  The set of radial velocity measurements of the HD 160691 has been recently
published by Jones et.al 2002 (MNRAS). It reveals a linear trend that indicates
a presence of the second planet in this system. The preliminary
double-Keplerian orbital fit to the observations, announced by the discovery
team, describes a highly unstable, self-disrupting configuration. Because the
observational window of the HD 160691 system is narrow, the orbital parameters
of the hypothetical second companion are unconstrained. In this paper we try to
find out whether a second giant planet can exist up to the distance of Jupiter
and search for the dynamical constraints on its orbital parameters. Our
analysis employs a combination of fitting algorithms and simultaneous
examination of the dynamical stability of the obtained orbital fits. It reveals
that if the semi-major axis of the second planet is smaller than $\simeq 5.2$
AU, the observations are consistent with quasi-periodic, regular motions of the
system confined to the islands of various low-order mean motion resonances,
e.g., 3:1, 7:2, 4:1, 5:1, or to their vicinity. In such cases the second planet
has smaller eccentricity $\simeq 0.2-0.5$ than estimated in the previous works.
We show that the currently available Doppler data rather preclude the 2:1 mean
motion resonance expected by some authors to be present in the HD 160691
planetary system. We also demonstrate that the MEGNO-penalty method, developed
in this paper, which is a combination of the genetic minimization algorithm and
the MEGNO analysis, can be efficiently used for predicting stable planetary
configurations when only a limited number of observations is given or the data
do not provide tight constraints on the orbital elements.
