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The Pursuit of 2003 CR20

By Bill Allen, A/CC editor & links librarian

All dates and times are UTC unless stated otherwise.


Previous essay: "How A/CC broke the 2002 NT7 story " — Next essay: "Double-E Sixteen"
Modified: 11 March 2003 — New: 26 February 2003

Participating Observatories
CamarilloJornada
KLENOT
La Palma – La Silla
LinzPla D'Arguines
PowellSormano
also
BeguesConsell
KletLINEARModra
NEAT/Hawaii
Following the case of potentially hazardous object 2003 CR20 is a special opportunity to watch the near-Earth object (NEO) impact risk monitoring community at work. Parts or all of this community are sometimes called "Spaceguard," borrowed from Arthur C. Clarke's Rendezvous with Rama s-f novel. However, the entire effort is actually a loose and unofficial but very cooperative ad hoc assemblage of groups and individuals. At the top is the International Astronomical Union (IAU) Minor Planet Center (MPC), which receives, processes, and reports out observations of an asteroid's sky location ("astrometry") and brightness ("photometry"), which are then used by the NEO Dynamic Site (NEODyS, at the University of Pisa in Italy) and the newer NASA JPL NEO Program (at Caltech in Pasadena, California) to prepare their independent risk analyses. The observations come from sources ranging from the NASA-funded and Air Force-assisted LINEAR and NEAT NEO surveys, to institutionally-backed NEO surveys such as LONEOS and Spacewatch, through many other professional and university observatories around the world, and a network of "amateurs" who at their own expense provide most of the very critical "follow-up" observational effort. (It wouldn't do much good for the big programs to discover NEOs if someone didn't track the objects further to keep from losing them.)

See below for a table showing the progression of risk analysis for 2003 CR20. And read on for a taste of the effort's daily progress.


Both NEODyS and JPL added 2003 CR20 to their Risk pages on 14 Feb., with it debuting in JPL's top slot with a cumulative Palermo Scale rating of -1.86, but with a Torino Scale rating of 0 (see hazard scales). This object was discovered by JPL's NEAT program with its Hawaiian telescope on 11 Feb. 2003 and was announced early on the 14th. It is now estimated at about 560 meters/yards wide.

In posting 2002 CR20 to its observing campaigns page on 14 Feb., the European Spaceguard Central Node noted that CR20 is "going to be visible for at least two months, leaving a lot of room for orbital improvement" to be accomplished.

Early on most days, the MPC issues a Daily Orbit Update (DOU) Minor Planet Electronic Circular (MPEC) with formatted revised orbital elements for asteroids generally, and new observations of near-Earth asteroids. The DOU MPEC is the primary means for conveying new positional data to the risk monitors, and most changes in NEODyS and JPL risk assessments follow receipt of this data. (Occasionally the data is passed via other channels when interest is high regarding a particular risk, as would be seen on 27 Feb. when NEODyS and JPL updated their 2003 CR20 risk assessment with data that hadn't appeared yet in an MPEC.)

The first DOU MPEC following 2003 CR20's announcement, that of the 15th, had no new observations. And no DOU MPECs were issued during 16-18 Feb., there being a lull in observations due to the full Moon, a time used by the MPC and risk monitors for database and systems maintenance.

The next DOU came on the 19th and reported four positions taken at La Silla in Chile on 15 Feb. for 2003 CR20. That was sufficient to remove 41% of JPL's initial impact solutions, also called "virtual impactors" (VIs), but also slightly raised the risk monitors' maximum and cumulative Palermo Scale ratings.


The DOU for the 20th reported 2003 CR20 observations of the 18th from La Palma in the Canary Islands, and on the 19th from KLENOT in the Czech Republic. The net result shown in the revised NEODyS hazard assessment was to remove six of 25 impact solutions while slightly bringing up its cumulative Palermo Scale rating for the remaining solutions. With this, NEODyS raised the Torino Scale rating from 0 to 1 ("merits special monitoring") for a VI for 17 March 2046. JPL did the same when it brought out its new assessment, while showing very slightly reduced Palermo Scale ratings overall, and while removing 105 of 139 VIs.

This feat of chopping 75% of JPL's remaining 139 VIs at one swoop from just two days' further observation demonstrated how the matter of 2003 CR20 was still very early in its follow-up effort, just over a week after discovery.

