The Asteroid Orbital Elements Database

Introduction astorb.dat is an ASCII file of high-precision osculating orbital elements and some additional data for all the numbered asteroids and the vast majority of unnumbered asteroids (multi-apparition and single-apparition) for which it is possible to make reasonably determinate computations. It is currently about 1.5 Mb in size in its compressed form (astorb.dat.gz), 5.6 Mb in size when decompressed, and contains 30020 orbits computed by me. Each orbit, based on astrometric observations maintained by the Minor Planet Center, occupies one 187-column record.

Landmarks Click here.

Downloading astorb.dat The file may be obtained by the following means:

File Structure astorb.dat contains one record per asteroid and, as of Wednesday 14 February 1996, is in a format different from that previously available.

Here are two sample records (with one line of parameter numbers above and three lines of column counts below):

(1)  (2)                (3)             (4)    (5)  (6)  (7)   (8)
   1 Ceres              E. Bowell        3.34  0.12 0.72 913.0 G?
1693 Hertzsprung        E. Bowell       10.97  0.15 0.74  39.5 C
         0         0         0         0         0         0         0
         1         2         3         4         5         6         7
1234567890123456789012345678901234567890123456789012345678901234567890
 
 (9)                   (10) (11)  (12)     (13)       (14)       (15)
 0   0   0   0   0   0 56959 4743 19960118  59.263953  71.607504  80.6
 0   0   0   0   0   0 20972   25 19960118 301.153857 234.740741  70.3
         0         0         1         1         1         1         1
         8         9         0         1         2         3         4
1234567890123456789012345678901234567890123456789012345678901234567890
 
      (16)      (17)       (18)        (19)
58552 10.600768 0.07599035  2.76714045 19960210
92409 11.943084 0.27451762  2.79559927 19950513
         1         1         1         1
         5         6         7         8
12345678901234567890123456789012345678901234567
    

A FORTRAN format statement for reading a record in astorb.dat is:

A4,1X,A18,1X,A15,1X,2(F5.2,1X),A4,1X,A5,1X,A4, 1X,6I4,1X,
2I5,1X,I4,2I2.2,1X,3(F10.6,1X),F9.6,1X,F10.8, 1X,F11.8,1X,I4,2I2.2

Note that some numerical data (e.g., asteroid number) are encoded as character variables. You may need to decode them.

Parameters are:

Parameter Description
(1) Asteroid number (blank if unnumbered).
(2) Name or preliminary designation.
(3) Orbit computer.
(4) Absolute magnitude H, mag [see E. Bowell et al., pp. 549-554, in "Asteroids II", R. P. Binzel et al. (eds.), The University of Arizona Press, Tucson, 1989 and more recent Minor Planet Circulars]. Note that H may be given to 2 decimal places (e.g., 13.41), 1 decimal place (13.4) or as an integer (13), depending on its estimated accuracy. H is given to two decimal places for all unnumbered asteroids, even though it may be very poorly known.
(5) Slope parameter G ( ibid.).
(6) Color index B-V, mag (blank if unknown; see E. F. Tedesco, pp. 1090-1138, op. cit. ).
(7) IRAS diameter, km (blank if unknown; see E. F. Tedesco et al., pp. 1151-1161, op.cit.).
(8) IRAS Taxonomic classification (blank if unknown; ibid.).
(9) Six integer codes (see table of explanation below). Note that not all codes have been correctly computed.
(10) Orbital arc, days, spanned by observations used in orbit computation.
(11) Number of observations used in orbit computation.
(12) Epoch of osculation, yyyymmdd (TDT). The epoch is the Julian date ending in 00.5 nearest the date the file was created. Thus, as the file is updated, epochs will succeed each other at 100-day intervals on or after Julian dates ending in 50.5 (19960308, 19960616, 19960924, 19970102,...)
(13) Mean anomaly, deg.
(14) Argument of perihelion, deg (J2000.0).
(15) Longitude of ascending node, deg (J2000.0).
(16) Inclination, deg (J2000.0).
(17) Eccentricity.
(18) Semimajor axis, AU.
(19) Date of orbit computation, yymmdd (MST, = UTC - 7 hr).

