Understanding MPEC 2010-U20 - Asteroid Discovery Credit
I have been heavily involved in the amateur side of hunting asteroids for a few years now. The learning curve has been steep to say the least. 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. Quite the service they are providing and I personally am grateful for it. 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). This simple text file is currently about 1GB in size and ever growing.
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. 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. 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.
Okay, so I found an unidentified asteroid flying around in my images and submitted some observations to the MPC. Now what?
The MPC is busy. They process A LOT of observations each month. Some of the larger surveys are sending multi-millions of observations to the MPC on a yearly basis. If your object is not determined to potentially be a near earth object, your observations will not be high priority. Be patient, they will get to you. Another thing they really don't have the time or resources to do is track your custom user designation for the asteroid across multiple nights. I can see how this would be a lot of extra work. When I submit a new rock I usually use my initials followed by a 4 digit sequence DR0150 or something to this effect. This presents a problem if you want to be sure to force the MPC processing routines to link your observations of an object after you do the right thing and follow up with a second night of observations. So if I find DR0150 on night 1, and email it to the MPC, I am not allowed to obtain night 2 and also send the object as DR0150. This makes sense for another reason. They don't want multiple designations in the ITF that have the same ID! There is one way they permit a user to link an asteroid across multiple nights.
1. Obtain observations on DR0150 for night 1.
2. Send night 1 to the MPC.
3. Obtain more observations for DR0150 for night 2.
4. Combine the observations from night 1 with night 2, using the same designation, and resend night 1 along with night 2 using a subject like "DR0150 Resend with 2nd Night".
5. Do not include any extra observations in this report so they are not having to sort them out separately.
Here's and example:
Email subject line was "DR0184 Resend with 2nd Night"
COD V03 CON David Rankin [David@rankinstudio.com] OBS D. Rankin MEA D. Rankin TEL .30-m F4 Reflector + CCD ACK MPCReport file updated 2017.09.19 03:48:03 AC2 David@rankinstudio.com NET Gaia DR1 DR0184 KC2017 09 18.17411721 11 17.98 +02 58 56.7 20.0 G V03 DR0184 KC2017 09 18.18050021 11 17.92 +02 58 46.7 20.4 G V03 DR0184 KC2017 09 18.20969721 11 17.87 +02 57 59.1 20.7 G V03 DR0184 KC2017 09 18.23182421 11 17.86 +02 57 24.0 V03 DR0184 KC2017 09 19.11506121 11 19.39 +02 33 46.2 20.2 G V03 DR0184 KC2017 09 19.12528921 11 19.33 +02 33 29.7 20.1 G V03 DR0184 KC2017 09 19.13040021 11 19.34 +02 33 21.2 V03 DR0184 KC2017 09 19.15521121 11 19.33 +02 32 42.1 20.4 G V03 ----- end -----
Why all the extra work? Well, as discussed above, the credit is assigned by the *earliest reported* message. So in this way, you can report the object asap on night 1, and also force a linkage with a second night of observations by resending the first night along with the second. I have found this works very well. This is important because if you find a new object, another amateur or another professional observatory may be in the same area of the night sky reporting at the same time you are! This has actually happened to me twice now.
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 rocks 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 over 6 months for the computer to take your month long arc and link it up to lost observations. This is also somewhere you have to be very patient.
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 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 a 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.
This hobby has been a lot of fun, and there are enough rocks out there for amateurs to still find new ones. I hope this will help those out there who, like me, had struggled a bit to understand how discovery credit is finally assigned when the asteroids get numbered. Personally I think it is a good, fair, system.