The DOU for 21 Feb. reported observations of the 20th from Powell Observatory in Kansas and Sormano Observatory in Italy. An updated NEODyS assessment had one less impact solution and very slightly lowered its cumulative Palermo Scale rating, although a revision later in the day reversed that. JPL took until after lunch to update its assessment, dropping nine more impact solutions while very slightly raising its cumulative and maximum PS ratings.

2003 CR20 on 21 Feb. 2003, credit: Rafael Ferrando, Pla D'Arguines Obs.
From 21 Feb. comes this image and animation of 2003 CR20 by Rafael Ferrando at Pla D'Arguines, forwarded by Pepe Manteca.

On 22 Feb., the DOU reported 2003 CR20 observations of the 21st from KLENOT, and from Camarillo Observatory in California and Pla D'Arguines Observatory in Spain. With these, NEODyS shed another seven impact solutions, but the maximum and cumulative Palermo Scale ratings for the dozen remaining were up from the day before. The JPL NEO Program's new CR20 assessment removed three more impactors while raising cumulative and specific PS ratings. And both monitors this day raised the Torino Scale rating to 1 for a pair of impact solutions for 16 March 2061.

With less than eleven days of tracking, the 2003 CR20 observing effort was still producing only preliminary results. What you see reported here is a routine night-and-day progression of observation and analysis. Out of many potentially hazardous objects (PHOs) newly discovered every year, several such as 2003 CR20 rise in the evolving analyses to Torino Scale 1 before being determined to pose no risk at all. The Torino Scale is for public consumption, while the Palermo Scale is a more complex scientific tool. To learn more about how impact risk monitoring works, and how astronomers around the world track concerns until the risks are disproven, read "Understanding Risk Pages" by Jon Giorgini of JPL.


The DOUs for 23 to 25 Feb. carried 2003 CR20 observations mostly from KLENOT, but also from La Palma and Sormano, and from Jornada Observatory in New Mexico. These helped shed more impact solutions while generally but only slightly raising the Palermo Scale ratings. On 26 Feb., new observations from KLENOT were reported in the day's DOU, and the upward trend in risk concern seemed to continue, except that the NEODyS and JPL cumulative PS ratings for CR20 dropped very slightly.

At this early point, with little more than 14 days of observation, both risk monitors were showing 13 impact possibilities spanning the years 2031 to 2073 that still needed to be eliminated. They weren't quite the same 13 impact solutions — JPL had one VI in 2031 and three in 2034, while NEODyS had two VIs in 2031 and one in 2034, but overall the analysis was converging.

Something to understand about impact risk monitoring is that a "virtual impactor," or "impact solution," is not a single-line path (and a single-point impact) but rather a very large set of solutions for the Earth's immediate vicinity. The risk monitors work to eliminate a general possibility rather than to determine a specific certainty. Using a sports analogy, it's like trying to decide whether a ball can even get into the ballpark rather than will it score a goal or home run. In an explanation for general readers, JPL describes an asteroid's path as having a region of uncertain position that is a "three-dimensional tube stretched along its orbit." If that tube doesn't come to within an Earth radius of Earth's orbital path, a collision can't happen.


The DOU MPEC time-stamped 0707 UT on 27 Feb. carried no new observations of 2003 CR20, but it did report new orbital elements, which can be a sign that new observations are in but aren't being passed through yet. And, in fact, both NEODyS and JPL later updated their CR20 assessments based on six new positions, which the NEODyS 2003 CR20 optical observations page showed were taken by KLENOT during 2043-2050 UT on the 26th. With this, both NEODyS and JPL dropped one impact solution, and backed off on both their maximum and their cumulative PS ratings. While the maximum Torino Scale (TS) rating remained at 1 (for the March 2046 VI), both monitors put the pair of March 2061 impact solutions back to TS 0. So, on this day it began to look like maybe the corner had been turned in the risk analysis.

The 28th started off with the DOU MPEC carrying both the 26 Feb. KLENOT observation set used in the previous day's CR20 risk assessments, and another batch of six taken by KLENOT about 24 hours later, on the 27th. NEODyS subsequently dropped four of its remaining impact solutions, and further reduced its maximum and cumulative Palermo Scale ratings. The pair of March 2061 impactors that both monitors just the day before had dropped from Torino Scale 1 to 0 were this day eliminated altogether from the NEODyS assessment. JPL also lowered both its maximum and cumulative Palermo Scale ratings for 2003 CR20 in its assessment of the 28th, but retained the 2061 solutions.


