My first numbered minor planet

June 23, 2010 11:10 by scibuff

I was first exposed to observation of minor planets while working on a high school project in summer of 2001 under the supervision of RNDr. Juraj Tóth, PhD, at the Astronomical and Geophysical Observatory Modra, Slovakia. Unfortunately, for various reason, I didn’t go back to the area of minor planets until early this year. With no suitable telescope on hands, I began sieving through the data in the Near Earth Asteroid Tracking (NEAT) archives accessible to public via the Skymorph pages.

Despite having logged hours and hours of CCD data collection and reduction, Skymorph really helped me to get familiar with the latest tools (such as Astrometrica). I definitely recommend it to anyone wishing to start an astrometry program as you will learn the step-by-step process of using tools such as the MPC services, services from, Astrometrica, etc. You’ll find new unknown objects and learn to distinguish them from false signatures; gain experience to follow up on your the discoveries (and even do precovery work) and learn to produce astrometry reports in the format accepted by the MPC.

Discovery of 2002 RO282

My discovery of 2002 RO282 in NEAT/Skymorph data

In the 90’s and early years of the last decade, anyone with a medium-sized telescope and a CCD camera had pretty good chances to discover asteroids. Nevertheless, since NASA funded big surveys have started sweeping virtually the entire sky (visible from the northern hemisphere) every month, amateur discoveries require much bigger telescopes (0.5m and more) to allow one to reach beyond the 20th magnitude. A much cheaper alternative to owning a big telescope is to rent time on one. There are a few options out there, but I personally prefer the Lightbuckets remote observatory and the incredible 24″ Ritchey–Chrétien telescope from RC Optical Systems.

Lightbuckets LB-0001

Lightbuckets LB-0001 - 0.61m (24") Ritchey-Chrétien

Located under the excellent northern hemisphere skies of southwestern New Mexico, LB-0001 equipped with Apogee Ulta 42 CCD camera (with quantum efficiency reaching staggering 90%) can easily reach beyond the 20th magnitude in a single 60s unfiltered exposure. The ability to observe objects fainter than 20th magnitude is crucial for minor planet hunting as the vast majority of brighter objects have already been found.

I discovered my first minor planet in the very first image set taken with LB-0001 (statistically, the odds of finding an object of ~21st magnitude in the 20’x20′ field of wiew of LB-0001 are pretty good). But the discovery of a minor planet is only the beginning. Further observations are necessary to determine the orbit well enough so that the object can be recovered at next opposition. This usually requires an arc of at least 2-3 weeks, but the longer the better.

The discovery animation of minor planet 239792

The discovery animation of minor planet 239792. At the first measured position the object had brightness of V21.1, i.e. about million times fainter than one can see with a naked eye.

Once an object has been observed for 2 or more weeks, it is possible to search for identifications with previously-discovered provisionally-designated objects observed at only one opposition in the past. If an identification is made, one of the provisional designations is defined to be the principal designation. This is generally the earliest opposition at which a reasonable orbit was computed. An orbit is considered to be “reasonable” if it is good enough to use as a starting orbit to link the other observations.

Although numbering of a Main Belt asteroid usually requires observations from four oppositions (i.e. takes at least 4-5 years), with a good amount of luck your newly discovered object could be numbered within 1-2 months. If the observed arc from the current opposition can be used to link a few observations from the past, it is possible that the orbit will be refined well enough so that the object can be numbered. That is exactly the story of a minor planet (239792) 2010 EM34 I discovered using LB-0001.

2010 EM34 Discovery Astrometry

2010 EM34 Discovery Astrometry

On March 9, 2010, during one of my regular searches in the area close to the ecliptic just before opposition, I noticed a previously unknown moving target. The data from the same night showed a few other brighter targets, so I did not select this object for a follow-up and reported it as a 1-nighter. Fortunately, the  Mt. Lemmon Survey (G96 ) swept the area of the sky into which my 1-nighter moved in 4 days and reported it to MPC. The processing routine determined that the two one-nighter observations belong to the same object and thus assigned it a provisional designation 2010 EM34.

2010 EM34 follow-up from March 21

2010 EM34 follow-up from March 21. The brighter minor planet close to the bottom is 171343.

After a week, on March 21, I observed the objects again extending the observed arc to 12 days. This follow-up observation was of a crucial importance. Thanks to the 12-day arc, MPC was able to link an observation by Kitt Peak-Spacewatch (691) on February 18, and later, two observations of 2010 EM34 by G96 on April 10 and April 12, extending the observed arc to 52 days. The 52-day arc determined the orbit well enough to find observations of the object from past years. Namely, the automated procedures linked observations from 1999 (1), 2003 (4), 2005 (1), 2006 (4) and 2007 (1).

2010 EM34, as it turned out, corresponds to 2003 US321 and 2006 JK71 but 2010 EM34 remained the principal designation because it was the observations of 2010 EM34 which were used to link all the past positions together.

Both 2003 US321 and 2006 JK71 were observed on two nights only. 2003 US321 was discovered by 691 on October 16, 2003 and observed again by LPL/Spacewatch II (291) on October 23, 2003. Two one-night observations of the object from September 16 and 28 were also reported but the automated routines at MPC were not able to link the observations to 2003 US321, because they were spaced too far apart (and the two-night orbit of 2003 US321 wasn’t accurate enough). 2006 JK71 was discovered at Mauna Kea (568) on May 1, 2006 and observed again by G96 on May 2, 2006.

Once the link was established, the orbit of 2010 EM34 could be calculated with sufficient precision to link one-night observations from 1999, 2005 and 2007. Consequently, the orbit was determined to be accurate enough so that minor planet could be numbered. 2010 EM34 received a permanent designation 239792 in the Minor Planet Circular 69935 and can now be named.

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