2011 ES4 possible recovery effort


Denis Denisenko
 

This asteroid has made the news as the possible close approacher to Earth on Sep. 1st within 1/3rd lunar distance. Actually, the uncertainty position has grown to ~0.1 AU after 8+ revolutions around the Sun since the discovery 9.5 years ago. Most likely, it has already passed the closest approach at some 12 LD (0.032 AU) on Aug. 30th, give or take a day or two (JPL NASA gives perihelion passage time uncertain by 2.15 days).

The current position uncertainty is about 20-25 deg, but the line of variation is shrinking, reaching the minimum value of merely ~2.5 deg by Sep. 01.6 UT. The object should be about 21m on Aug. 31 - Sep. 01, moving at 16" per minute essentially towards the West. The object should be near zenith (declination around +20) before the morning twilight for the most Northern hemisphere observatories (G96, 703, F51, 381, J04). That would be easily doable were Pan-STARRS and Catalina / Mount Lemmon operating, but this is not the case because of the Moon that will be full on Sep. 02.2 UT.

Today (Aug. 31 UT) we have a 20-minutes gap between the moonset and astronomical twilight, but the sky position is uncertain by ~20 deg.

Tomorrow (Sep. 01 UT) the Moon will still be low in the West when the morning twilight starts, but the object could be covered by two-three Mount Lemmon Survey search fields.

Here is the geocentric ephemeris from Find_Orb after removing 5 worst observations with residuals larger than 1.5". The last two columns give the position uncertainty and angle of line of variation. The uncertainty is in degrees if it's larger than 1000', in arcminutes when larger than 10000", and in arcseconds otherwise.

Date (UTC).d   RA              Dec         delta   r     elong  mag  '/hr    PA   " sig PA
---- -- ----  -------------   -----------  ------ ------ -----  --- ------ ------ ---- ---
2020 08 31.0  04 21 57.324   +20 58 07.92  .03206 1.0103  90.6 21.4  17.51 275.5   30d  98
2020 08 31.1  04 18 58.255   +21 02 03.91  .03209 1.0107  91.3 21.3  17.47 275.2   28d  98
2020 08 31.2  04 15 59.458   +21 05 47.66  .03213 1.0111  92.1 21.3  17.43 275.0   27d  98
2020 08 31.3  04 13 00.989   +21 09 19.16  .03218 1.0115  92.9 21.3  17.38 274.7   25d  99
2020 08 31.4  04 10 02.904   +21 12 38.39  .03223 1.0119  93.6 21.3  17.33 274.4   23d  99
2020 08 31.5  04 07 05.259   +21 15 45.35  .03228 1.0123  94.4 21.2  17.27 274.2   21d  99
2020 08 31.6  04 04 08.110   +21 18 40.07  .03234 1.0127  95.2 21.2  17.21 273.9   20d 100
2020 08 31.7  04 01 11.509   +21 21 22.59  .03240 1.0131  95.9 21.2  17.14 273.6   18d 100
2020 08 31.8  03 58 15.509   +21 23 52.97  .03247 1.0135  96.7 21.2  17.07 273.4  949' 101
2020 08 31.9  03 55 20.163   +21 26 11.26  .03254 1.0139  97.4 21.1  16.99 273.1  833' 102
2020 09 01.0  03 52 25.521   +21 28 17.55  .03262 1.0144  98.2 21.1  16.91 272.8  715' 103
2020 09 01.1  03 49 31.631   +21 30 11.95  .03270 1.0148  98.9 21.1  16.83 272.6  599' 106
2020 09 01.2  03 46 38.541   +21 31 54.56  .03279 1.0152  99.7 21.1  16.74 272.3  484' 109
2020 09 01.3  03 43 46.299   +21 33 25.50  .03288 1.0156 100.4 21.1  16.65 272.0  373' 114
2020 09 01.4  03 40 54.949   +21 34 44.92  .03297 1.0160 101.2 21.0  16.56 271.8  270' 124
2020 09 01.5  03 38 04.533   +21 35 52.95  .03307 1.0164 101.9 21.0  16.46 271.5  185' 144
2020 09 01.6  03 35 15.095   +21 36 49.76  .03317 1.0168 102.6 21.0  16.36 271.2  8859   0
2020 09 01.7  03 32 26.673   +21 37 35.52  .03328 1.0172 103.4 21.0  16.26 271.0  183'  36
2020 09 01.8  03 29 39.307   +21 38 10.40  .03339 1.0176 104.1 21.0  16.15 270.7  259'  55
2020 09 01.9  03 26 53.033   +21 38 34.60  .03351 1.0180 104.8 21.0  16.05 270.5  347'  65
---- -- ----  -------------   -----------  ------ ------ -----  --- ------ ------ ---- ---

Denis Denisenko

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