saying "remember that Xena thing that was in the news?" to my family and friends so they'd know what I was talking about when I was trying to discuss Eris was bad enough. We didn't want to unofficial names to have a life of their own.
By the fall, we had 11, e3 and g1 left as targetable in the fall, so how about PT1, PT2 and PT3-- Potential Targets 1, 2, 3. And those names stuck with us so much that we stopped using 11, e3 and g1-- I've been asked if PT3 was e3 or g1 more than once.
So here are our names: 0720090F = 2014_MT69 1110113Y = 2014_MU69 (PT1) e31007AI = 2014_OS393 (PT2) g12000JZ = 2014_PN70 (PT3)
The minor planet center gives us these names based on when the object was discovered (they explain how here).
Here's how it works. I did not invent this system, so do not blame me for it. Objects 11 and 7 were discovered in the 12th half-month of 2014, designated "M" (because they skip I and Z). So the first 25 new objects (because they just skip “I” now) found from June 16-30 are 2014 MA, 2014 MB, ... 2014 MZ. The next 25 are 2014 MA1, 2014 MB1, ... 2014 MZ1. So by the time we sent our positions in, they'd been through the truncated alphabet 69 times already. Thus, 2014 MT69 and 2014 MU69, are consecutive designations. If we sent our designations in earlier or later, we might have gotten nicer numbers (I've also made all the jokes about the designations already, so you don't have to). Boy, July 16-31, 2014 (half month "O") was a busy, busy month, I wonder what was going on then.
Why is object 45 not on the list? Well, you only get a name if you see an object on more than two nights. We never followed up on it because we knew immediately that New Horizons couldn't reach it, even based on what little we know of its orbit. It would have been dishonest to request Hubble time for an object what we knowingly couldn't reach. Hubble time is very limited, and wasting the orbits that we had been given for following up an object for the sake of chasing it, would have jeopardized our ability to get more time to characterize the good objects. Object 7 was a different story. Our first calculations had object 7 as a more reachable target than object 11, but we weren't able to rule it out without follow-up observations.
So, which will we go to, 2014 MU69 or 2014 PN70? We won't know until we get more Hubble follow-up when the objects pop out from behind the sun and get agreement from NASA on a favored target. We will interrupt our work on the Pluto encounter data analysis just enough to figure that out and answer this question before next fall, but I don't know anything at present, and I'm looking forward to Pluto first.