Perseverance pays off
Sets of observations from individual observatories usually appear in the formatted data of Minor Planet Electronic Circulars (MPECs) as tight groups of three or more, but the positions reported from Pla D'Arguines for 2002 CR20 the night of 28 Feb. were interspersed between others' work, and were the first and last from Europe, spanning more than 2-1/2 hours beginning at 1945 UT. When asked about this, Rafael Ferrando responded:
The night was cloudy, and the prediction was for it to stay that way, but I set up the telescope, anyway, and aimed it at where 2003 CR20 would be found. After more than an hour, some clear spaces appeared between the clouds, and I began to shoot CCD frames. CR20 was barely perceptible in the majority, due to the clouds, but once in awhile there would be a frame with CR20 appearing sharply. The final result was more than 60 frames of two minutes' exposure each, but measurements could be taken from only seven of these. All the time spent on this was paid back by being able to help with establishing the orbit of one of the asteroids needing it most.

The month of March began with 2003 CR20's maximum risk assessment going back to Torino Scale 0 in the day's new assessments by NEODyS and JPL, and with their maximum Palermo Scale ratings falling significantly — to the lowest since CR20 was announced. This followed the MPC's DOU MPEC with 18 observations from four observatories overnight, 28 Feb.–1 March: Jornada, KLENOT, Linz, and Pla D'Arguines.

The impact solution of most concern, for 16 March 2046, which had been at Torino Scale 1 since 20 Feb., went straight from TS1 to being dropped altogether by both monitors. This wasn't quite a clean sweep, however, as JPL added a new solution for the next day, 17 March 2046, but this was put at TS0 with a low Palermo Scale rating of -4.72. JPL also removed from its assessment the pair of March 2061 impactors that NEODyS had dropped the day before.

From this point until the 7th of March, it was just a cleanup operation to eliminate the few remaining impact solutions. NEODyS removed 2002 CR20 on the 6th, and JPL the next day. There can be the occasional rare surprise in risk monitoring where an object thought to be eliminated from concern attracts new attention, but what most likely lays ahead for this asteroid is routine observation to help calculate its orbit well enough that CR20 can be easily found again and tracked over the years. Since minor object orbits can and do change, this is one among many that we and coming generations will want to keep a close eye on.