The osculating elements [parameters (13) through (18)] are heliocentric. The meanings of the six integer codes [parameter (9)] are as follows (reference to "type 6:7", for example, means code 6, value 7):

CodeValueExplanation
1 Planet-crossing asteroids.
Note: Because some orbits are very poor (or erroneously linked), there may be errors in assignment of these parameter values.
1 Earth-crossing asteroid (ECA), according to Shoemaker et al.'s definition (In "Asteroids", pp. 253-282, T. Gehrels, ed., The University of Arizona Press, Tucson, 1979 ). Some ECAs are currently Amors (q.v.). ECAs have been identified prior to May 1991. After that date, asteroids having q < 1.0167 AU have been assumed to be ECAs. Thus, in the latter group, some may not be ECAs, and some asteroids assumed to be Amors may be ECAs.
2 Asteroids having perihelia less than the aphelion distance of the Earth (1.0167 AU), but which are not ECAs.
4 Amors (1.0167 < q < 1.3 AU) (but see also type 1:1).
8 Mars crossers (1.3 < q < 1.6660 AU).
16 Outer-planet crossers (excluding Jupiter Trojans).
n Asteroids (excluding Mars and Jupiter Trojans) that cross both inner- and outer-planet orbits. For example, n = 24 crosses the orbits of Mars (q < 1.6660 AU) and Jupiter (Q > 4.950 AU).
2 Orbit computation.
1 Orbits derived from uncertainly, perhaps erroneously linked observations.
2 Eccentricity assumed.
4 Eccentricity and semimajor axis assumed.
8 For numbered asteroids, omitted observations have resulted in degradation of a so-called orbit-quality parameter (OQP, see K. Muinonen and E. Bowell, Icarus 104, 255-279, 1993), generally by more than 0.1. The corresponding ephemeris uncertainty has increased by about 25% or more.
16 OQP degrades by more than 0.1 if unsubstantiated observations (e.g., one-night apparitions) are omitted.
n Sum of preceding entries. For example, n = 3 pertains to an uncertainly linked orbit for which the eccentricity was assumed.
3 Asteroids observed during the course of major surveys. Our definition includes asteroids that were observed but not discovered during the course of a survey.
1 Palomar-Leiden survey (PLS) asteroids.
2 Palomar-Leiden T-2 survey asteroids.
4 Palomar-Leiden T-3 survey asteroids.
8 U.K. Schmidt Telescope-Caltech asteroid survey (UCAS) asteroids.
16 Palomar-Leiden T-1 survey asteroids.
n Asteroids observed in more than one survey. For example, n = 3 denotes an asteroid observed in both the PLS and T-2 surveys.
4 Minor Planet Center (MPC) critical-list numbered asteroids.
1 Lost asteroid.
2 Asteroids observed at only two apparitions.
3 Asteroids observed at only three apparitions.
4 Asteroids observed at four or more apparitions, last more than ten years ago.
5 Asteroids observed at four or more apparitions, only one night in last ten years.
6 Other poorly observed asteroids observed at four or more apparitions.
7 Absolute magnitude poorly known (not on MPC critical-list).
5 Lowell Observatory and related discoveries
1 Asteroids discovered by E. Bowell.
2 Non-Bowell discoveries from Lowell search programs.
6 Rank, in decreasing importance, for our collaborative program of astrometry using the transit circle of the U.S. Naval Observatory Flagstaff Station.
10 Exceptionally important, to be observed frequently. Principally space mission targets and occultation candidates.
9 Asteroids useful for mass determination.
8 Asteroids for which one or two additional nights' observation are required to satisfy orbit-update requirements. Asteroids of type 6:7 whose ephemeris uncertainties are between 2 and 5 arcsec within the next ten years or so.
7 Bowell unnumbered discoveries whose ephemeris uncertainties are less than 2 arcsec within the next ten years or so. MPC critical-list asteroids.
6 Planet-crossers of type 6:5.
5 Numbered asteroids whose ephemeris uncertainties are between 2 and 5 arcsec within the next ten years or so. Unnumbered asteroids that should be numberable after one or two more nights' observation.

Note that the codes have not been carefully checked. There are doubtless many errors.

Computational Details To produce the database, our variable-timestep differential orbit correction program was run in an automatic mode. Perturbation due to all major planets (Mercury through Pluto, Earth and Moon separately), Ceres (assumed mass 5.0×10^(-10) M_Sun), Pallas (1.1×10^(-10) M_Sun), and Vesta (1.4×10^(-10) M_Sun) were included. Planetary positions were derived from JPL planetary ephemerides DE245 (orbits computed on or before 15 November 1995) and DE403 (after 15 November 1995). Positions of the three perturbing asteroids were derived, by iteration, from our own orbits. Relativistic effects were not included. To save time for a few unnumbered asteroids, we used an integration-step parameter slightly larger than optimum. As a consequence, the orbits of a few unnumbered planet-approaching asteroids could stand slight improvement. The orbit of one numbered asteroid is known to be imperfect: 1566 Icarus requires inclusion of relativistic effects.

