[Forwarded from Paul Chodas, JPL]
Here are revised impact parameters predictions for the remaining 10 fragments.
The solutions have not changed for fragments N, T, U, and V, as we have no new data for these. The solutions for fragments P2, Q1, Q2, R, S, and W have been updated using Dave Jewitt's astrometric positions of July 19.3, the only new data we have received since the impacts began.
It is clear from the observed impact phenomena that our predicted impact times have been early by an average of 5-10 minutes. We attribute this to systematic errors in the Guide Star Catalog, which was used to reduce most of our astrometric positions. Consistent with this is the fact that the latest data, which are reduced relative to more accurate catalogs, invariably tend to move the predicted impact times later in our solutions. As a result, we feel the times below are still likely to be early, but we have refrained from applying an arbitrary correction or extrapolating the trend towards later impact times. We have, however, inflated the impact time uncertainties to account for the observed systematic errors.
Except for Q2, these revised impact times are only a only few minutes later than those in our previous table, dated July 16. The impact time for Q2 took a large jump (15 minutes later), because we now compute its orbit directly from the data, instead of using a tidal disruption approach as before. The predicted impact time for Q2 is now only 17 minutes before Q1.
Paul Chodas 1994 July 20 07:00 UT
The predictions for all fragments are based on independent orbit solutions; our orbit reference identifier is given. Immediately to the right of the predicted impact times, we give the 1-sigma uncertainties in those times. We have made an effort to make these uncertainties realistic: they are not formal uncertainty values. NOTE: To obtain a 95% confidence level, one should use a +/- 2 sigma window around the predicted impact time.
The dynamical model used for these predictions includes perturbations due to the Sun, planets, Galilean satellites and the oblateness of Jupiter. The planetary ephemeris used was DE245.
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Fragment Impact 1-sig Jovicentric Meridian Angle Orbit Date of
Date/Time Unc. Lat. Long. Angle E-J-F Ref. Last Data
July (UTC) (min) (deg) (deg) (deg) (deg) (July UT)
--------------h--m--s----------------------------------------------------------
N = 9 20 10:20:02 7.4 -44.29 66 67.77 96.10 N22 15.0
P2= 8b 20 15:16:20 6.0 -44.62 246 67.07 96.53 P28 19.3
Q2= 7b 20 19:47:11 12.0 -44.25 47 69.42 94.93 QB6 19.3
Q1= 7a 20 20:04:09 6.0 -44.03 58 69.51 94.90 Q43 19.3
R = 6 21 05:28:50 6.2 -44.06 39 69.65 94.80 R38 19.3
S = 5 21 15:12:49 5.6 -44.15 31 69.95 94.56 S49 19.3
T = 4 21 18:03:45 17.5 -44.99 137 67.34 96.26 T16 4.1
U = 3 21 21:48:30 19.6 -44.43 272 68.81 95.33 U17 8.0
V = 2 22 04:16:53 12.4 -44.43 146 69.50 94.83 V18 15.0
W = 1 22 07:59:45 7.2 -44.14 279 70.57 94.12 W37 19.3
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Notes:
1. The impact date/time is the time the impact would be seen at the Earth, if
the limb of Jupiter were not in the way (i.e., the time listed is the time
of impact plus the light travel time to the Earth); the date is the day in
July 1994; The impact time uncertainty is a 1-sigma value in minutes.
2. The impact latitude is Jovicentric (latitude measured at the center of
Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.
3. The impact longitude is System III, measured westwards on the planet.
4. The meridian angle is the Jovicentric longitude of impact measured from
the midnight meridian towards the morning terminator. This relative
longitude is known much more accurately than the absolute longitude.
At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
and the terminator is at meridian angle 87 deg.
5. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
than 90 deg indicate a farside impact. All impacts will be just on the
farside as viewed from Earth; later impacts will be closer to the limb.
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