| |
*Astron. Astrophys. 346, L65-L68 (1999)*
## 1. The 2027 encounter with 1999 AN_{10}
The asteroid 1999 AN_{10} was discovered by the LINEAR
telescope on 13 January 1999 (MPEC 1999-B03). The discovery was
somewhat unusual in that the declination was
. The nominal orbit computed by our
online information service (NEODyS), that is the solution of the least
squares fit to 94 observations (with one outlier removed, RMS of the
residuals 0.59 arc-sec), is as follows (J2000):
AU, ,
, ,
, ,
for epoch . The absolute magnitude is
estimated at ; given that the albedo
is unknown, this object could be between 0.5 and 2 km in diameter. The
ascending node is only AU closer to
the Sun than a point where the Earth is in early August; the
descending node is AU inward from a
position of the Earth in early February. This means that, whenever the
asteroid and the Earth are in phase at each node, close approaches are
possible. Indeed a close approach is possible in August 2027. To
analyse the 2027 encounter, we need to consider not only the nominal
solution, but also all the solutions compatible with the observations,
that is resulting in residuals which are not much larger than the ones
of the nominal orbit (Milani 1999). The region of these compatible
solutions can be approximated by an ellipsoid of confidence, which,
for a value up to 3, contains
solutions with RMS of the residuals up to 0.63 arc-sec.
The nominal solution undergoes a close approach in August 2027 with
a minimum distance from Earth's center of
AU. The plane normal to the
geocentric velocity at closest approach is the Modified Target Plane
(Milani & Valsecchi 1999). The hypothetical objects filling the
confidence region evolve along a bundle of orbits; their intersections
with the MTP define the confidence region of the encounter. If the
Earth is not touched by this confidence region, then a collision can
be ruled out. The confidence regions are very thin, the width being
only km, and 0.42 AU long. Thus the
occurrence of a very close approach is not very likely: the true orbit
could be anywhere along a very long line, including long stretches
corresponding to very shallow encounters.
In conclusion, the 2027 encounter could be a shallow approach, or
could be, with a low, non-negligible probability, very close. In any
case it cannot result in an impact. But the case for a possible
dangerous encounter is not closed after 2027; indeed, it is just
opened.
© European Southern Observatory (ESO) 1999
Online publication: June 17, 1999
helpdesk.link@springer.de |