For numbered asteroids, we have adopted a uniform policy regarding the inclusion or exclusion of observations in the orbit determination: namely, to exclude observations whose great-circle sky-plane residuals exceed 2.3 arcsec. (We have found from experience that, for well-determined orbits, 2.3 arcsec is an appropriate residual threshold separating "good" and "bad" observations.) For numbered asteroids of type 2:8 in the integer-code table above, our policy has resulted in degradation of the orbit-quality parameter (OQP), which is a reliable (logarithmic) measure of an asteroid orbit's quality, and which (for non-Earth approachers) correlates well with ephemeris uncertainty. Such asteroids need orbit improvement to the point where the exclusion of "poor" observations no longer degrades the OQP. For unnumbered asteroids, we have retained obviously inferior observations where doing so improved the OQP and ephemeris uncertainty, thus making it easier to reobserve them.

Special Features of astorb.dat There are two primary differences between our database and conventional asteroid orbit files. First, it is our intention to update the orbits in the database frequently. Thus, observations in each new batch of Minor Planet Circulars will be incorporated in new orbits on a monthly basis, and those in the Minor Planet Electronic Circulars shortly after they are published. Other modifications will be made on a quasi-daily basis. Second, all the orbits in a given version of the file have an epoch of osculation near the present. It follows that the ephemerides of most non-Earth-approaching asteroids can be computed to better than about 1 arcsec accuracy within ± 50 days of the epoch using a 2-body ephemeris program. Most single-apparition asteroids are hopelessly lost, however. Until we make available current ephemeris uncertainties for these asteroids, users may make use of the approximate formula (formula requires Netscape 2.0 for proper rendering)

sigma(t) = ±4500(q - 1) (t - tl) / [tarc2 (N - 3)1/2 Delta] arcsec,

derived from K. Muinonen, E. Bowell, and L. H. Wasserman (Planet. Space Sci. 42, 307-313, 1994). Here, sigma(t) is the 1-sigma sky-plane uncertainty, along the line of variation, at time t; q is the perihelion distance in AU; tl is the time of the last observation (t - tl is in days); tarc and N are parameters (10) and (11) above; and Delta is the Earth-asteroid distance in AU. For long-unobserved asteroids, tl may be approximated from the designation. Thus, for 1982 EE, tl may be taken as 15 March 1982. The formula should be accurate to within a factor of five.

Upcoming Changes in astorb.dat We will shortly add information on ephemeris uncertainty: current uncertainty, the date and values of the next peak emphemeris uncertainty (generally near the time of the next opposition), and the date and value of the largest peak ephemeris uncertainty over the next ten years. Following that, we intend to produce a version of the database in a format resembling that espoused in our ACM93 paper [E. Bowell, K. Muinonen, and L. H. Wasserman (1994). A public-domain asteroid orbit database. In "Asteroids, Comets, Meteors 1993" (A. Milani et al., eds.), pp. 477-481. Kluwer, Dordrecht ]. We will not be making the latter file publicly accessible until we have checked it fairly thoroughly, incorporated it into our suite of asteroid-orbit software, and extracted data for a paper entitled something like "Orbit and ephemeris accuracy of multi-apparition asteroids". In addition, we are near to making a second run on orbits for numbered asteroids in which close asteroid-asteroid encounters will be noted and a new perturbation scheme that includes two or three dozen asteroid perturbers is implemented.

We are also looking into the possibility of allowing approved WWW users to run selected programs on our system (ephemerides; which asteroids are in a given region of sky at a given time; selecting subsets of asteroids by orbital elements, predicted magnitude, location in the sky, etc.).

File astorb.log is not currently available, but we're working on it.

Acknowledgment and Attribution The research and computing needed to generate astorb.dat were funded principally by NASA grant NAGW-1470, and in part by the Lowell Observatory endowment. astorb.dat may be freely used, copied, and transmitted provided attribution to Dr. Edward Bowell and the aforementioned funding sources is made. Hypertext links to this WWW site are welcome.

Ted Bowell


Last updated 5 Apr 1996 at 17:58:04 U.T.
Contact: Bruce Koehn (koehn@lowell.edu)
Web Curators: Ted Bowell and Bruce Koehn
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