Critical Lists of Asteroids
We present two so-called critical lists of numbered asteroids (in several categories) and
unnumbered asteroids whose orbits can be usefully improved by additional astrometric observation.
The numbered asteroids have, for various reasons, been inadequately observed, and the unnumbered
asteroids could perhaps be numbered after a modest astrometric effort. The
first critical list contains all
asteroids in need of observation, without regard to location in the sky and current observability.
The second critical list is a subset
of the first, and contains asteroids that come to opposition during the current lunation (full Moon
to full Moon).
Although our lists superficially resemble the one put out monthly by the Minor Planet Center, they
are based on different precepts, and are updated on a quasi-daily basis. The MPC list consists
primarily of asteroids that have been observed at a small number of apparitions or that have not
been adequately observed for 10 yr or more, whereas our lists derive entirely from parameters
related to ephemeris uncertainties.
We consider the listed numbered asteroids to have been inadequately observed. Our criteria for
A numbered asteroid's computed ephemeris uncertainty must not exceed 2 arcsec in the coming
A numbered asteroid's orbit must be robust. That is, it must not degrade significantly when
temporally isolated observations (one-night apparitions) are omitted.
Our critical lists are based on two ephemeris uncertainty parameters:
|CEU|, the |current ephemeris uncertainty|.
OQP, the orbital quality parameter, defined by Muinonen and Bowell (1993, Icarus 104, 255-279)
as -log10leak , where leak is one of several orbital metrics developed by them. A rule of thumb
is that OQP > 5.47 for an asteroid to satisfy our numberability criteria. If OQP < 5.25, an
asteroid is certainly not numberable. Between these two values, a numbered asteroid's orbit is
considered to be of marginal quality.
We have subdivided the critical lists into six categories:
Lost numbered asteroid. Only 719 Albert is currently lost. It will probably be recovered
Numbered asteroids having |CEU| > 2.0 arcsec during the current lunation (full Moon to full
Numbered asteroids for which OQP fails (OQP < 5.25) or fails when a one-night apparition is
Numbered asteroids for which OQP is marginal (5.25 < OQP < 5.47) or is marginal when a one-night
apparition is omitted.
Numbered asteroids for which the last observation included in the orbit solution was made more
than 10 yr ago.
Unnumbered asteroids that could perhaps be numbered after one or two additional accurate
observations. The lists contain asteroids that, according to the aforementioned numberability
criteria, could at present be numbered. They are not numbered because of differences in the
criteria used by the MPC and us. However, they are certainly close to being numbered by the
MPC, so additional observations, particularly a month or more after the last observation,
might allow them to be.
Asteroids contained in the lists may be annotated in three ways:
* An asterisk following a number or designation signifies that the asteroid is also contained
in category 5 (above).
() Parentheses around a number or designation indicate that an asteroid has already been
observed on at least two nights during the current apparition. Although requiring additional
observation, it need not be observed during the current lunation.
+ A plus sign (in the second critical list only) indicates that an asteroid's CEU will reach
a 10-yr peak during the current lunation. Such an asteroid is a prime target for astrometric
We are posting the critical lists in the test phase, before they have been completely documented
and checked, in particular so that users can appreciate that many numbered asteroids are in need
of further observation and that many unnumbered asteroids are close to being numbered. Note that,
because we are at present only receiving observations from the Minor Planet Center on a monthly
basis, we cannot ensure that our critical lists are completely correct and up-to-date.
Our critical lists comprise a phase in the development of HOP: a hierarchical observing protocol
designed to optimize the astrometric observation of all asteroids. HOP is being developed by us in
collaboration with the MPC.