Understanding MPEC 2010-U20 - Asteroid Discovery Credit

BACKGROUND:

One thing that I have seen coming up over and over in the amateur and pro circles is the editorial notice released by the Minor Planet Center (MPC) regarding how discovery credit is defined when a new object is found. I have exchanged quite a few emails with the very patient Dr. Gareth Williams at the MPC trying to get a better understanding of how this all works. As an amateur astronomer, the prospect of finding a new asteroid is exciting. You will also find it proves to be very difficult. For some light reading before you dive into this post, I recommend The Guide to Minor Body Astrometry, and the Minor Planet Electronic Circular that deals with the discovery of minor planets MPEC 2010-U20. Finding a new asteroid these days is difficult because we have large surveys like Pan-STARRS and Catalina Sky Survey scanning the skies nightly looking for potentially hazardous asteroids that pose a threat to earth. During these nightly scans their automated processing routines pick up any moving object in their images and submit them to the MPC. Some of these have high Near Earth Object (NEO) ratings and end up published quickly so amateurs and professionals around the world can follow-up and help determine the orbit of the newly found object. The other non-threatening objects are also sent to the MPC for processing. The MPC looks at these isolated single night observations of these non-threatening objects and attempts to link them across nights and different surveys to get an idea of the orbit and size of the object. Sometimes no linkages are made from these observations and these single night observations end up in a file called the Isolated Tracklets File (ITF). In recent years many teams have started linking objects in the ITF, and are very good at it now.

"NEW" OBJECTS:

So, say I'm out imaging and find an unnumbered asteroid then report it to the MPC. How will I know if it is a discovery? First off, don't get too excited. With the surveys having covered a few decades of the night sky looking for objects in the magnitude 20 + range, it is not likely you are the first person to submit observations on this asteroid (especially for Main Belt Objects). But, it is not impossible. Asteroids are not officially assigned a discoverer, until they are officially numbered. Asteroids are only numbered after a few criteria are met. At least 4 oppositions for Main Belt Rocks, with 2 dark nights at at least 3 of the oppositions, and an uncertainty value of 2 or lower. All of this can easily be seen if you look up an asteroid on the MPC site. A few rules come into play here that are important. The first thing you should do after obtaining good astrometry on the object, is submit to the MPC right away. Waiting a night, or even an hour, could mean not getting discovery credit if the object is new. This is because when the asteroid is finally numbered they look at the earliest *submitted* observations at the opposition where a second night was also submitted. This means along with the observations themselves, a time stamp of when the message was received at the MPC is also recorded. This time stamp will be referenced when the MPCs processing routines decide the asteroid is ready to be numbered and credit will be assigned then to that earliest observation. This also means if you mine data for an object that has already had observations submitted on it looking for earlier observations, the discovery credit will not change at numbering time as the earlier observations will have been submitted to the MPC after the original, later, observations were submitted. There is another caveat to this. In order for credit to be assigned for discovery when the asteroid is numbered, it requires at least 2 nights of observations at least 12 hours apart to have been submitted at the discovery opposition (by any observatory). If an opposition is recovered from the ITF that only had 1 night of observations, the discovery credit will not go to that observatory. This is why it is imperative for you to try and obtain at least 2 nights of observations on any rocks you suspect to be new (but send the first night right away).

DESIGNATIONS:

So, I have submitted my two nights on this new rock. What now? You'll have to wait a few days to a week to get a designation for your rock (depending on how busy the MPC is). A note on how they create the designations can be found Here. Think about designations like segments of a toy railroad track. They are not the whole picture. The are a representation of a part of the orbit of the asteroid where the MPC has been able to link 2 or more nights of observations. It is a string of letters and numbers you will reference when submitting further observations of the asteroid to the MPC. It is provisional, and does NOT mean you have discovered a new asteroid. So after I receive my designation for DR0150, I will no longer use DR0150 when sending further observations of the asteroid to the MPC - I will use a designation like K16X01D. It can take a while to receive this designation from the MPC. In the meantime, keep tracking that rock and retain observations after the 2nd night for submission to the MPC after you receive your designation. 3 nights in a row won't hurt. After that you should be able to recover it in a few weeks, and if it is a decent size MBA track it for a month or two. I try to track the new MBAs I find for a month at least. There are a few reason for this as well. When you track your newly found rocks and obtain observations over the period of a month or so, you have helped the MPC obtain an orbit solution on the rock that is rather accurate. This is good because it helps the computers locate lost observations inside of the ITF and link them up to your object if they exist. This will help you determine if your object had been found previously, and if it may have even had an earlier designation assigned that they will now be able to link up. It can take a bit for the linking process to take place.

