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
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 numbering are:
- A numbered asteroid's computed ephemeris uncertainty must not exceed
2 arcsec in the coming 10 yr.
- A numbered asteroid's orbit must be robust. That is, it must not degrade
significantly when temporally isolated observations (one-night apparitions)
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 serendipitously.
- Numbered asteroids having |CEU| > 2.0 arcsec during the current
lunation (full Moon to full Moon).
- Numbered asteroids for which OQP fails (OQP < 5.25) or fails when
a one-night apparition is omitted.
- 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 observation.
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
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.
Last updated: 6 January 1999
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