Counter-streaming gas flows in solar prominences as evidence for vertical magnetic fields

Solar prominences are sheets of relatively cool and dense gas embedded in t he surrounding hotter corona. An erupting prominence can inject a mass of u p to 10(15) g into the solar wind(1) as part of a coronal mass ejection. Th ese eruptions must depend critically on the topology of the prominence's ma gnetic field. In all present models(2,3), the prominence hangs on horizonta l or helical field lines, while an overlying magnetic arcade temporarily re strains the prominence from erupting. Such models are inconsistent, however , with the slow upward vertical gas flows that are seen in prominences-(4,1 4). Here we report counter-streaming flows along closely spaced vertical re gions of a prominence, between its top and the lower solar atmosphere. As t he flows must be aligned with the magnetic field, this observation implies that a field connects the prominence directly to the photosphere, contrary to all existing models. These magnetic 'tethers' might help prevent a promi nence from erupting.