From jeff@astron.mit.edu
Date: Mon, 27 Jun 1994 16:32:12 +0700
Subject: New SL9 impact time predictions

[Courtesy of Paul Chodas, JPL]

---------------

Attached is the June 24 edition of our Predicted Impact Parameters table.

The predicted impact times continue to slide earlier, but generally only
about 5 minutes earlier than those in our table of June 14.  However, the
impact times for A, B, R, and S made larger jumps (15 to 20 minutes earlier),
and the times for T and U moved the most (half an hour and a full hour
earlier, respectively).  Fragment U's orbit is finally becoming reasonably
well-determined, the last one to fall into line.

Paul Chodas
1994 June 24

==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 June 24
  Date of last astrometric data in these solutions: 1994 June 16


The predictions for all fragments except Q2 are based on independent orbit
solutions; our orbit reference identifier is now given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.  The uncertainties for Q2 have not been quantified, but
are probably comparable to those for fragment P2.

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.


- -------------------------------------------------------------------------------
Frag-     Impact      Jovicentric  Merid.  Angle          Satellite Longitudes
  ment   Date/Time    Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
         July (UT)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
- --------------h--m-------------------------------------------------------------
A = 21   16  19:30   -42.87  162   62.87   99.92   A14   191t  341   105+   76+
                20      .27   12    1.07     .81          10     3     1     1

B = 20   17  02:34   -42.95   59   62.68  100.03   B15    45+   40+  135+   90+
                17      .25   10     .94     .71           9     2     1     1

C = 19   17  06:49   -43.09  211   64.42   98.76   C11   172t   76+  153+   99+
                17      .21   10     .93     .70           9     2     1     1

D = 18   17  11:13   -43.11   11   63.91   99.12   D12   305   113+  171   108+
                20      .25   12    1.09     .82          10     3     1     1

E = 17   17  15:10   -43.42  152   66.09   97.50   E28    64+  146+  188   117+
                13      .08    8     .58     .42           7     2     1     0

F = 16   18  00:12   -43.41  122   63.72   99.17   F19   336   224   225   136+
                15      .16    9     .79     .58           8     2     1     1

G = 15   18  07:30   -43.59   24   66.62   97.08   G28   195t  286   255   151+
                11      .07    7     .51     .37           6     2     1     0

H = 14   18  19:26   -43.68   96   66.96   96.81   H26   194t   27+  305   176
                12      .07    7     .52     .37           6     2     1     0

K = 12   19  10:21   -43.79  276   67.85   96.15   K27   284   153+    8+e 207
                11      .07    7     .50     .36           6     2     1     0

L = 11   19  22:18   -43.84  349   68.66   95.55   L28   283   254    60+  232
                12      .07    7     .52     .37           6     2     1     0

N = 9    20  10:08   -44.13   59   67.27   96.48   N16   279   355o  111+  257
                20      .14   12    1.01     .72          10     3     1     1

P2= 8b   20  14:52   -44.45  233   65.81   97.44   P14    62+   35+  131+  267
                17      .12   10     .88     .62           9     2     1     1

Q2= 7b   20  19:37   -44.49   50   69.37   94.93         204    75+  151+  277

Q1= 7a   20  20:04   -43.99   57   69.54   94.89   Q30   218    78+  153+  278
                11      .07    7     .50     .35           6     2     1     0

R = 6    21  05:31   -44.02   40   69.74   94.74   R26   143   158   192   298
                14      .09    8     .62     .43           7     2     1     0

S = 5    21  15:18   -44.12   35   70.15   94.43   S35    78+  242   232   318
                13      .08    8     .53     .37           7     2     1     0

T = 4    21  18:01   -45.01  136   66.97   96.51   T10   159t  265   244   324
                28      .18   17    1.30     .92          14     4     2     1

U = 3    21  21:52   -44.33  274   69.09   95.14   U12   275   298   260   332
                40      .22   24    1.75    1.23          20     6     3     1

V = 2    22  03:44   -44.25  128   67.70   96.14   V11    92+  348   284   344
                25      .19   15    1.32     .94          13     4     2     1

W = 1    22  08:12   -44.20  287   70.79   93.96   W28   226    25+  303   353
                15      .10    9     .64     .44           8     2     1     1

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
- -------------------------------------------------------------------------------

Notes:
1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from
   view.  The March'94 HST images show that P2=8b and G=15 have split; we do
   not as yet have sufficient data to obtain independent predictions for the
   sub-components.

2. 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); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. 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.

6. 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.

7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede.
   The longitudes are measured east from superior conjunction (the anti-Earth
   direction).  Longitude uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.



