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Sentry Notes
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- 2011-Sep-20
- We have transitioned to the debiasing and
weight scheme described in Chesley, Baer and Monet (Icarus, vol. 210,
pp. 158-181). This means that we are treating the asteroid
observational data in a way that is more consistent with the
statistical uncertainties and that has been shown to produce better
fits and more reliable predictions. As explained in our 2010-Dec-7
note below, such a recomputation necessarily leads to minor changes in
the listings, as well as some new additions and removals to the object
list.
- 2010-Dec-7
- As a part of fielding some enhancements to
our process we are rerunning all objects in order to bring them
up-to-date with our current software and dynamical models. Note that
many objects with very low impact probabilities are only detected on a
statistical basis, and so this recomputation can yield different
results than those obtained before for these low interest cases. In
particular, we will find some new potential impacts (and potential
impactors) and will not identify some that were found in previous
searches. Cases of higher interest will not change between runs.
- 2010-Nov-23
- Updating our note of 2010-Jul-26 below,
another object has been found to have potential impacts in the far
future, beyond 100 years. 2009 FD is roughly 130 m in diameter with an
estimated 1 in 435 chance of impact in 2185. The current analysis
assumes only gravitational accelerations and does not incorporate the
potentially important Yarkovsky (thermal) accelerations. Thus the 2009
FD Risk Table may be refined by future analyses that attempt to
incorporate a more complete dynamical model.
- 2010-Jul-26
-
In some cases, investigations into potential impacts are conducted for more
than 100 years into the future. Currently, there are two well-observed
objects for which long-term analyses have been carried out.
1. Asteroid (29075) 1950 DA, has a significant possibility of impact on
March 16, 2880. A careful computation of the impact probability, which is
less than 0.33%, is challenging because the orientation of its spin pole is
poorly known. Giorgini et al. (Science, Vol. 296. no. 5565, pp. 132 - 136,
2002) analyzed this object's motion, which is discussed here:
http://neo.jpl.nasa.gov/1950da
2. The second object, (101955) 1999 RQ36, currently has non-zero impact
probabilities on numerous occasions during the years after 2165. This is
analyzed in a paper published by Milani et al. (Icarus, Vol. 203, pp.
460-471, 2009), which is available as here:
http://arxiv.org/abs/0901.3631 .
Note the Torino Scale is formally undefined for potential impacts more than
one century into the future and so not applicable in such cases.
- 2009-Oct-07
- The risk assessment for Apophis has been
updated to reflect new astrometry released by Tholen et al. (DPS 2009)
and dispersions due to the Yarkovsky effect. Results reported by
Chesley et al. at the 2009 Div. of
Planetary Sciences meeting.
- 2008-May-18
- Sentry has switched to a new server and management
architecture. As a part of this transition, all objects in the NEA
catalog were reanalyzed with the new system. This recomputation leads
inevitably to minor differences in the results due to the statistical
nature of the impact monitoring algorithms.
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