Below is a table of the approaches closer than 10 Gm (10 million km) which are predicted by

Date
TDT Dmin (Gm) T error
(d)
D Error (Gm)

2028/05/07
03:32:05
2.93643
0.0007
0.012

2029/02/16
08:13:30
7.88746
0.31
0.020

2029/07/28
11:43:48
5.11718
0.55
0.017

2029/11/21
16:11:07
6.76341
0.65
0.033

2030/09/22
21:36:24
5.15947
0.11
0.10

2069/05/01
15:51:54
0.13535
20
6

If the orbit of SG344 becomes so much uncertain
after
2030, how can possibly an Earth impact be predicted ?

Indeed, it *cannot* be predicted: the chaotic
nature
of the asteroid's orbit forbids that. Nevertheless it is possible to
estimate
the *probability* of such event. How ?

The orbital elements of SG344, as any other
experimentally
determined entity, are *not* known *exactly*. They are just
what
appears to be (on the ground of the available experimental
measurements)
the *most likely approximation *to the "true" values. Suppose
that
we generate a large number of "virtual" asteroids, having orbital
elements
slightly different from the nominal ones, but not so much different to
represent unlikely orbits. Each of them will represent a *possible *asteroid,
i.e. an approximation to the *true* one not much less likely than
the nominal SG344. Suppose that we integrate the orbits of all these
virtual
bodies, checking for their close approaches to Earth, and we find out
that
a fraction of them will impact Earth within a given time interval. We
can
then say that this fraction represents our best estimate of the *probability*
that the *true* asteroid will *actually* impact Earth
within
the given time range.

The most reliable method of generating
representative
"virtual bodies" or "clones" is to start from the very beginning, i.e.
from the observations. We can (re)determine the orbital elements of our
body by a least-square fit to the observation (this can be done by **ExOrb
**(formerly named Findorb), the companion program to **Solex**).
From the fitting procedure,
we also get the root-mean-square deviation (or average residual). We
can
then generate a set of "virtual" observations (one for each of the
actual
observations), randomly distributed around the calculated positions
with
the same root-mean-square deviation determined by the original fitting.
This set of observations will represent a *possible* set, which *might*
have been the actual one, but just happened not to be. If we now
redetermine
the orbital elements from this "virtual" set of observations, we get *possible*
new elements, about equally likely than the original ones, which will
represent
an acceptable "clone" of the original body. By repeating the procedure
N times, we can generate N acceptable "clones". The larger N is, the
bigger
the statistical significance of the "cloud" of virtual bodies that we
obtain.

The whole procedure described above can be
automatically
performed by **ExOrb**, the companion program to **Solex**.
It is very time-consuming, but it is *computer* time, not your
time.
You can comfortably sleep or go fishing or attend your business, while
your computer does the job for you. Once you get your "cloud" of
virtual
bodies, you can feed it to Solex and investigate the future (or past)
evolution
of the original body from a statistical point of view.

By applying this method to SG344 one obtains that 10
out of a cloud of 4000 "clones" end up with an Earth impact on
September
16, 2071, from which an impact probability of 0.25% can be inferred.

All the 10 "virtual impactors" belong to a family of
"clones" having the same semimajor axis (0.97738964 AU at epoch March,
2, 2003), which is well within the 1-sigma deviation (7e-7 AU) from the
nominal value of the parent body (0.97738943 AU). When further
observations
will lead to the determination of the semimajor axis with a higher
precision
(by 1 or 2 orders of magnitude), then the chance of impact in 2071 will
probably be excluded. Unfortunately further observations are not likely
to be available until the next close approach of 2028, because the
small
body will never come closer than 0.6 AU before year 2026.

Here you can download the
orbital
elements of the "original" SG344 and those of a bunch of "virtual
impactors"
and a few "virtual grazers", in a form readable by Solex. Back
to Solex page