[Iaude] CBET 4786: 2015 EG

quai at eps.harvard.edu quai at eps.harvard.edu
Fri May 29 20:48:44 EDT 2020

                                                  Electronic Telegram No. 4786
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau at eps.harvard.edu (alternate cbat at iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network

2015 EG
     J. D. Giorgini, Jet Propulsion Laboratory (JPL); and S. E. Marshall and
F. Venditti, Arecibo Observatory, University of Central Florida, report that
a non-gravitational acceleration has been detected influencing the motion of
the Aten-class minor planet 2015 EG.  The initial echo Doppler-shift on 2019
Mar. 7 was found 4.9-sigma from the expectation of gravity-only dynamics.
Additional and recently reduced Arecibo S-band measurements (2380-MHz,
12.6-cm), also obtained 2019 Mar. 7-8, have mean offsets of -0.84 +/- 0.15 Hz
in Doppler-shift and 2.9-sigma mean offsets of 84 (+/- 2.8) x 10**-6 s in
round-trip delay relative to ballistic motion from the pre-experiment dataset
(95 plane-of-sky optical angle pairs spanning 2011-2019 in JPL orbit solution
16).  When combined with the current optical-angle dataset in a new orbit
solution (143 optical angle pairs, three delay, and two Dopplers over 2011-
2019), a heliocentric r**-2 transverse A_2 non-gravitational acceleration at
1 AU of -4.1 (+/- 0.4) x 10**-12 m/s**2 over the data arc was estimated,
reducing measurement residual chi-squared from 135 to 32 for JPL orbit
solution 31.  Estimates of radial (A_1) and normal (A_3) non-gravitational
acceleration components did not produce statistically significant detections.
The dataset cannot distinguish between outgassing dynamics (10.1-sigma
detection) or the r**-2 acceleration dynamic given above (10.3-sigma
detection).  The object was unresolved in delay-Doppler imaging, with an echo
bandwidth between 0.4 and 0.8 Hz.  The radar astrometry is available at
website URL https://ssd.jpl.nasa.gov/?radar.

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                         (C) Copyright 2020 CBAT
2020 May 29                      (CBET 4786)              Daniel W. E. Green

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