  The "new positive energy conjecture" Horowitz and Myers (1999) probes a
possible nonsupersymmetric AdS/CFT correspondence. We consider a version
formulated for complete, asymptotically Poincar\'e-Einstein Riemannian metrics
$(M,g)$ with bounded scalar curvature $R\ge -n(n-1)$. This version then asserts
that any such $(M,g)$ must have mass not less than the mass $m_0$ of a metric
$g_0$ induced on a time-symmetric slice of a certain AdS soliton spacetime. The
conjecture remains unproved, having so far resisted standard techniques. Little
is known other than that the conjecture is true for metrics which are
sufficiently small perturbations of $g_0$. We pose another test for the
conjecture. We assume its validity and attempt to prove as a corollary the
corresponding scalar curvature rigidity statement, that $g_0$ is the unique
asymptotically Poincar\'e-Einstein metric with mass $m=m_0$ obeying $R\ge
-n(n-1)$. Were a second such metric $g_1$ not isometric to $g_0$ to exist, it
then may well admit perturbations of lower mass, contradicting the assumed
validity of the conjecture. We find that the minimum mass metric must be static
Einstein, so the problem is reduced to that of static uniqueness. When $n=3$
the manifold is isometric to a time-symmetric slice of an AdS soliton
spacetime, unless it has a non-compact horizon. En route we study the mass
aspect, obtaining and generalizing known results. The mass aspect is (i)
related to the holographic energy density, (ii) a weighted invariant under
boundary conformal transformations when the bulk dimension is odd, and (iii)
zero for negative Einstein manifolds with Einstein conformal boundary.