2003 CR20 risk assessment progression
A Palermo Scale (PS) rating of 0.0 is equivalent to the random "background risk" of being hit by an asteroid without warning. Such ratings have only gone positive to publicly exceed 0.0 in two instances — the very brief case of 2002 NT7 last Summer, and 29075 1950 DA has a positive VI in the year 2880. A rating rising above -2.00 will attract special interest from those close to impact monitoring. A continuing rise may cause a Torino Scale rating to be raised from 0 ("no likely consequences") to 1 ("merits special monitoring"), such as has happened with 2003 CR20. A PS rating becoming more negative is what we want to see, showing an improvement in risk outlook.
          VI count years  PSmax  PScum* T  IAU MPC MPEC notes
14 Feb.   --------------  -----  -----  S  ----------------------------------
  NEODyS   24  2006-2079  -2.57  -2.22  0  discovery MPEC has 11 observations
     JPL  234  2006-2102  -2.37  -1.86  0    from 4 observatories 11-14 Feb.
15-18 Feb.--------------  -----  -----  -  ----------------------------------
          The 15 Feb. DOU had no CR20 observations. No DOU MPECs 16-18 Feb.
19 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   25  2028-2077  -2.26  -2.15  0  DOU had 1 set of 4 positions from
     JPL  139  2006-2099  -2.13  -1.69  0    La Silla 15 Feb.
20 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   19  2028-2073  -2.08  -1.76  1* DOU had 8 positions (2 sets) from 
     JPL   34  2026-2083  -2.22  -1.73  1*   2 observatories 18-19 Feb.
21 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS*  19  2026-2065  -2.09  -1.69  1  DOU had 6 positions (2 sets) from
     JPL   25  2026-2099  -2.18  -1.70  1    2 observatories 20 Feb.
22 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   12  2028-2061  -1.58  -1.30  1* DOU had 18 positions (a set of 2 &
     JPL*  22  2026-2073  -1.62  -1.32  1*   2 sets of 8) from 3 obs. 21 Feb.
23 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   15  2028-2061  -1.36  -1.12  1  DOU had 14 positions as 2 sets
     JPL   19  2028-2073  -1.42  -1.17  1    from 2 observatories 22 Feb.
24 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   12  2031-2073  -1.39  -1.10  1  DOU had 12 positions as 2 sets
     JPL   15  2031-2073  -1.45  -1.14  1    from 2 observatories 23 Feb.
25 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   13  2031-2073  -1.16  -0.94  1  DOU had 6 positions as 2 sets from
     JPL   14  2031-2073  -1.22  -0.98  1    2 observatories 24 Feb.
26 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   13  2031-2073  -1.09  -0.99  1  DOU had 1 set of 6 positions from
     JPL   13  2031-2073  -1.15  -1.04  1    KLENOT 25 Feb.
27 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS   12  2031-2079  -1.41  -1.37  1* None in today's DOU, but 6 new po-
     JPL   12  2031-2073  -1.46  -1.42  1*   sitions used from KLENOT 26 Feb.
28 Feb.   --------------  -----  -----  -  ----------------------------------
  NEODyS    8  2031-2052  -1.85  -1.80  1  DOU had 26 Feb. set + 6 positions 
     JPL   10  2031-2061  -1.92  -1.86  1    from KLENOT 27 Feb.
1 March   --------------  -----  -----  -  ----------------------------------
  NEODyS    2  2031-2034  -3.45  -3.20  0* DOU had 18 positions reported from
     JPL    5  2031-2046  -3.35  -3.09  0*   4 observatories 28 Feb.-1 March
2 March   --------------  -----  -----  -  ----------------------------------
  NEODyS    1  2031       -3.69  -3.69  0  DOU had 1 set of 6 positions from
     JPL    5  2034-2046  -3.82  -3.54  0    KLENOT 1 March
3 March   --------------  -----  -----  -  ----------------------------------
  NEODyS    2  2031-2034  -3.66  -3.39  0  DOU had 1 observation from Begues
     JPL    5  2034-2046  -3.86  -3.62  0    Observatory 1 March
4 March   --------------  -----  -----  -  ----------------------------------
  NEODyS    1  2031       -3.69  -3.69  0  DOU had 2 sets of observations
     JPL    4  2031-2034  -3.34  -3.13  0    from 2 observatories 3 March
5 March   --------------  -----  -----  -  ----------------------------------
  NEODyS    2  2031-2034  -4.08  -3.84  0  DOU had 2 sets of 8 observations 
     JPL    1  2031       -3.97  -3.97  0    from 2 observatories 4 March
6 March   --------------  -----  -----  -  ----------------------------------
     JPL    1  2031       -5.33  -5.33  0  DOU had 9 pos from 2 obs 4-5 March
7 March   --------------  -----  -----  -  ----------------------------------
          The DOU reported a set of 4 observations from LINEAR from 6 March
          and JPL joined NEODyS in eliminating all impact solutions.
__________
Footnotes:
*PScum = Cumulative Palermo Scale, as given by JPL and calculated for NEODyS.
*The Torino Scale rating of 1 first set on 20 Feb. is for a 17 March 2046 VI.
*The NEODyS 21 Feb. assessment shown is the second of two noted that day.
*Starting with the 22 Feb. JPL assessment, all VIs are within the NEODyS
 2080 time horizon.
*As of 22 Feb., a pair of VIs for 16 March 2061 have a Torino Scale 1 rating.
*On 27 Feb., the pair of 16 March 2061 VIs were put back to Torino Scale 0.
*On 1 March, NEODyS removed the Torino Scale 1 impact solution for 16 March
 2061. JPL removed it, too, but added a VI for a day later, rated at TS0.


Errata – corrections & changes

4 March:   Since 2003 CR20 began to be followed closely on the A/CC News Page, with those reports subsequently consolidated and continued on the page you are reading, the rise and fall of the averaged NEODyS Palermo Scale (PS) ratings were reported, while also reporting JPL's cumulative PS ratings. To better compare the two monitors' results, the cumulative PS ratings for the daily NEODyS CR20 risk assessments have been calculated put in place of the earlier averaged numbers. While making this change, some errors in tabulating the year ranges of NEODyS impact solutions were noticed and fixed.

1 March:   In this reporting, Klet Observatory was repeatedly mentioned for its major part in the 2003 CR20 observing effort, with 54 of 115 total observations as of March 1st. But, to be precise, 52 of those, and all of them since CR20's discovery announcement, have come from Klet's KLENOT Project, with its new 1.06m telescope.


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