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High velocity jets are among the most prominent features of a wide class ofplanetary nebulae, but their origins are not understood. Several differenttypes of physical model have been suggested to power the jets, but there is noconsensus or preferred scenario. We compare current theoretical ideas on jetformation with observations, using the best studied pre-planetary nebulae inmillimeter CO, where the dynamical properties are best defined. In addition tothe mass, velocity, momentum, and energy of the jets, the mass and energeticsof the equatorial mass-loss that typically accompanies jet formation prove tobe important diagnostics. Our integrated approach provides estimates for somekey physical quantities - such as the binding energy of the envelope when thejets are launched - and allows testing of model features using correlationsbetween parameters. Even with a relatively small sample of well-observedobjects, we find that some specific scenarios for powering jets can be ruledout or rendered implausible, and others are promising at a quantitative level.

Jet Power in Pre-Planetary Nebulae: Observations vs. Theory