Langmuir wave packets with short scale lengths l≲100 &lgr;e have been observed in Jupiter's foreshock. We assess whether the observations are consistent with the relatively new nucleation mechanism for nonlinear collapse of Langmuir waves. Theoretical constraints on the electric fields and scale sizes of collapsing wave packets are summarized, extended and placed in a form suitable for easy comparison with Voyager and Ulysses data. The published data are reviewed and possible instrumental underestimation of fields discussed. New upper limits for the fields of the published wave packets are estimated. our results are: (1) Wave packets formed at the nucleation scale from the observed large-scale fields cannot collapse because they are disrupted before collapse occurs. (2) The published wave packets are quantitatively inconsistent with strong turbulence collapse. (3) Strict constraints exist for more intense wave packets to be able to collapse: E>1-8 mV m-1 for scales l≲1000 &lgr;e. Means for testing these conclusions using Voyager and Ulysses data are suggested. ¿ American Geophysical Union 1992