Ulysses Status Report - February 2006
As reported earlier, Ulysses was one of the missions reviewed by NASA's Sun-Solar System Connections Senior Review panel at its meeting on 14-15 November. The formal recommendations from the Review are expected to be made known early in this year.
Operations and Archive
All science operations during the reporting period have been nominal. Payload operations are being conducted according to the pre-determined power-sharing plan. The current payload configuration will be maintained until spring 2007, when the spacecraft is close enough to the Sun to allow the Cold Case Heater to be switched off. The ESA Ulysses archive is accessible via the World Wide Web at URL: http://helio.esa.int/ulysses.
A recurring theme in many of the results obtained by Ulysses is the unexpectedly large degree to which the heliospheric magnetic field deviates from the pattern expected from the combination of radial solar wind outflow and rotation of the foot point fixed in the solar photosphere (an Archimedean spiral). Existing models of systematic deviations from the spiral pattern require radial distances of several AU for a deviation of order 1 AU to develop. However, observations of "jets" of energetic electrons from Jupiter's magnetosphere, acquired by Ulysses during the 2003/4 distant encounter, show that such deviations are common within a radial interval of as little as 0.1 AU. Electron Jets were discovered during Ulysses' first Jupiter flyby in 1992, and were identified as brief (time scale of minutes to hours), highly anisotropic increases in intensity of MeV electrons flowing away from Jupiter along the heliospheric magnetic field. Jets were observed up to distances of the order of an AU from Jupiter, and were interpreted as evidence for direct magnetic connection to Jupiter's magnetosphere.
In the recent cases, the position of Ulysses relative to Jupiter was such that magnetic connection along the average spiral field could not have occurred, implying large deviations. If such large deviations are indeed common, they may play a significant role in the distribution of particles throughout the heliosphere by providing paths for particles to propagate parallel to the local field while crossing the average field. On average, the spiral heliospheric magnetic field still provides strong guidance to particle propagation, but individual field lines or flux tubes may deviate strongly over large distances normal to the average field. It is not yet clear how or why such large-scale deviations develop, whether they are consistently present throughout the solar cycle, or how to incorporate them into models of particle propagation.