31st Annual Meeting of the DPS, October 1999
Session 26. Edgeworth-Kuiper Belt II
Contributed Oral Parallel Session, Tuesday, October 12, 1999, 10:30-11:20am, Sala Pietro d'Abano

## [26.04] Pioneer 10 Encounter with a Trans-Neptunian Object at 56 AU?

G. Giampieri (QMW), J.D. Anderson, E.K. Lau (JPL)

Using coherent radio Doppler data generated by the Deep Space Network (DSN) at S band (wavelength ~ 13 cm), we have produced averages of radial accelerations acting on the Pioneer 10 spacecraft between 40 and 70 AU. The one-sigma accuracy of the reduced accelerations is 2.5 \times 10-10 m s-2.

Here we develop the theory of weak gravitational interactions of a spacecraft with orbiting bodies, and search the data record for candidate flybys. We apply the theory to a candidate event at distance 56 AU, ecliptic longitude 73.9 Deg and latitude 3.1 Deg. Fitting these data provides constraints on the physical and orbital properties of the body allegedly encountered by Pioneer 10.

Finally, we consider the dynamical origin of the body, and speculate about its possible ejection from the solar system due to a close encounter with a major planet.