DISCOVERY CREDIT:

So say you have now found an asteroid, received your designation for it, tracked it for a month, and have waited many months after that. If your observations are still the earliest observations of the object published, you will probably receive credit for it in many years after it has been found again and again at 4 oppositions (2 for a NEO) once the asteroid is ready to be numbered. If the computers are able to recover isolated observations from the ITF, you will probably not get credit for the find. This is where some confusion comes in. These isolated tracks *do not* have to belong to an official "MPC designation" to receive credit for the find. The only criteria is that the earliest single night observation recovered from the ITF has a second night also reported at the same opposition it was reported. This second night does not have to be by the same observatory, only at the earliest opposition. When the asteroid is numbered, the discoverer will be the observatory / individual that submitted those earliest observations. The only exception as mentioned above is if the observations found in the ITF only cover 1 night at 1 opposition

Here is a good example of this on an MBA (771739) I received discovery credit for:

My observations from V03 are not the first observations ever on the object. It was seen in 2011 by G96, 2013 by F51, and 2015 by F51. All of these observations were recovered from the ITF long after I received my temporary designation from MPC. Each of those 3 oppositions only has 1 night of observations so none of them were eligible for discovery credit. The first opposition which had 2 nights was the one I reported in 2016. If any of the previous three had gotten a second night by chance, discovery credit would have been assigned to that opposition instead of 2016. This is why it's important to track your finds! A second night is much easier to obtain when the objects have a digest score over 65 because they post to the NEO Conformation Page where many other observers will track the find for you.

NEOCP:

All of the above rules still apply when an object is posted to the Near Earth Object Conformation Page (NEOCP). An object must have a NEO score >= 65 in order to post to the NEOCP. These objects get special attention as they are more likely to be Near Earth Objects. If you post an object to the NEOCP, there is still a chance that another observatory reported the object before you during the current opposition, when the NEO score was < 65. Those observations would end up in the ITF. These ITF observations will likely be linked before the object is published as they get special attention. As noted above, the earliest submitted observations (ITF or not) are the ones that will provisionally receive discovery credit once that NEO candidate is designated and removed from the NEOCP.

-------------------------

A note from Dr. Gareth Williams at IAU (Former MPC) detailing some uncommon situations where discovery credit can change:

Occasionally, the discovery credit changes after an object is numbered. Why is this? Well, in order to correctly assign credit in the first place, all the observations that belong to an object must be identified and published. In some cases, not all observations that are in the MPC's DB are extracted before numbering. This situation could affect the discovery date, discovery site and the discoverer names. In other cases, the discovery observation is the correct one but the discoverer names are in error: sometimes the wrong observer at a site is credited or the discovery is credited to the site when credit to an individual or pair of observers might be more appropriate.

Before making objects available to observers for naming, the WGSBN checks the discovery circumstances. This checking occurs after each full batch of Minor Planet Circulars is published. It also occurs after each mid-month Minor Planet Supplement is published, but only for objects subject to the MPEC 2010-U20 rules which have any observations that could possibly affect discovery credit. Any necessary corrections appear in the next regular WGSBN Bulletin or, if there are many, in a special corrections-only issue. Machine-readable datafiles of the corrections are made available to MPC and JPL, as well as other interested parties. Most corrections concern the discoverer names, but a small percentage change the discovery observation.

A small percentage (but large number, given the 500+ million observations in the MPC observation DB) of observations at the MPC lack the necessary metadata to correctly assign the discoverer. The WGSBN has been recovering observation batches that were not processed when the MPC DB was first built. Those batches did not get the metadata added. The WGSBN has a DB table with several million entries of recovered metadata (the bulk of which are the multiple iterations of WISE astrometry), along with another table that enables extraction of discoverer information based on the submission date information. Special efforts are made to correctly assign credit to individuals or pairs of observers for non-survey discoveries, either based on the OBS line in the discovery submission or on the observer-assigned temporary designation given to new objects. Remember the advice that the MPC gave observers many years ago? "If credit is important, use temporary designations that clearly show who is to be credited for each object." The discoverer-information table mentioned above can handle cases where objects in a single batch are to be credited to observer A + observer B, observer A alone, observer B alone, or observer B + observer C.

Cheers!

David Rankin